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-rw-r--r--src/boost/assert.hpp38
-rw-r--r--src/boost/checked_delete.hpp71
-rw-r--r--src/boost/detail/shared_count.hpp555
-rw-r--r--src/boost/detail/workaround.hpp74
-rw-r--r--src/boost/enable_shared_from_this.hpp68
-rw-r--r--src/boost/format.hpp64
-rw-r--r--src/boost/format/exceptions.hpp96
-rw-r--r--src/boost/format/feed_args.hpp247
-rw-r--r--src/boost/format/format_class.hpp135
-rw-r--r--src/boost/format/format_fwd.hpp49
-rw-r--r--src/boost/format/format_implementation.cc256
-rw-r--r--src/boost/format/free_funcs.cc71
-rw-r--r--src/boost/format/group.hpp680
-rw-r--r--src/boost/format/internals.hpp167
-rw-r--r--src/boost/format/internals_fwd.hpp65
-rw-r--r--src/boost/format/local.mk7
-rw-r--r--src/boost/format/macros_default.hpp48
-rw-r--r--src/boost/format/parsing.cc454
-rw-r--r--src/boost/shared_ptr.hpp474
-rw-r--r--src/boost/throw_exception.hpp47
-rw-r--r--src/boost/weak_ptr.hpp193
-rw-r--r--src/bsdiff-4.3/bsdiff.163
-rw-r--r--src/bsdiff-4.3/bsdiff.c405
-rw-r--r--src/bsdiff-4.3/bspatch.159
-rw-r--r--src/bsdiff-4.3/bspatch.c224
-rw-r--r--src/bsdiff-4.3/compat-include/err.h12
-rw-r--r--src/bsdiff-4.3/local.mk11
-rw-r--r--src/libexpr/attr-path.cc97
-rw-r--r--src/libexpr/attr-path.hh13
-rw-r--r--src/libexpr/common-opts.cc59
-rw-r--r--src/libexpr/common-opts.hh17
-rw-r--r--src/libexpr/eval-inline.hh59
-rw-r--r--src/libexpr/eval.cc1435
-rw-r--r--src/libexpr/eval.hh294
-rw-r--r--src/libexpr/get-drvs.cc305
-rw-r--r--src/libexpr/get-drvs.hh93
-rw-r--r--src/libexpr/lexer.l193
-rw-r--r--src/libexpr/local.mk22
-rw-r--r--src/libexpr/names.cc104
-rw-r--r--src/libexpr/names.hh24
-rw-r--r--src/libexpr/nix.sdf141
-rw-r--r--src/libexpr/nixexpr.cc391
-rw-r--r--src/libexpr/nixexpr.hh332
-rw-r--r--src/libexpr/parser.y650
-rw-r--r--src/libexpr/primops.cc1336
-rw-r--r--src/libexpr/symbol-table.hh95
-rw-r--r--src/libexpr/value-to-json.cc86
-rw-r--r--src/libexpr/value-to-json.hh64
-rw-r--r--src/libexpr/value-to-xml.cc163
-rw-r--r--src/libexpr/value-to-xml.hh14
-rw-r--r--src/libexpr/value.hh162
-rw-r--r--src/libmain/local.mk11
-rw-r--r--src/libmain/shared.cc297
-rw-r--r--src/libmain/shared.hh58
-rw-r--r--src/libmain/stack.cc72
-rw-r--r--src/libstore/build.cc3258
-rw-r--r--src/libstore/derivations.cc278
-rw-r--r--src/libstore/derivations.hh93
-rw-r--r--src/libstore/gc.cc752
-rw-r--r--src/libstore/globals.cc218
-rw-r--r--src/libstore/globals.hh209
-rw-r--r--src/libstore/local-store.cc1996
-rw-r--r--src/libstore/local-store.hh333
-rw-r--r--src/libstore/local.mk28
-rw-r--r--src/libstore/misc.cc220
-rw-r--r--src/libstore/misc.hh38
-rw-r--r--src/libstore/optimise-store.cc180
-rw-r--r--src/libstore/pathlocks.cc199
-rw-r--r--src/libstore/pathlocks.hh45
-rw-r--r--src/libstore/references.cc122
-rw-r--r--src/libstore/references.hh11
-rw-r--r--src/libstore/remote-store.cc602
-rw-r--r--src/libstore/remote-store.hh104
-rw-r--r--src/libstore/schema.sql44
-rw-r--r--src/libstore/store-api.cc331
-rw-r--r--src/libstore/store-api.hh364
-rw-r--r--src/libstore/worker-protocol.hh60
-rw-r--r--src/libutil/affinity.cc55
-rw-r--r--src/libutil/affinity.hh9
-rw-r--r--src/libutil/archive.cc336
-rw-r--r--src/libutil/archive.hh75
-rw-r--r--src/libutil/hash.cc382
-rw-r--r--src/libutil/hash.hh113
-rw-r--r--src/libutil/local.mk15
-rw-r--r--src/libutil/md32_common.h620
-rw-r--r--src/libutil/md5.c365
-rw-r--r--src/libutil/md5.h82
-rw-r--r--src/libutil/serialise.cc259
-rw-r--r--src/libutil/serialise.hh133
-rw-r--r--src/libutil/sha1.c369
-rw-r--r--src/libutil/sha1.h28
-rw-r--r--src/libutil/sha256.c238
-rw-r--r--src/libutil/sha256.h35
-rw-r--r--src/libutil/types.hh77
-rw-r--r--src/libutil/util.cc1145
-rw-r--r--src/libutil/util.hh353
-rw-r--r--src/libutil/xml-writer.cc131
-rw-r--r--src/libutil/xml-writer.hh71
-rw-r--r--src/nix-daemon/local.mk9
-rw-r--r--src/nix-daemon/nix-daemon.cc932
-rw-r--r--src/nix-env/local.mk7
-rw-r--r--src/nix-env/nix-env.cc1426
-rw-r--r--src/nix-env/profiles.cc148
-rw-r--r--src/nix-env/profiles.hh55
-rw-r--r--src/nix-env/user-env.cc148
-rw-r--r--src/nix-env/user-env.hh13
-rw-r--r--src/nix-hash/local.mk7
-rw-r--r--src/nix-hash/nix-hash.cc64
-rw-r--r--src/nix-instantiate/local.mk7
-rw-r--r--src/nix-instantiate/nix-instantiate.cc176
-rw-r--r--src/nix-log2xml/local.mk8
-rw-r--r--src/nix-log2xml/log2html.xsl83
-rw-r--r--src/nix-log2xml/log2xml.cc200
-rw-r--r--src/nix-log2xml/logfile.css86
-rw-r--r--src/nix-log2xml/mark-errors.xsl24
-rw-r--r--src/nix-log2xml/treebits.js50
-rw-r--r--src/nix-store/dotgraph.cc162
-rw-r--r--src/nix-store/dotgraph.hh9
-rw-r--r--src/nix-store/local.mk9
-rw-r--r--src/nix-store/nix-store.cc929
-rw-r--r--src/nix-store/xmlgraph.cc71
-rw-r--r--src/nix-store/xmlgraph.hh9
122 files changed, 30228 insertions, 0 deletions
diff --git a/src/boost/assert.hpp b/src/boost/assert.hpp
new file mode 100644
index 000000000000..754ebb954bce
--- /dev/null
+++ b/src/boost/assert.hpp
@@ -0,0 +1,38 @@
+//
+//  boost/assert.hpp - BOOST_ASSERT(expr)
+//
+//  Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  Note: There are no include guards. This is intentional.
+//
+//  See http://www.boost.org/libs/utility/assert.html for documentation.
+//
+
+#undef BOOST_ASSERT
+
+#if defined(BOOST_DISABLE_ASSERTS)
+
+# define BOOST_ASSERT(expr) ((void)0)
+
+#elif defined(BOOST_ENABLE_ASSERT_HANDLER)
+
+#include <boost/current_function.hpp>
+
+namespace boost
+{
+
+void assertion_failed(char const * expr, char const * function, char const * file, long line); // user defined
+
+} // namespace boost
+
+#define BOOST_ASSERT(expr) ((expr)? ((void)0): ::boost::assertion_failed(#expr, BOOST_CURRENT_FUNCTION, __FILE__, __LINE__))
+
+#else
+# include <assert.h>
+# define BOOST_ASSERT(expr) assert(expr)
+#endif
diff --git a/src/boost/checked_delete.hpp b/src/boost/checked_delete.hpp
new file mode 100644
index 000000000000..d7f52122de73
--- /dev/null
+++ b/src/boost/checked_delete.hpp
@@ -0,0 +1,71 @@
+#ifndef BOOST_CHECKED_DELETE_HPP_INCLUDED
+#define BOOST_CHECKED_DELETE_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  boost/checked_delete.hpp
+//
+//  Copyright (c) 1999, 2000, 2001, 2002 boost.org
+//  Copyright (c) 2002, 2003 Peter Dimov
+//  Copyright (c) 2003 Daniel Frey
+//  Copyright (c) 2003 Howard Hinnant
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  See http://www.boost.org/libs/utility/checked_delete.html for documentation.
+//
+
+namespace boost
+{
+
+// verify that types are complete for increased safety
+
+template<class T> inline void checked_delete(T * x)
+{
+    // intentionally complex - simplification causes regressions
+    typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
+    (void) sizeof(type_must_be_complete);
+    delete x;
+}
+
+template<class T> inline void checked_array_delete(T * x)
+{
+    typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
+    (void) sizeof(type_must_be_complete);
+    delete [] x;
+}
+
+template<class T> struct checked_deleter
+{
+    typedef void result_type;
+    typedef T * argument_type;
+
+    void operator()(T * x) const
+    {
+        // boost:: disables ADL
+        boost::checked_delete(x);
+    }
+};
+
+template<class T> struct checked_array_deleter
+{
+    typedef void result_type;
+    typedef T * argument_type;
+
+    void operator()(T * x) const
+    {
+        boost::checked_array_delete(x);
+    }
+};
+
+} // namespace boost
+
+#endif  // #ifndef BOOST_CHECKED_DELETE_HPP_INCLUDED
diff --git a/src/boost/detail/shared_count.hpp b/src/boost/detail/shared_count.hpp
new file mode 100644
index 000000000000..23e78413f721
--- /dev/null
+++ b/src/boost/detail/shared_count.hpp
@@ -0,0 +1,555 @@
+#ifndef BOOST_DETAIL_SHARED_COUNT_HPP_INCLUDED
+#define BOOST_DETAIL_SHARED_COUNT_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  detail/shared_count.hpp
+//
+//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+
+//#include <boost/config.hpp>
+
+#if defined(BOOST_SP_USE_STD_ALLOCATOR) && defined(BOOST_SP_USE_QUICK_ALLOCATOR)
+# error BOOST_SP_USE_STD_ALLOCATOR and BOOST_SP_USE_QUICK_ALLOCATOR are incompatible.
+#endif
+
+#include <boost/checked_delete.hpp>
+#include <boost/throw_exception.hpp>
+//#include <boost/detail/lightweight_mutex.hpp>
+
+#if defined(BOOST_SP_USE_QUICK_ALLOCATOR)
+#include <boost/detail/quick_allocator.hpp>
+#endif
+
+#include <memory>           // std::auto_ptr, std::allocator
+#include <functional>       // std::less
+#include <exception>        // std::exception
+#include <new>              // std::bad_alloc
+#include <typeinfo>         // std::type_info in get_deleter
+#include <cstddef>          // std::size_t
+
+#ifdef __BORLANDC__
+# pragma warn -8026     // Functions with excep. spec. are not expanded inline
+# pragma warn -8027     // Functions containing try are not expanded inline
+#endif
+
+namespace boost
+{
+
+// Debug hooks
+
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+
+void sp_scalar_constructor_hook(void * px, std::size_t size, void * pn);
+void sp_array_constructor_hook(void * px);
+void sp_scalar_destructor_hook(void * px, std::size_t size, void * pn);
+void sp_array_destructor_hook(void * px);
+
+#endif
+
+
+// The standard library that comes with Borland C++ 5.5.1
+// defines std::exception and its members as having C calling
+// convention (-pc). When the definition of bad_weak_ptr
+// is compiled with -ps, the compiler issues an error.
+// Hence, the temporary #pragma option -pc below. The version
+// check is deliberately conservative.
+
+#if defined(__BORLANDC__) && __BORLANDC__ == 0x551
+# pragma option push -pc
+#endif
+
+class bad_weak_ptr: public std::exception
+{
+public:
+
+    virtual char const * what() const throw()
+    {
+        return "boost::bad_weak_ptr";
+    }
+};
+
+#if defined(__BORLANDC__) && __BORLANDC__ == 0x551
+# pragma option pop
+#endif
+
+namespace detail
+{
+
+class sp_counted_base
+{
+private:
+
+    //    typedef detail::lightweight_mutex mutex_type;
+
+public:
+
+    sp_counted_base(): use_count_(1), weak_count_(1)
+    {
+    }
+
+    virtual ~sp_counted_base() // nothrow
+    {
+    }
+
+    // dispose() is called when use_count_ drops to zero, to release
+    // the resources managed by *this.
+
+    virtual void dispose() = 0; // nothrow
+
+    // destruct() is called when weak_count_ drops to zero.
+
+    virtual void destruct() // nothrow
+    {
+        delete this;
+    }
+
+    virtual void * get_deleter(std::type_info const & ti) = 0;
+
+    void add_ref_copy()
+    {
+#if defined(BOOST_HAS_THREADS)
+        mutex_type::scoped_lock lock(mtx_);
+#endif
+        ++use_count_;
+    }
+
+    void add_ref_lock()
+    {
+#if defined(BOOST_HAS_THREADS)
+        mutex_type::scoped_lock lock(mtx_);
+#endif
+        if(use_count_ == 0) boost::throw_exception(boost::bad_weak_ptr());
+        ++use_count_;
+    }
+
+    void release() // nothrow
+    {
+        {
+#if defined(BOOST_HAS_THREADS)
+            mutex_type::scoped_lock lock(mtx_);
+#endif
+            long new_use_count = --use_count_;
+
+            if(new_use_count != 0) return;
+        }
+
+        dispose();
+        weak_release();
+    }
+
+    void weak_add_ref() // nothrow
+    {
+#if defined(BOOST_HAS_THREADS)
+        mutex_type::scoped_lock lock(mtx_);
+#endif
+        ++weak_count_;
+    }
+
+    void weak_release() // nothrow
+    {
+        long new_weak_count;
+
+        {
+#if defined(BOOST_HAS_THREADS)
+            mutex_type::scoped_lock lock(mtx_);
+#endif
+            new_weak_count = --weak_count_;
+        }
+
+        if(new_weak_count == 0)
+        {
+            destruct();
+        }
+    }
+
+    long use_count() const // nothrow
+    {
+#if defined(BOOST_HAS_THREADS)
+        mutex_type::scoped_lock lock(mtx_);
+#endif
+        return use_count_;
+    }
+
+private:
+
+    sp_counted_base(sp_counted_base const &);
+    sp_counted_base & operator= (sp_counted_base const &);
+
+    long use_count_;        // #shared
+    long weak_count_;       // #weak + (#shared != 0)
+
+#if defined(BOOST_HAS_THREADS) || defined(BOOST_LWM_WIN32)
+    mutable mutex_type mtx_;
+#endif
+};
+
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+
+template<class T> void cbi_call_constructor_hook(sp_counted_base * pn, T * px, checked_deleter<T> const &, int)
+{
+    boost::sp_scalar_constructor_hook(px, sizeof(T), pn);
+}
+
+template<class T> void cbi_call_constructor_hook(sp_counted_base *, T * px, checked_array_deleter<T> const &, int)
+{
+    boost::sp_array_constructor_hook(px);
+}
+
+template<class P, class D> void cbi_call_constructor_hook(sp_counted_base *, P const &, D const &, long)
+{
+}
+
+template<class T> void cbi_call_destructor_hook(sp_counted_base * pn, T * px, checked_deleter<T> const &, int)
+{
+    boost::sp_scalar_destructor_hook(px, sizeof(T), pn);
+}
+
+template<class T> void cbi_call_destructor_hook(sp_counted_base *, T * px, checked_array_deleter<T> const &, int)
+{
+    boost::sp_array_destructor_hook(px);
+}
+
+template<class P, class D> void cbi_call_destructor_hook(sp_counted_base *, P const &, D const &, long)
+{
+}
+
+#endif
+
+//
+// Borland's Codeguard trips up over the -Vx- option here:
+//
+#ifdef __CODEGUARD__
+# pragma option push -Vx-
+#endif
+
+template<class P, class D> class sp_counted_base_impl: public sp_counted_base
+{
+private:
+
+    P ptr; // copy constructor must not throw
+    D del; // copy constructor must not throw
+
+    sp_counted_base_impl(sp_counted_base_impl const &);
+    sp_counted_base_impl & operator= (sp_counted_base_impl const &);
+
+    typedef sp_counted_base_impl<P, D> this_type;
+
+public:
+
+    // pre: initial_use_count <= initial_weak_count, d(p) must not throw
+
+    sp_counted_base_impl(P p, D d): ptr(p), del(d)
+    {
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        detail::cbi_call_constructor_hook(this, p, d, 0);
+#endif
+    }
+
+    virtual void dispose() // nothrow
+    {
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        detail::cbi_call_destructor_hook(this, ptr, del, 0);
+#endif
+        del(ptr);
+    }
+
+    virtual void * get_deleter(std::type_info const & ti)
+    {
+        return ti == typeid(D)? &del: 0;
+    }
+
+#if defined(BOOST_SP_USE_STD_ALLOCATOR)
+
+    void * operator new(std::size_t)
+    {
+        return std::allocator<this_type>().allocate(1, static_cast<this_type *>(0));
+    }
+
+    void operator delete(void * p)
+    {
+        std::allocator<this_type>().deallocate(static_cast<this_type *>(p), 1);
+    }
+
+#endif
+
+#if defined(BOOST_SP_USE_QUICK_ALLOCATOR)
+
+    void * operator new(std::size_t)
+    {
+        return quick_allocator<this_type>::alloc();
+    }
+
+    void operator delete(void * p)
+    {
+        quick_allocator<this_type>::dealloc(p);
+    }
+
+#endif
+};
+
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+
+int const shared_count_id = 0x2C35F101;
+int const   weak_count_id = 0x298C38A4;
+
+#endif
+
+class weak_count;
+
+class shared_count
+{
+private:
+
+    sp_counted_base * pi_;
+
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+    int id_;
+#endif
+
+    friend class weak_count;
+
+public:
+
+    shared_count(): pi_(0) // nothrow
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+    }
+
+    template<class P, class D> shared_count(P p, D d): pi_(0)
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+#ifndef BOOST_NO_EXCEPTIONS
+
+        try
+        {
+            pi_ = new sp_counted_base_impl<P, D>(p, d);
+        }
+        catch(...)
+        {
+            d(p); // delete p
+            throw;
+        }
+
+#else
+
+        pi_ = new sp_counted_base_impl<P, D>(p, d);
+
+        if(pi_ == 0)
+        {
+            d(p); // delete p
+            boost::throw_exception(std::bad_alloc());
+        }
+
+#endif
+    }
+
+#ifndef BOOST_NO_AUTO_PTR
+
+    // auto_ptr<Y> is special cased to provide the strong guarantee
+
+    template<class Y>
+    explicit shared_count(std::auto_ptr<Y> & r): pi_(new sp_counted_base_impl< Y *, checked_deleter<Y> >(r.get(), checked_deleter<Y>()))
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+        r.release();
+    }
+
+#endif 
+
+    ~shared_count() // nothrow
+    {
+        if(pi_ != 0) pi_->release();
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        id_ = 0;
+#endif
+    }
+
+    shared_count(shared_count const & r): pi_(r.pi_) // nothrow
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+        if(pi_ != 0) pi_->add_ref_copy();
+    }
+
+    explicit shared_count(weak_count const & r); // throws bad_weak_ptr when r.use_count() == 0
+
+    shared_count & operator= (shared_count const & r) // nothrow
+    {
+        sp_counted_base * tmp = r.pi_;
+        if(tmp != 0) tmp->add_ref_copy();
+        if(pi_ != 0) pi_->release();
+        pi_ = tmp;
+
+        return *this;
+    }
+
+    void swap(shared_count & r) // nothrow
+    {
+        sp_counted_base * tmp = r.pi_;
+        r.pi_ = pi_;
+        pi_ = tmp;
+    }
+
+    long use_count() const // nothrow
+    {
+        return pi_ != 0? pi_->use_count(): 0;
+    }
+
+    bool unique() const // nothrow
+    {
+        return use_count() == 1;
+    }
+
+    friend inline bool operator==(shared_count const & a, shared_count const & b)
+    {
+        return a.pi_ == b.pi_;
+    }
+
+    friend inline bool operator<(shared_count const & a, shared_count const & b)
+    {
+        return std::less<sp_counted_base *>()(a.pi_, b.pi_);
+    }
+
+    void * get_deleter(std::type_info const & ti) const
+    {
+        return pi_? pi_->get_deleter(ti): 0;
+    }
+};
+
+#ifdef __CODEGUARD__
+# pragma option pop
+#endif
+
+
+class weak_count
+{
+private:
+
+    sp_counted_base * pi_;
+
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+    int id_;
+#endif
+
+    friend class shared_count;
+
+public:
+
+    weak_count(): pi_(0) // nothrow
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(weak_count_id)
+#endif
+    {
+    }
+
+    weak_count(shared_count const & r): pi_(r.pi_) // nothrow
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+        if(pi_ != 0) pi_->weak_add_ref();
+    }
+
+    weak_count(weak_count const & r): pi_(r.pi_) // nothrow
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+        if(pi_ != 0) pi_->weak_add_ref();
+    }
+
+    ~weak_count() // nothrow
+    {
+        if(pi_ != 0) pi_->weak_release();
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        id_ = 0;
+#endif
+    }
+
+    weak_count & operator= (shared_count const & r) // nothrow
+    {
+        sp_counted_base * tmp = r.pi_;
+        if(tmp != 0) tmp->weak_add_ref();
+        if(pi_ != 0) pi_->weak_release();
+        pi_ = tmp;
+
+        return *this;
+    }
+
+    weak_count & operator= (weak_count const & r) // nothrow
+    {
+        sp_counted_base * tmp = r.pi_;
+        if(tmp != 0) tmp->weak_add_ref();
+        if(pi_ != 0) pi_->weak_release();
+        pi_ = tmp;
+
+        return *this;
+    }
+
+    void swap(weak_count & r) // nothrow
+    {
+        sp_counted_base * tmp = r.pi_;
+        r.pi_ = pi_;
+        pi_ = tmp;
+    }
+
+    long use_count() const // nothrow
+    {
+        return pi_ != 0? pi_->use_count(): 0;
+    }
+
+    friend inline bool operator==(weak_count const & a, weak_count const & b)
+    {
+        return a.pi_ == b.pi_;
+    }
+
+    friend inline bool operator<(weak_count const & a, weak_count const & b)
+    {
+        return std::less<sp_counted_base *>()(a.pi_, b.pi_);
+    }
+};
+
+inline shared_count::shared_count(weak_count const & r): pi_(r.pi_)
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+{
+    if(pi_ != 0)
+    {
+        pi_->add_ref_lock();
+    }
+    else
+    {
+        boost::throw_exception(boost::bad_weak_ptr());
+    }
+}
+
+} // namespace detail
+
+} // namespace boost
+
+#ifdef __BORLANDC__
+# pragma warn .8027     // Functions containing try are not expanded inline
+# pragma warn .8026     // Functions with excep. spec. are not expanded inline
+#endif
+
+#endif  // #ifndef BOOST_DETAIL_SHARED_COUNT_HPP_INCLUDED
diff --git a/src/boost/detail/workaround.hpp b/src/boost/detail/workaround.hpp
new file mode 100644
index 000000000000..0d5a2b2bcbe9
--- /dev/null
+++ b/src/boost/detail/workaround.hpp
@@ -0,0 +1,74 @@
+// Copyright David Abrahams 2002. Permission to copy, use,
+// modify, sell and distribute this software is granted provided this
+// copyright notice appears in all copies. This software is provided
+// "as is" without express or implied warranty, and with no claim as
+// to its suitability for any purpose.
+#ifndef WORKAROUND_DWA2002126_HPP
+# define WORKAROUND_DWA2002126_HPP
+
+// Compiler/library version workaround macro
+//
+// Usage:
+//
+//     #if BOOST_WORKAROUND(BOOST_MSVC, <= 1200)
+//        ... // workaround code here
+//     #endif
+//
+// When BOOST_STRICT_CONFIG is defined, expands to 0. Otherwise, the
+// first argument must be undefined or expand to a numeric
+// value. The above expands to:
+//
+//     (BOOST_MSVC) != 0 && (BOOST_MSVC) <= 1200
+//
+// When used for workarounds that apply to the latest known version 
+// and all earlier versions of a compiler, the following convention 
+// should be observed:
+//
+//     #if BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1301))
+//
+// The version number in this case corresponds to the last version in
+// which the workaround was known to have been required. When
+// BOOST_DETECT_OUTDATED_WORKAROUNDS is not the defined, the macro
+// BOOST_TESTED_AT(x) expands to "!= 0", which effectively activates
+// the workaround for any version of the compiler. When
+// BOOST_DETECT_OUTDATED_WORKAROUNDS is defined, a compiler warning or
+// error will be issued if the compiler version exceeds the argument
+// to BOOST_TESTED_AT().  This can be used to locate workarounds which
+// may be obsoleted by newer versions.
+
+# ifndef BOOST_STRICT_CONFIG
+
+#  define BOOST_WORKAROUND(symbol, test)                \
+        ((symbol != 0) && (1 % (( (symbol test) ) + 1)))
+//                              ^ ^           ^ ^
+// The extra level of parenthesis nesting above, along with the
+// BOOST_OPEN_PAREN indirection below, is required to satisfy the
+// broken preprocessor in MWCW 8.3 and earlier.
+//
+// The basic mechanism works as follows:
+//      (symbol test) + 1        =>   if (symbol test) then 2 else 1
+//      1 % ((symbol test) + 1)  =>   if (symbol test) then 1 else 0
+//
+// The complication with % is for cooperation with BOOST_TESTED_AT().
+// When "test" is BOOST_TESTED_AT(x) and
+// BOOST_DETECT_OUTDATED_WORKAROUNDS is #defined,
+//
+//      symbol test              =>   if (symbol <= x) then 1 else -1
+//      (symbol test) + 1        =>   if (symbol <= x) then 2 else 0
+//      1 % ((symbol test) + 1)  =>   if (symbol <= x) then 1 else divide-by-zero
+//
+
+#  ifdef BOOST_DETECT_OUTDATED_WORKAROUNDS
+#   define BOOST_OPEN_PAREN (
+#   define BOOST_TESTED_AT(value)  > value) ?(-1): BOOST_OPEN_PAREN 1
+#  else
+#   define BOOST_TESTED_AT(value) != ((value)-(value))
+#  endif
+
+# else
+
+#  define BOOST_WORKAROUND(symbol, test) 0
+
+# endif 
+
+#endif // WORKAROUND_DWA2002126_HPP
diff --git a/src/boost/enable_shared_from_this.hpp b/src/boost/enable_shared_from_this.hpp
new file mode 100644
index 000000000000..1d52e72c2077
--- /dev/null
+++ b/src/boost/enable_shared_from_this.hpp
@@ -0,0 +1,68 @@
+#ifndef BOOST_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED
+#define BOOST_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED
+
+//
+//  enable_shared_from_this.hpp
+//
+//  Copyright (c) 2002 Peter Dimov
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  http://www.boost.org/libs/smart_ptr/enable_shared_from_this.html
+//
+
+#include <boost/weak_ptr.hpp>
+#include <boost/shared_ptr.hpp>
+#include <boost/assert.hpp>
+//#include <boost/config.hpp>
+
+namespace boost
+{
+
+template<class T> class enable_shared_from_this
+{
+protected:
+
+    enable_shared_from_this()
+    {
+    }
+
+    enable_shared_from_this(enable_shared_from_this const &)
+    {
+    }
+
+    enable_shared_from_this & operator=(enable_shared_from_this const &)
+    {
+        return *this;
+    }
+
+    ~enable_shared_from_this()
+    {
+    }
+
+public:
+
+    shared_ptr<T> shared_from_this()
+    {
+        shared_ptr<T> p(_internal_weak_this);
+        BOOST_ASSERT(p.get() == this);
+        return p;
+    }
+
+    shared_ptr<T const> shared_from_this() const
+    {
+        shared_ptr<T const> p(_internal_weak_this);
+        BOOST_ASSERT(p.get() == this);
+        return p;
+    }
+
+    typedef T _internal_element_type; // for bcc 5.5.1
+    weak_ptr<_internal_element_type> _internal_weak_this;
+};
+
+} // namespace boost
+
+#endif  // #ifndef BOOST_ENABLE_SHARED_FROM_THIS_HPP_INCLUDED
diff --git a/src/boost/format.hpp b/src/boost/format.hpp
new file mode 100644
index 000000000000..f965f0f33e9a
--- /dev/null
+++ b/src/boost/format.hpp
@@ -0,0 +1,64 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream
+
+// ----------------------------------------------------------------------------
+// format.hpp :  primary header
+// ----------------------------------------------------------------------------
+
+#ifndef BOOST_FORMAT_HPP
+#define BOOST_FORMAT_HPP
+
+#include <vector>
+#include <string>
+#include <sstream>
+#include <cassert>
+
+#if HAVE_LOCALE
+#include <locale>
+#else
+#define BOOST_NO_STD_LOCALE
+#define BOOST_NO_LOCALE_ISIDIGIT
+#include <cctype>
+#endif
+
+#include <boost/format/macros_default.hpp>
+
+
+// ****  Forward declarations ----------------------------------
+#include <boost/format/format_fwd.hpp>           // basic_format<Ch,Tr>, and other frontends
+#include <boost/format/internals_fwd.hpp>        // misc forward declarations for internal use
+
+
+// ****  Auxiliary structs (stream_format_state<Ch,Tr> , and format_item<Ch,Tr> )
+#include <boost/format/internals.hpp>    
+
+// ****  Format  class  interface --------------------------------
+#include <boost/format/format_class.hpp>
+
+// **** Exceptions -----------------------------------------------
+#include <boost/format/exceptions.hpp>
+
+// **** Implementation -------------------------------------------
+//#include <boost/format/format_implementation.hpp>   // member functions
+
+#include <boost/format/group.hpp>                   // class for grouping arguments
+
+#include <boost/format/feed_args.hpp>               // argument-feeding functions
+//#include <boost/format/parsing.hpp>                 // format-string parsing (member-)functions
+
+// **** Implementation of the free functions ----------------------
+//#include <boost/format/free_funcs.hpp>
+
+
+#endif // BOOST_FORMAT_HPP
diff --git a/src/boost/format/exceptions.hpp b/src/boost/format/exceptions.hpp
new file mode 100644
index 000000000000..79e452449ef8
--- /dev/null
+++ b/src/boost/format/exceptions.hpp
@@ -0,0 +1,96 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// exceptions.hpp 
+// ------------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_EXCEPTIONS_HPP
+#define BOOST_FORMAT_EXCEPTIONS_HPP
+
+
+#include <stdexcept>
+
+
+namespace boost {
+
+namespace io {
+
+// **** exceptions -----------------------------------------------
+
+class format_error : public std::exception
+{
+public:
+  format_error() {}
+  virtual const char *what() const throw()
+  {
+    return "boost::format_error: "
+      "format generic failure";
+  }
+};
+
+class bad_format_string : public format_error
+{
+public:
+  bad_format_string() {}
+  virtual const char *what() const throw()
+  {
+    return "boost::bad_format_string: "
+      "format-string is ill-formed";
+  }
+};
+
+class too_few_args : public format_error
+{
+public:
+  too_few_args() {}
+  virtual const char *what() const throw()
+  {
+    return "boost::too_few_args: "
+      "format-string refered to more arguments than were passed";
+  }
+};
+
+class too_many_args : public format_error
+{
+public:
+  too_many_args() {}
+  virtual const char *what() const throw()
+  {
+    return "boost::too_many_args: "
+      "format-string refered to less arguments than were passed";
+  }
+};
+
+
+class  out_of_range : public format_error
+{
+public:
+  out_of_range() {}
+  virtual const char *what() const throw()
+  {
+    return "boost::out_of_range: "
+      "tried to refer to an argument (or item) number which is out of range, "
+      "according to the format string.";
+  }
+};
+
+
+} // namespace io
+
+} // namespace boost
+
+
+#endif // BOOST_FORMAT_EXCEPTIONS_HPP
diff --git a/src/boost/format/feed_args.hpp b/src/boost/format/feed_args.hpp
new file mode 100644
index 000000000000..3d0b47b4a12e
--- /dev/null
+++ b/src/boost/format/feed_args.hpp
@@ -0,0 +1,247 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream
+
+// ----------------------------------------------------------------------------
+// feed_args.hpp :  functions for processing each argument 
+//                      (feed, feed_manip, and distribute)
+// ----------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_FEED_ARGS_HPP
+#define BOOST_FORMAT_FEED_ARGS_HPP
+
+#include "boost/format/format_class.hpp"
+#include "boost/format/group.hpp"
+
+#include "boost/throw_exception.hpp"
+
+namespace boost {
+namespace io {
+namespace detail {
+namespace  { 
+
+  inline
+  void empty_buf(BOOST_IO_STD ostringstream & os) { 
+    static const std::string emptyStr;
+    os.str(emptyStr); 
+  }
+
+  void do_pad( std::string & s, 
+                std::streamsize w, 
+                const char c, 
+                std::ios::fmtflags f, 
+                bool center) 
+    // applies centered / left / right  padding  to the string s.
+    // Effects : string s is padded.
+  {
+    std::streamsize n=w-s.size();
+    if(n<=0) {
+      return;
+    }
+    if(center) 
+      {
+        s.reserve(w); // allocate once for the 2 inserts
+        const std::streamsize n1 = n /2, n0 = n - n1; 
+        s.insert(s.begin(), n0, c);
+        s.append(n1, c);
+      } 
+    else 
+      {
+        if(f & std::ios::left) {
+          s.append(n, c);
+        }
+        else {
+          s.insert(s.begin(), n, c);
+        }
+      }
+  } // -do_pad(..) 
+
+
+  template<class T> inline
+  void put_head(BOOST_IO_STD ostream& , const T& ) {
+  }
+
+  template<class T> inline
+  void put_head( BOOST_IO_STD ostream& os, const group1<T>& x ) {
+    os << group_head(x.a1_); // send the first N-1 items, not the last
+  }
+
+  template<class T> inline
+  void put_last( BOOST_IO_STD ostream& os, const T& x ) {
+    os << x ;
+  }
+
+  template<class T> inline
+  void put_last( BOOST_IO_STD ostream& os, const group1<T>& x ) {
+    os << group_last(x.a1_); // this selects the last element
+  }
+
+#ifndef BOOST_NO_OVERLOAD_FOR_NON_CONST 
+  template<class T> inline
+  void put_head( BOOST_IO_STD ostream& , T& ) {
+  }
+
+  template<class T> inline
+  void put_last( BOOST_IO_STD ostream& os, T& x ) {
+    os << x ;
+  }
+#endif
+
+
+
+  
+template<class T> 
+void put( T x, 
+          const format_item& specs, 
+          std::string & res, 
+          BOOST_IO_STD ostringstream& oss_ )
+{
+  // does the actual conversion of x, with given params, into a string
+  // using the *supplied* strinstream. (the stream state is important)
+
+  typedef std::string string_t;
+  typedef format_item  format_item_t;
+
+  stream_format_state   prev_state(oss_);
+    
+  specs.state_.apply_on(oss_);
+
+  // in case x is a group, apply the manip part of it, 
+  // in order to find width
+  put_head( oss_, x );
+  empty_buf( oss_);
+
+  const std::streamsize w=oss_.width();
+  const std::ios::fmtflags fl=oss_.flags();
+  const bool internal = (fl & std::ios::internal) != 0;
+  const bool two_stepped_padding = internal
+    &&  ! ( specs.pad_scheme_ & format_item_t::spacepad ) 
+    && specs.truncate_ < 0 ;
+      
+
+  if(! two_stepped_padding) 
+    {
+      if(w>0) // handle simple padding via do_pad, not natively in stream 
+        oss_.width(0);
+      put_last( oss_, x);
+      res = oss_.str();
+
+      if (specs.truncate_ >= 0)
+        res.erase(specs.truncate_);
+
+      // complex pads :
+      if(specs.pad_scheme_ & format_item_t::spacepad)
+        {
+          if( res.size()==0 ||   ( res[0]!='+' && res[0]!='-'  ))
+            {
+              res.insert(res.begin(), 1, ' '); // insert 1 space at  pos 0
+            }
+        }
+      if(w > 0) // need do_pad
+        {
+          do_pad(res,w,oss_.fill(), fl, (specs.pad_scheme_ & format_item_t::centered) !=0 );
+        }
+    } 
+  else  // 2-stepped padding
+    {
+      put_last( oss_, x); // oss_.width() may result in padding.
+      res = oss_.str();
+      
+      if (specs.truncate_ >= 0)
+        res.erase(specs.truncate_);
+
+      if( res.size() - w > 0)
+        { //   length w exceeded
+          // either it was multi-output with first output padding up all width..
+          // either it was one big arg and we are fine.
+          empty_buf( oss_);
+          oss_.width(0);
+          put_last(oss_, x );
+          string_t tmp = oss_.str();  // minimal-length output
+          std::streamsize d;
+          if( (d=w - tmp.size()) <=0 ) 
+            {
+              // minimal length is already >= w, so no padding  (cool!)
+              res.swap(tmp);
+            }
+          else
+            { // hum..  we need to pad (it was necessarily multi-output)
+              typedef typename string_t::size_type size_type;
+              size_type i = 0;
+              while( i<tmp.size() && tmp[i] == res[i] ) // find where we should pad.
+                ++i;
+              tmp.insert(i, static_cast<size_type>( d ), oss_.fill());
+              res.swap( tmp );
+            }
+        }
+      else 
+        { // okay, only one thing was printed and padded, so res is fine.
+        }
+    }
+
+  prev_state.apply_on(oss_);
+  empty_buf( oss_);
+  oss_.clear();
+} // end- put(..)
+
+
+}  // local namespace
+
+
+
+
+
+template<class T> 
+void distribute(basic_format& self, T x) 
+  // call put(x, ..) on every occurence of the current argument :
+{
+  if(self.cur_arg_ >= self.num_args_)
+    {
+      if( self.exceptions() & too_many_args_bit )
+        boost::throw_exception(too_many_args()); // too many variables have been supplied !
+      else return;
+    }
+  for(unsigned long i=0; i < self.items_.size(); ++i)
+    {
+      if(self.items_[i].argN_ == self.cur_arg_)
+        {
+          put<T> (x, self.items_[i], self.items_[i].res_, self.oss_ );
+        }
+    }
+}
+
+template<class T> 
+basic_format&  feed(basic_format& self, T x) 
+{
+  if(self.dumped_) self.clear();
+  distribute<T> (self, x);
+  ++self.cur_arg_;
+  if(self.bound_.size() != 0)
+    {
+      while( self.cur_arg_ < self.num_args_ && self.bound_[self.cur_arg_] )
+        ++self.cur_arg_;
+    }
+
+  // this arg is finished, reset the stream's format state
+  self.state0_.apply_on(self.oss_);
+  return self;
+}
+    
+
+} // namespace detail
+} // namespace io
+} // namespace boost
+
+
+#endif //  BOOST_FORMAT_FEED_ARGS_HPP
diff --git a/src/boost/format/format_class.hpp b/src/boost/format/format_class.hpp
new file mode 100644
index 000000000000..6875623acb47
--- /dev/null
+++ b/src/boost/format/format_class.hpp
@@ -0,0 +1,135 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// format_class.hpp :  class interface
+// ------------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_CLASS_HPP
+#define BOOST_FORMAT_CLASS_HPP
+
+#include <vector>
+#include <string>
+
+#include <boost/format/format_fwd.hpp>
+#include <boost/format/internals_fwd.hpp>
+
+#include <boost/format/internals.hpp>
+
+namespace boost {
+
+class basic_format 
+{
+public:
+  typedef std::string                string_t;
+  typedef BOOST_IO_STD ostringstream internal_stream_t;
+private:
+  typedef BOOST_IO_STD ostream       stream_t;
+  typedef io::detail::stream_format_state  stream_format_state;
+  typedef io::detail::format_item          format_item_t;
+
+public:
+  basic_format(const char* str);
+  basic_format(const string_t& s);
+#ifndef BOOST_NO_STD_LOCALE
+  basic_format(const char* str, const std::locale & loc);
+  basic_format(const string_t& s, const std::locale & loc);
+#endif // no locale
+  basic_format(const basic_format& x);
+  basic_format& operator= (const basic_format& x);
+
+  basic_format& clear(); // empty the string buffers (except bound arguments, see clear_binds() )
+
+  // pass arguments through those operators :
+  template<class T>  basic_format&   operator%(const T& x) 
+  { 
+    return io::detail::feed<const T&>(*this,x);
+  }
+
+#ifndef BOOST_NO_OVERLOAD_FOR_NON_CONST
+  template<class T>  basic_format&   operator%(T& x) 
+  {
+    return io::detail::feed<T&>(*this,x);
+  }
+#endif
+
+
+  // system for binding arguments :
+  template<class T>  
+  basic_format&         bind_arg(int argN, const T& val) 
+  {
+    return io::detail::bind_arg_body(*this, argN, val); 
+  }
+  basic_format&         clear_bind(int argN);
+  basic_format&         clear_binds();
+
+  // modify the params of a directive, by applying a manipulator :
+  template<class T> 
+  basic_format&  modify_item(int itemN, const T& manipulator) 
+  {
+    return io::detail::modify_item_body(*this, itemN, manipulator) ;
+  }
+
+  // Choosing which errors will throw exceptions :
+  unsigned char exceptions() const;
+  unsigned char exceptions(unsigned char newexcept);
+
+  // final output
+  string_t str() const;
+  friend BOOST_IO_STD ostream& 
+  operator<< ( BOOST_IO_STD ostream& , const basic_format& ); 
+                      
+
+  template<class T>  friend basic_format&  
+  io::detail::feed(basic_format&, T);
+    
+  template<class T>  friend   
+  void io::detail::distribute(basic_format&, T);
+  
+  template<class T>  friend
+  basic_format&  io::detail::modify_item_body(basic_format&, int, const T&);
+
+  template<class T> friend
+  basic_format&  io::detail::bind_arg_body(basic_format&, int, const T&);
+
+// make the members private only if the friend templates are supported
+private:
+
+  // flag bits, used for style_
+  enum style_values  { ordered = 1,        // set only if all directives are  positional directives
+                       special_needs = 4 };     
+
+  // parse the format string :
+  void parse(const string_t&);
+
+  int                           style_;         // style of format-string :  positional or not, etc
+  int                           cur_arg_;       // keep track of wich argument will come
+  int                           num_args_;      // number of expected arguments
+  mutable bool                  dumped_;        // true only after call to str() or <<
+  std::vector<format_item_t>    items_;         // vector of directives (aka items)
+  string_t                      prefix_;        // piece of string to insert before first item
+
+  std::vector<bool>             bound_;         // stores which arguments were bound
+                                                //   size = num_args OR zero
+  internal_stream_t             oss_;           // the internal stream.
+  stream_format_state           state0_;        // reference state for oss_
+  unsigned char                 exceptions_;
+}; // class basic_format
+
+
+} // namespace boost
+
+
+#endif // BOOST_FORMAT_CLASS_HPP
diff --git a/src/boost/format/format_fwd.hpp b/src/boost/format/format_fwd.hpp
new file mode 100644
index 000000000000..97c55f6684c3
--- /dev/null
+++ b/src/boost/format/format_fwd.hpp
@@ -0,0 +1,49 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// format_fwd.hpp :  forward declarations, for primary header format.hpp
+// ------------------------------------------------------------------------------
+
+#ifndef BOOST_FORMAT_FWD_HPP
+#define BOOST_FORMAT_FWD_HPP
+
+#include <string>
+#include <iosfwd>
+
+namespace boost {
+
+class basic_format;
+
+typedef basic_format    format;
+
+namespace io {
+enum format_error_bits { bad_format_string_bit = 1, 
+                         too_few_args_bit = 2, too_many_args_bit = 4,
+                         out_of_range_bit = 8,
+                         all_error_bits = 255, no_error_bits=0 };
+                  
+// Convertion:  format   to   string
+std::string     str(const basic_format& ) ;
+
+} // namespace io
+
+
+BOOST_IO_STD ostream& 
+operator<<( BOOST_IO_STD ostream&, const basic_format&);
+
+
+} // namespace boost
+
+#endif // BOOST_FORMAT_FWD_HPP
diff --git a/src/boost/format/format_implementation.cc b/src/boost/format/format_implementation.cc
new file mode 100644
index 000000000000..aa191afe1132
--- /dev/null
+++ b/src/boost/format/format_implementation.cc
@@ -0,0 +1,256 @@
+// -*- C++ -*-
+//  Boost general library format ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream
+
+// ----------------------------------------------------------------------------
+// format_implementation.hpp  Implementation of the basic_format class
+// ----------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_IMPLEMENTATION_HPP
+#define BOOST_FORMAT_IMPLEMENTATION_HPP
+
+#include <boost/throw_exception.hpp>
+#include <boost/assert.hpp>
+#include <boost/format.hpp>
+
+namespace boost {
+
+// --------  format:: -------------------------------------------
+basic_format::basic_format(const char* str)
+    : style_(0), cur_arg_(0), num_args_(0), dumped_(false),
+      items_(), oss_(), exceptions_(io::all_error_bits)
+{
+    state0_.set_by_stream(oss_);
+    string_t emptyStr;
+    if( !str) str = emptyStr.c_str();
+    parse( str );
+}
+
+#ifndef BOOST_NO_STD_LOCALE
+basic_format::basic_format(const char* str, const std::locale & loc)
+    : style_(0), cur_arg_(0), num_args_(0), dumped_(false),
+      items_(), oss_(), exceptions_(io::all_error_bits)
+{
+    oss_.imbue( loc );
+    state0_.set_by_stream(oss_);
+    string_t emptyStr;
+    if( !str) str = emptyStr.c_str();
+    parse( str );
+}
+
+basic_format::basic_format(const string_t& s, const std::locale & loc)
+    : style_(0), cur_arg_(0), num_args_(0), dumped_(false),
+      items_(),  oss_(), exceptions_(io::all_error_bits)
+{
+    oss_.imbue( loc );
+    state0_.set_by_stream(oss_);
+    parse(s);  
+}
+#endif //BOOST_NO_STD_LOCALE
+
+basic_format::basic_format(const string_t& s)
+    : style_(0), cur_arg_(0), num_args_(0), dumped_(false),
+      items_(),  oss_(), exceptions_(io::all_error_bits)
+{
+    state0_.set_by_stream(oss_);
+    parse(s);  
+}
+
+basic_format:: basic_format(const basic_format& x)
+    : style_(x.style_), cur_arg_(x.cur_arg_), num_args_(x.num_args_), dumped_(false), 
+      items_(x.items_), prefix_(x.prefix_), bound_(x.bound_), 
+      oss_(),   // <- we obviously can't copy x.oss_
+      state0_(x.state0_), exceptions_(x.exceptions_)
+{ 
+    state0_.apply_on(oss_);
+} 
+
+basic_format& basic_format::operator= (const basic_format& x)
+{
+    if(this == &x)
+      return *this;
+    state0_ = x.state0_;
+    state0_.apply_on(oss_);
+
+    // plus all the other (trivial) assignments :
+    exceptions_ = x.exceptions_;
+    items_ = x.items_;
+    prefix_ = x.prefix_;
+    bound_=x.bound_;
+    style_=x.style_; 
+    cur_arg_=x.cur_arg_; 
+    num_args_=x.num_args_;
+    dumped_=x.dumped_;
+    return *this;
+}
+
+
+unsigned char basic_format::exceptions() const 
+{
+  return exceptions_; 
+}
+
+unsigned char basic_format::exceptions(unsigned char newexcept) 
+{ 
+  unsigned char swp = exceptions_; 
+  exceptions_ = newexcept; 
+  return swp; 
+}
+
+
+basic_format& basic_format ::clear()
+  // empty the string buffers (except bound arguments, see clear_binds() )
+  // and make the format object ready for formatting a new set of arguments
+{
+    BOOST_ASSERT( bound_.size()==0 || num_args_ == static_cast<int>(bound_.size()) );
+
+    for(unsigned long i=0; i<items_.size(); ++i){
+      items_[i].state_ = items_[i].ref_state_;
+      // clear converted strings only if the corresponding argument is not  bound :
+      if( bound_.size()==0 || !bound_[ items_[i].argN_ ] )  items_[i].res_.resize(0);
+    }
+    cur_arg_=0; dumped_=false;
+    // maybe first arg is bound:
+    if(bound_.size() != 0)
+      {
+        while(cur_arg_ < num_args_ && bound_[cur_arg_] )      ++cur_arg_;
+      }
+    return *this;
+}
+
+basic_format& basic_format ::clear_binds() 
+  // cancel all bindings, and clear()
+{
+    bound_.resize(0);
+    clear();
+    return *this;
+}
+
+basic_format& basic_format::clear_bind(int argN) 
+  // cancel the binding of ONE argument, and clear()
+{
+    if(argN<1 || argN > num_args_ || bound_.size()==0 || !bound_[argN-1] ) 
+      {
+        if( exceptions() & io::out_of_range_bit )
+          boost::throw_exception(io::out_of_range()); // arg not in range.
+        else return *this;
+      }
+    bound_[argN-1]=false;
+    clear();
+    return *this;
+}
+
+
+
+std::string basic_format::str() const
+{
+  dumped_=true;
+  if(items_.size()==0)
+    return prefix_;
+  if( cur_arg_ < num_args_)
+      if( exceptions() & io::too_few_args_bit )
+        boost::throw_exception(io::too_few_args()); // not enough variables have been supplied !
+
+  unsigned long sz = prefix_.size();
+  unsigned long i;
+  for(i=0; i < items_.size(); ++i) 
+    sz += items_[i].res_.size() + items_[i].appendix_.size();
+  string_t res;
+  res.reserve(sz);
+
+  res += prefix_;
+  for(i=0; i < items_.size(); ++i) 
+  {
+    const format_item_t& item = items_[i];
+    res += item.res_;
+    if( item.argN_ == format_item_t::argN_tabulation) 
+    { 
+      BOOST_ASSERT( item.pad_scheme_ & format_item_t::tabulation);
+      std::streamsize  n = item.state_.width_ - res.size();
+      if( n > 0 )
+        res.append( n, item.state_.fill_ );
+    }
+    res += item.appendix_;
+  }
+  return res;
+}
+
+namespace io {
+namespace detail {
+
+template<class T>
+basic_format&  bind_arg_body( basic_format& self, 
+                                      int argN, 
+                                      const T& val)
+  // bind one argument to a fixed value
+  // this is persistent over clear() calls, thus also over str() and <<
+{
+    if(self.dumped_) self.clear(); // needed, because we will modify cur_arg_..
+    if(argN<1 || argN > self.num_args_) 
+      {
+        if( self.exceptions() & io::out_of_range_bit )
+          boost::throw_exception(io::out_of_range()); // arg not in range.
+        else return self;
+      }
+    if(self.bound_.size()==0) 
+      self.bound_.assign(self.num_args_,false);
+    else 
+      BOOST_ASSERT( self.num_args_ == static_cast<signed int>(self.bound_.size()) );
+    int o_cur_arg = self.cur_arg_;
+    self.cur_arg_ = argN-1; // arrays begin at 0
+
+    self.bound_[self.cur_arg_]=false; // if already set, we unset and re-sets..
+    self.operator%(val); // put val at the right place, because cur_arg is set
+    
+
+    // Now re-position cur_arg before leaving :
+    self.cur_arg_ = o_cur_arg; 
+    self.bound_[argN-1]=true;
+    if(self.cur_arg_ == argN-1 )
+      // hum, now this arg is bound, so move to next free arg
+      {
+        while(self.cur_arg_ < self.num_args_ && self.bound_[self.cur_arg_])   ++self.cur_arg_;
+      }
+    // In any case, we either have all args, or are on a non-binded arg :
+    BOOST_ASSERT( self.cur_arg_ >= self.num_args_ || ! self.bound_[self.cur_arg_]);
+    return self;
+}
+
+template<class T>
+basic_format&  modify_item_body( basic_format& self,
+                                      int itemN, 
+                                      const T& manipulator)
+  // applies a manipulator to the format_item describing a given directive.
+  // this is a permanent change, clear or clear_binds won't cancel that.
+{
+  if(itemN<1 || itemN >= static_cast<signed int>(self.items_.size() )) 
+    {
+      if( self.exceptions() & io::out_of_range_bit ) 
+        boost::throw_exception(io::out_of_range()); // item not in range.
+      else return self;
+    }
+  self.items_[itemN-1].ref_state_.apply_manip( manipulator );
+  self.items_[itemN-1].state_ = self.items_[itemN-1].ref_state_;
+  return self;
+}
+
+} // namespace detail
+
+} // namespace io
+
+} // namespace boost
+
+
+
+#endif  // BOOST_FORMAT_IMPLEMENTATION_HPP
diff --git a/src/boost/format/free_funcs.cc b/src/boost/format/free_funcs.cc
new file mode 100644
index 000000000000..151db37a0ac9
--- /dev/null
+++ b/src/boost/format/free_funcs.cc
@@ -0,0 +1,71 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// free_funcs.hpp :  implementation of the free functions declared in namespace format
+// ------------------------------------------------------------------------------
+
+#ifndef BOOST_FORMAT_FUNCS_HPP
+#define BOOST_FORMAT_FUNCS_HPP
+
+#include "boost/format.hpp"
+#include "boost/throw_exception.hpp"
+
+namespace boost {
+
+namespace io {
+  inline 
+  std::string str(const basic_format& f) 
+    // adds up all pieces of strings and converted items, and return the formatted string
+  {
+    return f.str();
+  }
+}   // - namespace io
+
+BOOST_IO_STD ostream& 
+operator<<( BOOST_IO_STD ostream& os, 
+            const boost::basic_format& f) 
+  // effect: "return os << str(f);" but we can try to do it faster
+{
+  typedef boost::basic_format   format_t;
+  if(f.items_.size()==0) 
+    os << f.prefix_;
+  else {
+    if(f.cur_arg_ < f.num_args_)
+      if( f.exceptions() & io::too_few_args_bit )
+        boost::throw_exception(io::too_few_args()); // not enough variables have been supplied !
+    if(f.style_ & format_t::special_needs) 
+        os << f.str();
+    else {
+    // else we dont have to count chars output, so we dump directly to os :
+      os << f.prefix_;
+      for(unsigned long i=0; i<f.items_.size(); ++i) 
+        {
+          const format_t::format_item_t& item = f.items_[i];
+          os << item.res_;
+          os << item.appendix_;
+
+        }
+    }
+  }
+  f.dumped_=true;
+  return os;
+}
+
+
+
+} // namespace boost
+
+
+#endif // BOOST_FORMAT_FUNCS_HPP
diff --git a/src/boost/format/group.hpp b/src/boost/format/group.hpp
new file mode 100644
index 000000000000..ac63f3f0bab0
--- /dev/null
+++ b/src/boost/format/group.hpp
@@ -0,0 +1,680 @@
+
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream
+
+// ----------------------------------------------------------------------------
+
+// group.hpp :  encapsulates a group of manipulators along with an argument
+//                      
+// group_head : cut the last element of a group out.
+// (is overloaded below on each type of group)
+
+// group_last : returns the last element of a group
+// (is overloaded below on each type of group)
+
+// ----------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_GROUP_HPP
+#define BOOST_FORMAT_GROUP_HPP
+
+
+namespace boost {
+namespace io {
+
+
+namespace detail {
+
+
+// empty group, but useful even though.
+struct group0 
+{
+    group0()      {}
+};
+
+template <class Ch, class Tr>
+inline
+BOOST_IO_STD ostream&
+operator << ( BOOST_IO_STD ostream& os,
+             const group0& )
+{ 
+   return os; 
+}
+
+template <class T1>
+struct group1
+{
+    T1 a1_;
+    group1(T1 a1)
+      : a1_(a1)
+      {}
+};
+
+template <class Ch, class Tr, class T1>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group1<T1>& x)
+{ 
+   os << x.a1_;  
+   return os; 
+}
+
+
+
+
+template <class T1,class T2>
+struct group2
+{
+    T1 a1_;
+    T2 a2_;
+    group2(T1 a1,T2 a2)
+      : a1_(a1),a2_(a2)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group2<T1,T2>& x)
+{ 
+   os << x.a1_<< x.a2_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3>
+struct group3
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    group3(T1 a1,T2 a2,T3 a3)
+      : a1_(a1),a2_(a2),a3_(a3)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group3<T1,T2,T3>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4>
+struct group4
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    group4(T1 a1,T2 a2,T3 a3,T4 a4)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group4<T1,T2,T3,T4>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4,class T5>
+struct group5
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    T5 a5_;
+    group5(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4),a5_(a5)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4,class T5>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group5<T1,T2,T3,T4,T5>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_<< x.a5_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6>
+struct group6
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    T5 a5_;
+    T6 a6_;
+    group6(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4),a5_(a5),a6_(a6)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4,class T5,class T6>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group6<T1,T2,T3,T4,T5,T6>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_<< x.a5_<< x.a6_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7>
+struct group7
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    T5 a5_;
+    T6 a6_;
+    T7 a7_;
+    group7(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4),a5_(a5),a6_(a6),a7_(a7)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4,class T5,class T6,class T7>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group7<T1,T2,T3,T4,T5,T6,T7>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_<< x.a5_<< x.a6_<< x.a7_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8>
+struct group8
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    T5 a5_;
+    T6 a6_;
+    T7 a7_;
+    T8 a8_;
+    group8(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4),a5_(a5),a6_(a6),a7_(a7),a8_(a8)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group8<T1,T2,T3,T4,T5,T6,T7,T8>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_<< x.a5_<< x.a6_<< x.a7_<< x.a8_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9>
+struct group9
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    T5 a5_;
+    T6 a6_;
+    T7 a7_;
+    T8 a8_;
+    T9 a9_;
+    group9(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8,T9 a9)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4),a5_(a5),a6_(a6),a7_(a7),a8_(a8),a9_(a9)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group9<T1,T2,T3,T4,T5,T6,T7,T8,T9>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_<< x.a5_<< x.a6_<< x.a7_<< x.a8_<< x.a9_;  
+   return os; 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9,class T10>
+struct group10
+{
+    T1 a1_;
+    T2 a2_;
+    T3 a3_;
+    T4 a4_;
+    T5 a5_;
+    T6 a6_;
+    T7 a7_;
+    T8 a8_;
+    T9 a9_;
+    T10 a10_;
+    group10(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8,T9 a9,T10 a10)
+      : a1_(a1),a2_(a2),a3_(a3),a4_(a4),a5_(a5),a6_(a6),a7_(a7),a8_(a8),a9_(a9),a10_(a10)
+      {}
+};
+
+template <class Ch, class Tr, class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9,class T10>
+inline
+BOOST_IO_STD ostream&
+operator << (BOOST_IO_STD ostream& os,
+             const group10<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10>& x)
+{ 
+   os << x.a1_<< x.a2_<< x.a3_<< x.a4_<< x.a5_<< x.a6_<< x.a7_<< x.a8_<< x.a9_<< x.a10_;  
+   return os; 
+}
+
+
+
+
+template <class T1,class T2>
+inline
+group1<T1> 
+group_head( group2<T1,T2> const& x)
+{
+   return group1<T1> (x.a1_); 
+}
+
+template <class T1,class T2>
+inline
+group1<T2> 
+group_last( group2<T1,T2> const& x)
+{
+   return group1<T2> (x.a2_); 
+}
+
+
+
+template <class T1,class T2,class T3>
+inline
+group2<T1,T2> 
+group_head( group3<T1,T2,T3> const& x)
+{
+   return group2<T1,T2> (x.a1_,x.a2_); 
+}
+
+template <class T1,class T2,class T3>
+inline
+group1<T3> 
+group_last( group3<T1,T2,T3> const& x)
+{
+   return group1<T3> (x.a3_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4>
+inline
+group3<T1,T2,T3> 
+group_head( group4<T1,T2,T3,T4> const& x)
+{
+   return group3<T1,T2,T3> (x.a1_,x.a2_,x.a3_); 
+}
+
+template <class T1,class T2,class T3,class T4>
+inline
+group1<T4> 
+group_last( group4<T1,T2,T3,T4> const& x)
+{
+   return group1<T4> (x.a4_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4,class T5>
+inline
+group4<T1,T2,T3,T4> 
+group_head( group5<T1,T2,T3,T4,T5> const& x)
+{
+   return group4<T1,T2,T3,T4> (x.a1_,x.a2_,x.a3_,x.a4_); 
+}
+
+template <class T1,class T2,class T3,class T4,class T5>
+inline
+group1<T5> 
+group_last( group5<T1,T2,T3,T4,T5> const& x)
+{
+   return group1<T5> (x.a5_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4,class T5,class T6>
+inline
+group5<T1,T2,T3,T4,T5> 
+group_head( group6<T1,T2,T3,T4,T5,T6> const& x)
+{
+   return group5<T1,T2,T3,T4,T5> (x.a1_,x.a2_,x.a3_,x.a4_,x.a5_); 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6>
+inline
+group1<T6> 
+group_last( group6<T1,T2,T3,T4,T5,T6> const& x)
+{
+   return group1<T6> (x.a6_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7>
+inline
+group6<T1,T2,T3,T4,T5,T6> 
+group_head( group7<T1,T2,T3,T4,T5,T6,T7> const& x)
+{
+   return group6<T1,T2,T3,T4,T5,T6> (x.a1_,x.a2_,x.a3_,x.a4_,x.a5_,x.a6_); 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7>
+inline
+group1<T7> 
+group_last( group7<T1,T2,T3,T4,T5,T6,T7> const& x)
+{
+   return group1<T7> (x.a7_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8>
+inline
+group7<T1,T2,T3,T4,T5,T6,T7> 
+group_head( group8<T1,T2,T3,T4,T5,T6,T7,T8> const& x)
+{
+   return group7<T1,T2,T3,T4,T5,T6,T7> (x.a1_,x.a2_,x.a3_,x.a4_,x.a5_,x.a6_,x.a7_); 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8>
+inline
+group1<T8> 
+group_last( group8<T1,T2,T3,T4,T5,T6,T7,T8> const& x)
+{
+   return group1<T8> (x.a8_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9>
+inline
+group8<T1,T2,T3,T4,T5,T6,T7,T8> 
+group_head( group9<T1,T2,T3,T4,T5,T6,T7,T8,T9> const& x)
+{
+   return group8<T1,T2,T3,T4,T5,T6,T7,T8> (x.a1_,x.a2_,x.a3_,x.a4_,x.a5_,x.a6_,x.a7_,x.a8_); 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9>
+inline
+group1<T9> 
+group_last( group9<T1,T2,T3,T4,T5,T6,T7,T8,T9> const& x)
+{
+   return group1<T9> (x.a9_); 
+}
+
+
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9,class T10>
+inline
+group9<T1,T2,T3,T4,T5,T6,T7,T8,T9> 
+group_head( group10<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10> const& x)
+{
+   return group9<T1,T2,T3,T4,T5,T6,T7,T8,T9> (x.a1_,x.a2_,x.a3_,x.a4_,x.a5_,x.a6_,x.a7_,x.a8_,x.a9_); 
+}
+
+template <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9,class T10>
+inline
+group1<T10> 
+group_last( group10<T1,T2,T3,T4,T5,T6,T7,T8,T9,T10> const& x)
+{
+   return group1<T10> (x.a10_); 
+}
+
+
+
+
+
+} // namespace detail
+
+
+
+// helper functions
+
+
+inline detail::group1< detail::group0 >  
+group() { return detail::group1< detail::group0 > ( detail::group0() ); }
+
+template  <class T1, class Var> 
+inline
+detail::group1< detail::group2<T1, Var const&> >
+  group(T1 a1, Var const& var)
+{ 
+   return detail::group1< detail::group2<T1, Var const&> >
+                   ( detail::group2<T1, Var const&> 
+                        (a1, var) 
+                  );
+}
+
+template  <class T1,class T2, class Var> 
+inline
+detail::group1< detail::group3<T1,T2, Var const&> >
+  group(T1 a1,T2 a2, Var const& var)
+{ 
+   return detail::group1< detail::group3<T1,T2, Var const&> >
+                   ( detail::group3<T1,T2, Var const&> 
+                        (a1,a2, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3, class Var> 
+inline
+detail::group1< detail::group4<T1,T2,T3, Var const&> >
+  group(T1 a1,T2 a2,T3 a3, Var const& var)
+{ 
+   return detail::group1< detail::group4<T1,T2,T3, Var const&> >
+                   ( detail::group4<T1,T2,T3, Var const&> 
+                        (a1,a2,a3, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4, class Var> 
+inline
+detail::group1< detail::group5<T1,T2,T3,T4, Var const&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4, Var const& var)
+{ 
+   return detail::group1< detail::group5<T1,T2,T3,T4, Var const&> >
+                   ( detail::group5<T1,T2,T3,T4, Var const&> 
+                        (a1,a2,a3,a4, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5, class Var> 
+inline
+detail::group1< detail::group6<T1,T2,T3,T4,T5, Var const&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5, Var const& var)
+{ 
+   return detail::group1< detail::group6<T1,T2,T3,T4,T5, Var const&> >
+                   ( detail::group6<T1,T2,T3,T4,T5, Var const&> 
+                        (a1,a2,a3,a4,a5, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6, class Var> 
+inline
+detail::group1< detail::group7<T1,T2,T3,T4,T5,T6, Var const&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6, Var const& var)
+{ 
+   return detail::group1< detail::group7<T1,T2,T3,T4,T5,T6, Var const&> >
+                   ( detail::group7<T1,T2,T3,T4,T5,T6, Var const&> 
+                        (a1,a2,a3,a4,a5,a6, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6,class T7, class Var> 
+inline
+detail::group1< detail::group8<T1,T2,T3,T4,T5,T6,T7, Var const&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7, Var const& var)
+{ 
+   return detail::group1< detail::group8<T1,T2,T3,T4,T5,T6,T7, Var const&> >
+                   ( detail::group8<T1,T2,T3,T4,T5,T6,T7, Var const&> 
+                        (a1,a2,a3,a4,a5,a6,a7, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8, class Var> 
+inline
+detail::group1< detail::group9<T1,T2,T3,T4,T5,T6,T7,T8, Var const&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8, Var const& var)
+{ 
+   return detail::group1< detail::group9<T1,T2,T3,T4,T5,T6,T7,T8, Var const&> >
+                   ( detail::group9<T1,T2,T3,T4,T5,T6,T7,T8, Var const&> 
+                        (a1,a2,a3,a4,a5,a6,a7,a8, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9, class Var> 
+inline
+detail::group1< detail::group10<T1,T2,T3,T4,T5,T6,T7,T8,T9, Var const&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8,T9 a9, Var const& var)
+{ 
+   return detail::group1< detail::group10<T1,T2,T3,T4,T5,T6,T7,T8,T9, Var const&> >
+                   ( detail::group10<T1,T2,T3,T4,T5,T6,T7,T8,T9, Var const&> 
+                        (a1,a2,a3,a4,a5,a6,a7,a8,a9, var) 
+                  );
+}
+
+
+#ifndef BOOST_NO_OVERLOAD_FOR_NON_CONST
+
+template  <class T1, class Var> 
+inline
+detail::group1< detail::group2<T1, Var&> >
+  group(T1 a1, Var& var)
+{ 
+   return detail::group1< detail::group2<T1, Var&> >
+                   ( detail::group2<T1, Var&> 
+                        (a1, var) 
+                  );
+}
+
+template  <class T1,class T2, class Var> 
+inline
+detail::group1< detail::group3<T1,T2, Var&> >
+  group(T1 a1,T2 a2, Var& var)
+{ 
+   return detail::group1< detail::group3<T1,T2, Var&> >
+                   ( detail::group3<T1,T2, Var&> 
+                        (a1,a2, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3, class Var> 
+inline
+detail::group1< detail::group4<T1,T2,T3, Var&> >
+  group(T1 a1,T2 a2,T3 a3, Var& var)
+{ 
+   return detail::group1< detail::group4<T1,T2,T3, Var&> >
+                   ( detail::group4<T1,T2,T3, Var&> 
+                        (a1,a2,a3, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4, class Var> 
+inline
+detail::group1< detail::group5<T1,T2,T3,T4, Var&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4, Var& var)
+{ 
+   return detail::group1< detail::group5<T1,T2,T3,T4, Var&> >
+                   ( detail::group5<T1,T2,T3,T4, Var&> 
+                        (a1,a2,a3,a4, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5, class Var> 
+inline
+detail::group1< detail::group6<T1,T2,T3,T4,T5, Var&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5, Var& var)
+{ 
+   return detail::group1< detail::group6<T1,T2,T3,T4,T5, Var&> >
+                   ( detail::group6<T1,T2,T3,T4,T5, Var&> 
+                        (a1,a2,a3,a4,a5, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6, class Var> 
+inline
+detail::group1< detail::group7<T1,T2,T3,T4,T5,T6, Var&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6, Var& var)
+{ 
+   return detail::group1< detail::group7<T1,T2,T3,T4,T5,T6, Var&> >
+                   ( detail::group7<T1,T2,T3,T4,T5,T6, Var&> 
+                        (a1,a2,a3,a4,a5,a6, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6,class T7, class Var> 
+inline
+detail::group1< detail::group8<T1,T2,T3,T4,T5,T6,T7, Var&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7, Var& var)
+{ 
+   return detail::group1< detail::group8<T1,T2,T3,T4,T5,T6,T7, Var&> >
+                   ( detail::group8<T1,T2,T3,T4,T5,T6,T7, Var&> 
+                        (a1,a2,a3,a4,a5,a6,a7, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8, class Var> 
+inline
+detail::group1< detail::group9<T1,T2,T3,T4,T5,T6,T7,T8, Var&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8, Var& var)
+{ 
+   return detail::group1< detail::group9<T1,T2,T3,T4,T5,T6,T7,T8, Var&> >
+                   ( detail::group9<T1,T2,T3,T4,T5,T6,T7,T8, Var&> 
+                        (a1,a2,a3,a4,a5,a6,a7,a8, var) 
+                  );
+}
+
+template  <class T1,class T2,class T3,class T4,class T5,class T6,class T7,class T8,class T9, class Var> 
+inline
+detail::group1< detail::group10<T1,T2,T3,T4,T5,T6,T7,T8,T9, Var&> >
+  group(T1 a1,T2 a2,T3 a3,T4 a4,T5 a5,T6 a6,T7 a7,T8 a8,T9 a9, Var& var)
+{ 
+   return detail::group1< detail::group10<T1,T2,T3,T4,T5,T6,T7,T8,T9, Var&> >
+                   ( detail::group10<T1,T2,T3,T4,T5,T6,T7,T8,T9, Var&> 
+                        (a1,a2,a3,a4,a5,a6,a7,a8,a9, var) 
+                  );
+}
+
+
+#endif  //end- #ifndef BOOST_NO_OVERLOAD_FOR_NON_CONST
+
+
+} // namespace io
+
+} // namespace boost
+
+
+#endif   // BOOST_FORMAT_GROUP_HPP
diff --git a/src/boost/format/internals.hpp b/src/boost/format/internals.hpp
new file mode 100644
index 000000000000..d25eb4c864c4
--- /dev/null
+++ b/src/boost/format/internals.hpp
@@ -0,0 +1,167 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream
+
+// ----------------------------------------------------------------------------
+// internals.hpp :  internal structs. included by format.hpp
+//                              stream_format_state, and format_item
+// ----------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_INTERNALS_HPP
+#define BOOST_FORMAT_INTERNALS_HPP
+
+
+#include <string>
+#include <sstream>
+
+namespace boost {
+namespace io {
+namespace detail {
+
+
+// --------------
+// set of params that define the format state of a stream
+
+struct stream_format_state 
+{
+  typedef std::ios   basic_ios;
+
+  std::streamsize width_;
+  std::streamsize precision_;
+  char fill_; 
+  std::ios::fmtflags flags_;
+
+  stream_format_state()       : width_(-1), precision_(-1), fill_(0), flags_(std::ios::dec)  {}
+  stream_format_state(basic_ios& os)                  {set_by_stream(os); }
+
+  void apply_on(basic_ios & os) const;                //- applies format_state to the stream
+  template<class T> void apply_manip(T manipulator)   //- modifies state by applying manipulator.
+       { apply_manip_body<T>( *this, manipulator) ; }
+  void reset();                                       //- sets to default state.
+  void set_by_stream(const basic_ios& os);            //- sets to os's state.
+};  
+
+
+
+// --------------
+// format_item : stores all parameters that can be defined by directives in the format-string
+
+struct format_item 
+{     
+  enum pad_values { zeropad = 1, spacepad =2, centered=4, tabulation = 8 };
+
+  enum arg_values { argN_no_posit   = -1, // non-positional directive. argN will be set later.
+                    argN_tabulation = -2, // tabulation directive. (no argument read) 
+                    argN_ignored    = -3  // ignored directive. (no argument read)
+  };
+  typedef BOOST_IO_STD ios              basic_ios;
+  typedef detail::stream_format_state         stream_format_state;
+  typedef std::string           string_t;
+  typedef BOOST_IO_STD ostringstream    internal_stream_t;
+
+
+  int         argN_;           //- argument number (starts at 0,  eg : %1 => argN=0)
+                               //  negative values are used for items that don't process
+                               //  an argument
+  string_t    res_;            //- result of the formatting of this item
+  string_t    appendix_;       //- piece of string between this item and the next
+
+  stream_format_state ref_state_;// set by parsing the format_string, is only affected by modify_item
+  stream_format_state state_;  // always same as ref_state, _unless_ modified by manipulators 'group(..)'
+
+  // non-stream format-state parameters
+  signed int truncate_;        //- is >=0 for directives like %.5s (take 5 chars from the string)
+  unsigned int pad_scheme_;    //- several possible padding schemes can mix. see pad_values
+
+  format_item() : argN_(argN_no_posit), truncate_(-1), pad_scheme_(0)  {}
+
+  void compute_states();      // sets states  according to truncate and pad_scheme.
+}; 
+
+
+
+// -----------------------------------------------------------
+// Definitions
+// -----------------------------------------------------------
+
+// --- stream_format_state:: -------------------------------------------
+inline
+void stream_format_state::apply_on(basic_ios & os) const
+  // set the state of this stream according to our params
+{
+      if(width_ != -1)
+        os.width(width_);
+      if(precision_ != -1)
+        os.precision(precision_);
+      if(fill_ != 0)
+        os.fill(fill_);
+      os.flags(flags_);
+}
+
+inline
+void stream_format_state::set_by_stream(const basic_ios& os) 
+  // set our params according to the state of this stream
+{
+      flags_ = os.flags();
+      width_ = os.width();
+      precision_ = os.precision();
+      fill_ = os.fill();
+}
+
+template<class T>  inline
+void apply_manip_body( stream_format_state& self,
+                       T manipulator) 
+  // modify our params according to the manipulator
+{
+      BOOST_IO_STD stringstream  ss;
+      self.apply_on( ss );
+      ss << manipulator;
+      self.set_by_stream( ss );
+}
+
+inline
+void stream_format_state::reset() 
+  // set our params to standard's default state
+{
+      width_=-1; precision_=-1; fill_=0; 
+      flags_ = std::ios::dec; 
+}
+
+
+// --- format_items:: -------------------------------------------
+inline
+void format_item::compute_states() 
+  // reflect pad_scheme_   on  state_ and ref_state_ 
+  //   because some pad_schemes has complex consequences on several state params.
+{
+  if(pad_scheme_ & zeropad) 
+  {
+    if(ref_state_.flags_ & std::ios::left) 
+    {
+      pad_scheme_ = pad_scheme_ & (~zeropad); // ignore zeropad in left alignment
+    }
+    else 
+    { 
+      ref_state_.fill_='0'; 
+      ref_state_.flags_ |= std::ios::internal;
+    }
+  }
+  state_ = ref_state_;
+}
+
+
+} } } // namespaces boost :: io :: detail
+
+
+#endif // BOOST_FORMAT_INTERNALS_HPP
diff --git a/src/boost/format/internals_fwd.hpp b/src/boost/format/internals_fwd.hpp
new file mode 100644
index 000000000000..a8ebf7c3abc1
--- /dev/null
+++ b/src/boost/format/internals_fwd.hpp
@@ -0,0 +1,65 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// internals_fwd.hpp :  forward declarations, for internal headers
+// ------------------------------------------------------------------------------
+
+#ifndef BOOST_FORMAT_INTERNAL_FWD_HPP
+#define BOOST_FORMAT_INTERNAL_FWD_HPP
+
+#include "boost/format/format_fwd.hpp"
+
+
+namespace boost {
+namespace io {
+
+namespace detail {
+  struct stream_format_state;
+  struct format_item;
+}
+
+
+namespace detail {
+
+  // these functions were intended as methods, 
+  // but MSVC have problems with template member functions :
+
+  // defined in format_implementation.hpp :
+     template<class T> 
+     basic_format&  modify_item_body( basic_format& self, 
+                                          int itemN, const T& manipulator);
+
+     template<class T> 
+     basic_format&  bind_arg_body( basic_format& self,
+                                           int argN, const T& val);
+
+    template<class T> 
+    void apply_manip_body( stream_format_state& self,
+                           T manipulator);
+
+  // argument feeding (defined in feed_args.hpp ) :
+     template<class T> 
+     void distribute(basic_format& self, T x);
+
+     template<class T> 
+     basic_format& feed(basic_format& self, T x);
+ 
+} // namespace detail
+
+} // namespace io
+} // namespace boost
+
+
+#endif //  BOOST_FORMAT_INTERNAL_FWD_HPP
diff --git a/src/boost/format/local.mk b/src/boost/format/local.mk
new file mode 100644
index 000000000000..3776eff382fe
--- /dev/null
+++ b/src/boost/format/local.mk
@@ -0,0 +1,7 @@
+libraries += libformat
+
+libformat_NAME = libnixformat
+
+libformat_DIR := $(d)
+
+libformat_SOURCES := $(wildcard $(d)/*.cc)
diff --git a/src/boost/format/macros_default.hpp b/src/boost/format/macros_default.hpp
new file mode 100644
index 000000000000..4fd84a163fb3
--- /dev/null
+++ b/src/boost/format/macros_default.hpp
@@ -0,0 +1,48 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rüdiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// macros_default.hpp : configuration for the format library
+//                       provides default values for the stl workaround macros
+// ------------------------------------------------------------------------------
+
+#ifndef BOOST_FORMAT_MACROS_DEFAULT_HPP
+#define BOOST_FORMAT_MACROS_DEFAULT_HPP
+
+// *** This should go to "boost/config/suffix.hpp".
+
+#ifndef BOOST_IO_STD
+#  define BOOST_IO_STD std::
+#endif
+
+// **** Workaround for io streams, stlport and msvc.
+#ifdef BOOST_IO_NEEDS_USING_DECLARATION
+namespace boost {
+  using std::char_traits;
+  using std::basic_ostream;
+  using std::basic_ostringstream;
+  namespace io {
+    using std::basic_ostream;
+    namespace detail {
+      using std::basic_ios;
+      using std::basic_ostream;
+      using std::basic_ostringstream;
+    }
+  }
+}
+#endif
+
+// ------------------------------------------------------------------------------
+
+#endif // BOOST_FORMAT_MACROS_DEFAULT_HPP
diff --git a/src/boost/format/parsing.cc b/src/boost/format/parsing.cc
new file mode 100644
index 000000000000..34c36adeb734
--- /dev/null
+++ b/src/boost/format/parsing.cc
@@ -0,0 +1,454 @@
+// -*- C++ -*-
+//  Boost general library 'format'   ---------------------------
+//  See http://www.boost.org for updates, documentation, and revision history.
+
+//  (C) Samuel Krempp 2001
+//                  krempp@crans.ens-cachan.fr
+//  Permission to copy, use, modify, sell and
+//  distribute this software is granted provided this copyright notice appears
+//  in all copies. This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+
+// ideas taken from Rudiger Loos's format class
+// and Karl Nelson's ofstream (also took its parsing code as basis for printf parsing)
+
+// ------------------------------------------------------------------------------
+// parsing.hpp :  implementation of the parsing member functions
+//                      ( parse, parse_printf_directive)
+// ------------------------------------------------------------------------------
+
+
+#ifndef BOOST_FORMAT_PARSING_HPP
+#define BOOST_FORMAT_PARSING_HPP
+
+
+#include <boost/format.hpp>
+#include <boost/throw_exception.hpp>
+#include <boost/assert.hpp>
+
+
+namespace boost {
+namespace io {
+namespace detail {
+
+  template<class Stream> inline
+  bool wrap_isdigit(char c, Stream &os) 
+  {
+#ifndef BOOST_NO_LOCALE_ISIDIGIT
+    return std::isdigit(c, os.rdbuf()->getloc() );
+# else
+    using namespace std;
+    return isdigit(c); 
+#endif 
+  } //end- wrap_isdigit(..)
+
+  template<class Res> inline
+  Res str2int(const std::string& s, 
+              std::string::size_type start, 
+              BOOST_IO_STD ios &os,
+              const Res = Res(0)  ) 
+    // Input : char string, with starting index
+    //         a basic_ios& merely to call its widen/narrow member function in the desired locale.
+    // Effects : reads s[start:] and converts digits into an integral n, of type Res
+    // Returns : n
+  {
+    Res n = 0;
+    while(start<s.size() && wrap_isdigit(s[start], os) ) {
+      char cur_ch = s[start];
+      BOOST_ASSERT(cur_ch != 0 ); // since we called isdigit, this should not happen.
+      n *= 10;
+      n += cur_ch - '0'; // 22.2.1.1.2 of the C++ standard
+      ++start;
+    }
+    return n;
+  }
+
+  void skip_asterisk(const std::string & buf, 
+                     std::string::size_type * pos_p,
+                     BOOST_IO_STD ios &os)
+    // skip printf's "asterisk-fields" directives in the format-string buf
+    // Input : char string, with starting index *pos_p
+    //         a basic_ios& merely to call its widen/narrow member function in the desired locale.
+    // Effects : advance *pos_p by skipping printf's asterisk fields.
+    // Returns : nothing
+  {
+    using namespace std;
+    BOOST_ASSERT( pos_p != 0);
+    if(*pos_p >= buf.size() ) return;
+    if(buf[ *pos_p]=='*') {
+      ++ (*pos_p);
+      while (*pos_p < buf.size() && wrap_isdigit(buf[*pos_p],os)) ++(*pos_p);
+      if(buf[*pos_p]=='$') ++(*pos_p);
+    }
+  }
+
+
+  inline void maybe_throw_exception( unsigned char exceptions)
+    // auxiliary func called by parse_printf_directive
+    // for centralising error handling
+    // it either throws if user sets the corresponding flag, or does nothing.
+  {
+    if(exceptions & io::bad_format_string_bit)
+          boost::throw_exception(io::bad_format_string());
+  }
+    
+
+
+  bool parse_printf_directive(const std::string & buf,
+                              std::string::size_type * pos_p,
+                              detail::format_item * fpar,
+                              BOOST_IO_STD ios &os,
+                              unsigned char exceptions)
+    // Input   : a 'printf-directive' in the format-string, starting at buf[ *pos_p ]
+    //           a basic_ios& merely to call its widen/narrow member function in the desired locale.
+    //           a bitset'excpetions' telling whether to throw exceptions on errors.
+    // Returns : true if parse somehow succeeded (possibly ignoring errors if exceptions disabled) 
+    //           false if it failed so bad that the directive should be printed verbatim
+    // Effects : - *pos_p is incremented so that buf[*pos_p] is the first char after the directive
+    //           - *fpar is set with the parameters read in the directive
+  {
+    typedef format_item  format_item_t;
+    BOOST_ASSERT( pos_p != 0);
+    std::string::size_type       &i1 = *pos_p,      
+                                                        i0; 
+    fpar->argN_ = format_item_t::argN_no_posit;  // if no positional-directive
+
+    bool in_brackets=false;
+    if(buf[i1]=='|')
+      {
+        in_brackets=true;
+        if( ++i1 >= buf.size() ) {
+          maybe_throw_exception(exceptions);
+          return false;
+        }
+      }
+
+    // the flag '0' would be picked as a digit for argument order, but here it's a flag :
+    if(buf[i1]=='0') 
+      goto parse_flags;
+
+    // handle argument order (%2$d)  or possibly width specification: %2d
+    i0 = i1;  // save position before digits
+    while (i1 < buf.size() && wrap_isdigit(buf[i1], os))
+      ++i1;
+    if (i1!=i0) 
+      {
+        if( i1 >= buf.size() ) {
+          maybe_throw_exception(exceptions);
+          return false;
+        }
+        int n=str2int(buf,i0, os, int(0) );
+        
+        // %N% case : this is already the end of the directive
+        if( buf[i1] == '%' ) 
+          {
+            fpar->argN_ = n-1;
+            ++i1;
+            if( in_brackets) 
+              maybe_throw_exception(exceptions); 
+              // but don't return.  maybe "%" was used in lieu of '$', so we go on.
+            else return true;
+          }
+
+        if ( buf[i1]=='$' ) 
+          {
+            fpar->argN_ = n-1;
+            ++i1;
+          } 
+        else  
+          {
+            // non-positionnal directive
+            fpar->ref_state_.width_ = n;
+            fpar->argN_  = format_item_t::argN_no_posit;
+            goto parse_precision;
+          }
+      }
+    
+  parse_flags: 
+    // handle flags
+    while ( i1 <buf.size()) // as long as char is one of + - = # 0 l h   or ' '
+      {  
+        // misc switches
+        switch (buf[i1]) 
+          {
+          case '\'' : break; // no effect yet. (painful to implement)
+          case 'l':
+          case 'h':  // short/long modifier : for printf-comaptibility (no action needed)
+             break;
+          case '-':
+            fpar->ref_state_.flags_ |= std::ios::left;
+            break;
+          case '=':
+            fpar->pad_scheme_ |= format_item_t::centered;
+            break;
+          case ' ':
+            fpar->pad_scheme_ |= format_item_t::spacepad;
+            break;
+          case '+':
+            fpar->ref_state_.flags_ |= std::ios::showpos;
+            break;
+          case '0':
+            fpar->pad_scheme_ |= format_item_t::zeropad; 
+            // need to know alignment before really setting flags,
+            // so just add 'zeropad' flag for now, it will be processed later.
+            break;
+          case '#':
+            fpar->ref_state_.flags_ |= std::ios::showpoint | std::ios::showbase;
+            break;
+          default:
+            goto parse_width;
+          }
+        ++i1;
+      } // loop on flag.
+    if( i1>=buf.size()) {
+      maybe_throw_exception(exceptions);
+      return true; 
+    }
+
+  parse_width:
+    // handle width spec
+    skip_asterisk(buf, &i1, os); // skips 'asterisk fields' :  *, or *N$
+    i0 = i1;  // save position before digits
+    while (i1<buf.size() && wrap_isdigit(buf[i1], os))
+      i1++;
+    
+    if (i1!=i0) 
+      { fpar->ref_state_.width_ = str2int( buf,i0, os, std::streamsize(0) ); }
+
+  parse_precision:
+    if( i1>=buf.size()) { 
+      maybe_throw_exception(exceptions);
+      return true;
+    }
+    // handle precision spec
+    if (buf[i1]=='.')  
+      {
+        ++i1;
+        skip_asterisk(buf, &i1, os);
+        i0 = i1;  // save position before digits
+        while (i1<buf.size() && wrap_isdigit(buf[i1], os))
+          ++i1;
+
+        if(i1==i0)
+          fpar->ref_state_.precision_ = 0;
+        else 
+          fpar->ref_state_.precision_ = str2int(buf,i0, os, std::streamsize(0) );
+      }
+    
+    // handle  formatting-type flags :
+    while( i1<buf.size() && 
+           ( buf[i1]=='l' || buf[i1]=='L' || buf[i1]=='h') )
+      ++i1;
+    if( i1>=buf.size()) {
+      maybe_throw_exception(exceptions);
+      return true;
+    }
+    
+    if( in_brackets && buf[i1]=='|' ) 
+      {
+        ++i1;
+        return true;
+      }
+    switch (buf[i1])  
+      {
+      case 'X':
+        fpar->ref_state_.flags_ |= std::ios::uppercase;
+      case 'p': // pointer => set hex.
+      case 'x':
+        fpar->ref_state_.flags_ &= ~std::ios::basefield;
+        fpar->ref_state_.flags_ |= std::ios::hex;
+        break;
+      
+      case 'o':
+        fpar->ref_state_.flags_ &= ~std::ios::basefield;
+        fpar->ref_state_.flags_ |=  std::ios::oct;
+        break;
+
+      case 'E':
+        fpar->ref_state_.flags_ |=  std::ios::uppercase;
+      case 'e':
+        fpar->ref_state_.flags_ &= ~std::ios::floatfield;
+        fpar->ref_state_.flags_ |=  std::ios::scientific;
+
+        fpar->ref_state_.flags_ &= ~std::ios::basefield;
+        fpar->ref_state_.flags_ |=  std::ios::dec;
+        break;
+      
+      case 'f':
+        fpar->ref_state_.flags_ &= ~std::ios::floatfield;
+        fpar->ref_state_.flags_ |=  std::ios::fixed;
+      case 'u':
+      case 'd':
+      case 'i':
+        fpar->ref_state_.flags_ &= ~std::ios::basefield;
+        fpar->ref_state_.flags_ |=  std::ios::dec;
+        break;
+
+      case 'T':
+        ++i1;
+        if( i1 >= buf.size())
+          maybe_throw_exception(exceptions);
+        else
+          fpar->ref_state_.fill_ = buf[i1];
+        fpar->pad_scheme_ |= format_item_t::tabulation;
+        fpar->argN_ = format_item_t::argN_tabulation; 
+        break;
+      case 't': 
+        fpar->ref_state_.fill_ = ' ';
+        fpar->pad_scheme_ |= format_item_t::tabulation;
+        fpar->argN_ = format_item_t::argN_tabulation; 
+        break;
+
+      case 'G':
+        fpar->ref_state_.flags_ |= std::ios::uppercase;
+        break;
+      case 'g': // 'g' conversion is default for floats.
+        fpar->ref_state_.flags_ &= ~std::ios::basefield;
+        fpar->ref_state_.flags_ |=  std::ios::dec;
+
+        // CLEAR all floatield flags, so stream will CHOOSE
+        fpar->ref_state_.flags_ &= ~std::ios::floatfield; 
+        break;
+
+      case 'C':
+      case 'c': 
+        fpar->truncate_ = 1;
+        break;
+      case 'S':
+      case 's': 
+        fpar->truncate_ = fpar->ref_state_.precision_;
+        fpar->ref_state_.precision_ = -1;
+        break;
+      case 'n' :  
+        fpar->argN_ = format_item_t::argN_ignored;
+        break;
+      default: 
+        maybe_throw_exception(exceptions);
+      }
+    ++i1;
+
+    if( in_brackets )
+      {
+        if( i1<buf.size() && buf[i1]=='|' ) 
+          {
+            ++i1;
+            return true;
+          }
+        else  maybe_throw_exception(exceptions);
+      }
+    return true;
+  }
+
+} // detail namespace
+} // io namespace
+
+
+// -----------------------------------------------
+//  format :: parse(..)
+
+void basic_format::parse(const string_t & buf) 
+  // parse the format-string
+{
+    using namespace std;
+    const char arg_mark = '%';
+    bool ordered_args=true; 
+    int max_argN=-1;
+    string_t::size_type i1=0;
+    int num_items=0;
+    
+    // A: find upper_bound on num_items and allocates arrays
+    i1=0; 
+    while( (i1=buf.find(arg_mark,i1)) != string::npos ) 
+    {
+      if( i1+1 >= buf.size() ) {
+        if(exceptions() & io::bad_format_string_bit)
+          boost::throw_exception(io::bad_format_string()); // must not end in "bla bla %"
+        else break; // stop there, ignore last '%'
+      }
+      if(buf[i1+1] == buf[i1] ) { i1+=2; continue; } // escaped "%%" / "##"
+      ++i1;
+      
+      // in case of %N% directives, dont count it double (wastes allocations..) :
+      while(i1 < buf.size() && io::detail::wrap_isdigit(buf[i1],oss_)) ++i1;
+      if( i1 < buf.size() && buf[i1] == arg_mark ) ++ i1;
+
+      ++num_items;
+    }
+    items_.assign( num_items, format_item_t() );
+    
+    // B: Now the real parsing of the format string :
+    num_items=0;
+    i1 = 0;
+    string_t::size_type i0 = i1;
+    bool special_things=false;
+    int cur_it=0;
+    while( (i1=buf.find(arg_mark,i1)) != string::npos ) 
+    {
+      string_t & piece = (cur_it==0) ? prefix_ : items_[cur_it-1].appendix_;
+
+      if( buf[i1+1] == buf[i1] ) // escaped mark, '%%'
+      {
+        piece += buf.substr(i0, i1-i0) + buf[i1]; 
+        i1+=2; i0=i1;
+        continue; 
+      }
+      BOOST_ASSERT(  static_cast<unsigned int>(cur_it) < items_.size() || cur_it==0);
+
+      if(i1!=i0) piece += buf.substr(i0, i1-i0);
+      ++i1;
+      
+      bool parse_ok;
+      parse_ok = io::detail::parse_printf_directive(buf, &i1, &items_[cur_it], oss_, exceptions());
+      if( ! parse_ok ) continue; // the directive will be printed verbatim
+
+      i0=i1;
+      items_[cur_it].compute_states(); // process complex options, like zeropad, into stream params.
+
+      int argN=items_[cur_it].argN_;
+      if(argN == format_item_t::argN_ignored)
+        continue;
+      if(argN ==format_item_t::argN_no_posit)
+        ordered_args=false;
+      else if(argN == format_item_t::argN_tabulation) special_things=true;
+      else if(argN > max_argN) max_argN = argN;
+      ++num_items;
+      ++cur_it;
+    } // loop on %'s
+    BOOST_ASSERT(cur_it == num_items);
+    
+    // store the final piece of string
+    string_t & piece = (cur_it==0) ? prefix_ : items_[cur_it-1].appendix_;
+    piece += buf.substr(i0);
+    
+    if( !ordered_args) 
+    {
+      if(max_argN >= 0 )  // dont mix positional with non-positionnal directives
+        {
+          if(exceptions() & io::bad_format_string_bit)
+            boost::throw_exception(io::bad_format_string());
+          // else do nothing. => positionnal arguments are processed as non-positionnal
+        }
+      // set things like it would have been with positional directives :
+      int non_ordered_items = 0;
+      for(int i=0; i< num_items; ++i)
+        if(items_[i].argN_ == format_item_t::argN_no_posit) 
+          {
+            items_[i].argN_ = non_ordered_items;
+            ++non_ordered_items;
+          }
+      max_argN = non_ordered_items-1;
+    }
+    
+    // C: set some member data :
+    items_.resize(num_items);
+
+    if(special_things) style_ |= special_needs;
+    num_args_ = max_argN + 1;
+    if(ordered_args) style_ |=  ordered;
+    else style_ &= ~ordered;
+}
+
+} // namespace boost
+
+
+#endif //  BOOST_FORMAT_PARSING_HPP
diff --git a/src/boost/shared_ptr.hpp b/src/boost/shared_ptr.hpp
new file mode 100644
index 000000000000..1702ad268811
--- /dev/null
+++ b/src/boost/shared_ptr.hpp
@@ -0,0 +1,474 @@
+#ifndef BOOST_SHARED_PTR_HPP_INCLUDED
+#define BOOST_SHARED_PTR_HPP_INCLUDED
+
+//
+//  shared_ptr.hpp
+//
+//  (C) Copyright Greg Colvin and Beman Dawes 1998, 1999.
+//  Copyright (c) 2001, 2002, 2003 Peter Dimov
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  See http://www.boost.org/libs/smart_ptr/shared_ptr.htm for documentation.
+//
+
+//#include <boost/config.hpp>   // for broken compiler workarounds
+
+#if defined(BOOST_NO_MEMBER_TEMPLATES) && !defined(BOOST_MSVC6_MEMBER_TEMPLATES)
+#include <boost/detail/shared_ptr_nmt.hpp>
+#else
+
+#include <boost/assert.hpp>
+#include <boost/checked_delete.hpp>
+#include <boost/throw_exception.hpp>
+#include <boost/detail/shared_count.hpp>
+#include <boost/detail/workaround.hpp>
+
+#include <memory>               // for std::auto_ptr
+#include <algorithm>            // for std::swap
+#include <functional>           // for std::less
+#include <typeinfo>             // for std::bad_cast
+#include <iosfwd>               // for std::basic_ostream
+
+#ifdef BOOST_MSVC  // moved here to work around VC++ compiler crash
+# pragma warning(push)
+# pragma warning(disable:4284) // odd return type for operator->
+#endif
+
+namespace boost
+{
+
+template<class T> class weak_ptr;
+template<class T> class enable_shared_from_this;
+
+namespace detail
+{
+
+struct static_cast_tag {};
+struct const_cast_tag {};
+struct dynamic_cast_tag {};
+struct polymorphic_cast_tag {};
+
+template<class T> struct shared_ptr_traits
+{
+    typedef T & reference;
+};
+
+template<> struct shared_ptr_traits<void>
+{
+    typedef void reference;
+};
+
+#if !defined(BOOST_NO_CV_VOID_SPECIALIZATIONS)
+
+template<> struct shared_ptr_traits<void const>
+{
+    typedef void reference;
+};
+
+template<> struct shared_ptr_traits<void volatile>
+{
+    typedef void reference;
+};
+
+template<> struct shared_ptr_traits<void const volatile>
+{
+    typedef void reference;
+};
+
+#endif
+
+// enable_shared_from_this support
+
+template<class T, class Y> void sp_enable_shared_from_this(boost::enable_shared_from_this<T> * pe, Y * px, shared_count const & pn)
+{
+    if(pe != 0) pe->_internal_weak_this._internal_assign(px, pn);
+}
+
+inline void sp_enable_shared_from_this(void const volatile *, void const volatile *, shared_count const &)
+{
+}
+
+} // namespace detail
+
+
+//
+//  shared_ptr
+//
+//  An enhanced relative of scoped_ptr with reference counted copy semantics.
+//  The object pointed to is deleted when the last shared_ptr pointing to it
+//  is destroyed or reset.
+//
+
+template<class T> class shared_ptr
+{
+private:
+
+    // Borland 5.5.1 specific workaround
+    typedef shared_ptr<T> this_type;
+
+public:
+
+    typedef T element_type;
+    typedef T value_type;
+    typedef T * pointer;
+    typedef typename detail::shared_ptr_traits<T>::reference reference;
+
+    shared_ptr(): px(0), pn() // never throws in 1.30+
+    {
+    }
+
+    template<class Y>
+    explicit shared_ptr(Y * p): px(p), pn(p, checked_deleter<Y>()) // Y must be complete
+    {
+        detail::sp_enable_shared_from_this(p, p, pn);
+    }
+
+    //
+    // Requirements: D's copy constructor must not throw
+    //
+    // shared_ptr will release p by calling d(p)
+    //
+
+    template<class Y, class D> shared_ptr(Y * p, D d): px(p), pn(p, d)
+    {
+        detail::sp_enable_shared_from_this(p, p, pn);
+    }
+
+//  generated copy constructor, assignment, destructor are fine...
+
+//  except that Borland C++ has a bug, and g++ with -Wsynth warns
+#if defined(__BORLANDC__) || defined(__GNUC__)
+
+    shared_ptr & operator=(shared_ptr const & r) // never throws
+    {
+        px = r.px;
+        pn = r.pn; // shared_count::op= doesn't throw
+        return *this;
+    }
+
+#endif
+
+    template<class Y>
+    explicit shared_ptr(weak_ptr<Y> const & r): pn(r.pn) // may throw
+    {
+        // it is now safe to copy r.px, as pn(r.pn) did not throw
+        px = r.px;
+    }
+
+    template<class Y>
+    shared_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+    {
+    }
+
+    template<class Y>
+    shared_ptr(shared_ptr<Y> const & r, detail::static_cast_tag): px(static_cast<element_type *>(r.px)), pn(r.pn)
+    {
+    }
+
+    template<class Y>
+    shared_ptr(shared_ptr<Y> const & r, detail::const_cast_tag): px(const_cast<element_type *>(r.px)), pn(r.pn)
+    {
+    }
+
+    template<class Y>
+    shared_ptr(shared_ptr<Y> const & r, detail::dynamic_cast_tag): px(dynamic_cast<element_type *>(r.px)), pn(r.pn)
+    {
+        if(px == 0) // need to allocate new counter -- the cast failed
+        {
+            pn = detail::shared_count();
+        }
+    }
+
+    template<class Y>
+    shared_ptr(shared_ptr<Y> const & r, detail::polymorphic_cast_tag): px(dynamic_cast<element_type *>(r.px)), pn(r.pn)
+    {
+        if(px == 0)
+        {
+            boost::throw_exception(std::bad_cast());
+        }
+    }
+
+#ifndef BOOST_NO_AUTO_PTR
+
+    template<class Y>
+    explicit shared_ptr(std::auto_ptr<Y> & r): px(r.get()), pn()
+    {
+        Y * tmp = r.get();
+        pn = detail::shared_count(r);
+        detail::sp_enable_shared_from_this(tmp, tmp, pn);
+    }
+
+#endif
+
+#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
+
+    template<class Y>
+    shared_ptr & operator=(shared_ptr<Y> const & r) // never throws
+    {
+        px = r.px;
+        pn = r.pn; // shared_count::op= doesn't throw
+        return *this;
+    }
+
+#endif
+
+#ifndef BOOST_NO_AUTO_PTR
+
+    template<class Y>
+    shared_ptr & operator=(std::auto_ptr<Y> & r)
+    {
+        this_type(r).swap(*this);
+        return *this;
+    }
+
+#endif
+
+    void reset() // never throws in 1.30+
+    {
+        this_type().swap(*this);
+    }
+
+    template<class Y> void reset(Y * p) // Y must be complete
+    {
+        BOOST_ASSERT(p == 0 || p != px); // catch self-reset errors
+        this_type(p).swap(*this);
+    }
+
+    template<class Y, class D> void reset(Y * p, D d)
+    {
+        this_type(p, d).swap(*this);
+    }
+
+    reference operator* () const // never throws
+    {
+        BOOST_ASSERT(px != 0);
+        return *px;
+    }
+
+    T * operator-> () const // never throws
+    {
+        BOOST_ASSERT(px != 0);
+        return px;
+    }
+    
+    T * get() const // never throws
+    {
+        return px;
+    }
+
+    // implicit conversion to "bool"
+
+#if defined(__SUNPRO_CC) && BOOST_WORKAROUND(__SUNPRO_CC, <= 0x530)
+
+    operator bool () const
+    {
+        return px != 0;
+    }
+
+#elif defined(__MWERKS__) && BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3003))
+    typedef T * (this_type::*unspecified_bool_type)() const;
+    
+    operator unspecified_bool_type() const // never throws
+    {
+        return px == 0? 0: &this_type::get;
+    }
+
+#else 
+
+    typedef T * this_type::*unspecified_bool_type;
+
+    operator unspecified_bool_type() const // never throws
+    {
+        return px == 0? 0: &this_type::px;
+    }
+
+#endif
+
+    // operator! is redundant, but some compilers need it
+
+    bool operator! () const // never throws
+    {
+        return px == 0;
+    }
+
+    bool unique() const // never throws
+    {
+        return pn.unique();
+    }
+
+    long use_count() const // never throws
+    {
+        return pn.use_count();
+    }
+
+    void swap(shared_ptr<T> & other) // never throws
+    {
+        std::swap(px, other.px);
+        pn.swap(other.pn);
+    }
+
+    template<class Y> bool _internal_less(shared_ptr<Y> const & rhs) const
+    {
+        return pn < rhs.pn;
+    }
+
+    void * _internal_get_deleter(std::type_info const & ti) const
+    {
+        return pn.get_deleter(ti);
+    }
+
+// Tasteless as this may seem, making all members public allows member templates
+// to work in the absence of member template friends. (Matthew Langston)
+
+#if 0
+
+private:
+
+    template<class Y> friend class shared_ptr;
+    template<class Y> friend class weak_ptr;
+
+
+#endif
+
+    T * px;                     // contained pointer
+    detail::shared_count pn;    // reference counter
+
+};  // shared_ptr
+
+template<class T, class U> inline bool operator==(shared_ptr<T> const & a, shared_ptr<U> const & b)
+{
+    return a.get() == b.get();
+}
+
+template<class T, class U> inline bool operator!=(shared_ptr<T> const & a, shared_ptr<U> const & b)
+{
+    return a.get() != b.get();
+}
+
+#if __GNUC__ == 2 && __GNUC_MINOR__ <= 96
+
+// Resolve the ambiguity between our op!= and the one in rel_ops
+
+template<class T> inline bool operator!=(shared_ptr<T> const & a, shared_ptr<T> const & b)
+{
+    return a.get() != b.get();
+}
+
+#endif
+
+template<class T, class U> inline bool operator<(shared_ptr<T> const & a, shared_ptr<U> const & b)
+{
+    return a._internal_less(b);
+}
+
+template<class T> inline void swap(shared_ptr<T> & a, shared_ptr<T> & b)
+{
+    a.swap(b);
+}
+
+template<class T, class U> shared_ptr<T> static_pointer_cast(shared_ptr<U> const & r)
+{
+    return shared_ptr<T>(r, detail::static_cast_tag());
+}
+
+template<class T, class U> shared_ptr<T> const_pointer_cast(shared_ptr<U> const & r)
+{
+    return shared_ptr<T>(r, detail::const_cast_tag());
+}
+
+template<class T, class U> shared_ptr<T> dynamic_pointer_cast(shared_ptr<U> const & r)
+{
+    return shared_ptr<T>(r, detail::dynamic_cast_tag());
+}
+
+// shared_*_cast names are deprecated. Use *_pointer_cast instead.
+
+template<class T, class U> shared_ptr<T> shared_static_cast(shared_ptr<U> const & r)
+{
+    return shared_ptr<T>(r, detail::static_cast_tag());
+}
+
+template<class T, class U> shared_ptr<T> shared_dynamic_cast(shared_ptr<U> const & r)
+{
+    return shared_ptr<T>(r, detail::dynamic_cast_tag());
+}
+
+template<class T, class U> shared_ptr<T> shared_polymorphic_cast(shared_ptr<U> const & r)
+{
+    return shared_ptr<T>(r, detail::polymorphic_cast_tag());
+}
+
+template<class T, class U> shared_ptr<T> shared_polymorphic_downcast(shared_ptr<U> const & r)
+{
+    BOOST_ASSERT(dynamic_cast<T *>(r.get()) == r.get());
+    return shared_static_cast<T>(r);
+}
+
+// get_pointer() enables boost::mem_fn to recognize shared_ptr
+
+template<class T> inline T * get_pointer(shared_ptr<T> const & p)
+{
+    return p.get();
+}
+
+// operator<<
+
+#if defined(__GNUC__) &&  (__GNUC__ < 3)
+
+template<class Y> std::ostream & operator<< (std::ostream & os, shared_ptr<Y> const & p)
+{
+    os << p.get();
+    return os;
+}
+
+#else
+
+# if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, <= 1200 && __SGI_STL_PORT)
+// MSVC6 has problems finding std::basic_ostream through the using declaration in namespace _STL
+using std::basic_ostream;
+template<class E, class T, class Y> basic_ostream<E, T> & operator<< (basic_ostream<E, T> & os, shared_ptr<Y> const & p)
+# else
+template<class E, class T, class Y> std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, shared_ptr<Y> const & p)
+# endif 
+{
+    os << p.get();
+    return os;
+}
+
+#endif
+
+// get_deleter (experimental)
+
+#if (defined(__GNUC__) &&  (__GNUC__ < 3)) || (defined(__EDG_VERSION__) && (__EDG_VERSION__ <= 238))
+
+// g++ 2.9x doesn't allow static_cast<X const *>(void *)
+// apparently EDG 2.38 also doesn't accept it
+
+template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
+{
+    void const * q = p._internal_get_deleter(typeid(D));
+    return const_cast<D *>(static_cast<D const *>(q));
+}
+
+#else
+
+template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
+{
+    return static_cast<D *>(p._internal_get_deleter(typeid(D)));
+}
+
+#endif
+
+} // namespace boost
+
+#ifdef BOOST_MSVC
+# pragma warning(pop)
+#endif    
+
+#endif  // #if defined(BOOST_NO_MEMBER_TEMPLATES) && !defined(BOOST_MSVC6_MEMBER_TEMPLATES)
+
+#endif  // #ifndef BOOST_SHARED_PTR_HPP_INCLUDED
diff --git a/src/boost/throw_exception.hpp b/src/boost/throw_exception.hpp
new file mode 100644
index 000000000000..07b4ae5ceae7
--- /dev/null
+++ b/src/boost/throw_exception.hpp
@@ -0,0 +1,47 @@
+#ifndef BOOST_THROW_EXCEPTION_HPP_INCLUDED
+#define BOOST_THROW_EXCEPTION_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//
+//  boost/throw_exception.hpp
+//
+//  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  http://www.boost.org/libs/utility/throw_exception.html
+//
+
+//#include <boost/config.hpp>
+
+#ifdef BOOST_NO_EXCEPTIONS
+# include <exception>
+#endif
+
+namespace boost
+{
+
+#ifdef BOOST_NO_EXCEPTIONS
+
+void throw_exception(std::exception const & e); // user defined
+
+#else
+
+template<class E> void throw_exception(E const & e)
+{
+    throw e;
+}
+
+#endif
+
+} // namespace boost
+
+#endif // #ifndef BOOST_THROW_EXCEPTION_HPP_INCLUDED
diff --git a/src/boost/weak_ptr.hpp b/src/boost/weak_ptr.hpp
new file mode 100644
index 000000000000..3d3b3eb79df1
--- /dev/null
+++ b/src/boost/weak_ptr.hpp
@@ -0,0 +1,193 @@
+#ifndef BOOST_WEAK_PTR_HPP_INCLUDED
+#define BOOST_WEAK_PTR_HPP_INCLUDED
+
+//
+//  weak_ptr.hpp
+//
+//  Copyright (c) 2001, 2002, 2003 Peter Dimov
+//
+//  Permission to copy, use, modify, sell and distribute this software
+//  is granted provided this copyright notice appears in all copies.
+//  This software is provided "as is" without express or implied
+//  warranty, and with no claim as to its suitability for any purpose.
+//
+//  See http://www.boost.org/libs/smart_ptr/weak_ptr.htm for documentation.
+//
+
+#include <boost/shared_ptr.hpp>
+
+#ifdef BOOST_MSVC  // moved here to work around VC++ compiler crash
+# pragma warning(push)
+# pragma warning(disable:4284) // odd return type for operator->
+#endif
+
+namespace boost
+{
+
+template<class T> class weak_ptr
+{
+private:
+
+    // Borland 5.5.1 specific workarounds
+    typedef weak_ptr<T> this_type;
+
+public:
+
+    typedef T element_type;
+
+    weak_ptr(): px(0), pn() // never throws in 1.30+
+    {
+    }
+
+//  generated copy constructor, assignment, destructor are fine
+
+
+//
+//  The "obvious" converting constructor implementation:
+//
+//  template<class Y>
+//  weak_ptr(weak_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+//  {
+//  }
+//
+//  has a serious problem.
+//
+//  r.px may already have been invalidated. The px(r.px)
+//  conversion may require access to *r.px (virtual inheritance).
+//
+//  It is not possible to avoid spurious access violations since
+//  in multithreaded programs r.px may be invalidated at any point.
+//
+
+    template<class Y>
+    weak_ptr(weak_ptr<Y> const & r): pn(r.pn) // never throws
+    {
+        px = r.lock().get();
+    }
+
+    template<class Y>
+    weak_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
+    {
+    }
+
+#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)
+
+    template<class Y>
+    weak_ptr & operator=(weak_ptr<Y> const & r) // never throws
+    {
+        px = r.lock().get();
+        pn = r.pn;
+        return *this;
+    }
+
+    template<class Y>
+    weak_ptr & operator=(shared_ptr<Y> const & r) // never throws
+    {
+        px = r.px;
+        pn = r.pn;
+        return *this;
+    }
+
+#endif
+
+    shared_ptr<T> lock() const // never throws
+    {
+#if defined(BOOST_HAS_THREADS)
+
+        // optimization: avoid throw overhead
+        if(expired())
+        {
+            return shared_ptr<element_type>();
+        }
+
+        try
+        {
+            return shared_ptr<element_type>(*this);
+        }
+        catch(bad_weak_ptr const &)
+        {
+            // Q: how can we get here?
+            // A: another thread may have invalidated r after the use_count test above.
+            return shared_ptr<element_type>();
+        }
+
+#else
+
+        // optimization: avoid try/catch overhead when single threaded
+        return expired()? shared_ptr<element_type>(): shared_ptr<element_type>(*this);
+
+#endif
+    }
+
+    long use_count() const // never throws
+    {
+        return pn.use_count();
+    }
+
+    bool expired() const // never throws
+    {
+        return pn.use_count() == 0;
+    }
+
+    void reset() // never throws in 1.30+
+    {
+        this_type().swap(*this);
+    }
+
+    void swap(this_type & other) // never throws
+    {
+        std::swap(px, other.px);
+        pn.swap(other.pn);
+    }
+
+    void _internal_assign(T * px2, detail::shared_count const & pn2)
+    {
+        px = px2;
+        pn = pn2;
+    }
+
+    template<class Y> bool _internal_less(weak_ptr<Y> const & rhs) const
+    {
+        return pn < rhs.pn;
+    }
+
+// Tasteless as this may seem, making all members public allows member templates
+// to work in the absence of member template friends. (Matthew Langston)
+
+#if 0
+
+private:
+
+    template<class Y> friend class weak_ptr;
+    template<class Y> friend class shared_ptr;
+
+#endif
+
+    T * px;                     // contained pointer
+    detail::weak_count pn;      // reference counter
+
+};  // weak_ptr
+
+template<class T, class U> inline bool operator<(weak_ptr<T> const & a, weak_ptr<U> const & b)
+{
+    return a._internal_less(b);
+}
+
+template<class T> void swap(weak_ptr<T> & a, weak_ptr<T> & b)
+{
+    a.swap(b);
+}
+
+// deprecated, provided for backward compatibility
+template<class T> shared_ptr<T> make_shared(weak_ptr<T> const & r)
+{
+    return r.lock();
+}
+
+} // namespace boost
+
+#ifdef BOOST_MSVC
+# pragma warning(pop)
+#endif    
+
+#endif  // #ifndef BOOST_WEAK_PTR_HPP_INCLUDED
diff --git a/src/bsdiff-4.3/bsdiff.1 b/src/bsdiff-4.3/bsdiff.1
new file mode 100644
index 000000000000..ead6c4deb57f
--- /dev/null
+++ b/src/bsdiff-4.3/bsdiff.1
@@ -0,0 +1,63 @@
+.\"-
+.\" Copyright 2003-2005 Colin Percival
+.\" All rights reserved
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted providing that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+.\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+.\" POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD: src/usr.bin/bsdiff/bsdiff/bsdiff.1,v 1.1 2005/08/06 01:59:05 cperciva Exp $
+.\"
+.Dd May 18, 2003
+.Dt BSDIFF 1
+.Os FreeBSD
+.Sh NAME
+.Nm bsdiff
+.Nd generate a patch between two binary files
+.Sh SYNOPSIS
+.Nm
+.Ao Ar oldfile Ac Ao Ar newfile Ac Ao Ar patchfile Ac
+.Sh DESCRIPTION
+.Nm
+compares
+.Ao Ar oldfile Ac
+to
+.Ao Ar newfile Ac
+and writes to
+.Ao Ar patchfile Ac
+a binary patch suitable for use by bspatch(1).
+When
+.Ao Ar oldfile Ac
+and
+.Ao Ar newfile Ac
+are two versions of an executable program, the
+patches produced are on average a factor of five smaller
+than those produced by any other binary patch tool known
+to the author.
+.Pp
+.Nm
+uses memory equal to 17 times the size of 
+.Ao Ar oldfile Ac ,
+and requires
+an absolute minimum working set size of 8 times the size of oldfile.
+.Sh SEE ALSO
+.Xr bspatch 1
+.Sh AUTHORS
+.An Colin Percival Aq cperciva@freebsd.org
diff --git a/src/bsdiff-4.3/bsdiff.c b/src/bsdiff-4.3/bsdiff.c
new file mode 100644
index 000000000000..374ed038fa1f
--- /dev/null
+++ b/src/bsdiff-4.3/bsdiff.c
@@ -0,0 +1,405 @@
+/*-
+ * Copyright 2003-2005 Colin Percival
+ * All rights reserved
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted providing that the following conditions 
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#if 0
+__FBSDID("$FreeBSD: src/usr.bin/bsdiff/bsdiff/bsdiff.c,v 1.1 2005/08/06 01:59:05 cperciva Exp $");
+#endif
+
+#include <sys/types.h>
+
+#include <bzlib.h>
+#include <err.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define MIN(x,y) (((x)<(y)) ? (x) : (y))
+
+static void split(off_t *I,off_t *V,off_t start,off_t len,off_t h)
+{
+	off_t i,j,k,x,tmp,jj,kk;
+
+	if(len<16) {
+		for(k=start;k<start+len;k+=j) {
+			j=1;x=V[I[k]+h];
+			for(i=1;k+i<start+len;i++) {
+				if(V[I[k+i]+h]<x) {
+					x=V[I[k+i]+h];
+					j=0;
+				};
+				if(V[I[k+i]+h]==x) {
+					tmp=I[k+j];I[k+j]=I[k+i];I[k+i]=tmp;
+					j++;
+				};
+			};
+			for(i=0;i<j;i++) V[I[k+i]]=k+j-1;
+			if(j==1) I[k]=-1;
+		};
+		return;
+	};
+
+	x=V[I[start+len/2]+h];
+	jj=0;kk=0;
+	for(i=start;i<start+len;i++) {
+		if(V[I[i]+h]<x) jj++;
+		if(V[I[i]+h]==x) kk++;
+	};
+	jj+=start;kk+=jj;
+
+	i=start;j=0;k=0;
+	while(i<jj) {
+		if(V[I[i]+h]<x) {
+			i++;
+		} else if(V[I[i]+h]==x) {
+			tmp=I[i];I[i]=I[jj+j];I[jj+j]=tmp;
+			j++;
+		} else {
+			tmp=I[i];I[i]=I[kk+k];I[kk+k]=tmp;
+			k++;
+		};
+	};
+
+	while(jj+j<kk) {
+		if(V[I[jj+j]+h]==x) {
+			j++;
+		} else {
+			tmp=I[jj+j];I[jj+j]=I[kk+k];I[kk+k]=tmp;
+			k++;
+		};
+	};
+
+	if(jj>start) split(I,V,start,jj-start,h);
+
+	for(i=0;i<kk-jj;i++) V[I[jj+i]]=kk-1;
+	if(jj==kk-1) I[jj]=-1;
+
+	if(start+len>kk) split(I,V,kk,start+len-kk,h);
+}
+
+static void qsufsort(off_t *I,off_t *V,u_char *old,off_t oldsize)
+{
+	off_t buckets[256];
+	off_t i,h,len;
+
+	for(i=0;i<256;i++) buckets[i]=0;
+	for(i=0;i<oldsize;i++) buckets[old[i]]++;
+	for(i=1;i<256;i++) buckets[i]+=buckets[i-1];
+	for(i=255;i>0;i--) buckets[i]=buckets[i-1];
+	buckets[0]=0;
+
+	for(i=0;i<oldsize;i++) I[++buckets[old[i]]]=i;
+	I[0]=oldsize;
+	for(i=0;i<oldsize;i++) V[i]=buckets[old[i]];
+	V[oldsize]=0;
+	for(i=1;i<256;i++) if(buckets[i]==buckets[i-1]+1) I[buckets[i]]=-1;
+	I[0]=-1;
+
+	for(h=1;I[0]!=-(oldsize+1);h+=h) {
+		len=0;
+		for(i=0;i<oldsize+1;) {
+			if(I[i]<0) {
+				len-=I[i];
+				i-=I[i];
+			} else {
+				if(len) I[i-len]=-len;
+				len=V[I[i]]+1-i;
+				split(I,V,i,len,h);
+				i+=len;
+				len=0;
+			};
+		};
+		if(len) I[i-len]=-len;
+	};
+
+	for(i=0;i<oldsize+1;i++) I[V[i]]=i;
+}
+
+static off_t matchlen(u_char *old,off_t oldsize,u_char *new,off_t newsize)
+{
+	off_t i;
+
+	for(i=0;(i<oldsize)&&(i<newsize);i++)
+		if(old[i]!=new[i]) break;
+
+	return i;
+}
+
+static off_t search(off_t *I,u_char *old,off_t oldsize,
+		u_char *new,off_t newsize,off_t st,off_t en,off_t *pos)
+{
+	off_t x,y;
+
+	if(en-st<2) {
+		x=matchlen(old+I[st],oldsize-I[st],new,newsize);
+		y=matchlen(old+I[en],oldsize-I[en],new,newsize);
+
+		if(x>y) {
+			*pos=I[st];
+			return x;
+		} else {
+			*pos=I[en];
+			return y;
+		}
+	};
+
+	x=st+(en-st)/2;
+	if(memcmp(old+I[x],new,MIN(oldsize-I[x],newsize))<0) {
+		return search(I,old,oldsize,new,newsize,x,en,pos);
+	} else {
+		return search(I,old,oldsize,new,newsize,st,x,pos);
+	};
+}
+
+static void offtout(off_t x,u_char *buf)
+{
+	off_t y;
+
+	if(x<0) y=-x; else y=x;
+
+		buf[0]=y%256;y-=buf[0];
+	y=y/256;buf[1]=y%256;y-=buf[1];
+	y=y/256;buf[2]=y%256;y-=buf[2];
+	y=y/256;buf[3]=y%256;y-=buf[3];
+	y=y/256;buf[4]=y%256;y-=buf[4];
+	y=y/256;buf[5]=y%256;y-=buf[5];
+	y=y/256;buf[6]=y%256;y-=buf[6];
+	y=y/256;buf[7]=y%256;
+
+	if(x<0) buf[7]|=0x80;
+}
+
+int main(int argc,char *argv[])
+{
+	int fd;
+	u_char *old,*new;
+	off_t oldsize,newsize;
+	off_t *I,*V;
+	off_t scan,pos,len;
+	off_t lastscan,lastpos,lastoffset;
+	off_t oldscore,scsc;
+	off_t s,Sf,lenf,Sb,lenb;
+	off_t overlap,Ss,lens;
+	off_t i;
+	off_t dblen,eblen;
+	u_char *db,*eb;
+	u_char buf[8];
+	u_char header[32];
+	FILE * pf;
+	BZFILE * pfbz2;
+	int bz2err;
+
+	if(argc!=4) errx(1,"usage: %s oldfile newfile patchfile\n",argv[0]);
+
+	/* Allocate oldsize+1 bytes instead of oldsize bytes to ensure
+		that we never try to malloc(0) and get a NULL pointer */
+	if(((fd=open(argv[1],O_RDONLY,0))<0) ||
+		((oldsize=lseek(fd,0,SEEK_END))==-1) ||
+		((old=malloc(oldsize+1))==NULL) ||
+		(lseek(fd,0,SEEK_SET)!=0) ||
+		(read(fd,old,oldsize)!=oldsize) ||
+		(close(fd)==-1)) err(1,"%s",argv[1]);
+
+	if(((I=malloc((oldsize+1)*sizeof(off_t)))==NULL) ||
+		((V=malloc((oldsize+1)*sizeof(off_t)))==NULL)) err(1,NULL);
+
+	qsufsort(I,V,old,oldsize);
+
+	free(V);
+
+	/* Allocate newsize+1 bytes instead of newsize bytes to ensure
+		that we never try to malloc(0) and get a NULL pointer */
+	if(((fd=open(argv[2],O_RDONLY,0))<0) ||
+		((newsize=lseek(fd,0,SEEK_END))==-1) ||
+		((new=malloc(newsize+1))==NULL) ||
+		(lseek(fd,0,SEEK_SET)!=0) ||
+		(read(fd,new,newsize)!=newsize) ||
+		(close(fd)==-1)) err(1,"%s",argv[2]);
+
+	if(((db=malloc(newsize+1))==NULL) ||
+		((eb=malloc(newsize+1))==NULL)) err(1,NULL);
+	dblen=0;
+	eblen=0;
+
+	/* Create the patch file */
+	if ((pf = fopen(argv[3], "w")) == NULL)
+		err(1, "%s", argv[3]);
+
+	/* Header is
+		0	8	 "BSDIFF40"
+		8	8	length of bzip2ed ctrl block
+		16	8	length of bzip2ed diff block
+		24	8	length of new file */
+	/* File is
+		0	32	Header
+		32	??	Bzip2ed ctrl block
+		??	??	Bzip2ed diff block
+		??	??	Bzip2ed extra block */
+	memcpy(header,"BSDIFF40",8);
+	offtout(0, header + 8);
+	offtout(0, header + 16);
+	offtout(newsize, header + 24);
+	if (fwrite(header, 32, 1, pf) != 1)
+		err(1, "fwrite(%s)", argv[3]);
+
+	/* Compute the differences, writing ctrl as we go */
+	if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
+		errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
+	scan=0;len=0;
+	lastscan=0;lastpos=0;lastoffset=0;
+	while(scan<newsize) {
+		oldscore=0;
+
+		for(scsc=scan+=len;scan<newsize;scan++) {
+			len=search(I,old,oldsize,new+scan,newsize-scan,
+					0,oldsize,&pos);
+			if (len > 64 * 1024) break;
+
+			for(;scsc<scan+len;scsc++)
+			if((scsc+lastoffset<oldsize) &&
+				(old[scsc+lastoffset] == new[scsc]))
+				oldscore++;
+
+			if(((len==oldscore) && (len!=0)) || 
+				(len>oldscore+8)) break;
+
+			if((scan+lastoffset<oldsize) &&
+				(old[scan+lastoffset] == new[scan]))
+				oldscore--;
+		};
+
+		if((len!=oldscore) || (scan==newsize)) {
+			s=0;Sf=0;lenf=0;
+			for(i=0;(lastscan+i<scan)&&(lastpos+i<oldsize);) {
+				if(old[lastpos+i]==new[lastscan+i]) s++;
+				i++;
+				if(s*2-i>Sf*2-lenf) { Sf=s; lenf=i; };
+			};
+
+			lenb=0;
+			if(scan<newsize) {
+				s=0;Sb=0;
+				for(i=1;(scan>=lastscan+i)&&(pos>=i);i++) {
+					if(old[pos-i]==new[scan-i]) s++;
+					if(s*2-i>Sb*2-lenb) { Sb=s; lenb=i; };
+				};
+			};
+
+			if(lastscan+lenf>scan-lenb) {
+				overlap=(lastscan+lenf)-(scan-lenb);
+				s=0;Ss=0;lens=0;
+				for(i=0;i<overlap;i++) {
+					if(new[lastscan+lenf-overlap+i]==
+					   old[lastpos+lenf-overlap+i]) s++;
+					if(new[scan-lenb+i]==
+					   old[pos-lenb+i]) s--;
+					if(s>Ss) { Ss=s; lens=i+1; };
+				};
+
+				lenf+=lens-overlap;
+				lenb-=lens;
+			};
+
+			for(i=0;i<lenf;i++)
+				db[dblen+i]=new[lastscan+i]-old[lastpos+i];
+			for(i=0;i<(scan-lenb)-(lastscan+lenf);i++)
+				eb[eblen+i]=new[lastscan+lenf+i];
+
+			dblen+=lenf;
+			eblen+=(scan-lenb)-(lastscan+lenf);
+
+			offtout(lenf,buf);
+			BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
+			if (bz2err != BZ_OK)
+				errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
+
+			offtout((scan-lenb)-(lastscan+lenf),buf);
+			BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
+			if (bz2err != BZ_OK)
+				errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
+
+			offtout((pos-lenb)-(lastpos+lenf),buf);
+			BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
+			if (bz2err != BZ_OK)
+				errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
+
+			lastscan=scan-lenb;
+			lastpos=pos-lenb;
+			lastoffset=pos-scan;
+		};
+	};
+	BZ2_bzWriteClose(&bz2err, pfbz2, 0, NULL, NULL);
+	if (bz2err != BZ_OK)
+		errx(1, "BZ2_bzWriteClose, bz2err = %d", bz2err);
+
+	/* Compute size of compressed ctrl data */
+	if ((len = ftello(pf)) == -1)
+		err(1, "ftello");
+	offtout(len-32, header + 8);
+
+	/* Write compressed diff data */
+	if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
+		errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
+	BZ2_bzWrite(&bz2err, pfbz2, db, dblen);
+	if (bz2err != BZ_OK)
+		errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
+	BZ2_bzWriteClose(&bz2err, pfbz2, 0, NULL, NULL);
+	if (bz2err != BZ_OK)
+		errx(1, "BZ2_bzWriteClose, bz2err = %d", bz2err);
+
+	/* Compute size of compressed diff data */
+	if ((newsize = ftello(pf)) == -1)
+		err(1, "ftello");
+	offtout(newsize - len, header + 16);
+
+	/* Write compressed extra data */
+	if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
+		errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
+	BZ2_bzWrite(&bz2err, pfbz2, eb, eblen);
+	if (bz2err != BZ_OK)
+		errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
+	BZ2_bzWriteClose(&bz2err, pfbz2, 0, NULL, NULL);
+	if (bz2err != BZ_OK)
+		errx(1, "BZ2_bzWriteClose, bz2err = %d", bz2err);
+
+	/* Seek to the beginning, write the header, and close the file */
+	if (fseeko(pf, 0, SEEK_SET))
+		err(1, "fseeko");
+	if (fwrite(header, 32, 1, pf) != 1)
+		err(1, "fwrite(%s)", argv[3]);
+	if (fclose(pf))
+		err(1, "fclose");
+
+	/* Free the memory we used */
+	free(db);
+	free(eb);
+	free(I);
+	free(old);
+	free(new);
+
+	return 0;
+}
diff --git a/src/bsdiff-4.3/bspatch.1 b/src/bsdiff-4.3/bspatch.1
new file mode 100644
index 000000000000..82a2781aa7dc
--- /dev/null
+++ b/src/bsdiff-4.3/bspatch.1
@@ -0,0 +1,59 @@
+.\"-
+.\" Copyright 2003-2005 Colin Percival
+.\" All rights reserved
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted providing that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+.\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+.\" POSSIBILITY OF SUCH DAMAGE.
+.\"
+.\" $FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.1,v 1.1 2005/08/06 01:59:06 cperciva Exp $
+.\"
+.Dd May 18, 2003
+.Dt BSPATCH 1
+.Os FreeBSD
+.Sh NAME
+.Nm bspatch
+.Nd apply a patch built with bsdiff(1)
+.Sh SYNOPSIS
+.Nm
+.Ao Ar oldfile Ac Ao Ar newfile Ac Ao Ar patchfile Ac
+.Sh DESCRIPTION
+.Nm
+generates
+.Ao Ar newfile Ac
+from
+.Ao Ar oldfile Ac
+and
+.Ao Ar patchfile Ac
+where
+.Ao Ar patchfile Ac
+is a binary patch built by bsdiff(1).
+.Pp
+.Nm
+uses memory equal to the size of 
+.Ao Ar oldfile Ac
+plus the size of 
+.Ao Ar newfile Ac ,
+but can tolerate a very small working set without a dramatic loss
+of performance.
+.Sh SEE ALSO
+.Xr bsdiff 1
+.Sh AUTHORS
+.An Colin Percival Aq cperciva@freebsd.org
diff --git a/src/bsdiff-4.3/bspatch.c b/src/bsdiff-4.3/bspatch.c
new file mode 100644
index 000000000000..f9d33ddd64a2
--- /dev/null
+++ b/src/bsdiff-4.3/bspatch.c
@@ -0,0 +1,224 @@
+/*-
+ * Copyright 2003-2005 Colin Percival
+ * All rights reserved
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted providing that the following conditions 
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#if 0
+__FBSDID("$FreeBSD: src/usr.bin/bsdiff/bspatch/bspatch.c,v 1.1 2005/08/06 01:59:06 cperciva Exp $");
+#endif
+
+#include <bzlib.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <err.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/types.h>
+
+static off_t offtin(u_char *buf)
+{
+	off_t y;
+
+	y=buf[7]&0x7F;
+	y=y*256;y+=buf[6];
+	y=y*256;y+=buf[5];
+	y=y*256;y+=buf[4];
+	y=y*256;y+=buf[3];
+	y=y*256;y+=buf[2];
+	y=y*256;y+=buf[1];
+	y=y*256;y+=buf[0];
+
+	if(buf[7]&0x80) y=-y;
+
+	return y;
+}
+
+
+void writeFull(const char * name, int fd,
+    const unsigned char * buf, size_t count)
+{
+    while (count) {
+        ssize_t res = write(fd, (char *) buf, count);
+        if (res == -1) {
+            if (errno == EINTR) continue;
+            err(1,"writing to %s",name);
+        }
+        count -= res;
+        buf += res;
+    }
+}
+
+
+int main(int argc,char * argv[])
+{
+	FILE * f, * cpf, * dpf, * epf;
+	BZFILE * cpfbz2, * dpfbz2, * epfbz2;
+	int cbz2err, dbz2err, ebz2err;
+	int fd;
+	ssize_t oldsize,newsize;
+	ssize_t bzctrllen,bzdatalen;
+	u_char header[32],buf[8];
+	u_char *old, *new;
+	off_t oldpos,newpos;
+	off_t ctrl[3];
+	off_t lenread;
+	off_t i;
+
+	if(argc!=4) errx(1,"usage: %s oldfile newfile patchfile\n",argv[0]);
+
+	/* Open patch file */
+	if ((f = fopen(argv[3], "r")) == NULL)
+		err(1, "fopen(%s)", argv[3]);
+
+	/*
+	File format:
+		0	8	"BSDIFF40"
+		8	8	X
+		16	8	Y
+		24	8	sizeof(newfile)
+		32	X	bzip2(control block)
+		32+X	Y	bzip2(diff block)
+		32+X+Y	???	bzip2(extra block)
+	with control block a set of triples (x,y,z) meaning "add x bytes
+	from oldfile to x bytes from the diff block; copy y bytes from the
+	extra block; seek forwards in oldfile by z bytes".
+	*/
+
+	/* Read header */
+	if (fread(header, 1, 32, f) < 32) {
+		if (feof(f))
+			errx(1, "Corrupt patch\n");
+		err(1, "fread(%s)", argv[3]);
+	}
+
+	/* Check for appropriate magic */
+	if (memcmp(header, "BSDIFF40", 8) != 0)
+		errx(1, "Corrupt patch\n");
+
+	/* Read lengths from header */
+	bzctrllen=offtin(header+8);
+	bzdatalen=offtin(header+16);
+	newsize=offtin(header+24);
+	if((bzctrllen<0) || (bzdatalen<0) || (newsize<0))
+		errx(1,"Corrupt patch\n");
+
+	/* Close patch file and re-open it via libbzip2 at the right places */
+	if (fclose(f))
+		err(1, "fclose(%s)", argv[3]);
+	if ((cpf = fopen(argv[3], "r")) == NULL)
+		err(1, "fopen(%s)", argv[3]);
+	if (fseeko(cpf, 32, SEEK_SET))
+		err(1, "fseeko(%s, %lld)", argv[3],
+		    (long long)32);
+	if ((cpfbz2 = BZ2_bzReadOpen(&cbz2err, cpf, 0, 0, NULL, 0)) == NULL)
+		errx(1, "BZ2_bzReadOpen, bz2err = %d", cbz2err);
+	if ((dpf = fopen(argv[3], "r")) == NULL)
+		err(1, "fopen(%s)", argv[3]);
+	if (fseeko(dpf, 32 + bzctrllen, SEEK_SET))
+		err(1, "fseeko(%s, %lld)", argv[3],
+		    (long long)(32 + bzctrllen));
+	if ((dpfbz2 = BZ2_bzReadOpen(&dbz2err, dpf, 0, 0, NULL, 0)) == NULL)
+		errx(1, "BZ2_bzReadOpen, bz2err = %d", dbz2err);
+	if ((epf = fopen(argv[3], "r")) == NULL)
+		err(1, "fopen(%s)", argv[3]);
+	if (fseeko(epf, 32 + bzctrllen + bzdatalen, SEEK_SET))
+		err(1, "fseeko(%s, %lld)", argv[3],
+		    (long long)(32 + bzctrllen + bzdatalen));
+	if ((epfbz2 = BZ2_bzReadOpen(&ebz2err, epf, 0, 0, NULL, 0)) == NULL)
+		errx(1, "BZ2_bzReadOpen, bz2err = %d", ebz2err);
+
+	if(((fd=open(argv[1],O_RDONLY,0))<0) ||
+		((oldsize=lseek(fd,0,SEEK_END))==-1) ||
+		((old=malloc(oldsize+1))==NULL) ||
+		(lseek(fd,0,SEEK_SET)!=0) ||
+		(read(fd,old,oldsize)!=oldsize) ||
+		(close(fd)==-1)) err(1,"%s",argv[1]);
+	if((new=malloc(newsize+1))==NULL) err(1,NULL);
+
+	oldpos=0;newpos=0;
+	while(newpos<newsize) {
+		/* Read control data */
+		for(i=0;i<=2;i++) {
+			lenread = BZ2_bzRead(&cbz2err, cpfbz2, buf, 8);
+			if ((lenread < 8) || ((cbz2err != BZ_OK) &&
+			    (cbz2err != BZ_STREAM_END)))
+				errx(1, "Corrupt patch\n");
+			ctrl[i]=offtin(buf);
+		};
+
+		/* Sanity-check */
+		if(newpos+ctrl[0]>newsize)
+			errx(1,"Corrupt patch\n");
+
+		/* Read diff string */
+		lenread = BZ2_bzRead(&dbz2err, dpfbz2, new + newpos, ctrl[0]);
+		if ((lenread < ctrl[0]) ||
+		    ((dbz2err != BZ_OK) && (dbz2err != BZ_STREAM_END)))
+			errx(1, "Corrupt patch\n");
+
+		/* Add old data to diff string */
+		for(i=0;i<ctrl[0];i++)
+			if((oldpos+i>=0) && (oldpos+i<oldsize))
+				new[newpos+i]+=old[oldpos+i];
+
+		/* Adjust pointers */
+		newpos+=ctrl[0];
+		oldpos+=ctrl[0];
+
+		/* Sanity-check */
+		if(newpos+ctrl[1]>newsize)
+			errx(1,"Corrupt patch\n");
+
+		/* Read extra string */
+		lenread = BZ2_bzRead(&ebz2err, epfbz2, new + newpos, ctrl[1]);
+		if ((lenread < ctrl[1]) ||
+		    ((ebz2err != BZ_OK) && (ebz2err != BZ_STREAM_END)))
+			errx(1, "Corrupt patch\n");
+
+		/* Adjust pointers */
+		newpos+=ctrl[1];
+		oldpos+=ctrl[2];
+	};
+
+	/* Clean up the bzip2 reads */
+	BZ2_bzReadClose(&cbz2err, cpfbz2);
+	BZ2_bzReadClose(&dbz2err, dpfbz2);
+	BZ2_bzReadClose(&ebz2err, epfbz2);
+	if (fclose(cpf) || fclose(dpf) || fclose(epf))
+		err(1, "fclose(%s)", argv[3]);
+
+	/* Write the new file */
+	if((fd=open(argv[2],O_CREAT|O_TRUNC|O_WRONLY,0666))<0)
+                err(1,"%s",argv[2]);
+        writeFull(argv[2], fd, new, newsize);
+        if(close(fd)==-1)
+		err(1,"%s",argv[2]);
+
+	free(new);
+	free(old);
+
+	return 0;
+}
diff --git a/src/bsdiff-4.3/compat-include/err.h b/src/bsdiff-4.3/compat-include/err.h
new file mode 100644
index 000000000000..a851ded6f907
--- /dev/null
+++ b/src/bsdiff-4.3/compat-include/err.h
@@ -0,0 +1,12 @@
+/* Simulate BSD's <err.h> functionality. */
+
+#ifndef COMPAT_ERR_H_INCLUDED
+#define COMPAT_ERR_H_INCLUDED 1
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define err(rc,...)  do { fprintf(stderr,__VA_ARGS__); exit(rc); } while(0)
+#define errx(rc,...) do { fprintf(stderr,__VA_ARGS__); exit(rc); } while(0)
+
+#endif
diff --git a/src/bsdiff-4.3/local.mk b/src/bsdiff-4.3/local.mk
new file mode 100644
index 000000000000..c957ceab0c0f
--- /dev/null
+++ b/src/bsdiff-4.3/local.mk
@@ -0,0 +1,11 @@
+programs += bsdiff bspatch
+
+bsdiff_DIR := $(d)
+bsdiff_SOURCES := $(d)/bsdiff.c
+bsdiff_LDFLAGS = -lbz2 $(bsddiff_compat_include)
+bsdiff_INSTALL_DIR = $(libexecdir)/nix
+
+bspatch_DIR := $(d)
+bspatch_SOURCES := $(d)/bspatch.c
+bspatch_LDFLAGS = -lbz2 $(bsddiff_compat_include)
+bspatch_INSTALL_DIR = $(libexecdir)/nix
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
new file mode 100644
index 000000000000..4f28a549f035
--- /dev/null
+++ b/src/libexpr/attr-path.cc
@@ -0,0 +1,97 @@
+#include "attr-path.hh"
+#include "eval-inline.hh"
+#include "util.hh"
+
+
+namespace nix {
+
+
+static Strings parseAttrPath(const string & s)
+{
+    Strings res;
+    string cur;
+    string::const_iterator i = s.begin();
+    while (i != s.end()) {
+        if (*i == '.') {
+            res.push_back(cur);
+            cur.clear();
+        } else if (*i == '"') {
+            ++i;
+            while (1) {
+                if (i == s.end())
+                    throw Error(format("missing closing quote in selection path `%1%'") % s);
+                if (*i == '"') break;
+                cur.push_back(*i++);
+            }
+        } else
+            cur.push_back(*i);
+        ++i;
+    }
+    if (!cur.empty()) res.push_back(cur);
+    return res;
+}
+
+
+Value * findAlongAttrPath(EvalState & state, const string & attrPath,
+    Bindings & autoArgs, Value & vIn)
+{
+    Strings tokens = parseAttrPath(attrPath);
+
+    Error attrError =
+        Error(format("attribute selection path `%1%' does not match expression") % attrPath);
+
+    Value * v = &vIn;
+
+    foreach (Strings::iterator, i, tokens) {
+
+        /* Is *i an index (integer) or a normal attribute name? */
+        enum { apAttr, apIndex } apType = apAttr;
+        string attr = *i;
+        unsigned int attrIndex;
+        if (string2Int(attr, attrIndex)) apType = apIndex;
+
+        /* Evaluate the expression. */
+        Value * vNew = state.allocValue();
+        state.autoCallFunction(autoArgs, *v, *vNew);
+        v = vNew;
+        state.forceValue(*v);
+
+        /* It should evaluate to either a set or an expression,
+           according to what is specified in the attrPath. */
+
+        if (apType == apAttr) {
+
+            if (v->type != tAttrs)
+                throw TypeError(
+                    format("the expression selected by the selection path `%1%' should be a set but is %2%")
+                    % attrPath % showType(*v));
+
+            if (attr.empty())
+                throw Error(format("empty attribute name in selection path `%1%'") % attrPath);
+
+            Bindings::iterator a = v->attrs->find(state.symbols.create(attr));
+            if (a == v->attrs->end())
+                throw Error(format("attribute `%1%' in selection path `%2%' not found") % attr % attrPath);
+            v = &*a->value;
+        }
+
+        else if (apType == apIndex) {
+
+            if (v->type != tList)
+                throw TypeError(
+                    format("the expression selected by the selection path `%1%' should be a list but is %2%")
+                    % attrPath % showType(*v));
+
+            if (attrIndex >= v->list.length)
+                throw Error(format("list index %1% in selection path `%2%' is out of range") % attrIndex % attrPath);
+
+            v = v->list.elems[attrIndex];
+        }
+
+    }
+
+    return v;
+}
+
+
+}
diff --git a/src/libexpr/attr-path.hh b/src/libexpr/attr-path.hh
new file mode 100644
index 000000000000..46a341950939
--- /dev/null
+++ b/src/libexpr/attr-path.hh
@@ -0,0 +1,13 @@
+#pragma once
+
+#include "eval.hh"
+
+#include <string>
+#include <map>
+
+namespace nix {
+
+Value * findAlongAttrPath(EvalState & state, const string & attrPath,
+    Bindings & autoArgs, Value & vIn);
+
+}
diff --git a/src/libexpr/common-opts.cc b/src/libexpr/common-opts.cc
new file mode 100644
index 000000000000..0ee889a995ef
--- /dev/null
+++ b/src/libexpr/common-opts.cc
@@ -0,0 +1,59 @@
+#include "common-opts.hh"
+#include "../libmain/shared.hh"
+#include "util.hh"
+
+
+namespace nix {
+
+
+bool parseOptionArg(const string & arg, Strings::iterator & i,
+    const Strings::iterator & argsEnd, EvalState & state,
+    Bindings & autoArgs)
+{
+    if (arg != "--arg" && arg != "--argstr") return false;
+
+    UsageError error(format("`%1%' requires two arguments") % arg);
+    
+    if (i == argsEnd) throw error;
+    string name = *i++;
+    if (i == argsEnd) throw error;
+    string value = *i++;
+
+    /* !!! check for duplicates! */
+    Value * v = state.allocValue();
+    autoArgs.push_back(Attr(state.symbols.create(name), v));
+
+    if (arg == "--arg")
+        state.mkThunk_(*v, state.parseExprFromString(value, absPath(".")));
+    else
+        mkString(*v, value);
+
+    autoArgs.sort(); // !!! inefficient
+
+    return true;
+}
+
+
+bool parseSearchPathArg(const string & arg, Strings::iterator & i,
+    const Strings::iterator & argsEnd, EvalState & state)
+{
+    if (arg != "-I") return false;
+    if (i == argsEnd) throw UsageError(format("`%1%' requires an argument") % arg);;
+    state.addToSearchPath(*i++);
+    return true;
+}
+
+
+Path lookupFileArg(EvalState & state, string s)
+{
+    if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
+        Path p = s.substr(1, s.size() - 2);
+        Path p2 = state.findFile(p);
+        if (p2 == "") throw Error(format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % p);
+        return p2;
+    } else
+        return absPath(s);
+}
+
+
+}
diff --git a/src/libexpr/common-opts.hh b/src/libexpr/common-opts.hh
new file mode 100644
index 000000000000..e2e3fe77171c
--- /dev/null
+++ b/src/libexpr/common-opts.hh
@@ -0,0 +1,17 @@
+#pragma once
+
+#include "eval.hh"
+
+namespace nix {
+
+/* Some common option parsing between nix-env and nix-instantiate. */
+bool parseOptionArg(const string & arg, Strings::iterator & i,
+    const Strings::iterator & argsEnd, EvalState & state,
+    Bindings & autoArgs);
+    
+bool parseSearchPathArg(const string & arg, Strings::iterator & i,
+    const Strings::iterator & argsEnd, EvalState & state);
+
+Path lookupFileArg(EvalState & state, string s);
+
+}
diff --git a/src/libexpr/eval-inline.hh b/src/libexpr/eval-inline.hh
new file mode 100644
index 000000000000..5801a20c3b10
--- /dev/null
+++ b/src/libexpr/eval-inline.hh
@@ -0,0 +1,59 @@
+#pragma once
+
+#include "eval.hh"
+
+#define LocalNoInline(f) static f __attribute__((noinline)); f
+#define LocalNoInlineNoReturn(f) static f __attribute__((noinline, noreturn)); f
+
+namespace nix {
+
+LocalNoInlineNoReturn(void throwEvalError(const char * s))
+{
+    throw EvalError(s);
+}
+
+LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v))
+{
+    throw TypeError(format(s) % showType(v));
+}
+
+
+void EvalState::forceValue(Value & v)
+{
+    if (v.type == tThunk) {
+        Env * env = v.thunk.env;
+        Expr * expr = v.thunk.expr;
+        try {
+            v.type = tBlackhole;
+            //checkInterrupt();
+            expr->eval(*this, *env, v);
+        } catch (Error & e) {
+            v.type = tThunk;
+            v.thunk.env = env;
+            v.thunk.expr = expr;
+            throw;
+        }
+    }
+    else if (v.type == tApp)
+        callFunction(*v.app.left, *v.app.right, v);
+    else if (v.type == tBlackhole)
+        throwEvalError("infinite recursion encountered");
+}
+
+
+inline void EvalState::forceAttrs(Value & v)
+{
+    forceValue(v);
+    if (v.type != tAttrs)
+        throwTypeError("value is %1% while a set was expected", v);
+}
+
+
+inline void EvalState::forceList(Value & v)
+{
+    forceValue(v);
+    if (v.type != tList)
+        throwTypeError("value is %1% while a list was expected", v);
+}
+
+}
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
new file mode 100644
index 000000000000..2087c7c43ffb
--- /dev/null
+++ b/src/libexpr/eval.cc
@@ -0,0 +1,1435 @@
+#include "eval.hh"
+#include "hash.hh"
+#include "util.hh"
+#include "store-api.hh"
+#include "derivations.hh"
+#include "globals.hh"
+#include "eval-inline.hh"
+
+#include <cstring>
+#include <unistd.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+
+#if HAVE_BOEHMGC
+
+#include <gc/gc.h>
+#include <gc/gc_cpp.h>
+
+#define NEW new (UseGC)
+
+#else
+
+#define GC_STRDUP strdup
+#define GC_MALLOC malloc
+
+#define NEW new
+
+#endif
+
+
+namespace nix {
+
+
+Bindings::iterator Bindings::find(const Symbol & name)
+{
+    Attr key(name, 0);
+    iterator i = lower_bound(begin(), end(), key);
+    if (i != end() && i->name == name) return i;
+    return end();
+}
+
+
+void Bindings::sort()
+{
+    std::sort(begin(), end());
+}
+
+
+std::ostream & operator << (std::ostream & str, const Value & v)
+{
+    switch (v.type) {
+    case tInt:
+        str << v.integer;
+        break;
+    case tBool:
+        str << (v.boolean ? "true" : "false");
+        break;
+    case tString:
+        str << "\"";
+        for (const char * i = v.string.s; *i; i++)
+            if (*i == '\"' || *i == '\\') str << "\\" << *i;
+            else if (*i == '\n') str << "\\n";
+            else if (*i == '\r') str << "\\r";
+            else if (*i == '\t') str << "\\t";
+            else str << *i;
+        str << "\"";
+        break;
+    case tPath:
+        str << v.path; // !!! escaping?
+        break;
+    case tNull:
+        str << "null";
+        break;
+    case tAttrs: {
+        str << "{ ";
+        typedef std::map<string, Value *> Sorted;
+        Sorted sorted;
+        foreach (Bindings::iterator, i, *v.attrs)
+            sorted[i->name] = i->value;
+        foreach (Sorted::iterator, i, sorted)
+            str << i->first << " = " << *i->second << "; ";
+        str << "}";
+        break;
+    }
+    case tList:
+        str << "[ ";
+        for (unsigned int n = 0; n < v.list.length; ++n)
+            str << *v.list.elems[n] << " ";
+        str << "]";
+        break;
+    case tThunk:
+    case tApp:
+        str << "<CODE>";
+        break;
+    case tLambda:
+        str << "<LAMBDA>";
+        break;
+    case tPrimOp:
+        str << "<PRIMOP>";
+        break;
+    case tPrimOpApp:
+        str << "<PRIMOP-APP>";
+        break;
+    default:
+        throw Error("invalid value");
+    }
+    return str;
+}
+
+
+string showType(const Value & v)
+{
+    switch (v.type) {
+        case tInt: return "an integer";
+        case tBool: return "a boolean";
+        case tString: return "a string";
+        case tPath: return "a path";
+        case tNull: return "null";
+        case tAttrs: return "a set";
+        case tList: return "a list";
+        case tThunk: return "a thunk";
+        case tApp: return "a function application";
+        case tLambda: return "a function";
+        case tBlackhole: return "a black hole";
+        case tPrimOp: return "a built-in function";
+        case tPrimOpApp: return "a partially applied built-in function";
+    }
+    abort();
+}
+
+
+/* Called when the Boehm GC runs out of memory. */
+static void * oomHandler(size_t requested)
+{
+    /* Convert this to a proper C++ exception. */
+    throw std::bad_alloc();
+}
+
+
+static Symbol getName(const AttrName & name, EvalState & state, Env & env) {
+    if (name.symbol.set()) {
+        return name.symbol;
+    } else {
+        Value nameValue;
+        name.expr->eval(state, env, nameValue);
+        state.forceStringNoCtx(nameValue);
+        return state.symbols.create(nameValue.string.s);
+    }
+}
+
+
+EvalState::EvalState()
+    : sWith(symbols.create("<with>"))
+    , sOutPath(symbols.create("outPath"))
+    , sDrvPath(symbols.create("drvPath"))
+    , sType(symbols.create("type"))
+    , sMeta(symbols.create("meta"))
+    , sName(symbols.create("name"))
+    , sValue(symbols.create("value"))
+    , sSystem(symbols.create("system"))
+    , sOverrides(symbols.create("__overrides"))
+    , sOutputs(symbols.create("outputs"))
+    , sOutputName(symbols.create("outputName"))
+    , sIgnoreNulls(symbols.create("__ignoreNulls"))
+    , sFile(symbols.create("file"))
+    , sLine(symbols.create("line"))
+    , sColumn(symbols.create("column"))
+    , repair(false)
+    , baseEnv(allocEnv(128))
+    , staticBaseEnv(false, 0)
+    , baseEnvDispl(0)
+{
+    nrEnvs = nrValuesInEnvs = nrValues = nrListElems = 0;
+    nrAttrsets = nrOpUpdates = nrOpUpdateValuesCopied = 0;
+    nrListConcats = nrPrimOpCalls = nrFunctionCalls = 0;
+    countCalls = getEnv("NIX_COUNT_CALLS", "0") != "0";
+
+#if HAVE_BOEHMGC
+    static bool gcInitialised = false;
+    if (!gcInitialised) {
+
+        /* Initialise the Boehm garbage collector.  This isn't
+           necessary on most platforms, but for portability we do it
+           anyway. */
+        GC_INIT();
+
+        GC_oom_fn = oomHandler;
+
+        /* Set the initial heap size to something fairly big (25% of
+           physical RAM, up to a maximum of 384 MiB) so that in most
+           cases we don't need to garbage collect at all.  (Collection
+           has a fairly significant overhead.)  The heap size can be
+           overridden through libgc's GC_INITIAL_HEAP_SIZE environment
+           variable.  We should probably also provide a nix.conf
+           setting for this.  Note that GC_expand_hp() causes a lot of
+           virtual, but not physical (resident) memory to be
+           allocated.  This might be a problem on systems that don't
+           overcommit. */
+        if (!getenv("GC_INITIAL_HEAP_SIZE")) {
+            size_t maxSize = 384 * 1024 * 1024;
+            size_t size = 32 * 1024 * 1024;
+#if HAVE_SYSCONF && defined(_SC_PAGESIZE) && defined(_SC_PHYS_PAGES)
+            long pageSize = sysconf(_SC_PAGESIZE);
+            long pages = sysconf(_SC_PHYS_PAGES);
+            if (pageSize != -1)
+                size = (pageSize * pages) / 4; // 25% of RAM
+            if (size > maxSize) size = maxSize;
+#endif
+            debug(format("setting initial heap size to %1% bytes") % size);
+            GC_expand_hp(size);
+        }
+
+        gcInitialised = true;
+    }
+#endif
+
+    /* Initialise the Nix expression search path. */
+    searchPathInsertionPoint = searchPath.end();
+    Strings paths = tokenizeString<Strings>(getEnv("NIX_PATH", ""), ":");
+    foreach (Strings::iterator, i, paths) addToSearchPath(*i);
+    addToSearchPath("nix=" + settings.nixDataDir + "/nix/corepkgs");
+    searchPathInsertionPoint = searchPath.begin();
+
+    createBaseEnv();
+}
+
+
+EvalState::~EvalState()
+{
+}
+
+
+void EvalState::addConstant(const string & name, Value & v)
+{
+    Value * v2 = allocValue();
+    *v2 = v;
+    staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
+    baseEnv.values[baseEnvDispl++] = v2;
+    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    baseEnv.values[0]->attrs->push_back(Attr(symbols.create(name2), v2));
+}
+
+
+void EvalState::addPrimOp(const string & name,
+    unsigned int arity, PrimOpFun primOp)
+{
+    Value * v = allocValue();
+    string name2 = string(name, 0, 2) == "__" ? string(name, 2) : name;
+    Symbol sym = symbols.create(name2);
+    v->type = tPrimOp;
+    v->primOp = NEW PrimOp(primOp, arity, sym);
+    staticBaseEnv.vars[symbols.create(name)] = baseEnvDispl;
+    baseEnv.values[baseEnvDispl++] = v;
+    baseEnv.values[0]->attrs->push_back(Attr(sym, v));
+}
+
+
+void EvalState::getBuiltin(const string & name, Value & v)
+{
+    v = *baseEnv.values[0]->attrs->find(symbols.create(name))->value;
+}
+
+
+/* Every "format" object (even temporary) takes up a few hundred bytes
+   of stack space, which is a real killer in the recursive
+   evaluator.  So here are some helper functions for throwing
+   exceptions. */
+
+LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2))
+{
+    throw EvalError(format(s) % s2);
+}
+
+LocalNoInlineNoReturn(void throwEvalError(const char * s, const string & s2, const string & s3))
+{
+    throw EvalError(format(s) % s2 % s3);
+}
+
+LocalNoInlineNoReturn(void throwEvalError(const char * s, const Symbol & sym, const Pos & p1, const Pos & p2))
+{
+    throw EvalError(format(s) % sym % p1 % p2);
+}
+
+LocalNoInlineNoReturn(void throwTypeError(const char * s))
+{
+    throw TypeError(s);
+}
+
+LocalNoInlineNoReturn(void throwTypeError(const char * s, const string & s1))
+{
+    throw TypeError(format(s) % s1);
+}
+
+LocalNoInlineNoReturn(void throwTypeError(const char * s, const string & s1, const string & s2))
+{
+    throw TypeError(format(s) % s1 % s2);
+}
+
+LocalNoInlineNoReturn(void throwTypeError(const char * s, const ExprLambda & fun, const Symbol & s2))
+{
+    throw TypeError(format(s) % fun.showNamePos() % s2);
+}
+
+LocalNoInlineNoReturn(void throwAssertionError(const char * s, const Pos & pos))
+{
+    throw AssertionError(format(s) % pos);
+}
+
+LocalNoInlineNoReturn(void throwUndefinedVarError(const char * s, const string & s1, const Pos & pos))
+{
+    throw UndefinedVarError(format(s) % s1 % pos);
+}
+
+LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2))
+{
+    e.addPrefix(format(s) % s2);
+}
+
+LocalNoInline(void addErrorPrefix(Error & e, const char * s, const ExprLambda & fun))
+{
+    e.addPrefix(format(s) % fun.showNamePos());
+}
+
+LocalNoInline(void addErrorPrefix(Error & e, const char * s, const string & s2, const Pos & pos))
+{
+    e.addPrefix(format(s) % s2 % pos);
+}
+
+
+void mkString(Value & v, const char * s)
+{
+    mkStringNoCopy(v, GC_STRDUP(s));
+}
+
+
+void mkString(Value & v, const string & s, const PathSet & context)
+{
+    mkString(v, s.c_str());
+    if (!context.empty()) {
+        unsigned int n = 0;
+        v.string.context = (const char * *)
+            GC_MALLOC((context.size() + 1) * sizeof(char *));
+        foreach (PathSet::const_iterator, i, context)
+            v.string.context[n++] = GC_STRDUP(i->c_str());
+        v.string.context[n] = 0;
+    }
+}
+
+
+void mkPath(Value & v, const char * s)
+{
+    mkPathNoCopy(v, GC_STRDUP(s));
+}
+
+
+inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
+{
+    for (unsigned int l = var.level; l; --l, env = env->up) ;
+
+    if (!var.fromWith) return env->values[var.displ];
+
+    while (1) {
+        if (!env->haveWithAttrs) {
+            if (noEval) return 0;
+            Value * v = allocValue();
+            evalAttrs(*env->up, (Expr *) env->values[0], *v);
+            env->values[0] = v;
+            env->haveWithAttrs = true;
+        }
+        Bindings::iterator j = env->values[0]->attrs->find(var.name);
+        if (j != env->values[0]->attrs->end()) {
+            if (countCalls && j->pos) attrSelects[*j->pos]++;
+            return j->value;
+        }
+        if (!env->prevWith)
+            throwUndefinedVarError("undefined variable `%1%' at %2%", var.name, var.pos);
+        for (unsigned int l = env->prevWith; l; --l, env = env->up) ;
+    }
+}
+
+
+Value * EvalState::allocValue()
+{
+    nrValues++;
+    return (Value *) GC_MALLOC(sizeof(Value));
+}
+
+
+Env & EvalState::allocEnv(unsigned int size)
+{
+    nrEnvs++;
+    nrValuesInEnvs += size;
+    Env * env = (Env *) GC_MALLOC(sizeof(Env) + size * sizeof(Value *));
+
+    /* Clear the values because maybeThunk() and lookupVar fromWith expects this. */
+    for (unsigned i = 0; i < size; ++i)
+        env->values[i] = 0;
+
+    return *env;
+}
+
+
+Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
+{
+    Value * v = allocValue();
+    vAttrs.attrs->push_back(Attr(name, v));
+    return v;
+}
+
+
+void EvalState::mkList(Value & v, unsigned int length)
+{
+    v.type = tList;
+    v.list.length = length;
+    v.list.elems = length ? (Value * *) GC_MALLOC(length * sizeof(Value *)) : 0;
+    nrListElems += length;
+}
+
+
+void EvalState::mkAttrs(Value & v, unsigned int expected)
+{
+    clearValue(v);
+    v.type = tAttrs;
+    v.attrs = NEW Bindings;
+    v.attrs->reserve(expected);
+    nrAttrsets++;
+}
+
+
+unsigned long nrThunks = 0;
+
+static inline void mkThunk(Value & v, Env & env, Expr * expr)
+{
+    v.type = tThunk;
+    v.thunk.env = &env;
+    v.thunk.expr = expr;
+    nrThunks++;
+}
+
+
+void EvalState::mkThunk_(Value & v, Expr * expr)
+{
+    mkThunk(v, baseEnv, expr);
+}
+
+
+void EvalState::mkPos(Value & v, Pos * pos)
+{
+    if (pos) {
+        mkAttrs(v, 3);
+        mkString(*allocAttr(v, sFile), pos->file);
+        mkInt(*allocAttr(v, sLine), pos->line);
+        mkInt(*allocAttr(v, sColumn), pos->column);
+        v.attrs->sort();
+    } else
+        mkNull(v);
+}
+
+
+/* Create a thunk for the delayed computation of the given expression
+   in the given environment.  But if the expression is a variable,
+   then look it up right away.  This significantly reduces the number
+   of thunks allocated. */
+Value * Expr::maybeThunk(EvalState & state, Env & env)
+{
+    Value * v = state.allocValue();
+    mkThunk(*v, env, this);
+    return v;
+}
+
+
+unsigned long nrAvoided = 0;
+
+Value * ExprVar::maybeThunk(EvalState & state, Env & env)
+{
+    Value * v = state.lookupVar(&env, *this, true);
+    /* The value might not be initialised in the environment yet.
+       In that case, ignore it. */
+    if (v) { nrAvoided++; return v; }
+    return Expr::maybeThunk(state, env);
+}
+
+
+Value * ExprString::maybeThunk(EvalState & state, Env & env)
+{
+    nrAvoided++;
+    return &v;
+}
+
+Value * ExprInt::maybeThunk(EvalState & state, Env & env)
+{
+    nrAvoided++;
+    return &v;
+}
+
+Value * ExprPath::maybeThunk(EvalState & state, Env & env)
+{
+    nrAvoided++;
+    return &v;
+}
+
+
+void EvalState::evalFile(const Path & path, Value & v)
+{
+    FileEvalCache::iterator i;
+    if ((i = fileEvalCache.find(path)) != fileEvalCache.end()) {
+        v = i->second;
+        return;
+    }
+
+    Path path2 = resolveExprPath(path);
+    if ((i = fileEvalCache.find(path2)) != fileEvalCache.end()) {
+        v = i->second;
+        return;
+    }
+
+    startNest(nest, lvlTalkative, format("evaluating file `%1%'") % path2);
+    Expr * e = parseExprFromFile(path2);
+    try {
+        eval(e, v);
+    } catch (Error & e) {
+        addErrorPrefix(e, "while evaluating the file `%1%':\n", path2);
+        throw;
+    }
+
+    fileEvalCache[path2] = v;
+    if (path != path2) fileEvalCache[path] = v;
+}
+
+
+void EvalState::resetFileCache()
+{
+    fileEvalCache.clear();
+}
+
+
+void EvalState::eval(Expr * e, Value & v)
+{
+    e->eval(*this, baseEnv, v);
+}
+
+
+inline bool EvalState::evalBool(Env & env, Expr * e, Value & v)
+{
+    e->eval(*this, env, v);
+    if (v.type != tBool)
+        throwTypeError("value is %1% while a Boolean was expected", v);
+    return v.boolean;
+}
+
+
+inline bool EvalState::evalBool(Env & env, Expr * e)
+{
+    Value v;
+    return evalBool(env, e, v);
+}
+
+
+inline void EvalState::evalAttrs(Env & env, Expr * e, Value & v)
+{
+    e->eval(*this, env, v);
+    if (v.type != tAttrs)
+        throwTypeError("value is %1% while a set was expected", v);
+}
+
+
+void Expr::eval(EvalState & state, Env & env, Value & v)
+{
+    abort();
+}
+
+
+void ExprInt::eval(EvalState & state, Env & env, Value & v)
+{
+    v = this->v;
+}
+
+
+void ExprString::eval(EvalState & state, Env & env, Value & v)
+{
+    v = this->v;
+}
+
+
+void ExprPath::eval(EvalState & state, Env & env, Value & v)
+{
+    v = this->v;
+}
+
+
+void ExprAttrs::eval(EvalState & state, Env & env, Value & v)
+{
+    state.mkAttrs(v, attrs.size());
+    Env *dynamicEnv = &env;
+
+    if (recursive) {
+        /* Create a new environment that contains the attributes in
+           this `rec'. */
+        Env & env2(state.allocEnv(attrs.size()));
+        env2.up = &env;
+        dynamicEnv = &env2;
+
+        AttrDefs::iterator overrides = attrs.find(state.sOverrides);
+        bool hasOverrides = overrides != attrs.end();
+
+        /* The recursive attributes are evaluated in the new
+           environment, while the inherited attributes are evaluated
+           in the original environment. */
+        unsigned int displ = 0;
+        foreach (AttrDefs::iterator, i, attrs) {
+            Value * vAttr;
+            if (hasOverrides && !i->second.inherited) {
+                vAttr = state.allocValue();
+                mkThunk(*vAttr, env2, i->second.e);
+            } else
+                vAttr = i->second.e->maybeThunk(state, i->second.inherited ? env : env2);
+            env2.values[displ++] = vAttr;
+            v.attrs->push_back(Attr(i->first, vAttr, &i->second.pos));
+        }
+
+        /* If the rec contains an attribute called `__overrides', then
+           evaluate it, and add the attributes in that set to the rec.
+           This allows overriding of recursive attributes, which is
+           otherwise not possible.  (You can use the // operator to
+           replace an attribute, but other attributes in the rec will
+           still reference the original value, because that value has
+           been substituted into the bodies of the other attributes.
+           Hence we need __overrides.) */
+        if (hasOverrides) {
+            Value * vOverrides = (*v.attrs)[overrides->second.displ].value;
+            state.forceAttrs(*vOverrides);
+            foreach (Bindings::iterator, i, *vOverrides->attrs) {
+                AttrDefs::iterator j = attrs.find(i->name);
+                if (j != attrs.end()) {
+                    (*v.attrs)[j->second.displ] = *i;
+                    env2.values[j->second.displ] = i->value;
+                } else
+                    v.attrs->push_back(*i);
+            }
+            v.attrs->sort();
+        }
+    }
+
+    else
+        foreach (AttrDefs::iterator, i, attrs)
+            v.attrs->push_back(Attr(i->first, i->second.e->maybeThunk(state, env), &i->second.pos));
+
+    /* dynamic attrs apply *after* rec and __overrides */
+    foreach (DynamicAttrDefs::iterator, i, dynamicAttrs) {
+        Value nameVal;
+        i->nameExpr->eval(state, *dynamicEnv, nameVal);
+        state.forceStringNoCtx(nameVal);
+        Symbol nameSym = state.symbols.create(nameVal.string.s);
+        Bindings::iterator j = v.attrs->find(nameSym);
+        if (j != v.attrs->end())
+            throwEvalError("dynamic attribute `%1%' at %2% already defined at %3%", nameSym, i->pos, *j->pos);
+
+        i->valueExpr->setName(nameSym);
+        /* Keep sorted order so find can catch duplicates */
+        v.attrs->insert(lower_bound(v.attrs->begin(), v.attrs->end(), Attr(nameSym, 0)),
+                Attr(nameSym, i->valueExpr->maybeThunk(state, *dynamicEnv), &i->pos));
+    }
+}
+
+
+void ExprLet::eval(EvalState & state, Env & env, Value & v)
+{
+    /* Create a new environment that contains the attributes in this
+       `let'. */
+    Env & env2(state.allocEnv(attrs->attrs.size()));
+    env2.up = &env;
+
+    /* The recursive attributes are evaluated in the new environment,
+       while the inherited attributes are evaluated in the original
+       environment. */
+    unsigned int displ = 0;
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        env2.values[displ++] = i->second.e->maybeThunk(state, i->second.inherited ? env : env2);
+
+    body->eval(state, env2, v);
+}
+
+
+void ExprList::eval(EvalState & state, Env & env, Value & v)
+{
+    state.mkList(v, elems.size());
+    for (unsigned int n = 0; n < v.list.length; ++n)
+        v.list.elems[n] = elems[n]->maybeThunk(state, env);
+}
+
+
+void ExprVar::eval(EvalState & state, Env & env, Value & v)
+{
+    Value * v2 = state.lookupVar(&env, *this, false);
+    state.forceValue(*v2);
+    v = *v2;
+}
+
+
+unsigned long nrLookups = 0;
+
+void ExprSelect::eval(EvalState & state, Env & env, Value & v)
+{
+    Value vTmp;
+    Pos * pos = 0;
+    Value * vAttrs = &vTmp;
+
+    e->eval(state, env, vTmp);
+
+    try {
+
+        foreach (AttrPath::const_iterator, i, attrPath) {
+            nrLookups++;
+            Bindings::iterator j;
+            Symbol name = getName(*i, state, env);
+            if (def) {
+                state.forceValue(*vAttrs);
+                if (vAttrs->type != tAttrs ||
+                    (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
+                {
+                    def->eval(state, env, v);
+                    return;
+                }
+            } else {
+                state.forceAttrs(*vAttrs);
+                if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
+                    throwEvalError("attribute `%1%' missing", showAttrPath(attrPath));
+            }
+            vAttrs = j->value;
+            pos = j->pos;
+            if (state.countCalls && pos) state.attrSelects[*pos]++;
+        }
+
+        state.forceValue(*vAttrs);
+
+    } catch (Error & e) {
+        if (pos && pos->file != state.sDerivationNix)
+            addErrorPrefix(e, "while evaluating the attribute `%1%' at %2%:\n",
+                showAttrPath(attrPath), *pos);
+        throw;
+    }
+
+    v = *vAttrs;
+}
+
+
+void ExprOpHasAttr::eval(EvalState & state, Env & env, Value & v)
+{
+    Value vTmp;
+    Value * vAttrs = &vTmp;
+
+    e->eval(state, env, vTmp);
+
+    foreach (AttrPath::const_iterator, i, attrPath) {
+        state.forceValue(*vAttrs);
+        Bindings::iterator j;
+        Symbol name = getName(*i, state, env);
+        if (vAttrs->type != tAttrs ||
+            (j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
+        {
+            mkBool(v, false);
+            return;
+        } else {
+            vAttrs = j->value;
+        }
+    }
+
+    mkBool(v, true);
+}
+
+
+void ExprLambda::eval(EvalState & state, Env & env, Value & v)
+{
+    v.type = tLambda;
+    v.lambda.env = &env;
+    v.lambda.fun = this;
+}
+
+
+void ExprApp::eval(EvalState & state, Env & env, Value & v)
+{
+    e1->eval(state, env, v);
+    state.callFunction(v, *(e2->maybeThunk(state, env)), v);
+}
+
+
+void EvalState::callPrimOp(Value & fun, Value & arg, Value & v)
+{
+    /* Figure out the number of arguments still needed. */
+    unsigned int argsDone = 0;
+    Value * primOp = &fun;
+    while (primOp->type == tPrimOpApp) {
+        argsDone++;
+        primOp = primOp->primOpApp.left;
+    }
+    assert(primOp->type == tPrimOp);
+    unsigned int arity = primOp->primOp->arity;
+    unsigned int argsLeft = arity - argsDone;
+
+    if (argsLeft == 1) {
+        /* We have all the arguments, so call the primop. */
+
+        /* Put all the arguments in an array. */
+        Value * vArgs[arity];
+        unsigned int n = arity - 1;
+        vArgs[n--] = &arg;
+        for (Value * arg = &fun; arg->type == tPrimOpApp; arg = arg->primOpApp.left)
+            vArgs[n--] = arg->primOpApp.right;
+
+        /* And call the primop. */
+        nrPrimOpCalls++;
+        if (countCalls) primOpCalls[primOp->primOp->name]++;
+        primOp->primOp->fun(*this, vArgs, v);
+    } else {
+        Value * fun2 = allocValue();
+        *fun2 = fun;
+        v.type = tPrimOpApp;
+        v.primOpApp.left = fun2;
+        v.primOpApp.right = &arg;
+    }
+}
+
+
+void EvalState::callFunction(Value & fun, Value & arg, Value & v)
+{
+    if (fun.type == tPrimOp || fun.type == tPrimOpApp) {
+        callPrimOp(fun, arg, v);
+        return;
+    }
+
+    if (fun.type != tLambda)
+        throwTypeError("attempt to call something which is not a function but %1%", fun);
+
+    ExprLambda & lambda(*fun.lambda.fun);
+
+    unsigned int size =
+        (lambda.arg.empty() ? 0 : 1) +
+        (lambda.matchAttrs ? lambda.formals->formals.size() : 0);
+    Env & env2(allocEnv(size));
+    env2.up = fun.lambda.env;
+
+    unsigned int displ = 0;
+
+    if (!lambda.matchAttrs)
+        env2.values[displ++] = &arg;
+
+    else {
+        forceAttrs(arg);
+
+        if (!lambda.arg.empty())
+            env2.values[displ++] = &arg;
+
+        /* For each formal argument, get the actual argument.  If
+           there is no matching actual argument but the formal
+           argument has a default, use the default. */
+        unsigned int attrsUsed = 0;
+        foreach (Formals::Formals_::iterator, i, lambda.formals->formals) {
+            Bindings::iterator j = arg.attrs->find(i->name);
+            if (j == arg.attrs->end()) {
+                if (!i->def) throwTypeError("%1% called without required argument `%2%'",
+                    lambda, i->name);
+                env2.values[displ++] = i->def->maybeThunk(*this, env2);
+            } else {
+                attrsUsed++;
+                env2.values[displ++] = j->value;
+            }
+        }
+
+        /* Check that each actual argument is listed as a formal
+           argument (unless the attribute match specifies a `...'). */
+        if (!lambda.formals->ellipsis && attrsUsed != arg.attrs->size()) {
+            /* Nope, so show the first unexpected argument to the
+               user. */
+            foreach (Bindings::iterator, i, *arg.attrs)
+                if (lambda.formals->argNames.find(i->name) == lambda.formals->argNames.end())
+                    throwTypeError("%1% called with unexpected argument `%2%'", lambda, i->name);
+            abort(); // can't happen
+        }
+    }
+
+    nrFunctionCalls++;
+    if (countCalls) incrFunctionCall(&lambda);
+
+    /* Evaluate the body.  This is conditional on showTrace, because
+       catching exceptions makes this function not tail-recursive. */
+    if (settings.showTrace)
+        try {
+            lambda.body->eval(*this, env2, v);
+        } catch (Error & e) {
+            addErrorPrefix(e, "while evaluating %1%:\n", lambda);
+            throw;
+        }
+    else
+        fun.lambda.fun->body->eval(*this, env2, v);
+}
+
+
+// Lifted out of callFunction() because it creates a temporary that
+// prevents tail-call optimisation.
+void EvalState::incrFunctionCall(ExprLambda * fun)
+{
+    functionCalls[fun]++;
+}
+
+
+void EvalState::autoCallFunction(Bindings & args, Value & fun, Value & res)
+{
+    forceValue(fun);
+
+    if (fun.type != tLambda || !fun.lambda.fun->matchAttrs) {
+        res = fun;
+        return;
+    }
+
+    Value * actualArgs = allocValue();
+    mkAttrs(*actualArgs, fun.lambda.fun->formals->formals.size());
+
+    foreach (Formals::Formals_::iterator, i, fun.lambda.fun->formals->formals) {
+        Bindings::iterator j = args.find(i->name);
+        if (j != args.end())
+            actualArgs->attrs->push_back(*j);
+        else if (!i->def)
+            throwTypeError("cannot auto-call a function that has an argument without a default value (`%1%')", i->name);
+    }
+
+    actualArgs->attrs->sort();
+
+    callFunction(fun, *actualArgs, res);
+}
+
+
+void ExprWith::eval(EvalState & state, Env & env, Value & v)
+{
+    Env & env2(state.allocEnv(1));
+    env2.up = &env;
+    env2.prevWith = prevWith;
+    env2.haveWithAttrs = false;
+    env2.values[0] = (Value *) attrs;
+
+    body->eval(state, env2, v);
+}
+
+
+void ExprIf::eval(EvalState & state, Env & env, Value & v)
+{
+    (state.evalBool(env, cond, v) ? then : else_)->eval(state, env, v);
+}
+
+
+void ExprAssert::eval(EvalState & state, Env & env, Value & v)
+{
+    if (!state.evalBool(env, cond, v))
+        throwAssertionError("assertion failed at %1%", pos);
+    body->eval(state, env, v);
+}
+
+
+void ExprOpNot::eval(EvalState & state, Env & env, Value & v)
+{
+    mkBool(v, !state.evalBool(env, e));
+}
+
+
+void ExprBuiltin::eval(EvalState & state, Env & env, Value & v)
+{
+    // Not a hot path at all, but would be nice to access state.baseEnv directly
+    Env *baseEnv = &env;
+    while (baseEnv->up) baseEnv = baseEnv->up;
+    Bindings::iterator binding = baseEnv->values[0]->attrs->find(name);
+    assert(binding != baseEnv->values[0]->attrs->end());
+    v = *binding->value;
+}
+
+
+void ExprOpEq::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v1; e1->eval(state, env, v1);
+    Value v2; e2->eval(state, env, v2);
+    mkBool(v, state.eqValues(v1, v2));
+}
+
+
+void ExprOpNEq::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v1; e1->eval(state, env, v1);
+    Value v2; e2->eval(state, env, v2);
+    mkBool(v, !state.eqValues(v1, v2));
+}
+
+
+void ExprOpAnd::eval(EvalState & state, Env & env, Value & v)
+{
+    mkBool(v, state.evalBool(env, e1) && state.evalBool(env, e2));
+}
+
+
+void ExprOpOr::eval(EvalState & state, Env & env, Value & v)
+{
+    mkBool(v, state.evalBool(env, e1) || state.evalBool(env, e2));
+}
+
+
+void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
+{
+    mkBool(v, !state.evalBool(env, e1) || state.evalBool(env, e2));
+}
+
+
+void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v1, v2;
+    state.evalAttrs(env, e1, v1);
+    state.evalAttrs(env, e2, v2);
+
+    state.nrOpUpdates++;
+
+    if (v1.attrs->size() == 0) { v = v2; return; }
+    if (v2.attrs->size() == 0) { v = v1; return; }
+
+    state.mkAttrs(v, v1.attrs->size() + v2.attrs->size());
+
+    /* Merge the sets, preferring values from the second set.  Make
+       sure to keep the resulting vector in sorted order. */
+    Bindings::iterator i = v1.attrs->begin();
+    Bindings::iterator j = v2.attrs->begin();
+
+    while (i != v1.attrs->end() && j != v2.attrs->end()) {
+        if (i->name == j->name) {
+            v.attrs->push_back(*j);
+            ++i; ++j;
+        }
+        else if (i->name < j->name)
+            v.attrs->push_back(*i++);
+        else
+            v.attrs->push_back(*j++);
+    }
+
+    while (i != v1.attrs->end()) v.attrs->push_back(*i++);
+    while (j != v2.attrs->end()) v.attrs->push_back(*j++);
+
+    state.nrOpUpdateValuesCopied += v.attrs->size();
+}
+
+
+void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
+{
+    Value v1; e1->eval(state, env, v1);
+    Value v2; e2->eval(state, env, v2);
+    Value * lists[2] = { &v1, &v2 };
+    state.concatLists(v, 2, lists);
+}
+
+
+void EvalState::concatLists(Value & v, unsigned int nrLists, Value * * lists)
+{
+    nrListConcats++;
+
+    Value * nonEmpty = 0;
+    unsigned int len = 0;
+    for (unsigned int n = 0; n < nrLists; ++n) {
+        forceList(*lists[n]);
+        unsigned int l = lists[n]->list.length;
+        len += l;
+        if (l) nonEmpty = lists[n];
+    }
+
+    if (nonEmpty && len == nonEmpty->list.length) {
+        v = *nonEmpty;
+        return;
+    }
+
+    mkList(v, len);
+    for (unsigned int n = 0, pos = 0; n < nrLists; ++n) {
+        unsigned int l = lists[n]->list.length;
+        memcpy(v.list.elems + pos, lists[n]->list.elems, l * sizeof(Value *));
+        pos += l;
+    }
+}
+
+
+void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
+{
+    PathSet context;
+    std::ostringstream s;
+    NixInt n = 0;
+
+    bool first = !forceString;
+    ValueType firstType = tString;
+
+    foreach (vector<Expr *>::iterator, i, *es) {
+        Value vTmp;
+        (*i)->eval(state, env, vTmp);
+
+        /* If the first element is a path, then the result will also
+           be a path, we don't copy anything (yet - that's done later,
+           since paths are copied when they are used in a derivation),
+           and none of the strings are allowed to have contexts. */
+        if (first) {
+            firstType = vTmp.type;
+            first = false;
+        }
+
+        if (firstType == tInt) {
+            if (vTmp.type != tInt)
+                throwEvalError("cannot add %1% to an integer", showType(vTmp));
+            n += vTmp.integer;
+        } else
+            s << state.coerceToString(vTmp, context, false, firstType == tString);
+    }
+
+    if (firstType == tInt)
+        mkInt(v, n);
+    else if (firstType == tPath) {
+        if (!context.empty())
+            throwEvalError("a string that refers to a store path cannot be appended to a path, in `%1%'", s.str());
+        mkPath(v, s.str().c_str());
+    } else
+        mkString(v, s.str(), context);
+}
+
+
+void ExprPos::eval(EvalState & state, Env & env, Value & v)
+{
+    state.mkPos(v, &pos);
+}
+
+
+void EvalState::strictForceValue(Value & v)
+{
+    forceValue(v);
+
+    if (v.type == tAttrs) {
+        foreach (Bindings::iterator, i, *v.attrs)
+            strictForceValue(*i->value);
+    }
+
+    else if (v.type == tList) {
+        for (unsigned int n = 0; n < v.list.length; ++n)
+            strictForceValue(*v.list.elems[n]);
+    }
+}
+
+
+NixInt EvalState::forceInt(Value & v)
+{
+    forceValue(v);
+    if (v.type != tInt)
+        throwTypeError("value is %1% while an integer was expected", v);
+    return v.integer;
+}
+
+
+bool EvalState::forceBool(Value & v)
+{
+    forceValue(v);
+    if (v.type != tBool)
+        throwTypeError("value is %1% while a Boolean was expected", v);
+    return v.boolean;
+}
+
+
+void EvalState::forceFunction(Value & v)
+{
+    forceValue(v);
+    if (v.type != tLambda && v.type != tPrimOp && v.type != tPrimOpApp)
+        throwTypeError("value is %1% while a function was expected", v);
+}
+
+
+string EvalState::forceString(Value & v)
+{
+    forceValue(v);
+    if (v.type != tString)
+        throwTypeError("value is %1% while a string was expected", v);
+    return string(v.string.s);
+}
+
+
+void copyContext(const Value & v, PathSet & context)
+{
+    if (v.string.context)
+        for (const char * * p = v.string.context; *p; ++p)
+            context.insert(*p);
+}
+
+
+string EvalState::forceString(Value & v, PathSet & context)
+{
+    string s = forceString(v);
+    copyContext(v, context);
+    return s;
+}
+
+
+string EvalState::forceStringNoCtx(Value & v)
+{
+    string s = forceString(v);
+    if (v.string.context)
+        throwEvalError("the string `%1%' is not allowed to refer to a store path (such as `%2%')",
+            v.string.s, v.string.context[0]);
+    return s;
+}
+
+
+bool EvalState::isDerivation(Value & v)
+{
+    if (v.type != tAttrs) return false;
+    Bindings::iterator i = v.attrs->find(sType);
+    if (i == v.attrs->end()) return false;
+    forceValue(*i->value);
+    if (i->value->type != tString) return false;
+    return strcmp(i->value->string.s, "derivation") == 0;
+}
+
+
+string EvalState::coerceToString(Value & v, PathSet & context,
+    bool coerceMore, bool copyToStore)
+{
+    forceValue(v);
+
+    string s;
+
+    if (v.type == tString) {
+        copyContext(v, context);
+        return v.string.s;
+    }
+
+    if (v.type == tPath) {
+        Path path(canonPath(v.path));
+        return copyToStore ? copyPathToStore(context, path) : path;
+    }
+
+    if (v.type == tAttrs) {
+        Bindings::iterator i = v.attrs->find(sOutPath);
+        if (i == v.attrs->end()) throwTypeError("cannot coerce a set to a string");
+        return coerceToString(*i->value, context, coerceMore, copyToStore);
+    }
+
+    if (coerceMore) {
+
+        /* Note that `false' is represented as an empty string for
+           shell scripting convenience, just like `null'. */
+        if (v.type == tBool && v.boolean) return "1";
+        if (v.type == tBool && !v.boolean) return "";
+        if (v.type == tInt) return int2String(v.integer);
+        if (v.type == tNull) return "";
+
+        if (v.type == tList) {
+            string result;
+            for (unsigned int n = 0; n < v.list.length; ++n) {
+                result += coerceToString(*v.list.elems[n],
+                    context, coerceMore, copyToStore);
+                if (n < v.list.length - 1
+                    /* !!! not quite correct */
+                    && (v.list.elems[n]->type != tList || v.list.elems[n]->list.length != 0))
+                    result += " ";
+            }
+            return result;
+        }
+    }
+
+    throwTypeError("cannot coerce %1% to a string", v);
+}
+
+
+string EvalState::copyPathToStore(PathSet & context, const Path & path)
+{
+    if (nix::isDerivation(path))
+        throwEvalError("file names are not allowed to end in `%1%'", drvExtension);
+
+    Path dstPath;
+    if (srcToStore[path] != "")
+        dstPath = srcToStore[path];
+    else {
+        dstPath = settings.readOnlyMode
+            ? computeStorePathForPath(path).first
+            : store->addToStore(path, true, htSHA256, defaultPathFilter, repair);
+        srcToStore[path] = dstPath;
+        printMsg(lvlChatty, format("copied source `%1%' -> `%2%'")
+            % path % dstPath);
+    }
+
+    context.insert(dstPath);
+    return dstPath;
+}
+
+
+Path EvalState::coerceToPath(Value & v, PathSet & context)
+{
+    string path = coerceToString(v, context, false, false);
+    if (path == "" || path[0] != '/')
+        throwEvalError("string `%1%' doesn't represent an absolute path", path);
+    return path;
+}
+
+
+bool EvalState::eqValues(Value & v1, Value & v2)
+{
+    forceValue(v1);
+    forceValue(v2);
+
+    /* !!! Hack to support some old broken code that relies on pointer
+       equality tests between sets.  (Specifically, builderDefs calls
+       uniqList on a list of sets.)  Will remove this eventually. */
+    if (&v1 == &v2) return true;
+
+    if (v1.type != v2.type) return false;
+
+    switch (v1.type) {
+
+        case tInt:
+            return v1.integer == v2.integer;
+
+        case tBool:
+            return v1.boolean == v2.boolean;
+
+        case tString: {
+            /* Compare both the string and its context. */
+            if (strcmp(v1.string.s, v2.string.s) != 0) return false;
+            const char * * p = v1.string.context, * * q = v2.string.context;
+            if (!p && !q) return true;
+            if (!p || !q) return false;
+            for ( ; *p && *q; ++p, ++q)
+                if (strcmp(*p, *q) != 0) return false;
+            if (*p || *q) return false;
+            return true;
+        }
+
+        case tPath:
+            return strcmp(v1.path, v2.path) == 0;
+
+        case tNull:
+            return true;
+
+        case tList:
+            if (v1.list.length != v2.list.length) return false;
+            for (unsigned int n = 0; n < v1.list.length; ++n)
+                if (!eqValues(*v1.list.elems[n], *v2.list.elems[n])) return false;
+            return true;
+
+        case tAttrs: {
+            /* If both sets denote a derivation (type = "derivation"),
+               then compare their outPaths. */
+            if (isDerivation(v1) && isDerivation(v2)) {
+                Bindings::iterator i = v1.attrs->find(sOutPath);
+                Bindings::iterator j = v2.attrs->find(sOutPath);
+                if (i != v1.attrs->end() && j != v2.attrs->end())
+                    return eqValues(*i->value, *j->value);
+            }
+
+            if (v1.attrs->size() != v2.attrs->size()) return false;
+
+            /* Otherwise, compare the attributes one by one. */
+            Bindings::iterator i, j;
+            for (i = v1.attrs->begin(), j = v2.attrs->begin(); i != v1.attrs->end(); ++i, ++j)
+                if (i->name != j->name || !eqValues(*i->value, *j->value))
+                    return false;
+
+            return true;
+        }
+
+        /* Functions are incomparable. */
+        case tLambda:
+        case tPrimOp:
+        case tPrimOpApp:
+            return false;
+
+        default:
+            throwEvalError("cannot compare %1% with %2%", showType(v1), showType(v2));
+    }
+}
+
+
+void EvalState::printStats()
+{
+    bool showStats = getEnv("NIX_SHOW_STATS", "0") != "0";
+    Verbosity v = showStats ? lvlInfo : lvlDebug;
+    printMsg(v, "evaluation statistics:");
+
+    struct rusage buf;
+    getrusage(RUSAGE_SELF, &buf);
+    float cpuTime = buf.ru_utime.tv_sec + ((float) buf.ru_utime.tv_usec / 1000000);
+
+    printMsg(v, format("  time elapsed: %1%") % cpuTime);
+    printMsg(v, format("  size of a value: %1%") % sizeof(Value));
+    printMsg(v, format("  environments allocated: %1% (%2% bytes)")
+        % nrEnvs % (nrEnvs * sizeof(Env) + nrValuesInEnvs * sizeof(Value *)));
+    printMsg(v, format("  list elements: %1% (%2% bytes)")
+        % nrListElems % (nrListElems * sizeof(Value *)));
+    printMsg(v, format("  list concatenations: %1%") % nrListConcats);
+    printMsg(v, format("  values allocated: %1% (%2% bytes)")
+        % nrValues % (nrValues * sizeof(Value)));
+    printMsg(v, format("  sets allocated: %1%") % nrAttrsets);
+    printMsg(v, format("  right-biased unions: %1%") % nrOpUpdates);
+    printMsg(v, format("  values copied in right-biased unions: %1%") % nrOpUpdateValuesCopied);
+    printMsg(v, format("  symbols in symbol table: %1%") % symbols.size());
+    printMsg(v, format("  size of symbol table: %1%") % symbols.totalSize());
+    printMsg(v, format("  number of thunks: %1%") % nrThunks);
+    printMsg(v, format("  number of thunks avoided: %1%") % nrAvoided);
+    printMsg(v, format("  number of attr lookups: %1%") % nrLookups);
+    printMsg(v, format("  number of primop calls: %1%") % nrPrimOpCalls);
+    printMsg(v, format("  number of function calls: %1%") % nrFunctionCalls);
+
+    if (countCalls) {
+        v = lvlInfo;
+
+        printMsg(v, format("calls to %1% primops:") % primOpCalls.size());
+        typedef std::multimap<unsigned int, Symbol> PrimOpCalls_;
+        PrimOpCalls_ primOpCalls_;
+        foreach (PrimOpCalls::iterator, i, primOpCalls)
+            primOpCalls_.insert(std::pair<unsigned int, Symbol>(i->second, i->first));
+        foreach_reverse (PrimOpCalls_::reverse_iterator, i, primOpCalls_)
+            printMsg(v, format("%1$10d %2%") % i->first % i->second);
+
+        printMsg(v, format("calls to %1% functions:") % functionCalls.size());
+        typedef std::multimap<unsigned int, ExprLambda *> FunctionCalls_;
+        FunctionCalls_ functionCalls_;
+        foreach (FunctionCalls::iterator, i, functionCalls)
+            functionCalls_.insert(std::pair<unsigned int, ExprLambda *>(i->second, i->first));
+        foreach_reverse (FunctionCalls_::reverse_iterator, i, functionCalls_)
+            printMsg(v, format("%1$10d %2%") % i->first % i->second->showNamePos());
+
+        printMsg(v, format("evaluations of %1% attributes:") % attrSelects.size());
+        typedef std::multimap<unsigned int, Pos> AttrSelects_;
+        AttrSelects_ attrSelects_;
+        foreach (AttrSelects::iterator, i, attrSelects)
+            attrSelects_.insert(std::pair<unsigned int, Pos>(i->second, i->first));
+        foreach_reverse (AttrSelects_::reverse_iterator, i, attrSelects_)
+            printMsg(v, format("%1$10d %2%") % i->first % i->second);
+
+    }
+}
+
+
+}
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
new file mode 100644
index 000000000000..5ae5a1e3cf24
--- /dev/null
+++ b/src/libexpr/eval.hh
@@ -0,0 +1,294 @@
+#pragma once
+
+#include "value.hh"
+#include "nixexpr.hh"
+#include "symbol-table.hh"
+#include "hash.hh"
+
+#include <map>
+
+#if HAVE_BOEHMGC
+#include <gc/gc_allocator.h>
+#endif
+
+
+namespace nix {
+
+
+class EvalState;
+struct Attr;
+
+
+/* Sets are represented as a vector of attributes, sorted by symbol
+   (i.e. pointer to the attribute name in the symbol table). */
+#if HAVE_BOEHMGC
+typedef std::vector<Attr, gc_allocator<Attr> > BindingsBase;
+#else
+typedef std::vector<Attr> BindingsBase;
+#endif
+
+
+class Bindings : public BindingsBase
+{
+public:
+    iterator find(const Symbol & name);
+    void sort();
+};
+
+
+typedef void (* PrimOpFun) (EvalState & state, Value * * args, Value & v);
+
+
+struct PrimOp
+{
+    PrimOpFun fun;
+    unsigned int arity;
+    Symbol name;
+    PrimOp(PrimOpFun fun, unsigned int arity, Symbol name)
+        : fun(fun), arity(arity), name(name) { }
+};
+
+
+struct Env
+{
+    Env * up;
+    unsigned short prevWith; // nr of levels up to next `with' environment
+    bool haveWithAttrs;
+    Value * values[0];
+};
+
+
+struct Attr
+{
+    Symbol name;
+    Value * value;
+    Pos * pos;
+    Attr(Symbol name, Value * value, Pos * pos = &noPos)
+        : name(name), value(value), pos(pos) { };
+    Attr() : pos(&noPos) { };
+    bool operator < (const Attr & a) const
+    {
+        return name < a.name;
+    }
+};
+
+
+void mkString(Value & v, const string & s, const PathSet & context = PathSet());
+
+void copyContext(const Value & v, PathSet & context);
+
+
+/* Cache for calls to addToStore(); maps source paths to the store
+   paths. */
+typedef std::map<Path, Path> SrcToStore;
+
+
+std::ostream & operator << (std::ostream & str, const Value & v);
+
+
+class EvalState
+{
+public:
+    SymbolTable symbols;
+
+    const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
+        sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
+        sFile, sLine, sColumn;
+    Symbol sDerivationNix;
+
+    /* If set, force copying files to the Nix store even if they
+       already exist there. */
+    bool repair;
+
+private:
+    SrcToStore srcToStore;
+
+    /* A cache from path names to values. */
+#if HAVE_BOEHMGC
+    typedef std::map<Path, Value, std::less<Path>, gc_allocator<std::pair<const Path, Value> > > FileEvalCache;
+#else
+    typedef std::map<Path, Value> FileEvalCache;
+#endif
+    FileEvalCache fileEvalCache;
+
+    typedef list<std::pair<string, Path> > SearchPath;
+    SearchPath searchPath;
+    SearchPath::iterator searchPathInsertionPoint;
+
+public:
+
+    EvalState();
+    ~EvalState();
+
+    void addToSearchPath(const string & s);
+
+    /* Parse a Nix expression from the specified file. */
+    Expr * parseExprFromFile(const Path & path);
+
+    /* Parse a Nix expression from the specified string. */
+    Expr * parseExprFromString(const string & s, const Path & basePath, StaticEnv & staticEnv);
+    Expr * parseExprFromString(const string & s, const Path & basePath);
+
+    /* Evaluate an expression read from the given file to normal
+       form. */
+    void evalFile(const Path & path, Value & v);
+
+    void resetFileCache();
+
+    /* Look up a file in the search path. */
+    Path findFile(const string & path);
+
+    /* Evaluate an expression to normal form, storing the result in
+       value `v'. */
+    void eval(Expr * e, Value & v);
+
+    /* Evaluation the expression, then verify that it has the expected
+       type. */
+    inline bool evalBool(Env & env, Expr * e, Value & v);
+    inline bool evalBool(Env & env, Expr * e);
+    inline void evalAttrs(Env & env, Expr * e, Value & v);
+
+    /* If `v' is a thunk, enter it and overwrite `v' with the result
+       of the evaluation of the thunk.  If `v' is a delayed function
+       application, call the function and overwrite `v' with the
+       result.  Otherwise, this is a no-op. */
+    inline void forceValue(Value & v);
+
+    /* Force a value, then recursively force list elements and
+       attributes. */
+    void strictForceValue(Value & v);
+
+    /* Force `v', and then verify that it has the expected type. */
+    NixInt forceInt(Value & v);
+    bool forceBool(Value & v);
+    inline void forceAttrs(Value & v);
+    inline void forceList(Value & v);
+    void forceFunction(Value & v); // either lambda or primop
+    string forceString(Value & v);
+    string forceString(Value & v, PathSet & context);
+    string forceStringNoCtx(Value & v);
+
+    /* Return true iff the value `v' denotes a derivation (i.e. a
+       set with attribute `type = "derivation"'). */
+    bool isDerivation(Value & v);
+
+    /* String coercion.  Converts strings, paths and derivations to a
+       string.  If `coerceMore' is set, also converts nulls, integers,
+       booleans and lists to a string.  If `copyToStore' is set,
+       referenced paths are copied to the Nix store as a side effect. */
+    string coerceToString(Value & v, PathSet & context,
+        bool coerceMore = false, bool copyToStore = true);
+
+    string copyPathToStore(PathSet & context, const Path & path);
+
+    /* Path coercion.  Converts strings, paths and derivations to a
+       path.  The result is guaranteed to be a canonicalised, absolute
+       path.  Nothing is copied to the store. */
+    Path coerceToPath(Value & v, PathSet & context);
+
+public:
+
+    /* The base environment, containing the builtin functions and
+       values. */
+    Env & baseEnv;
+
+    /* The same, but used during parsing to resolve variables. */
+    StaticEnv staticBaseEnv; // !!! should be private
+
+private:
+
+    unsigned int baseEnvDispl;
+
+    void createBaseEnv();
+
+    void addConstant(const string & name, Value & v);
+
+    void addPrimOp(const string & name,
+        unsigned int arity, PrimOpFun primOp);
+
+public:
+
+    void getBuiltin(const string & name, Value & v);
+
+private:
+
+    inline Value * lookupVar(Env * env, const ExprVar & var, bool noEval);
+
+    friend struct ExprVar;
+    friend struct ExprAttrs;
+    friend struct ExprLet;
+
+    Expr * parse(const char * text, const Path & path,
+        const Path & basePath, StaticEnv & staticEnv);
+
+public:
+
+    /* Do a deep equality test between two values.  That is, list
+       elements and attributes are compared recursively. */
+    bool eqValues(Value & v1, Value & v2);
+
+    void callFunction(Value & fun, Value & arg, Value & v);
+    void callPrimOp(Value & fun, Value & arg, Value & v);
+
+    /* Automatically call a function for which each argument has a
+       default value or has a binding in the `args' map. */
+    void autoCallFunction(Bindings & args, Value & fun, Value & res);
+
+    /* Allocation primitives. */
+    Value * allocValue();
+    Env & allocEnv(unsigned int size);
+
+    Value * allocAttr(Value & vAttrs, const Symbol & name);
+
+    void mkList(Value & v, unsigned int length);
+    void mkAttrs(Value & v, unsigned int expected);
+    void mkThunk_(Value & v, Expr * expr);
+    void mkPos(Value & v, Pos * pos);
+
+    void concatLists(Value & v, unsigned int nrLists, Value * * lists);
+
+    /* Print statistics. */
+    void printStats();
+
+private:
+
+    unsigned long nrEnvs;
+    unsigned long nrValuesInEnvs;
+    unsigned long nrValues;
+    unsigned long nrListElems;
+    unsigned long nrAttrsets;
+    unsigned long nrOpUpdates;
+    unsigned long nrOpUpdateValuesCopied;
+    unsigned long nrListConcats;
+    unsigned long nrPrimOpCalls;
+    unsigned long nrFunctionCalls;
+
+    bool countCalls;
+
+    typedef std::map<Symbol, unsigned int> PrimOpCalls;
+    PrimOpCalls primOpCalls;
+
+    typedef std::map<ExprLambda *, unsigned int> FunctionCalls;
+    FunctionCalls functionCalls;
+
+    void incrFunctionCall(ExprLambda * fun);
+
+    typedef std::map<Pos, unsigned int> AttrSelects;
+    AttrSelects attrSelects;
+
+    friend struct ExprOpUpdate;
+    friend struct ExprOpConcatLists;
+    friend struct ExprSelect;
+    friend void prim_getAttr(EvalState & state, Value * * args, Value & v);
+};
+
+
+/* Return a string representing the type of the value `v'. */
+string showType(const Value & v);
+
+
+/* If `path' refers to a directory, then append "/default.nix". */
+Path resolveExprPath(Path path);
+
+
+}
diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
new file mode 100644
index 000000000000..0ed644e9bc5b
--- /dev/null
+++ b/src/libexpr/get-drvs.cc
@@ -0,0 +1,305 @@
+#include "get-drvs.hh"
+#include "util.hh"
+#include "eval-inline.hh"
+
+#include <cstring>
+
+
+namespace nix {
+
+
+string DrvInfo::queryDrvPath()
+{
+    if (drvPath == "" && attrs) {
+        Bindings::iterator i = attrs->find(state->sDrvPath);
+        PathSet context;
+        drvPath = i != attrs->end() ? state->coerceToPath(*i->value, context) : "";
+    }
+    return drvPath;
+}
+
+
+string DrvInfo::queryOutPath()
+{
+    if (outPath == "" && attrs) {
+        Bindings::iterator i = attrs->find(state->sOutPath);
+        PathSet context;
+        outPath = i != attrs->end() ? state->coerceToPath(*i->value, context) : "";
+    }
+    return outPath;
+}
+
+
+DrvInfo::Outputs DrvInfo::queryOutputs()
+{
+    if (outputs.empty()) {
+        /* Get the ‘outputs’ list. */
+        Bindings::iterator i;
+        if (attrs && (i = attrs->find(state->sOutputs)) != attrs->end()) {
+            state->forceList(*i->value);
+
+            /* For each output... */
+            for (unsigned int j = 0; j < i->value->list.length; ++j) {
+                /* Evaluate the corresponding set. */
+                string name = state->forceStringNoCtx(*i->value->list.elems[j]);
+                Bindings::iterator out = attrs->find(state->symbols.create(name));
+                if (out == attrs->end()) continue; // FIXME: throw error?
+                state->forceAttrs(*out->value);
+
+                /* And evaluate its ‘outPath’ attribute. */
+                Bindings::iterator outPath = out->value->attrs->find(state->sOutPath);
+                if (outPath == out->value->attrs->end()) continue; // FIXME: throw error?
+                PathSet context;
+                outputs[name] = state->coerceToPath(*outPath->value, context);
+            }
+        } else
+            outputs["out"] = queryOutPath();
+    }
+    return outputs;
+}
+
+
+string DrvInfo::queryOutputName()
+{
+    if (outputName == "" && attrs) {
+        Bindings::iterator i = attrs->find(state->sOutputName);
+        outputName = i != attrs->end() ? state->forceStringNoCtx(*i->value) : "";
+    }
+    return outputName;
+}
+
+
+Bindings * DrvInfo::getMeta()
+{
+    if (meta) return meta;
+    if (!attrs) return 0;
+    Bindings::iterator a = attrs->find(state->sMeta);
+    if (a == attrs->end()) return 0;
+    state->forceAttrs(*a->value);
+    meta = a->value->attrs;
+    return meta;
+}
+
+
+StringSet DrvInfo::queryMetaNames()
+{
+    StringSet res;
+    if (!getMeta()) return res;
+    foreach (Bindings::iterator, i, *meta)
+        res.insert(i->name);
+    return res;
+}
+
+
+bool DrvInfo::checkMeta(Value & v)
+{
+    state->forceValue(v);
+    if (v.type == tList) {
+        for (unsigned int n = 0; n < v.list.length; ++n)
+            if (!checkMeta(*v.list.elems[n])) return false;
+        return true;
+    }
+    else if (v.type == tAttrs) {
+        Bindings::iterator i = v.attrs->find(state->sOutPath);
+        if (i != v.attrs->end()) return false;
+        foreach (Bindings::iterator, i, *v.attrs)
+            if (!checkMeta(*i->value)) return false;
+        return true;
+    }
+    else return v.type == tInt || v.type == tBool || v.type == tString;
+}
+
+
+Value * DrvInfo::queryMeta(const string & name)
+{
+    if (!getMeta()) return 0;
+    Bindings::iterator a = meta->find(state->symbols.create(name));
+    if (a == meta->end() || !checkMeta(*a->value)) return 0;
+    return a->value;
+}
+
+
+string DrvInfo::queryMetaString(const string & name)
+{
+    Value * v = queryMeta(name);
+    if (!v || v->type != tString) return "";
+    return v->string.s;
+}
+
+
+int DrvInfo::queryMetaInt(const string & name, int def)
+{
+    Value * v = queryMeta(name);
+    if (!v) return def;
+    if (v->type == tInt) return v->integer;
+    if (v->type == tString) {
+        /* Backwards compatibility with before we had support for
+           integer meta fields. */
+        int n;
+        if (string2Int(v->string.s, n)) return n;
+    }
+    return def;
+}
+
+
+bool DrvInfo::queryMetaBool(const string & name, bool def)
+{
+    Value * v = queryMeta(name);
+    if (!v) return def;
+    if (v->type == tBool) return v->boolean;
+    if (v->type == tString) {
+        /* Backwards compatibility with before we had support for
+           Boolean meta fields. */
+        if (strcmp(v->string.s, "true") == 0) return true;
+        if (strcmp(v->string.s, "false") == 0) return false;
+    }
+    return def;
+}
+
+
+void DrvInfo::setMeta(const string & name, Value * v)
+{
+    getMeta();
+    Bindings * old = meta;
+    meta = new Bindings();
+    Symbol sym = state->symbols.create(name);
+    if (old)
+        foreach (Bindings::iterator, i, *old)
+            if (i->name != sym)
+                meta->push_back(*i);
+    if (v) meta->push_back(Attr(sym, v));
+    meta->sort();
+}
+
+
+/* Cache for already considered attrsets. */
+typedef set<Bindings *> Done;
+
+
+/* Evaluate value `v'.  If it evaluates to a set of type `derivation',
+   then put information about it in `drvs' (unless it's already in
+   `doneExprs').  The result boolean indicates whether it makes sense
+   for the caller to recursively search for derivations in `v'. */
+static bool getDerivation(EvalState & state, Value & v,
+    const string & attrPath, DrvInfos & drvs, Done & done,
+    bool ignoreAssertionFailures)
+{
+    try {
+        state.forceValue(v);
+        if (!state.isDerivation(v)) return true;
+
+        /* Remove spurious duplicates (e.g., a set like `rec { x =
+           derivation {...}; y = x;}'. */
+        if (done.find(v.attrs) != done.end()) return false;
+        done.insert(v.attrs);
+
+        Bindings::iterator i = v.attrs->find(state.sName);
+        /* !!! We really would like to have a decent back trace here. */
+        if (i == v.attrs->end()) throw TypeError("derivation name missing");
+
+        Bindings::iterator i2 = v.attrs->find(state.sSystem);
+
+        DrvInfo drv(
+            state,
+            state.forceStringNoCtx(*i->value),
+            attrPath,
+            i2 == v.attrs->end() ? "unknown" : state.forceStringNoCtx(*i2->value),
+            v.attrs);
+
+        drvs.push_back(drv);
+        return false;
+
+    } catch (AssertionError & e) {
+        if (ignoreAssertionFailures) return false;
+        throw;
+    }
+}
+
+
+bool getDerivation(EvalState & state, Value & v, DrvInfo & drv,
+    bool ignoreAssertionFailures)
+{
+    Done done;
+    DrvInfos drvs;
+    getDerivation(state, v, "", drvs, done, ignoreAssertionFailures);
+    if (drvs.size() != 1) return false;
+    drv = drvs.front();
+    return true;
+}
+
+
+static string addToPath(const string & s1, const string & s2)
+{
+    return s1.empty() ? s2 : s1 + "." + s2;
+}
+
+
+static void getDerivations(EvalState & state, Value & vIn,
+    const string & pathPrefix, Bindings & autoArgs,
+    DrvInfos & drvs, Done & done,
+    bool ignoreAssertionFailures)
+{
+    Value v;
+    state.autoCallFunction(autoArgs, vIn, v);
+
+    /* Process the expression. */
+    if (!getDerivation(state, v, pathPrefix, drvs, done, ignoreAssertionFailures)) ;
+
+    else if (v.type == tAttrs) {
+
+        /* !!! undocumented hackery to support combining channels in
+           nix-env.cc. */
+        bool combineChannels = v.attrs->find(state.symbols.create("_combineChannels")) != v.attrs->end();
+
+        /* Consider the attributes in sorted order to get more
+           deterministic behaviour in nix-env operations (e.g. when
+           there are names clashes between derivations, the derivation
+           bound to the attribute with the "lower" name should take
+           precedence). */
+        typedef std::map<string, Symbol> SortedSymbols;
+        SortedSymbols attrs;
+        foreach (Bindings::iterator, i, *v.attrs)
+            attrs.insert(std::pair<string, Symbol>(i->name, i->name));
+
+        foreach (SortedSymbols::iterator, i, attrs) {
+            startNest(nest, lvlDebug, format("evaluating attribute `%1%'") % i->first);
+            string pathPrefix2 = addToPath(pathPrefix, i->first);
+            Value & v2(*v.attrs->find(i->second)->value);
+            if (combineChannels)
+                getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+            else if (getDerivation(state, v2, pathPrefix2, drvs, done, ignoreAssertionFailures)) {
+                /* If the value of this attribute is itself a set,
+                   should we recurse into it?  => Only if it has a
+                   `recurseForDerivations = true' attribute. */
+                if (v2.type == tAttrs) {
+                    Bindings::iterator j = v2.attrs->find(state.symbols.create("recurseForDerivations"));
+                    if (j != v2.attrs->end() && state.forceBool(*j->value))
+                        getDerivations(state, v2, pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+                }
+            }
+        }
+    }
+
+    else if (v.type == tList) {
+        for (unsigned int n = 0; n < v.list.length; ++n) {
+            startNest(nest, lvlDebug,
+                format("evaluating list element"));
+            string pathPrefix2 = addToPath(pathPrefix, (format("%1%") % n).str());
+            if (getDerivation(state, *v.list.elems[n], pathPrefix2, drvs, done, ignoreAssertionFailures))
+                getDerivations(state, *v.list.elems[n], pathPrefix2, autoArgs, drvs, done, ignoreAssertionFailures);
+        }
+    }
+
+    else throw TypeError("expression does not evaluate to a derivation (or a set or list of those)");
+}
+
+
+void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
+    Bindings & autoArgs, DrvInfos & drvs, bool ignoreAssertionFailures)
+{
+    Done done;
+    getDerivations(state, v, pathPrefix, autoArgs, drvs, done, ignoreAssertionFailures);
+}
+
+
+}
diff --git a/src/libexpr/get-drvs.hh b/src/libexpr/get-drvs.hh
new file mode 100644
index 000000000000..aaafff1905e7
--- /dev/null
+++ b/src/libexpr/get-drvs.hh
@@ -0,0 +1,93 @@
+#pragma once
+
+#include "eval.hh"
+
+#include <string>
+#include <map>
+
+#include <boost/shared_ptr.hpp>
+
+
+namespace nix {
+
+
+struct DrvInfo
+{
+public:
+    typedef std::map<string, Path> Outputs;
+
+private:
+    EvalState * state;
+
+    string drvPath;
+    string outPath;
+    string outputName;
+    Outputs outputs;
+
+    bool failed; // set if we get an AssertionError
+
+    Bindings * attrs, * meta;
+
+    Bindings * getMeta();
+
+    bool checkMeta(Value & v);
+
+public:
+    string name;
+    string attrPath; /* path towards the derivation */
+    string system;
+
+    DrvInfo(EvalState & state) : state(&state), failed(false), attrs(0), meta(0) { };
+    DrvInfo(EvalState & state, const string & name, const string & attrPath, const string & system, Bindings * attrs)
+        : state(&state), failed(false), attrs(attrs), meta(0), name(name), attrPath(attrPath), system(system) { };
+
+    string queryDrvPath();
+    string queryOutPath();
+    string queryOutputName();
+    Outputs queryOutputs();
+
+    StringSet queryMetaNames();
+    Value * queryMeta(const string & name);
+    string queryMetaString(const string & name);
+    int queryMetaInt(const string & name, int def);
+    bool queryMetaBool(const string & name, bool def);
+    void setMeta(const string & name, Value * v);
+
+    /*
+    MetaInfo queryMetaInfo(EvalState & state) const;
+    MetaValue queryMetaInfo(EvalState & state, const string & name) const;
+    */
+
+    void setDrvPath(const string & s)
+    {
+        drvPath = s;
+    }
+
+    void setOutPath(const string & s)
+    {
+        outPath = s;
+    }
+
+    void setFailed() { failed = true; };
+    bool hasFailed() { return failed; };
+};
+
+
+#if HAVE_BOEHMGC
+typedef list<DrvInfo, traceable_allocator<DrvInfo> > DrvInfos;
+#else
+typedef list<DrvInfo> DrvInfos;
+#endif
+
+
+/* If value `v' denotes a derivation, store information about the
+   derivation in `drv' and return true.  Otherwise, return false. */
+bool getDerivation(EvalState & state, Value & v, DrvInfo & drv,
+    bool ignoreAssertionFailures);
+
+void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
+    Bindings & autoArgs, DrvInfos & drvs,
+    bool ignoreAssertionFailures);
+
+
+}
diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l
new file mode 100644
index 000000000000..911850cc5ba5
--- /dev/null
+++ b/src/libexpr/lexer.l
@@ -0,0 +1,193 @@
+%option reentrant bison-bridge bison-locations
+%option noyywrap
+%option never-interactive
+
+
+%x STRING
+%x IND_STRING
+
+
+%{
+#include "nixexpr.hh"
+#include "parser-tab.hh"
+
+using namespace nix;
+
+namespace nix {
+
+
+static void initLoc(YYLTYPE * loc)
+{
+    loc->first_line = loc->last_line = 1;
+    loc->first_column = loc->last_column = 1;
+}
+
+
+static void adjustLoc(YYLTYPE * loc, const char * s, size_t len)
+{
+    loc->first_line = loc->last_line;
+    loc->first_column = loc->last_column;
+
+    while (len--) {
+       switch (*s++) {
+       case '\r':
+           if (*s == '\n') /* cr/lf */
+               s++;
+           /* fall through */
+       case '\n':
+           ++loc->last_line;
+           loc->last_column = 1;
+           break;
+       default:
+           ++loc->last_column;
+       }
+    }
+}
+
+
+static Expr * unescapeStr(SymbolTable & symbols, const char * s)
+{
+    string t;
+    char c;
+    while ((c = *s++)) {
+        if (c == '\\') {
+            assert(*s);
+            c = *s++;
+            if (c == 'n') t += '\n';
+            else if (c == 'r') t += '\r';
+            else if (c == 't') t += '\t';
+            else t += c;
+        }
+        else if (c == '\r') {
+            /* Normalise CR and CR/LF into LF. */
+            t += '\n';
+            if (*s == '\n') s++; /* cr/lf */
+        }
+        else t += c;
+    }
+    return new ExprString(symbols.create(t));
+}
+
+
+}
+
+#define YY_USER_INIT initLoc(yylloc)
+#define YY_USER_ACTION adjustLoc(yylloc, yytext, yyleng);
+
+%}
+
+
+ID          [a-zA-Z\_][a-zA-Z0-9\_\'\-]*
+INT         [0-9]+
+PATH        [a-zA-Z0-9\.\_\-\+]*(\/[a-zA-Z0-9\.\_\-\+]+)+
+SPATH       \<[a-zA-Z0-9\.\_\-\+]+(\/[a-zA-Z0-9\.\_\-\+]+)*\>
+URI         [a-zA-Z][a-zA-Z0-9\+\-\.]*\:[a-zA-Z0-9\%\/\?\:\@\&\=\+\$\,\-\_\.\!\~\*\']+
+
+
+%%
+
+
+if          { return IF; }
+then        { return THEN; }
+else        { return ELSE; }
+assert      { return ASSERT; }
+with        { return WITH; }
+let         { return LET; }
+in          { return IN; }
+rec         { return REC; }
+inherit     { return INHERIT; }
+or          { return OR_KW; }
+\.\.\.      { return ELLIPSIS; }
+
+\=\=        { return EQ; }
+\!\=        { return NEQ; }
+\<\=        { return LEQ; }
+\>\=        { return GEQ; }
+\&\&        { return AND; }
+\|\|        { return OR; }
+\-\>        { return IMPL; }
+\/\/        { return UPDATE; }
+\+\+        { return CONCAT; }
+
+{ID}        { yylval->id = strdup(yytext); return ID; }
+{INT}       { errno = 0;
+              yylval->n = strtol(yytext, 0, 10);
+              if (errno != 0)
+                  throw ParseError(format("invalid integer `%1%'") % yytext);
+              return INT;
+            }
+
+\$\{        { return DOLLAR_CURLY; }
+
+\"          { BEGIN(STRING); return '"'; }
+<STRING>([^\$\"\\]|\$[^\{\"]|\\.)+ {
+              /* !!! Not quite right: we want a follow restriction on
+                 "$", it shouldn't be followed by a "{".  Right now
+                 "$\"" will be consumed as part of a string, rather
+                 than a "$" followed by the string terminator.
+                 Disallow "$\"" for now. */
+              yylval->e = unescapeStr(data->symbols, yytext);
+              return STR;
+            }
+<STRING>\$\{  { BEGIN(INITIAL); return DOLLAR_CURLY; }
+<STRING>\"  { BEGIN(INITIAL); return '"'; }
+<STRING>.   return yytext[0]; /* just in case: shouldn't be reached */
+
+\'\'(\ *\n)?     { BEGIN(IND_STRING); return IND_STRING_OPEN; }
+<IND_STRING>([^\$\']|\$[^\{\']|\'[^\'\$])+ {
+                   yylval->e = new ExprIndStr(yytext);
+                   return IND_STR;
+                 }
+<IND_STRING>\'\'\$ {
+                   yylval->e = new ExprIndStr("$");
+                   return IND_STR;
+                 }
+<IND_STRING>\'\'\' {
+                   yylval->e = new ExprIndStr("''");
+                   return IND_STR;
+                 }
+<IND_STRING>\'\'\\. {
+                   yylval->e = unescapeStr(data->symbols, yytext + 2);
+                   return IND_STR;
+                 }
+<IND_STRING>\$\{ { BEGIN(INITIAL); return DOLLAR_CURLY; }
+<IND_STRING>\'\' { BEGIN(INITIAL); return IND_STRING_CLOSE; }
+<IND_STRING>\'   {
+                   yylval->e = new ExprIndStr("'");
+                   return IND_STR;
+                 }
+<IND_STRING>.    return yytext[0]; /* just in case: shouldn't be reached */
+
+{PATH}      { yylval->path = strdup(yytext); return PATH; }
+{SPATH}     { yylval->path = strdup(yytext); return SPATH; }
+{URI}       { yylval->uri = strdup(yytext); return URI; }
+
+[ \t\r\n]+    /* eat up whitespace */
+\#[^\r\n]*    /* single-line comments */
+\/\*([^*]|\*[^\/])*\*\/  /* long comments */
+
+.           return yytext[0];
+
+
+%%
+
+
+namespace nix {
+
+/* Horrible, disgusting hack: allow the parser to set the scanner
+   start condition back to STRING.  Necessary in interpolations like
+   "foo${expr}bar"; after the close brace we have to go back to the
+   STRING state. */
+void backToString(yyscan_t scanner)
+{
+    struct yyguts_t * yyg = (struct yyguts_t *) scanner;
+    BEGIN(STRING);
+}
+
+void backToIndString(yyscan_t scanner)
+{
+    struct yyguts_t * yyg = (struct yyguts_t *) scanner;
+    BEGIN(IND_STRING);
+}
+
+}
diff --git a/src/libexpr/local.mk b/src/libexpr/local.mk
new file mode 100644
index 000000000000..85e476e39b21
--- /dev/null
+++ b/src/libexpr/local.mk
@@ -0,0 +1,22 @@
+libraries += libexpr
+
+libexpr_NAME = libnixexpr
+
+libexpr_DIR := $(d)
+
+libexpr_SOURCES := $(wildcard $(d)/*.cc) $(d)/lexer-tab.cc $(d)/parser-tab.cc
+
+libexpr_LIBS = libutil libstore libformat
+
+# The dependency on libgc must be propagated (i.e. meaning that
+# programs/libraries that use libexpr must explicitly pass -lgc),
+# because inline functions in libexpr's header files call libgc.
+libexpr_LDFLAGS_PROPAGATED = $(BDW_GC_LIBS)
+
+$(d)/parser-tab.cc $(d)/parser-tab.hh: $(d)/parser.y
+	$(trace-gen) bison -v -o $(libexpr_DIR)/parser-tab.cc $< -d
+
+$(d)/lexer-tab.cc $(d)/lexer-tab.hh: $(d)/lexer.l
+	$(trace-gen) flex --outfile $(libexpr_DIR)/lexer-tab.cc --header-file=$(libexpr_DIR)/lexer-tab.hh $<
+
+clean-files += $(d)/parser-tab.cc $(d)/parser-tab.hh $(d)/lexer-tab.cc $(d)/lexer-tab.hh
diff --git a/src/libexpr/names.cc b/src/libexpr/names.cc
new file mode 100644
index 000000000000..781c2b6468f9
--- /dev/null
+++ b/src/libexpr/names.cc
@@ -0,0 +1,104 @@
+#include "names.hh"
+#include "util.hh"
+
+
+namespace nix {
+
+
+DrvName::DrvName()
+{
+    name = "";
+}
+
+
+/* Parse a derivation name.  The `name' part of a derivation name is
+   everything up to but not including the first dash *not* followed by
+   a letter.  The `version' part is the rest (excluding the separating
+   dash).  E.g., `apache-httpd-2.0.48' is parsed to (`apache-httpd',
+   '2.0.48'). */
+DrvName::DrvName(const string & s) : hits(0)
+{
+    name = fullName = s;
+    for (unsigned int i = 0; i < s.size(); ++i) {
+        /* !!! isalpha/isdigit are affected by the locale. */
+        if (s[i] == '-' && i + 1 < s.size() && !isalpha(s[i + 1])) {
+            name = string(s, 0, i);
+            version = string(s, i + 1);
+            break;
+        }
+    }
+}
+
+
+bool DrvName::matches(DrvName & n)
+{
+    if (name != "*" && name != n.name) return false;
+    if (version != "" && version != n.version) return false;
+    return true;
+}
+
+
+static string nextComponent(string::const_iterator & p,
+    const string::const_iterator end)
+{
+    /* Skip any dots and dashes (component separators). */
+    while (p != end && (*p == '.' || *p == '-')) ++p;
+
+    if (p == end) return "";
+
+    /* If the first character is a digit, consume the longest sequence
+       of digits.  Otherwise, consume the longest sequence of
+       non-digit, non-separator characters. */
+    string s;
+    if (isdigit(*p))
+        while (p != end && isdigit(*p)) s += *p++;
+    else
+        while (p != end && (!isdigit(*p) && *p != '.' && *p != '-'))
+            s += *p++;
+
+    return s;
+}
+
+
+static bool componentsLT(const string & c1, const string & c2)
+{
+    int n1, n2;
+    bool c1Num = string2Int(c1, n1), c2Num = string2Int(c2, n2);
+
+    if (c1Num && c2Num) return n1 < n2;
+    else if (c1 == "" && c2Num) return true;
+    else if (c1 == "pre" && c2 != "pre") return true;
+    else if (c2 == "pre") return false;
+    /* Assume that `2.3a' < `2.3.1'. */
+    else if (c2Num) return true;
+    else if (c1Num) return false;
+    else return c1 < c2;
+}
+
+
+int compareVersions(const string & v1, const string & v2)
+{
+    string::const_iterator p1 = v1.begin();
+    string::const_iterator p2 = v2.begin();
+
+    while (p1 != v1.end() || p2 != v2.end()) {
+        string c1 = nextComponent(p1, v1.end());
+        string c2 = nextComponent(p2, v2.end());
+        if (componentsLT(c1, c2)) return -1;
+        else if (componentsLT(c2, c1)) return 1;
+    }
+
+    return 0;
+}
+
+
+DrvNames drvNamesFromArgs(const Strings & opArgs)
+{
+    DrvNames result;
+    foreach (Strings::const_iterator, i, opArgs)
+        result.push_back(DrvName(*i));
+    return result;
+}
+
+
+}
diff --git a/src/libexpr/names.hh b/src/libexpr/names.hh
new file mode 100644
index 000000000000..ebe113e82ac1
--- /dev/null
+++ b/src/libexpr/names.hh
@@ -0,0 +1,24 @@
+#pragma once
+
+#include "types.hh"
+
+namespace nix {
+
+struct DrvName
+{
+    string fullName;
+    string name;
+    string version;
+    unsigned int hits;
+
+    DrvName();
+    DrvName(const string & s);
+    bool matches(DrvName & n);
+};
+
+typedef list<DrvName> DrvNames;
+
+int compareVersions(const string & v1, const string & v2);
+DrvNames drvNamesFromArgs(const Strings & opArgs);
+
+}
diff --git a/src/libexpr/nix.sdf b/src/libexpr/nix.sdf
new file mode 100644
index 000000000000..42fb21c3baad
--- /dev/null
+++ b/src/libexpr/nix.sdf
@@ -0,0 +1,141 @@
+%% Note: this SDF grammar is no longer used in the Nix expression
+%% parser and may not be up to date.
+
+definition
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Top level syntax.
+
+module Main
+imports Nix-Exprs Nix-Layout
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Expressions.
+
+module Nix-Exprs
+imports Nix-Lexicals
+exports
+  sorts Expr Formal Bind ExprList
+  context-free start-symbols Expr
+  context-free syntax
+
+    Id -> Expr {cons("Var")}
+    Int -> Expr {cons("Int")}
+    Str -> Expr {cons("Str")}
+    Uri -> Expr {cons("Uri")}
+    Path -> Expr {cons("Path")}
+
+    "(" Expr ")" -> Expr {bracket}
+
+    Expr Expr -> Expr {cons("Call"), left}
+
+    Id ":" Expr -> Expr {cons("Function1")}
+    "{" {Formal ","}* "}" ":" Expr -> Expr {cons("Function")}
+    Id -> Formal {cons("NoDefFormal")}
+    Id "?" Expr -> Formal {cons("DefFormal")}
+
+    "assert" Expr ";" Expr -> Expr {cons("Assert")}
+
+    "with" Expr ";" Expr -> Expr {cons("With")}
+
+    "rec" "{" Bind* "}" -> Expr {cons("Rec")}
+    "let" Bind* "in" Expr -> Expr {cons("Let")}
+    "let" "{" Bind* "}" -> Expr {cons("LetRec")}
+    "{" Bind* "}" -> Expr {cons("Attrs")}
+
+    Id "=" Expr ";" -> Bind {cons("Bind")}
+    "inherit" ("(" Expr ")")? Id* ";" -> Bind {cons("Inherit")}
+
+    "[" ExprList "]" -> Expr {cons("List")}
+    -> ExprList {cons("ExprNil")}
+    Expr ExprList -> ExprList {cons("ExprCons")}
+
+    Expr "." Id -> Expr {cons("Select")}
+
+    "if" Expr "then" Expr "else" Expr -> Expr {cons("If")}
+
+    Expr "==" Expr -> Expr {cons("OpEq"), non-assoc}
+    Expr "!=" Expr -> Expr {cons("OpNEq"), non-assoc}
+
+    "!" Expr -> Expr {cons("OpNot")}
+    Expr "&&" Expr -> Expr {cons("OpAnd"), right}
+    Expr "||" Expr -> Expr {cons("OpOr"), right}
+    Expr "->" Expr -> Expr {cons("OpImpl"), right}
+
+    Expr "//" Expr -> Expr {cons("OpUpdate"), right}
+    Expr "~" Expr -> Expr {cons("SubPath"), non-assoc}
+    Expr "?" Id -> Expr {cons("OpHasAttr")}
+    Expr "+" Expr -> Expr {cons("OpPlus"), left}
+    Expr "++" Expr -> Expr {cons("OpConcat"), right}
+
+  context-free priorities
+
+    Expr "." Id -> Expr
+  > Expr ExprList -> ExprList
+  > Expr Expr -> Expr
+  > Expr "~" Expr -> Expr
+  > Expr "?" Id -> Expr
+  > Expr "++" Expr -> Expr
+  > Expr "+" Expr -> Expr
+  > "!" Expr -> Expr
+  > Expr "//" Expr -> Expr
+  > { Expr "==" Expr -> Expr
+      Expr "!=" Expr -> Expr
+    }
+  > Expr "&&" Expr -> Expr
+  > Expr "||" Expr -> Expr
+  > Expr "->" Expr -> Expr
+  > "if" Expr "then" Expr "else" Expr -> Expr
+  > "assert" Expr ";" Expr -> Expr
+  > "with" Expr ";" Expr -> Expr
+  > Id ":" Expr -> Expr
+  > "{" {Formal ","}* "}" ":" Expr -> Expr
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Lexical syntax.
+
+module Nix-Lexicals
+exports
+  sorts Id Int Str Path Uri
+  lexical syntax
+    [a-zA-Z\_][a-zA-Z0-9\_\']* -> Id
+    "rec" | "let" | "if" | "then" | "else" | "assert" | "with" | "inherit" -> Id {reject}
+
+    [0-9]+ -> Int
+
+    "\"" (~[\"\\] | ("\\" ~[]) )* "\"" -> Str
+    "''" (~[\"\\] | ("\\" ~[]) )* "''" -> Str
+
+    [a-zA-Z0-9\.\_\-\+]* ("/"[a-zA-Z0-9\.\_\-\+]+)+ -> Path
+
+    [a-zA-Z] [a-zA-Z0-9\+\-\.]* ":" [a-zA-Z0-9\%\/\?\:\@\&\=\+\$\,\-\_\.\!\~\*\']+ -> Uri
+
+  lexical restrictions
+    Id -/- [a-zA-Z0-9\_\']
+    Int -/- [0-9]
+    Path -/- [a-zA-Z0-9\.\_\-\+\/]
+    Uri -/- [a-zA-Z0-9\%\/\?\:\@\&\=\+\$\,\-\_\.\!\~\*\']
+    "rec" "let" "if" "then" "else" "assert" "with" "inherit" -/- [A-Za-z0-9\_\']
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Layout.
+
+module Nix-Layout
+exports
+  sorts HashComment Asterisk Comment
+  lexical syntax
+    [\ \t\n] -> LAYOUT
+    HashComment -> LAYOUT
+    Comment -> LAYOUT
+    "#" ~[\n]* -> HashComment
+    "/*" ( ~[\*] | Asterisk )* "*/" -> Comment
+    [\*] ~[\/] -> Asterisk
+  lexical restrictions
+    HashComment -/- ~[\n]
+  context-free restrictions
+    LAYOUT? -/- [\ \t\n\#]
+    LAYOUT? -/- [\/].[\*]
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
new file mode 100644
index 000000000000..9f0bc2630ddc
--- /dev/null
+++ b/src/libexpr/nixexpr.cc
@@ -0,0 +1,391 @@
+#include "nixexpr.hh"
+#include "derivations.hh"
+#include "util.hh"
+
+#include <cstdlib>
+
+
+namespace nix {
+
+
+/* Displaying abstract syntax trees. */
+
+std::ostream & operator << (std::ostream & str, Expr & e)
+{
+    e.show(str);
+    return str;
+}
+
+void Expr::show(std::ostream & str)
+{
+    abort();
+}
+
+void ExprInt::show(std::ostream & str)
+{
+    str << n;
+}
+
+void ExprString::show(std::ostream & str)
+{
+    str << "\"" << s << "\""; // !!! escaping
+}
+
+void ExprPath::show(std::ostream & str)
+{
+    str << s;
+}
+
+void ExprVar::show(std::ostream & str)
+{
+    str << name;
+}
+
+void ExprSelect::show(std::ostream & str)
+{
+    str << "(" << *e << ")." << showAttrPath(attrPath);
+    if (def) str << " or " << *def;
+}
+
+void ExprOpHasAttr::show(std::ostream & str)
+{
+    str << "(" << *e << ") ? " << showAttrPath(attrPath);
+}
+
+void ExprAttrs::show(std::ostream & str)
+{
+    if (recursive) str << "rec ";
+    str << "{ ";
+    foreach (AttrDefs::iterator, i, attrs)
+        if (i->second.inherited)
+            str << "inherit " << i->first << " " << "; ";
+        else
+            str << i->first << " = " << *i->second.e << "; ";
+    foreach (DynamicAttrDefs::iterator, i, dynamicAttrs)
+        str << "\"${" << *i->nameExpr << "}\" = " << *i->valueExpr << "; ";
+    str << "}";
+}
+
+void ExprList::show(std::ostream & str)
+{
+    str << "[ ";
+    foreach (vector<Expr *>::iterator, i, elems)
+        str << "(" << **i << ") ";
+    str << "]";
+}
+
+void ExprLambda::show(std::ostream & str)
+{
+    str << "(";
+    if (matchAttrs) {
+        str << "{ ";
+        bool first = true;
+        foreach (Formals::Formals_::iterator, i, formals->formals) {
+            if (first) first = false; else str << ", ";
+            str << i->name;
+            if (i->def) str << " ? " << *i->def;
+        }
+        str << " }";
+        if (!arg.empty()) str << " @ ";
+    }
+    if (!arg.empty()) str << arg;
+    str << ": " << *body << ")";
+}
+
+void ExprLet::show(std::ostream & str)
+{
+    str << "let ";
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        if (i->second.inherited)
+            str << "inherit " << i->first << "; ";
+        else
+            str << i->first << " = " << *i->second.e << "; ";
+    str << "in " << *body;
+}
+
+void ExprWith::show(std::ostream & str)
+{
+    str << "with " << *attrs << "; " << *body;
+}
+
+void ExprIf::show(std::ostream & str)
+{
+    str << "if " << *cond << " then " << *then << " else " << *else_;
+}
+
+void ExprAssert::show(std::ostream & str)
+{
+    str << "assert " << *cond << "; " << *body;
+}
+
+void ExprOpNot::show(std::ostream & str)
+{
+    str << "! " << *e;
+}
+
+void ExprBuiltin::show(std::ostream & str)
+{
+    str << "builtins." << name;
+}
+
+void ExprConcatStrings::show(std::ostream & str)
+{
+    bool first = true;
+    foreach (vector<Expr *>::iterator, i, *es) {
+        if (first) first = false; else str << " + ";
+        str << **i;
+    }
+}
+
+void ExprPos::show(std::ostream & str)
+{
+    str << "__curPos";
+}
+
+
+std::ostream & operator << (std::ostream & str, const Pos & pos)
+{
+    if (!pos.line)
+        str << "undefined position";
+    else
+        str << (format("`%1%:%2%:%3%'") % pos.file % pos.line % pos.column).str();
+    return str;
+}
+
+
+string showAttrPath(const AttrPath & attrPath)
+{
+    std::ostringstream out;
+    bool first = true;
+    foreach (AttrPath::const_iterator, i, attrPath) {
+        if (!first)
+            out << '.';
+        else
+            first = false;
+        if (i->symbol.set())
+            out << i->symbol;
+        else
+            out << "\"${" << *i->expr << "}\"";
+    }
+    return out.str();
+}
+
+
+Pos noPos;
+
+
+/* Computing levels/displacements for variables. */
+
+void Expr::bindVars(const StaticEnv & env)
+{
+    abort();
+}
+
+void ExprInt::bindVars(const StaticEnv & env)
+{
+}
+
+void ExprString::bindVars(const StaticEnv & env)
+{
+}
+
+void ExprPath::bindVars(const StaticEnv & env)
+{
+}
+
+void ExprVar::bindVars(const StaticEnv & env)
+{
+    /* Check whether the variable appears in the environment.  If so,
+       set its level and displacement. */
+    const StaticEnv * curEnv;
+    unsigned int level;
+    int withLevel = -1;
+    for (curEnv = &env, level = 0; curEnv; curEnv = curEnv->up, level++) {
+        if (curEnv->isWith) {
+            if (withLevel == -1) withLevel = level;
+        } else {
+            StaticEnv::Vars::const_iterator i = curEnv->vars.find(name);
+            if (i != curEnv->vars.end()) {
+                fromWith = false;
+                this->level = level;
+                displ = i->second;
+                return;
+            }
+        }
+    }
+
+    /* Otherwise, the variable must be obtained from the nearest
+       enclosing `with'.  If there is no `with', then we can issue an
+       "undefined variable" error now. */
+    if (withLevel == -1) throw UndefinedVarError(format("undefined variable `%1%' at %2%") % name % pos);
+
+    fromWith = true;
+    this->level = withLevel;
+}
+
+void ExprSelect::bindVars(const StaticEnv & env)
+{
+    e->bindVars(env);
+    if (def) def->bindVars(env);
+    foreach (AttrPath::iterator, i, attrPath)
+        if (!i->symbol.set())
+            i->expr->bindVars(env);
+}
+
+void ExprOpHasAttr::bindVars(const StaticEnv & env)
+{
+    e->bindVars(env);
+    foreach (AttrPath::iterator, i, attrPath)
+        if (!i->symbol.set())
+            i->expr->bindVars(env);
+}
+
+void ExprAttrs::bindVars(const StaticEnv & env)
+{
+    const StaticEnv *dynamicEnv = &env;
+    if (recursive) {
+        StaticEnv newEnv(false, &env);
+        dynamicEnv = &newEnv;
+
+        unsigned int displ = 0;
+        foreach (AttrDefs::iterator, i, attrs)
+            newEnv.vars[i->first] = i->second.displ = displ++;
+
+        foreach (AttrDefs::iterator, i, attrs)
+            i->second.e->bindVars(i->second.inherited ? env : newEnv);
+    }
+
+    else
+        foreach (AttrDefs::iterator, i, attrs)
+            i->second.e->bindVars(env);
+
+    foreach (DynamicAttrDefs::iterator, i, dynamicAttrs) {
+        i->nameExpr->bindVars(*dynamicEnv);
+        i->valueExpr->bindVars(*dynamicEnv);
+    }
+}
+
+void ExprList::bindVars(const StaticEnv & env)
+{
+    foreach (vector<Expr *>::iterator, i, elems)
+        (*i)->bindVars(env);
+}
+
+void ExprLambda::bindVars(const StaticEnv & env)
+{
+    StaticEnv newEnv(false, &env);
+
+    unsigned int displ = 0;
+
+    if (!arg.empty()) newEnv.vars[arg] = displ++;
+
+    if (matchAttrs) {
+        foreach (Formals::Formals_::iterator, i, formals->formals)
+            newEnv.vars[i->name] = displ++;
+
+        foreach (Formals::Formals_::iterator, i, formals->formals)
+            if (i->def) i->def->bindVars(newEnv);
+    }
+
+    body->bindVars(newEnv);
+}
+
+void ExprLet::bindVars(const StaticEnv & env)
+{
+    StaticEnv newEnv(false, &env);
+
+    unsigned int displ = 0;
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        newEnv.vars[i->first] = i->second.displ = displ++;
+
+    foreach (ExprAttrs::AttrDefs::iterator, i, attrs->attrs)
+        i->second.e->bindVars(i->second.inherited ? env : newEnv);
+
+    body->bindVars(newEnv);
+}
+
+void ExprWith::bindVars(const StaticEnv & env)
+{
+    /* Does this `with' have an enclosing `with'?  If so, record its
+       level so that `lookupVar' can look up variables in the previous
+       `with' if this one doesn't contain the desired attribute. */
+    const StaticEnv * curEnv;
+    unsigned int level;
+    prevWith = 0;
+    for (curEnv = &env, level = 1; curEnv; curEnv = curEnv->up, level++)
+        if (curEnv->isWith) {
+            prevWith = level;
+            break;
+        }
+
+    attrs->bindVars(env);
+    StaticEnv newEnv(true, &env);
+    body->bindVars(newEnv);
+}
+
+void ExprIf::bindVars(const StaticEnv & env)
+{
+    cond->bindVars(env);
+    then->bindVars(env);
+    else_->bindVars(env);
+}
+
+void ExprAssert::bindVars(const StaticEnv & env)
+{
+    cond->bindVars(env);
+    body->bindVars(env);
+}
+
+void ExprOpNot::bindVars(const StaticEnv & env)
+{
+    e->bindVars(env);
+}
+
+void ExprBuiltin::bindVars(const StaticEnv & env)
+{
+}
+
+void ExprConcatStrings::bindVars(const StaticEnv & env)
+{
+    foreach (vector<Expr *>::iterator, i, *es)
+        (*i)->bindVars(env);
+}
+
+void ExprPos::bindVars(const StaticEnv & env)
+{
+}
+
+
+/* Storing function names. */
+
+void Expr::setName(Symbol & name)
+{
+}
+
+
+void ExprLambda::setName(Symbol & name)
+{
+    this->name = name;
+    body->setName(name);
+}
+
+
+string ExprLambda::showNamePos() const
+{
+    return (format("%1% at %2%") % (name.set() ? "`" + (string) name + "'" : "an anonymous function") % pos).str();
+}
+
+
+
+/* Symbol table. */
+
+size_t SymbolTable::totalSize() const
+{
+    size_t n = 0;
+    foreach (Symbols::const_iterator, i, symbols)
+        n += i->size();
+    return n;
+}
+
+
+}
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
new file mode 100644
index 000000000000..7586fffb83d4
--- /dev/null
+++ b/src/libexpr/nixexpr.hh
@@ -0,0 +1,332 @@
+#pragma once
+
+#include "value.hh"
+#include "symbol-table.hh"
+
+#include <map>
+
+
+namespace nix {
+
+
+MakeError(EvalError, Error)
+MakeError(ParseError, Error)
+MakeError(AssertionError, EvalError)
+MakeError(ThrownError, AssertionError)
+MakeError(Abort, EvalError)
+MakeError(TypeError, EvalError)
+MakeError(ImportError, EvalError) // error building an imported derivation
+MakeError(UndefinedVarError, Error)
+
+
+/* Position objects. */
+
+struct Pos
+{
+    Symbol file;
+    unsigned int line, column;
+    Pos() : line(0), column(0) { };
+    Pos(const Symbol & file, unsigned int line, unsigned int column)
+        : file(file), line(line), column(column) { };
+    bool operator < (const Pos & p2) const
+    {
+        if (!line) return p2.line;
+        if (!p2.line) return false;
+        int d = ((string) file).compare((string) p2.file);
+        if (d < 0) return true;
+        if (d > 0) return false;
+        if (line < p2.line) return true;
+        if (line > p2.line) return false;
+        return column < p2.column;
+    }
+};
+
+extern Pos noPos;
+
+std::ostream & operator << (std::ostream & str, const Pos & pos);
+
+
+struct Env;
+struct Value;
+class EvalState;
+struct StaticEnv;
+struct Expr;
+
+
+/* An attribute path is a sequence of attribute names. */
+struct AttrName
+{
+    Symbol symbol;
+    Expr *expr;
+    AttrName(const Symbol & s) : symbol(s) {};
+    AttrName(Expr *e) : expr(e) {};
+};
+
+typedef std::vector<AttrName> AttrPath;
+
+string showAttrPath(const AttrPath & attrPath);
+
+
+/* Abstract syntax of Nix expressions. */
+
+struct Expr
+{
+    virtual ~Expr() { };
+    virtual void show(std::ostream & str);
+    virtual void bindVars(const StaticEnv & env);
+    virtual void eval(EvalState & state, Env & env, Value & v);
+    virtual Value * maybeThunk(EvalState & state, Env & env);
+    virtual void setName(Symbol & name);
+};
+
+std::ostream & operator << (std::ostream & str, Expr & e);
+
+#define COMMON_METHODS \
+    void show(std::ostream & str); \
+    void eval(EvalState & state, Env & env, Value & v); \
+    void bindVars(const StaticEnv & env);
+
+struct ExprInt : Expr
+{
+    NixInt n;
+    Value v;
+    ExprInt(NixInt n) : n(n) { mkInt(v, n); };
+    COMMON_METHODS
+    Value * maybeThunk(EvalState & state, Env & env);
+};
+
+struct ExprString : Expr
+{
+    Symbol s;
+    Value v;
+    ExprString(const Symbol & s) : s(s) { mkString(v, s); };
+    COMMON_METHODS
+    Value * maybeThunk(EvalState & state, Env & env);
+};
+
+/* Temporary class used during parsing of indented strings. */
+struct ExprIndStr : Expr
+{
+    string s;
+    ExprIndStr(const string & s) : s(s) { };
+};
+
+struct ExprPath : Expr
+{
+    string s;
+    Value v;
+    ExprPath(const string & s) : s(s) { mkPathNoCopy(v, this->s.c_str()); };
+    COMMON_METHODS
+    Value * maybeThunk(EvalState & state, Env & env);
+};
+
+struct ExprVar : Expr
+{
+    Pos pos;
+    Symbol name;
+
+    /* Whether the variable comes from an environment (e.g. a rec, let
+       or function argument) or from a "with". */
+    bool fromWith;
+
+    /* In the former case, the value is obtained by going `level'
+       levels up from the current environment and getting the
+       `displ'th value in that environment.  In the latter case, the
+       value is obtained by getting the attribute named `name' from
+       the set stored in the environment that is `level' levels up
+       from the current one.*/
+    unsigned int level;
+    unsigned int displ;
+
+    ExprVar(const Pos & pos, const Symbol & name) : pos(pos), name(name) { };
+    COMMON_METHODS
+    Value * maybeThunk(EvalState & state, Env & env);
+};
+
+struct ExprSelect : Expr
+{
+    Expr * e, * def;
+    AttrPath attrPath;
+    ExprSelect(Expr * e, const AttrPath & attrPath, Expr * def) : e(e), def(def), attrPath(attrPath) { };
+    ExprSelect(Expr * e, const Symbol & name) : e(e), def(0) { attrPath.push_back(AttrName(name)); };
+    COMMON_METHODS
+};
+
+struct ExprOpHasAttr : Expr
+{
+    Expr * e;
+    AttrPath attrPath;
+    ExprOpHasAttr(Expr * e, const AttrPath & attrPath) : e(e), attrPath(attrPath) { };
+    COMMON_METHODS
+};
+
+struct ExprAttrs : Expr
+{
+    bool recursive;
+    struct AttrDef {
+        bool inherited;
+        Expr * e;
+        Pos pos;
+        unsigned int displ; // displacement
+        AttrDef(Expr * e, const Pos & pos, bool inherited=false) : inherited(inherited), e(e), pos(pos) { };
+        AttrDef() { };
+    };
+    typedef std::map<Symbol, AttrDef> AttrDefs;
+    AttrDefs attrs;
+    struct DynamicAttrDef {
+        Expr * nameExpr;
+        Expr * valueExpr;
+        Pos pos;
+        DynamicAttrDef(Expr * nameExpr, Expr * valueExpr, const Pos & pos) : nameExpr(nameExpr), valueExpr(valueExpr), pos(pos) { };
+    };
+    typedef std::vector<DynamicAttrDef> DynamicAttrDefs;
+    DynamicAttrDefs dynamicAttrs;
+    ExprAttrs() : recursive(false) { };
+    COMMON_METHODS
+};
+
+struct ExprList : Expr
+{
+    std::vector<Expr *> elems;
+    ExprList() { };
+    COMMON_METHODS
+};
+
+struct Formal
+{
+    Symbol name;
+    Expr * def;
+    Formal(const Symbol & name, Expr * def) : name(name), def(def) { };
+};
+
+struct Formals
+{
+    typedef std::list<Formal> Formals_;
+    Formals_ formals;
+    std::set<Symbol> argNames; // used during parsing
+    bool ellipsis;
+};
+
+struct ExprLambda : Expr
+{
+    Pos pos;
+    Symbol name;
+    Symbol arg;
+    bool matchAttrs;
+    Formals * formals;
+    Expr * body;
+    ExprLambda(const Pos & pos, const Symbol & arg, bool matchAttrs, Formals * formals, Expr * body)
+        : pos(pos), arg(arg), matchAttrs(matchAttrs), formals(formals), body(body)
+    {
+        if (!arg.empty() && formals && formals->argNames.find(arg) != formals->argNames.end())
+            throw ParseError(format("duplicate formal function argument `%1%' at %2%")
+                % arg % pos);
+    };
+    void setName(Symbol & name);
+    string showNamePos() const;
+    COMMON_METHODS
+};
+
+struct ExprLet : Expr
+{
+    ExprAttrs * attrs;
+    Expr * body;
+    ExprLet(ExprAttrs * attrs, Expr * body) : attrs(attrs), body(body) { };
+    COMMON_METHODS
+};
+
+struct ExprWith : Expr
+{
+    Pos pos;
+    Expr * attrs, * body;
+    unsigned int prevWith;
+    ExprWith(const Pos & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
+    COMMON_METHODS
+};
+
+struct ExprIf : Expr
+{
+    Expr * cond, * then, * else_;
+    ExprIf(Expr * cond, Expr * then, Expr * else_) : cond(cond), then(then), else_(else_) { };
+    COMMON_METHODS
+};
+
+struct ExprAssert : Expr
+{
+    Pos pos;
+    Expr * cond, * body;
+    ExprAssert(const Pos & pos, Expr * cond, Expr * body) : pos(pos), cond(cond), body(body) { };
+    COMMON_METHODS
+};
+
+struct ExprOpNot : Expr
+{
+    Expr * e;
+    ExprOpNot(Expr * e) : e(e) { };
+    COMMON_METHODS
+};
+
+struct ExprBuiltin : Expr
+{
+    Symbol name;
+    ExprBuiltin(const Symbol & name) : name(name) { };
+    COMMON_METHODS
+};
+
+#define MakeBinOp(name, s) \
+    struct Expr##name : Expr \
+    { \
+        Expr * e1, * e2; \
+        Expr##name(Expr * e1, Expr * e2) : e1(e1), e2(e2) { }; \
+        void show(std::ostream & str) \
+        { \
+            str << *e1 << " " s " " << *e2; \
+        } \
+        void bindVars(const StaticEnv & env) \
+        { \
+            e1->bindVars(env); e2->bindVars(env); \
+        } \
+        void eval(EvalState & state, Env & env, Value & v); \
+    };
+
+MakeBinOp(App, "")
+MakeBinOp(OpEq, "==")
+MakeBinOp(OpNEq, "!=")
+MakeBinOp(OpAnd, "&&")
+MakeBinOp(OpOr, "||")
+MakeBinOp(OpImpl, "->")
+MakeBinOp(OpUpdate, "//")
+MakeBinOp(OpConcatLists, "++")
+
+struct ExprConcatStrings : Expr
+{
+    bool forceString;
+    vector<Expr *> * es;
+    ExprConcatStrings(bool forceString, vector<Expr *> * es)
+        : forceString(forceString), es(es) { };
+    COMMON_METHODS
+};
+
+struct ExprPos : Expr
+{
+    Pos pos;
+    ExprPos(const Pos & pos) : pos(pos) { };
+    COMMON_METHODS
+};
+
+
+/* Static environments are used to map variable names onto (level,
+   displacement) pairs used to obtain the value of the variable at
+   runtime. */
+struct StaticEnv
+{
+    bool isWith;
+    const StaticEnv * up;
+    typedef std::map<Symbol, unsigned int> Vars;
+    Vars vars;
+    StaticEnv(bool isWith, const StaticEnv * up) : isWith(isWith), up(up) { };
+};
+
+
+
+}
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
new file mode 100644
index 000000000000..8a084fea0697
--- /dev/null
+++ b/src/libexpr/parser.y
@@ -0,0 +1,650 @@
+%glr-parser
+%pure-parser
+%locations
+%error-verbose
+%defines
+/* %no-lines */
+%parse-param { void * scanner }
+%parse-param { nix::ParseData * data }
+%lex-param { void * scanner }
+%lex-param { nix::ParseData * data }
+%expect 1
+%expect-rr 1
+
+%code requires {
+
+#ifndef BISON_HEADER
+#define BISON_HEADER
+
+#include "util.hh"
+
+#include "nixexpr.hh"
+#include "eval.hh"
+
+namespace nix {
+
+    struct ParseData
+    {
+        EvalState & state;
+        SymbolTable & symbols;
+        Expr * result;
+        Path basePath;
+        Symbol path;
+        string error;
+        Symbol sLetBody;
+        ParseData(EvalState & state)
+            : state(state)
+            , symbols(state.symbols)
+            , sLetBody(symbols.create("<let-body>"))
+            { };
+    };
+
+}
+
+#define YY_DECL int yylex \
+    (YYSTYPE * yylval_param, YYLTYPE * yylloc_param, yyscan_t yyscanner, nix::ParseData * data)
+
+#endif
+
+}
+
+%{
+
+#include "parser-tab.hh"
+#include "lexer-tab.hh"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+YY_DECL;
+
+using namespace nix;
+
+
+namespace nix {
+
+
+static void dupAttr(const AttrPath & attrPath, const Pos & pos, const Pos & prevPos)
+{
+    throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
+        % showAttrPath(attrPath) % pos % prevPos);
+}
+
+
+static void dupAttr(Symbol attr, const Pos & pos, const Pos & prevPos)
+{
+    throw ParseError(format("attribute `%1%' at %2% already defined at %3%")
+        % attr % pos % prevPos);
+}
+
+
+static void addAttr(ExprAttrs * attrs, AttrPath & attrPath,
+    Expr * e, const Pos & pos)
+{
+    AttrPath::iterator i;
+    // All attrpaths have at least one attr
+    assert(!attrPath.empty());
+    for (i = attrPath.begin(); i + 1 < attrPath.end(); i++) {
+        if (i->symbol.set()) {
+            ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
+            if (j != attrs->attrs.end()) {
+                if (!j->second.inherited) {
+                    ExprAttrs * attrs2 = dynamic_cast<ExprAttrs *>(j->second.e);
+                    if (!attrs2) dupAttr(attrPath, pos, j->second.pos);
+                    attrs = attrs2;
+                } else
+                    dupAttr(attrPath, pos, j->second.pos);
+            } else {
+                ExprAttrs * nested = new ExprAttrs;
+                attrs->attrs[i->symbol] = ExprAttrs::AttrDef(nested, pos);
+                attrs = nested;
+            }
+        } else {
+            ExprAttrs *nested = new ExprAttrs;
+            attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, nested, pos));
+            attrs = nested;
+        }
+    }
+    if (i->symbol.set()) {
+        ExprAttrs::AttrDefs::iterator j = attrs->attrs.find(i->symbol);
+        if (j != attrs->attrs.end()) {
+            dupAttr(attrPath, pos, j->second.pos);
+        } else {
+            attrs->attrs[i->symbol] = ExprAttrs::AttrDef(e, pos);
+            e->setName(i->symbol);
+        }
+    } else {
+        attrs->dynamicAttrs.push_back(ExprAttrs::DynamicAttrDef(i->expr, e, pos));
+    }
+}
+
+
+static void addFormal(const Pos & pos, Formals * formals, const Formal & formal)
+{
+    if (formals->argNames.find(formal.name) != formals->argNames.end())
+        throw ParseError(format("duplicate formal function argument `%1%' at %2%")
+            % formal.name % pos);
+    formals->formals.push_front(formal);
+    formals->argNames.insert(formal.name);
+}
+
+
+static Expr * stripIndentation(SymbolTable & symbols, vector<Expr *> & es)
+{
+    if (es.empty()) return new ExprString(symbols.create(""));
+
+    /* Figure out the minimum indentation.  Note that by design
+       whitespace-only final lines are not taken into account.  (So
+       the " " in "\n ''" is ignored, but the " " in "\n foo''" is.) */
+    bool atStartOfLine = true; /* = seen only whitespace in the current line */
+    unsigned int minIndent = 1000000;
+    unsigned int curIndent = 0;
+    foreach (vector<Expr *>::iterator, i, es) {
+        ExprIndStr * e = dynamic_cast<ExprIndStr *>(*i);
+        if (!e) {
+            /* Anti-quotations end the current start-of-line whitespace. */
+            if (atStartOfLine) {
+                atStartOfLine = false;
+                if (curIndent < minIndent) minIndent = curIndent;
+            }
+            continue;
+        }
+        for (unsigned int j = 0; j < e->s.size(); ++j) {
+            if (atStartOfLine) {
+                if (e->s[j] == ' ')
+                    curIndent++;
+                else if (e->s[j] == '\n') {
+                    /* Empty line, doesn't influence minimum
+                       indentation. */
+                    curIndent = 0;
+                } else {
+                    atStartOfLine = false;
+                    if (curIndent < minIndent) minIndent = curIndent;
+                }
+            } else if (e->s[j] == '\n') {
+                atStartOfLine = true;
+                curIndent = 0;
+            }
+        }
+    }
+
+    /* Strip spaces from each line. */
+    vector<Expr *> * es2 = new vector<Expr *>;
+    atStartOfLine = true;
+    unsigned int curDropped = 0;
+    unsigned int n = es.size();
+    for (vector<Expr *>::iterator i = es.begin(); i != es.end(); ++i, --n) {
+        ExprIndStr * e = dynamic_cast<ExprIndStr *>(*i);
+        if (!e) {
+            atStartOfLine = false;
+            curDropped = 0;
+            es2->push_back(*i);
+            continue;
+        }
+
+        string s2;
+        for (unsigned int j = 0; j < e->s.size(); ++j) {
+            if (atStartOfLine) {
+                if (e->s[j] == ' ') {
+                    if (curDropped++ >= minIndent)
+                        s2 += e->s[j];
+                }
+                else if (e->s[j] == '\n') {
+                    curDropped = 0;
+                    s2 += e->s[j];
+                } else {
+                    atStartOfLine = false;
+                    curDropped = 0;
+                    s2 += e->s[j];
+                }
+            } else {
+                s2 += e->s[j];
+                if (e->s[j] == '\n') atStartOfLine = true;
+            }
+        }
+
+        /* Remove the last line if it is empty and consists only of
+           spaces. */
+        if (n == 1) {
+            string::size_type p = s2.find_last_of('\n');
+            if (p != string::npos && s2.find_first_not_of(' ', p + 1) == string::npos)
+                s2 = string(s2, 0, p + 1);
+        }
+
+        es2->push_back(new ExprString(symbols.create(s2)));
+    }
+
+    /* If this is a single string, then don't do a concatenation. */
+    return es2->size() == 1 && dynamic_cast<ExprString *>((*es2)[0]) ? (*es2)[0] : new ExprConcatStrings(true, es2);
+}
+
+
+void backToString(yyscan_t scanner);
+void backToIndString(yyscan_t scanner);
+
+
+static Pos makeCurPos(const YYLTYPE & loc, ParseData * data)
+{
+    return Pos(data->path, loc.first_line, loc.first_column);
+}
+
+#define CUR_POS makeCurPos(*yylocp, data)
+
+
+}
+
+
+void yyerror(YYLTYPE * loc, yyscan_t scanner, ParseData * data, const char * error)
+{
+    data->error = (format("%1%, at %2%")
+        % error % makeCurPos(*loc, data)).str();
+}
+
+
+%}
+
+%union {
+  // !!! We're probably leaking stuff here.
+  nix::Expr * e;
+  nix::ExprList * list;
+  nix::ExprAttrs * attrs;
+  nix::Formals * formals;
+  nix::Formal * formal;
+  nix::NixInt n;
+  const char * id; // !!! -> Symbol
+  char * path;
+  char * uri;
+  std::vector<nix::AttrName> * attrNames;
+  std::vector<nix::Expr *> * string_parts;
+}
+
+%type <e> start expr expr_function expr_if expr_op
+%type <e> expr_app expr_select expr_simple
+%type <list> expr_list
+%type <attrs> binds
+%type <formals> formals
+%type <formal> formal
+%type <attrNames> attrs attrpath
+%type <string_parts> string_parts_interpolated ind_string_parts
+%type <e> string_parts string_attr
+%type <id> attr
+%token <id> ID ATTRPATH
+%token <e> STR IND_STR
+%token <n> INT
+%token <path> PATH SPATH
+%token <uri> URI
+%token IF THEN ELSE ASSERT WITH LET IN REC INHERIT EQ NEQ AND OR IMPL OR_KW
+%token DOLLAR_CURLY /* == ${ */
+%token IND_STRING_OPEN IND_STRING_CLOSE
+%token ELLIPSIS
+
+%nonassoc IMPL
+%left OR
+%left AND
+%nonassoc EQ NEQ
+%left '<' '>' LEQ GEQ
+%right UPDATE
+%left NOT
+%left '+' '-'
+%left '*' '/'
+%right CONCAT
+%nonassoc '?'
+%nonassoc '~'
+%nonassoc NEGATE
+
+%%
+
+start: expr { data->result = $1; };
+
+expr: expr_function;
+
+expr_function
+  : ID ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), false, 0, $3); }
+  | '{' formals '}' ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create(""), true, $2, $5); }
+  | '{' formals '}' '@' ID ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($5), true, $2, $7); }
+  | ID '@' '{' formals '}' ':' expr_function
+    { $$ = new ExprLambda(CUR_POS, data->symbols.create($1), true, $4, $7); }
+  | ASSERT expr ';' expr_function
+    { $$ = new ExprAssert(CUR_POS, $2, $4); }
+  | WITH expr ';' expr_function
+    { $$ = new ExprWith(CUR_POS, $2, $4); }
+  | LET binds IN expr_function
+    { if (!$2->dynamicAttrs.empty())
+        throw ParseError(format("dynamic attributes not allowed in let at %1%")
+            % CUR_POS);
+      $$ = new ExprLet($2, $4);
+    }
+  | expr_if
+  ;
+
+expr_if
+  : IF expr THEN expr ELSE expr { $$ = new ExprIf($2, $4, $6); }
+  | expr_op
+  ;
+
+expr_op
+  : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
+| '-' expr_op %prec NEGATE { $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("sub")), new ExprInt(0)), $2); }
+  | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
+  | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
+  | expr_op '<' expr_op { $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("lessThan")), $1), $3); }
+  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("lessThan")), $3), $1)); }
+  | expr_op '>' expr_op { $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("lessThan")), $3), $1); }
+  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("lessThan")), $1), $3)); }
+  | expr_op AND expr_op { $$ = new ExprOpAnd($1, $3); }
+  | expr_op OR expr_op { $$ = new ExprOpOr($1, $3); }
+  | expr_op IMPL expr_op { $$ = new ExprOpImpl($1, $3); }
+  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate($1, $3); }
+  | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, *$3); }
+  | expr_op '+' expr_op
+    { vector<Expr *> * l = new vector<Expr *>;
+      l->push_back($1);
+      l->push_back($3);
+      $$ = new ExprConcatStrings(false, l);
+    }
+  | expr_op '-' expr_op { $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("sub")), $1), $3); }
+  | expr_op '*' expr_op { $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("mul")), $1), $3); }
+  | expr_op '/' expr_op { $$ = new ExprApp(new ExprApp(new ExprBuiltin(data->symbols.create("div")), $1), $3); }
+  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists($1, $3); }
+  | expr_app
+  ;
+
+expr_app
+  : expr_app expr_select
+    { $$ = new ExprApp($1, $2); }
+  | expr_select { $$ = $1; }
+  ;
+
+expr_select
+  : expr_simple '.' attrpath
+    { $$ = new ExprSelect($1, *$3, 0); }
+  | expr_simple '.' attrpath OR_KW expr_select
+    { $$ = new ExprSelect($1, *$3, $5); }
+  | /* Backwards compatibility: because Nixpkgs has a rarely used
+       function named ‘or’, allow stuff like ‘map or [...]’. */
+    expr_simple OR_KW
+    { $$ = new ExprApp($1, new ExprVar(CUR_POS, data->symbols.create("or"))); }
+  | expr_simple { $$ = $1; }
+  ;
+
+expr_simple
+  : ID {
+      if (strcmp($1, "__curPos") == 0)
+          $$ = new ExprPos(CUR_POS);
+      else
+          $$ = new ExprVar(CUR_POS, data->symbols.create($1));
+  }
+  | INT { $$ = new ExprInt($1); }
+  | '"' string_parts '"' { $$ = $2; }
+  | IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
+      $$ = stripIndentation(data->symbols, *$2);
+  }
+  | PATH { $$ = new ExprPath(absPath($1, data->basePath)); }
+  | SPATH {
+      string path($1 + 1, strlen($1) - 2);
+      Path path2 = data->state.findFile(path);
+      /* The file wasn't found in the search path.  However, we can't
+         throw an error here, because the expression might never be
+         evaluated.  So return an expression that lazily calls
+         ‘throw’. */
+      $$ = path2 == ""
+          ? (Expr * ) new ExprApp(
+              new ExprBuiltin(data->symbols.create("throw")),
+              new ExprString(data->symbols.create(
+                      (format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % path).str())))
+          : (Expr * ) new ExprPath(path2);
+  }
+  | URI { $$ = new ExprString(data->symbols.create($1)); }
+  | '(' expr ')' { $$ = $2; }
+  /* Let expressions `let {..., body = ...}' are just desugared
+     into `(rec {..., body = ...}).body'. */
+  | LET '{' binds '}'
+    { $3->recursive = true; $$ = new ExprSelect($3, data->symbols.create("body")); }
+  | REC '{' binds '}'
+    { $3->recursive = true; $$ = $3; }
+  | '{' binds '}'
+    { $$ = $2; }
+  | '[' expr_list ']' { $$ = $2; }
+  ;
+
+string_parts
+  : STR
+  | string_parts_interpolated { $$ = new ExprConcatStrings(true, $1); }
+  | { $$ = new ExprString(data->symbols.create("")); }
+  ;
+
+string_parts_interpolated
+  : string_parts_interpolated STR { $$ = $1; $1->push_back($2); }
+  | string_parts_interpolated DOLLAR_CURLY expr '}' { backToString(scanner); $$ = $1; $1->push_back($3); }
+  | STR DOLLAR_CURLY expr '}'
+    {
+      backToString(scanner);
+      $$ = new vector<Expr *>;
+      $$->push_back($1);
+      $$->push_back($3);
+    }
+  | DOLLAR_CURLY expr '}'
+    {
+      backToString(scanner);
+      $$ = new vector<Expr *>;
+      $$->push_back($2);
+    }
+  ;
+
+ind_string_parts
+  : ind_string_parts IND_STR { $$ = $1; $1->push_back($2); }
+  | ind_string_parts DOLLAR_CURLY expr '}' { backToIndString(scanner); $$ = $1; $1->push_back($3); }
+  | { $$ = new vector<Expr *>; }
+  ;
+
+binds
+  : binds attrpath '=' expr ';' { $$ = $1; addAttr($$, *$2, $4, makeCurPos(@2, data)); }
+  | binds INHERIT attrs ';'
+    { $$ = $1;
+      foreach (AttrPath::iterator, i, *$3) {
+          if ($$->attrs.find(i->symbol) != $$->attrs.end())
+              dupAttr(i->symbol, makeCurPos(@3, data), $$->attrs[i->symbol].pos);
+          Pos pos = makeCurPos(@3, data);
+          $$->attrs[i->symbol] = ExprAttrs::AttrDef(new ExprVar(CUR_POS, i->symbol), pos, true);
+      }
+    }
+  | binds INHERIT '(' expr ')' attrs ';'
+    { $$ = $1;
+      /* !!! Should ensure sharing of the expression in $4. */
+      foreach (AttrPath::iterator, i, *$6) {
+          if ($$->attrs.find(i->symbol) != $$->attrs.end())
+              dupAttr(i->symbol, makeCurPos(@6, data), $$->attrs[i->symbol].pos);
+          $$->attrs[i->symbol] = ExprAttrs::AttrDef(new ExprSelect($4, i->symbol), makeCurPos(@6, data));
+      }
+    }
+  | { $$ = new ExprAttrs; }
+  ;
+
+attrs
+  : attrs attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($2))); }
+  | attrs string_attr
+    { $$ = $1;
+      ExprString *str = dynamic_cast<ExprString *>($2);
+      if (str) {
+          $$->push_back(AttrName(str->s));
+          delete str;
+      } else
+        throw ParseError(format("dynamic attributes not allowed in inherit at %1%")
+            % makeCurPos(@2, data));
+    }
+  | { $$ = new AttrPath; }
+  ;
+
+attrpath
+  : attrpath '.' attr { $$ = $1; $1->push_back(AttrName(data->symbols.create($3))); }
+  | attrpath '.' string_attr
+    { $$ = $1;
+      ExprString *str = dynamic_cast<ExprString *>($3);
+      if (str) {
+          $$->push_back(AttrName(str->s));
+          delete str;
+      } else
+          $$->push_back(AttrName($3));
+    }
+  | attr { $$ = new vector<AttrName>; $$->push_back(AttrName(data->symbols.create($1))); }
+  | string_attr
+    { $$ = new vector<AttrName>;
+      ExprString *str = dynamic_cast<ExprString *>($1);
+      if (str) {
+          $$->push_back(AttrName(str->s));
+          delete str;
+      } else
+          $$->push_back(AttrName($1));
+    }
+  ;
+
+attr
+  : ID { $$ = $1; }
+  | OR_KW { $$ = "or"; }
+  ;
+
+string_attr
+  : '"' string_parts '"' { $$ = $2; }
+  | DOLLAR_CURLY expr '}' { $$ = new ExprConcatStrings(true, new vector<Expr*>(1, $2)); }
+  ;
+
+expr_list
+  : expr_list expr_select { $$ = $1; $1->elems.push_back($2); /* !!! dangerous */ }
+  | { $$ = new ExprList; }
+  ;
+
+formals
+  : formal ',' formals
+    { $$ = $3; addFormal(CUR_POS, $$, *$1); }
+  | formal
+    { $$ = new Formals; addFormal(CUR_POS, $$, *$1); $$->ellipsis = false; }
+  |
+    { $$ = new Formals; $$->ellipsis = false; }
+  | ELLIPSIS
+    { $$ = new Formals; $$->ellipsis = true; }
+  ;
+
+formal
+  : ID { $$ = new Formal(data->symbols.create($1), 0); }
+  | ID '?' expr { $$ = new Formal(data->symbols.create($1), $3); }
+  ;
+
+%%
+
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <eval.hh>
+
+
+namespace nix {
+
+
+Expr * EvalState::parse(const char * text,
+    const Path & path, const Path & basePath, StaticEnv & staticEnv)
+{
+    yyscan_t scanner;
+    ParseData data(*this);
+    data.basePath = basePath;
+    data.path = data.symbols.create(path);
+
+    yylex_init(&scanner);
+    yy_scan_string(text, scanner);
+    int res = yyparse(scanner, &data);
+    yylex_destroy(scanner);
+
+    if (res) throw ParseError(data.error);
+
+    data.result->bindVars(staticEnv);
+
+    return data.result;
+}
+
+
+Path resolveExprPath(Path path)
+{
+    assert(path[0] == '/');
+
+    /* If `path' is a symlink, follow it.  This is so that relative
+       path references work. */
+    struct stat st;
+    while (true) {
+        if (lstat(path.c_str(), &st))
+            throw SysError(format("getting status of `%1%'") % path);
+        if (!S_ISLNK(st.st_mode)) break;
+        path = absPath(readLink(path), dirOf(path));
+    }
+
+    /* If `path' refers to a directory, append `/default.nix'. */
+    if (S_ISDIR(st.st_mode))
+        path = canonPath(path + "/default.nix");
+
+    return path;
+}
+
+
+Expr * EvalState::parseExprFromFile(const Path & path)
+{
+    return parse(readFile(path).c_str(), path, dirOf(path), staticBaseEnv);
+}
+
+
+Expr * EvalState::parseExprFromString(const string & s, const Path & basePath, StaticEnv & staticEnv)
+{
+    return parse(s.c_str(), "(string)", basePath, staticEnv);
+}
+
+
+Expr * EvalState::parseExprFromString(const string & s, const Path & basePath)
+{
+    return parseExprFromString(s, basePath, staticBaseEnv);
+}
+
+
+void EvalState::addToSearchPath(const string & s)
+{
+    size_t pos = s.find('=');
+    string prefix;
+    Path path;
+    if (pos == string::npos) {
+        path = s;
+    } else {
+        prefix = string(s, 0, pos);
+        path = string(s, pos + 1);
+    }
+
+    path = absPath(path);
+    if (pathExists(path)) {
+        debug(format("adding path `%1%' to the search path") % path);
+        searchPath.insert(searchPathInsertionPoint, std::pair<string, Path>(prefix, path));
+    }
+}
+
+
+Path EvalState::findFile(const string & path)
+{
+    foreach (SearchPath::iterator, i, searchPath) {
+        Path res;
+        if (i->first.empty())
+            res = i->second + "/" + path;
+        else {
+            if (path.compare(0, i->first.size(), i->first) != 0 ||
+                (path.size() > i->first.size() && path[i->first.size()] != '/'))
+                continue;
+            res = i->second +
+                (path.size() == i->first.size() ? "" : "/" + string(path, i->first.size()));
+        }
+        if (pathExists(res)) return canonPath(res);
+    }
+    return "";
+}
+
+
+}
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
new file mode 100644
index 000000000000..ca316f08af13
--- /dev/null
+++ b/src/libexpr/primops.cc
@@ -0,0 +1,1336 @@
+#include "eval.hh"
+#include "misc.hh"
+#include "globals.hh"
+#include "store-api.hh"
+#include "util.hh"
+#include "archive.hh"
+#include "value-to-xml.hh"
+#include "value-to-json.hh"
+#include "names.hh"
+#include "eval-inline.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <cstring>
+
+
+namespace nix {
+
+
+/*************************************************************
+ * Miscellaneous
+ *************************************************************/
+
+
+/* Decode a context string ‘!<name>!<path>’ into a pair <path,
+   name>. */
+std::pair<string, string> decodeContext(const string & s)
+{
+    if (s.at(0) == '!') {
+        size_t index = s.find("!", 1);
+        return std::pair<string, string>(string(s, index + 1), string(s, 1, index - 1));
+    } else
+        return std::pair<string, string>(s, "");
+}
+
+
+/* Load and evaluate an expression from path specified by the
+   argument. */
+static void prim_import(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(*args[0], context);
+
+    foreach (PathSet::iterator, i, context) {
+        Path ctx = decodeContext(*i).first;
+        assert(isStorePath(ctx));
+        if (!store->isValidPath(ctx))
+            throw EvalError(format("cannot import `%1%', since path `%2%' is not valid")
+                % path % ctx);
+        if (isDerivation(ctx))
+            try {
+                /* For performance, prefetch all substitute info. */
+                PathSet willBuild, willSubstitute, unknown;
+                unsigned long long downloadSize, narSize;
+                queryMissing(*store, singleton<PathSet>(ctx),
+                    willBuild, willSubstitute, unknown, downloadSize, narSize);
+
+                /* !!! If using a substitute, we only need to fetch
+                   the selected output of this derivation. */
+                store->buildPaths(singleton<PathSet>(ctx));
+            } catch (Error & e) {
+                throw ImportError(e.msg());
+            }
+    }
+
+    if (isStorePath(path) && store->isValidPath(path) && isDerivation(path)) {
+        Derivation drv = parseDerivation(readFile(path));
+        Value & w = *state.allocValue();
+        state.mkAttrs(w, 1 + drv.outputs.size());
+        mkString(*state.allocAttr(w, state.sDrvPath), path, singleton<PathSet>("=" + path));
+        state.mkList(*state.allocAttr(w, state.symbols.create("outputs")), drv.outputs.size());
+        unsigned int outputs_index = 0;
+
+        Value * outputsVal = w.attrs->find(state.symbols.create("outputs"))->value;
+        foreach (DerivationOutputs::iterator, i, drv.outputs) {
+            mkString(*state.allocAttr(w, state.symbols.create(i->first)),
+                i->second.path, singleton<PathSet>("!" + i->first + "!" + path));
+            mkString(*(outputsVal->list.elems[outputs_index++] = state.allocValue()),
+                i->first);
+        }
+        w.attrs->sort();
+        Value fun;
+        state.evalFile(state.findFile("nix/imported-drv-to-derivation.nix"), fun);
+        state.forceFunction(fun);
+        mkApp(v, fun, w);
+        state.forceAttrs(v);
+    } else {
+        state.evalFile(path, v);
+    }
+}
+
+
+/* Return a string representing the type of the expression. */
+static void prim_typeOf(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    string t;
+    switch (args[0]->type) {
+        case tInt: t = "int"; break;
+        case tBool: t = "bool"; break;
+        case tString: t = "string"; break;
+        case tPath: t = "path"; break;
+        case tNull: t = "null"; break;
+        case tAttrs: t = "set"; break;
+        case tList: t = "list"; break;
+        case tLambda:
+        case tPrimOp:
+        case tPrimOpApp:
+            t = "lambda";
+            break;
+        default: abort();
+    }
+    mkString(v, state.symbols.create(t));
+}
+
+
+/* Determine whether the argument is the null value. */
+static void prim_isNull(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tNull);
+}
+
+
+/* Determine whether the argument is a function. */
+static void prim_isFunction(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tLambda);
+}
+
+
+/* Determine whether the argument is an integer. */
+static void prim_isInt(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tInt);
+}
+
+
+/* Determine whether the argument is a string. */
+static void prim_isString(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tString);
+}
+
+
+/* Determine whether the argument is a Boolean. */
+static void prim_isBool(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tBool);
+}
+
+
+struct CompareValues
+{
+    bool operator () (const Value * v1, const Value * v2) const
+    {
+        if (v1->type != v2->type)
+            throw EvalError("cannot compare values of different types");
+        switch (v1->type) {
+            case tInt:
+                return v1->integer < v2->integer;
+            case tString:
+                return strcmp(v1->string.s, v2->string.s) < 0;
+            case tPath:
+                return strcmp(v1->path, v2->path) < 0;
+            default:
+                throw EvalError(format("cannot compare %1% with %2%") % showType(*v1) % showType(*v2));
+        }
+    }
+};
+
+
+#if HAVE_BOEHMGC
+typedef list<Value *, gc_allocator<Value *> > ValueList;
+#else
+typedef list<Value *> ValueList;
+#endif
+
+
+static void prim_genericClosure(EvalState & state, Value * * args, Value & v)
+{
+    startNest(nest, lvlDebug, "finding dependencies");
+
+    state.forceAttrs(*args[0]);
+
+    /* Get the start set. */
+    Bindings::iterator startSet =
+        args[0]->attrs->find(state.symbols.create("startSet"));
+    if (startSet == args[0]->attrs->end())
+        throw EvalError("attribute `startSet' required");
+    state.forceList(*startSet->value);
+
+    ValueList workSet;
+    for (unsigned int n = 0; n < startSet->value->list.length; ++n)
+        workSet.push_back(startSet->value->list.elems[n]);
+
+    /* Get the operator. */
+    Bindings::iterator op =
+        args[0]->attrs->find(state.symbols.create("operator"));
+    if (op == args[0]->attrs->end())
+        throw EvalError("attribute `operator' required");
+    state.forceValue(*op->value);
+
+    /* Construct the closure by applying the operator to element of
+       `workSet', adding the result to `workSet', continuing until
+       no new elements are found. */
+    ValueList res;
+    // `doneKeys' doesn't need to be a GC root, because its values are
+    // reachable from res.
+    set<Value *, CompareValues> doneKeys;
+    while (!workSet.empty()) {
+        Value * e = *(workSet.begin());
+        workSet.pop_front();
+
+        state.forceAttrs(*e);
+
+        Bindings::iterator key =
+            e->attrs->find(state.symbols.create("key"));
+        if (key == e->attrs->end())
+            throw EvalError("attribute `key' required");
+        state.forceValue(*key->value);
+
+        if (doneKeys.find(key->value) != doneKeys.end()) continue;
+        doneKeys.insert(key->value);
+        res.push_back(e);
+
+        /* Call the `operator' function with `e' as argument. */
+        Value call;
+        mkApp(call, *op->value, *e);
+        state.forceList(call);
+
+        /* Add the values returned by the operator to the work set. */
+        for (unsigned int n = 0; n < call.list.length; ++n) {
+            state.forceValue(*call.list.elems[n]);
+            workSet.push_back(call.list.elems[n]);
+        }
+    }
+
+    /* Create the result list. */
+    state.mkList(v, res.size());
+    unsigned int n = 0;
+    foreach (ValueList::iterator, i, res)
+        v.list.elems[n++] = *i;
+}
+
+
+static void prim_abort(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    throw Abort(format("evaluation aborted with the following error message: `%1%'") %
+        state.coerceToString(*args[0], context));
+}
+
+
+static void prim_throw(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    throw ThrownError(format("%1%") % state.coerceToString(*args[0], context));
+}
+
+
+static void prim_addErrorContext(EvalState & state, Value * * args, Value & v)
+{
+    try {
+        state.forceValue(*args[1]);
+        v = *args[1];
+    } catch (Error & e) {
+        PathSet context;
+        e.addPrefix(format("%1%\n") % state.coerceToString(*args[0], context));
+        throw;
+    }
+}
+
+
+/* Try evaluating the argument. Success => {success=true; value=something;},
+ * else => {success=false; value=false;} */
+static void prim_tryEval(EvalState & state, Value * * args, Value & v)
+{
+    state.mkAttrs(v, 2);
+    try {
+        state.forceValue(*args[0]);
+        v.attrs->push_back(Attr(state.sValue, args[0]));
+        mkBool(*state.allocAttr(v, state.symbols.create("success")), true);
+    } catch (AssertionError & e) {
+        mkBool(*state.allocAttr(v, state.sValue), false);
+        mkBool(*state.allocAttr(v, state.symbols.create("success")), false);
+    }
+    v.attrs->sort();
+}
+
+
+/* Return an environment variable.  Use with care. */
+static void prim_getEnv(EvalState & state, Value * * args, Value & v)
+{
+    string name = state.forceStringNoCtx(*args[0]);
+    mkString(v, getEnv(name));
+}
+
+
+/* Evaluate the first expression and print it on standard error.  Then
+   return the second expression.  Useful for debugging. */
+static void prim_trace(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    if (args[0]->type == tString)
+        printMsg(lvlError, format("trace: %1%") % args[0]->string.s);
+    else
+        printMsg(lvlError, format("trace: %1%") % *args[0]);
+    state.forceValue(*args[1]);
+    v = *args[1];
+}
+
+
+/*************************************************************
+ * Derivations
+ *************************************************************/
+
+
+/* Construct (as a unobservable side effect) a Nix derivation
+   expression that performs the derivation described by the argument
+   set.  Returns the original set extended with the following
+   attributes: `outPath' containing the primary output path of the
+   derivation; `drvPath' containing the path of the Nix expression;
+   and `type' set to `derivation' to indicate that this is a
+   derivation. */
+static void prim_derivationStrict(EvalState & state, Value * * args, Value & v)
+{
+    startNest(nest, lvlVomit, "evaluating derivation");
+
+    state.forceAttrs(*args[0]);
+
+    /* Figure out the name first (for stack backtraces). */
+    Bindings::iterator attr = args[0]->attrs->find(state.sName);
+    if (attr == args[0]->attrs->end())
+        throw EvalError("required attribute `name' missing");
+    string drvName;
+    Pos & posDrvName(*attr->pos);
+    try {
+        drvName = state.forceStringNoCtx(*attr->value);
+    } catch (Error & e) {
+        e.addPrefix(format("while evaluating the derivation attribute `name' at %1%:\n") % posDrvName);
+        throw;
+    }
+
+    /* Check whether null attributes should be ignored. */
+    bool ignoreNulls = false;
+    attr = args[0]->attrs->find(state.sIgnoreNulls);
+    if (attr != args[0]->attrs->end())
+        ignoreNulls = state.forceBool(*attr->value);
+
+    /* Build the derivation expression by processing the attributes. */
+    Derivation drv;
+
+    PathSet context;
+
+    string outputHash, outputHashAlgo;
+    bool outputHashRecursive = false;
+
+    StringSet outputs;
+    outputs.insert("out");
+
+    foreach (Bindings::iterator, i, *args[0]->attrs) {
+        if (i->name == state.sIgnoreNulls) continue;
+        string key = i->name;
+        startNest(nest, lvlVomit, format("processing attribute `%1%'") % key);
+
+        try {
+
+            if (ignoreNulls) {
+                state.forceValue(*i->value);
+                if (i->value->type == tNull) continue;
+            }
+
+            /* The `args' attribute is special: it supplies the
+               command-line arguments to the builder. */
+            if (key == "args") {
+                state.forceList(*i->value);
+                for (unsigned int n = 0; n < i->value->list.length; ++n) {
+                    string s = state.coerceToString(*i->value->list.elems[n], context, true);
+                    drv.args.push_back(s);
+                }
+            }
+
+            /* All other attributes are passed to the builder through
+               the environment. */
+            else {
+                string s = state.coerceToString(*i->value, context, true);
+                drv.env[key] = s;
+                if (key == "builder") drv.builder = s;
+                else if (i->name == state.sSystem) drv.platform = s;
+                else if (i->name == state.sName) {
+                    drvName = s;
+                    printMsg(lvlVomit, format("derivation name is `%1%'") % drvName);
+                }
+                else if (key == "outputHash") outputHash = s;
+                else if (key == "outputHashAlgo") outputHashAlgo = s;
+                else if (key == "outputHashMode") {
+                    if (s == "recursive") outputHashRecursive = true;
+                    else if (s == "flat") outputHashRecursive = false;
+                    else throw EvalError(format("invalid value `%1%' for `outputHashMode' attribute") % s);
+                }
+                else if (key == "outputs") {
+                    Strings tmp = tokenizeString<Strings>(s);
+                    outputs.clear();
+                    foreach (Strings::iterator, j, tmp) {
+                        if (outputs.find(*j) != outputs.end())
+                            throw EvalError(format("duplicate derivation output `%1%'") % *j);
+                        /* !!! Check whether *j is a valid attribute
+                           name. */
+                        /* Derivations cannot be named ‘drv’, because
+                           then we'd have an attribute ‘drvPath’ in
+                           the resulting set. */
+                        if (*j == "drv")
+                            throw EvalError(format("invalid derivation output name `drv'") % *j);
+                        outputs.insert(*j);
+                    }
+                    if (outputs.empty())
+                        throw EvalError("derivation cannot have an empty set of outputs");
+                }
+            }
+
+        } catch (Error & e) {
+            e.addPrefix(format("while evaluating the attribute `%1%' of the derivation `%2%' at %3%:\n")
+                % key % drvName % posDrvName);
+            throw;
+        }
+    }
+
+    /* Everything in the context of the strings in the derivation
+       attributes should be added as dependencies of the resulting
+       derivation. */
+    foreach (PathSet::iterator, i, context) {
+        Path path = *i;
+
+        /* Paths marked with `=' denote that the path of a derivation
+           is explicitly passed to the builder.  Since that allows the
+           builder to gain access to every path in the dependency
+           graph of the derivation (including all outputs), all paths
+           in the graph must be added to this derivation's list of
+           inputs to ensure that they are available when the builder
+           runs. */
+        if (path.at(0) == '=') {
+            /* !!! This doesn't work if readOnlyMode is set. */
+            PathSet refs; computeFSClosure(*store, string(path, 1), refs);
+            foreach (PathSet::iterator, j, refs) {
+                drv.inputSrcs.insert(*j);
+                if (isDerivation(*j))
+                    drv.inputDrvs[*j] = store->queryDerivationOutputNames(*j);
+            }
+        }
+
+        /* See prim_unsafeDiscardOutputDependency. */
+        else if (path.at(0) == '~')
+            drv.inputSrcs.insert(string(path, 1));
+
+        /* Handle derivation outputs of the form ‘!<name>!<path>’. */
+        else if (path.at(0) == '!') {
+            std::pair<string, string> ctx = decodeContext(path);
+            drv.inputDrvs[ctx.first].insert(ctx.second);
+        }
+
+        /* Handle derivation contexts returned by
+           ‘builtins.storePath’. */
+        else if (isDerivation(path))
+            drv.inputDrvs[path] = store->queryDerivationOutputNames(path);
+
+        /* Otherwise it's a source file. */
+        else
+            drv.inputSrcs.insert(path);
+    }
+
+    /* Do we have all required attributes? */
+    if (drv.builder == "")
+        throw EvalError("required attribute `builder' missing");
+    if (drv.platform == "")
+        throw EvalError("required attribute `system' missing");
+
+    /* Check whether the derivation name is valid. */
+    checkStoreName(drvName);
+    if (isDerivation(drvName))
+        throw EvalError(format("derivation names are not allowed to end in `%1%'")
+            % drvExtension);
+
+    if (outputHash != "") {
+        /* Handle fixed-output derivations. */
+        if (outputs.size() != 1 || *(outputs.begin()) != "out")
+            throw Error("multiple outputs are not supported in fixed-output derivations");
+
+        HashType ht = parseHashType(outputHashAlgo);
+        if (ht == htUnknown)
+            throw EvalError(format("unknown hash algorithm `%1%'") % outputHashAlgo);
+        Hash h = parseHash16or32(ht, outputHash);
+        outputHash = printHash(h);
+        if (outputHashRecursive) outputHashAlgo = "r:" + outputHashAlgo;
+
+        Path outPath = makeFixedOutputPath(outputHashRecursive, ht, h, drvName);
+        drv.env["out"] = outPath;
+        drv.outputs["out"] = DerivationOutput(outPath, outputHashAlgo, outputHash);
+    }
+
+    else {
+        /* Construct the "masked" store derivation, which is the final
+           one except that in the list of outputs, the output paths
+           are empty, and the corresponding environment variables have
+           an empty value.  This ensures that changes in the set of
+           output names do get reflected in the hash. */
+        foreach (StringSet::iterator, i, outputs) {
+            drv.env[*i] = "";
+            drv.outputs[*i] = DerivationOutput("", "", "");
+        }
+
+        /* Use the masked derivation expression to compute the output
+           path. */
+        Hash h = hashDerivationModulo(*store, drv);
+
+        foreach (DerivationOutputs::iterator, i, drv.outputs)
+            if (i->second.path == "") {
+                Path outPath = makeOutputPath(i->first, h, drvName);
+                drv.env[i->first] = outPath;
+                i->second.path = outPath;
+            }
+    }
+
+    /* Write the resulting term into the Nix store directory. */
+    Path drvPath = writeDerivation(*store, drv, drvName, state.repair);
+
+    printMsg(lvlChatty, format("instantiated `%1%' -> `%2%'")
+        % drvName % drvPath);
+
+    /* Optimisation, but required in read-only mode! because in that
+       case we don't actually write store derivations, so we can't
+       read them later. */
+    drvHashes[drvPath] = hashDerivationModulo(*store, drv);
+
+    state.mkAttrs(v, 1 + drv.outputs.size());
+    mkString(*state.allocAttr(v, state.sDrvPath), drvPath, singleton<PathSet>("=" + drvPath));
+    foreach (DerivationOutputs::iterator, i, drv.outputs) {
+        mkString(*state.allocAttr(v, state.symbols.create(i->first)),
+            i->second.path, singleton<PathSet>("!" + i->first + "!" + drvPath));
+    }
+    v.attrs->sort();
+}
+
+
+/*************************************************************
+ * Paths
+ *************************************************************/
+
+
+/* Convert the argument to a path.  !!! obsolete? */
+static void prim_toPath(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(*args[0], context);
+    mkString(v, canonPath(path), context);
+}
+
+
+/* Allow a valid store path to be used in an expression.  This is
+   useful in some generated expressions such as in nix-push, which
+   generates a call to a function with an already existing store path
+   as argument.  You don't want to use `toPath' here because it copies
+   the path to the Nix store, which yields a copy like
+   /nix/store/newhash-oldhash-oldname.  In the past, `toPath' had
+   special case behaviour for store paths, but that created weird
+   corner cases. */
+static void prim_storePath(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(*args[0], context);
+    /* Resolve symlinks in ‘path’, unless ‘path’ itself is a symlink
+       directly in the store.  The latter condition is necessary so
+       e.g. nix-push does the right thing. */
+    if (!isStorePath(path)) path = canonPath(path, true);
+    if (!isInStore(path))
+        throw EvalError(format("path `%1%' is not in the Nix store") % path);
+    Path path2 = toStorePath(path);
+    if (!settings.readOnlyMode)
+        store->ensurePath(path2);
+    context.insert(path2);
+    mkString(v, path, context);
+}
+
+
+static void prim_pathExists(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(*args[0], context);
+    if (!context.empty())
+        throw EvalError(format("string `%1%' cannot refer to other paths") % path);
+    mkBool(v, pathExists(path));
+}
+
+
+/* Return the base name of the given string, i.e., everything
+   following the last slash. */
+static void prim_baseNameOf(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    mkString(v, baseNameOf(state.coerceToString(*args[0], context)), context);
+}
+
+
+/* Return the directory of the given path, i.e., everything before the
+   last slash.  Return either a path or a string depending on the type
+   of the argument. */
+static void prim_dirOf(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path dir = dirOf(state.coerceToPath(*args[0], context));
+    if (args[0]->type == tPath) mkPath(v, dir.c_str()); else mkString(v, dir, context);
+}
+
+
+/* Return the contents of a file as a string. */
+static void prim_readFile(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(*args[0], context);
+    if (!context.empty())
+        throw EvalError(format("string `%1%' cannot refer to other paths") % path);
+    mkString(v, readFile(path).c_str());
+}
+
+
+/*************************************************************
+ * Creating files
+ *************************************************************/
+
+
+/* Convert the argument (which can be any Nix expression) to an XML
+   representation returned in a string.  Not all Nix expressions can
+   be sensibly or completely represented (e.g., functions). */
+static void prim_toXML(EvalState & state, Value * * args, Value & v)
+{
+    std::ostringstream out;
+    PathSet context;
+    printValueAsXML(state, true, false, *args[0], out, context);
+    mkString(v, out.str(), context);
+}
+
+
+/* Convert the argument (which can be any Nix expression) to a JSON
+   string.  Not all Nix expressions can be sensibly or completely
+   represented (e.g., functions). */
+static void prim_toJSON(EvalState & state, Value * * args, Value & v)
+{
+    std::ostringstream out;
+    PathSet context;
+    printValueAsJSON(state, true, *args[0], out, context);
+    mkString(v, out.str(), context);
+}
+
+
+/* Store a string in the Nix store as a source file that can be used
+   as an input by derivations. */
+static void prim_toFile(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    string name = state.forceStringNoCtx(*args[0]);
+    string contents = state.forceString(*args[1], context);
+
+    PathSet refs;
+
+    foreach (PathSet::iterator, i, context) {
+        Path path = *i;
+        if (path.at(0) == '=') path = string(path, 1);
+        if (isDerivation(path))
+            throw EvalError(format("in `toFile': the file `%1%' cannot refer to derivation outputs") % name);
+        refs.insert(path);
+    }
+
+    Path storePath = settings.readOnlyMode
+        ? computeStorePathForText(name, contents, refs)
+        : store->addTextToStore(name, contents, refs, state.repair);
+
+    /* Note: we don't need to add `context' to the context of the
+       result, since `storePath' itself has references to the paths
+       used in args[1]. */
+
+    mkString(v, storePath, singleton<PathSet>(storePath));
+}
+
+
+struct FilterFromExpr : PathFilter
+{
+    EvalState & state;
+    Value & filter;
+
+    FilterFromExpr(EvalState & state, Value & filter)
+        : state(state), filter(filter)
+    {
+    }
+
+    bool operator () (const Path & path)
+    {
+        struct stat st;
+        if (lstat(path.c_str(), &st))
+            throw SysError(format("getting attributes of path `%1%'") % path);
+
+        /* Call the filter function.  The first argument is the path,
+           the second is a string indicating the type of the file. */
+        Value arg1;
+        mkString(arg1, path);
+
+        Value fun2;
+        state.callFunction(filter, arg1, fun2);
+
+        Value arg2;
+        mkString(arg2,
+            S_ISREG(st.st_mode) ? "regular" :
+            S_ISDIR(st.st_mode) ? "directory" :
+            S_ISLNK(st.st_mode) ? "symlink" :
+            "unknown" /* not supported, will fail! */);
+
+        Value res;
+        state.callFunction(fun2, arg2, res);
+
+        return state.forceBool(res);
+    }
+};
+
+
+static void prim_filterSource(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    Path path = state.coerceToPath(*args[1], context);
+    if (!context.empty())
+        throw EvalError(format("string `%1%' cannot refer to other paths") % path);
+
+    state.forceValue(*args[0]);
+    if (args[0]->type != tLambda)
+        throw TypeError(format("first argument in call to `filterSource' is not a function but %1%") % showType(*args[0]));
+
+    FilterFromExpr filter(state, *args[0]);
+
+    Path dstPath = settings.readOnlyMode
+        ? computeStorePathForPath(path, true, htSHA256, filter).first
+        : store->addToStore(path, true, htSHA256, filter, state.repair);
+
+    mkString(v, dstPath, singleton<PathSet>(dstPath));
+}
+
+
+/*************************************************************
+ * Sets
+ *************************************************************/
+
+
+/* Return the names of the attributes in a set as a sorted list of
+   strings. */
+static void prim_attrNames(EvalState & state, Value * * args, Value & v)
+{
+    state.forceAttrs(*args[0]);
+
+    state.mkList(v, args[0]->attrs->size());
+
+    StringSet names;
+    foreach (Bindings::iterator, i, *args[0]->attrs)
+        names.insert(i->name);
+
+    unsigned int n = 0;
+    foreach (StringSet::iterator, i, names)
+        mkString(*(v.list.elems[n++] = state.allocValue()), *i);
+}
+
+
+/* Dynamic version of the `.' operator. */
+void prim_getAttr(EvalState & state, Value * * args, Value & v)
+{
+    string attr = state.forceStringNoCtx(*args[0]);
+    state.forceAttrs(*args[1]);
+    // !!! Should we create a symbol here or just do a lookup?
+    Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
+    if (i == args[1]->attrs->end())
+        throw EvalError(format("attribute `%1%' missing") % attr);
+    // !!! add to stack trace?
+    if (state.countCalls && i->pos) state.attrSelects[*i->pos]++;
+    state.forceValue(*i->value);
+    v = *i->value;
+}
+
+
+/* Return position information of the specified attribute. */
+void prim_unsafeGetAttrPos(EvalState & state, Value * * args, Value & v)
+{
+    string attr = state.forceStringNoCtx(*args[0]);
+    state.forceAttrs(*args[1]);
+    Bindings::iterator i = args[1]->attrs->find(state.symbols.create(attr));
+    if (i == args[1]->attrs->end())
+        mkNull(v);
+    else
+        state.mkPos(v, i->pos);
+}
+
+
+/* Dynamic version of the `?' operator. */
+static void prim_hasAttr(EvalState & state, Value * * args, Value & v)
+{
+    string attr = state.forceStringNoCtx(*args[0]);
+    state.forceAttrs(*args[1]);
+    mkBool(v, args[1]->attrs->find(state.symbols.create(attr)) != args[1]->attrs->end());
+}
+
+
+/* Determine whether the argument is a set. */
+static void prim_isAttrs(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tAttrs);
+}
+
+
+static void prim_removeAttrs(EvalState & state, Value * * args, Value & v)
+{
+    state.forceAttrs(*args[0]);
+    state.forceList(*args[1]);
+
+    /* Get the attribute names to be removed. */
+    std::set<Symbol> names;
+    for (unsigned int i = 0; i < args[1]->list.length; ++i) {
+        state.forceStringNoCtx(*args[1]->list.elems[i]);
+        names.insert(state.symbols.create(args[1]->list.elems[i]->string.s));
+    }
+
+    /* Copy all attributes not in that set.  Note that we don't need
+       to sort v.attrs because it's a subset of an already sorted
+       vector. */
+    state.mkAttrs(v, args[0]->attrs->size());
+    foreach (Bindings::iterator, i, *args[0]->attrs) {
+        if (names.find(i->name) == names.end())
+            v.attrs->push_back(*i);
+    }
+}
+
+
+/* Builds a set from a list specifying (name, value) pairs.  To be
+   precise, a list [{name = "name1"; value = value1;} ... {name =
+   "nameN"; value = valueN;}] is transformed to {name1 = value1;
+   ... nameN = valueN;}.  In case of duplicate occurences of the same
+   name, the first takes precedence. */
+static void prim_listToAttrs(EvalState & state, Value * * args, Value & v)
+{
+    state.forceList(*args[0]);
+
+    state.mkAttrs(v, args[0]->list.length);
+
+    std::set<Symbol> seen;
+
+    for (unsigned int i = 0; i < args[0]->list.length; ++i) {
+        Value & v2(*args[0]->list.elems[i]);
+        state.forceAttrs(v2);
+
+        Bindings::iterator j = v2.attrs->find(state.sName);
+        if (j == v2.attrs->end())
+            throw TypeError("`name' attribute missing in a call to `listToAttrs'");
+        string name = state.forceStringNoCtx(*j->value);
+
+        Symbol sym = state.symbols.create(name);
+        if (seen.find(sym) == seen.end()) {
+            Bindings::iterator j2 = v2.attrs->find(state.symbols.create(state.sValue));
+            if (j2 == v2.attrs->end())
+                throw TypeError("`value' attribute missing in a call to `listToAttrs'");
+
+            v.attrs->push_back(Attr(sym, j2->value, j2->pos));
+            seen.insert(sym);
+        }
+    }
+
+    v.attrs->sort();
+}
+
+
+/* Return the right-biased intersection of two sets as1 and as2,
+   i.e. a set that contains every attribute from as2 that is also a
+   member of as1. */
+static void prim_intersectAttrs(EvalState & state, Value * * args, Value & v)
+{
+    state.forceAttrs(*args[0]);
+    state.forceAttrs(*args[1]);
+
+    state.mkAttrs(v, std::min(args[0]->attrs->size(), args[1]->attrs->size()));
+
+    foreach (Bindings::iterator, i, *args[0]->attrs) {
+        Bindings::iterator j = args[1]->attrs->find(i->name);
+        if (j != args[1]->attrs->end())
+            v.attrs->push_back(*j);
+    }
+}
+
+
+/* Return a set containing the names of the formal arguments expected
+   by the function `f'.  The value of each attribute is a Boolean
+   denoting whether has a default value.  For instance,
+
+      functionArgs ({ x, y ? 123}: ...)
+   => { x = false; y = true; }
+
+   "Formal argument" here refers to the attributes pattern-matched by
+   the function.  Plain lambdas are not included, e.g.
+
+      functionArgs (x: ...)
+   => { }
+*/
+static void prim_functionArgs(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    if (args[0]->type != tLambda)
+        throw TypeError("`functionArgs' requires a function");
+
+    if (!args[0]->lambda.fun->matchAttrs) {
+        state.mkAttrs(v, 0);
+        return;
+    }
+
+    state.mkAttrs(v, args[0]->lambda.fun->formals->formals.size());
+    foreach (Formals::Formals_::iterator, i, args[0]->lambda.fun->formals->formals)
+        // !!! should optimise booleans (allocate only once)
+        mkBool(*state.allocAttr(v, i->name), i->def);
+    v.attrs->sort();
+}
+
+
+/*************************************************************
+ * Lists
+ *************************************************************/
+
+
+/* Determine whether the argument is a list. */
+static void prim_isList(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    mkBool(v, args[0]->type == tList);
+}
+
+
+static void elemAt(EvalState & state, Value & list, int n, Value & v)
+{
+    state.forceList(list);
+    if (n < 0 || n >= list.list.length)
+        throw Error(format("list index %1% is out of bounds") % n);
+    state.forceValue(*list.list.elems[n]);
+    v = *list.list.elems[n];
+}
+
+
+/* Return the n-1'th element of a list. */
+static void prim_elemAt(EvalState & state, Value * * args, Value & v)
+{
+    elemAt(state, *args[0], state.forceInt(*args[1]), v);
+}
+
+
+/* Return the first element of a list. */
+static void prim_head(EvalState & state, Value * * args, Value & v)
+{
+    elemAt(state, *args[0], 0, v);
+}
+
+
+/* Return a list consisting of everything but the the first element of
+   a list.  Warning: this function takes O(n) time, so you probably
+   don't want to use it!  */
+static void prim_tail(EvalState & state, Value * * args, Value & v)
+{
+    state.forceList(*args[0]);
+    if (args[0]->list.length == 0)
+        throw Error("`tail' called on an empty list");
+    state.mkList(v, args[0]->list.length - 1);
+    for (unsigned int n = 0; n < v.list.length; ++n)
+        v.list.elems[n] = args[0]->list.elems[n + 1];
+}
+
+
+/* Apply a function to every element of a list. */
+static void prim_map(EvalState & state, Value * * args, Value & v)
+{
+    state.forceFunction(*args[0]);
+    state.forceList(*args[1]);
+
+    state.mkList(v, args[1]->list.length);
+
+    for (unsigned int n = 0; n < v.list.length; ++n)
+        mkApp(*(v.list.elems[n] = state.allocValue()),
+            *args[0], *args[1]->list.elems[n]);
+}
+
+
+/* Filter a list using a predicate; that is, return a list containing
+   every element from the list for which the predicate function
+   returns true. */
+static void prim_filter(EvalState & state, Value * * args, Value & v)
+{
+    state.forceFunction(*args[0]);
+    state.forceList(*args[1]);
+
+    // FIXME: putting this on the stack is risky.
+    Value * vs[args[1]->list.length];
+    unsigned int k = 0;
+
+    bool same = true;
+    for (unsigned int n = 0; n < args[1]->list.length; ++n) {
+        Value res;
+        state.callFunction(*args[0], *args[1]->list.elems[n], res);
+        if (state.forceBool(res))
+            vs[k++] = args[1]->list.elems[n];
+        else
+            same = false;
+    }
+
+    if (same)
+        v = *args[1];
+    else {
+        state.mkList(v, k);
+        for (unsigned int n = 0; n < k; ++n) v.list.elems[n] = vs[n];
+    }
+}
+
+
+/* Return true if a list contains a given element. */
+static void prim_elem(EvalState & state, Value * * args, Value & v)
+{
+    bool res = false;
+    state.forceList(*args[1]);
+    for (unsigned int n = 0; n < args[1]->list.length; ++n)
+        if (state.eqValues(*args[0], *args[1]->list.elems[n])) {
+            res = true;
+            break;
+        }
+    mkBool(v, res);
+}
+
+
+/* Concatenate a list of lists. */
+static void prim_concatLists(EvalState & state, Value * * args, Value & v)
+{
+    state.forceList(*args[0]);
+    state.concatLists(v, args[0]->list.length, args[0]->list.elems);
+}
+
+
+/* Return the length of a list.  This is an O(1) time operation. */
+static void prim_length(EvalState & state, Value * * args, Value & v)
+{
+    state.forceList(*args[0]);
+    mkInt(v, args[0]->list.length);
+}
+
+
+/*************************************************************
+ * Integer arithmetic
+ *************************************************************/
+
+
+static void prim_add(EvalState & state, Value * * args, Value & v)
+{
+    mkInt(v, state.forceInt(*args[0]) + state.forceInt(*args[1]));
+}
+
+
+static void prim_sub(EvalState & state, Value * * args, Value & v)
+{
+    mkInt(v, state.forceInt(*args[0]) - state.forceInt(*args[1]));
+}
+
+
+static void prim_mul(EvalState & state, Value * * args, Value & v)
+{
+    mkInt(v, state.forceInt(*args[0]) * state.forceInt(*args[1]));
+}
+
+
+static void prim_div(EvalState & state, Value * * args, Value & v)
+{
+    NixInt i2 = state.forceInt(*args[1]);
+    if (i2 == 0) throw EvalError("division by zero");
+    mkInt(v, state.forceInt(*args[0]) / i2);
+}
+
+
+static void prim_lessThan(EvalState & state, Value * * args, Value & v)
+{
+    state.forceValue(*args[0]);
+    state.forceValue(*args[1]);
+    CompareValues comp;
+    mkBool(v, comp(args[0], args[1]));
+}
+
+
+/*************************************************************
+ * String manipulation
+ *************************************************************/
+
+
+/* Convert the argument to a string.  Paths are *not* copied to the
+   store, so `toString /foo/bar' yields `"/foo/bar"', not
+   `"/nix/store/whatever..."'. */
+static void prim_toString(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(*args[0], context, true, false);
+    mkString(v, s, context);
+}
+
+
+/* `substring start len str' returns the substring of `str' starting
+   at character position `min(start, stringLength str)' inclusive and
+   ending at `min(start + len, stringLength str)'.  `start' must be
+   non-negative. */
+static void prim_substring(EvalState & state, Value * * args, Value & v)
+{
+    int start = state.forceInt(*args[0]);
+    int len = state.forceInt(*args[1]);
+    PathSet context;
+    string s = state.coerceToString(*args[2], context);
+
+    if (start < 0) throw EvalError("negative start position in `substring'");
+
+    mkString(v, start >= s.size() ? "" : string(s, start, len), context);
+}
+
+
+static void prim_stringLength(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(*args[0], context);
+    mkInt(v, s.size());
+}
+
+
+static void prim_unsafeDiscardStringContext(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(*args[0], context);
+    mkString(v, s, PathSet());
+}
+
+
+/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
+   builder without causing the derivation to be built (for instance,
+   in the derivation that builds NARs in nix-push, when doing
+   source-only deployment).  This primop marks the string context so
+   that builtins.derivation adds the path to drv.inputSrcs rather than
+   drv.inputDrvs. */
+static void prim_unsafeDiscardOutputDependency(EvalState & state, Value * * args, Value & v)
+{
+    PathSet context;
+    string s = state.coerceToString(*args[0], context);
+
+    PathSet context2;
+    foreach (PathSet::iterator, i, context) {
+        Path p = *i;
+        if (p.at(0) == '=') p = "~" + string(p, 1);
+        context2.insert(p);
+    }
+
+    mkString(v, s, context2);
+}
+
+
+/* Return the cryptographic hash of a string in base-16. */
+static void prim_hashString(EvalState & state, Value * * args, Value & v)
+{
+    string type = state.forceStringNoCtx(*args[0]);
+    HashType ht = parseHashType(type);
+    if (ht == htUnknown)
+      throw Error(format("unknown hash type `%1%'") % type);
+
+    PathSet context; // discarded
+    string s = state.forceString(*args[1], context);
+
+    mkString(v, printHash(hashString(ht, s)), context);
+};
+
+
+/*************************************************************
+ * Versions
+ *************************************************************/
+
+
+static void prim_parseDrvName(EvalState & state, Value * * args, Value & v)
+{
+    string name = state.forceStringNoCtx(*args[0]);
+    DrvName parsed(name);
+    state.mkAttrs(v, 2);
+    mkString(*state.allocAttr(v, state.sName), parsed.name);
+    mkString(*state.allocAttr(v, state.symbols.create("version")), parsed.version);
+    v.attrs->sort();
+}
+
+
+static void prim_compareVersions(EvalState & state, Value * * args, Value & v)
+{
+    string version1 = state.forceStringNoCtx(*args[0]);
+    string version2 = state.forceStringNoCtx(*args[1]);
+    mkInt(v, compareVersions(version1, version2));
+}
+
+
+/*************************************************************
+ * Primop registration
+ *************************************************************/
+
+
+void EvalState::createBaseEnv()
+{
+    baseEnv.up = 0;
+
+    /* Add global constants such as `true' to the base environment. */
+    Value v;
+
+    /* `builtins' must be first! */
+    mkAttrs(v, 128);
+    addConstant("builtins", v);
+
+    mkBool(v, true);
+    addConstant("true", v);
+
+    mkBool(v, false);
+    addConstant("false", v);
+
+    mkNull(v);
+    addConstant("null", v);
+
+    mkInt(v, time(0));
+    addConstant("__currentTime", v);
+
+    mkString(v, settings.thisSystem.c_str());
+    addConstant("__currentSystem", v);
+
+    mkString(v, nixVersion.c_str());
+    addConstant("__nixVersion", v);
+
+    /* Language version.  This should be increased every time a new
+       language feature gets added.  It's not necessary to increase it
+       when primops get added, because you can just use `builtins ?
+       primOp' to check. */
+    mkInt(v, 2);
+    addConstant("__langVersion", v);
+
+    // Miscellaneous
+    addPrimOp("import", 1, prim_import);
+    addPrimOp("__typeOf", 1, prim_typeOf);
+    addPrimOp("isNull", 1, prim_isNull);
+    addPrimOp("__isFunction", 1, prim_isFunction);
+    addPrimOp("__isString", 1, prim_isString);
+    addPrimOp("__isInt", 1, prim_isInt);
+    addPrimOp("__isBool", 1, prim_isBool);
+    addPrimOp("__genericClosure", 1, prim_genericClosure);
+    addPrimOp("abort", 1, prim_abort);
+    addPrimOp("throw", 1, prim_throw);
+    addPrimOp("__addErrorContext", 2, prim_addErrorContext);
+    addPrimOp("__tryEval", 1, prim_tryEval);
+    addPrimOp("__getEnv", 1, prim_getEnv);
+    addPrimOp("__trace", 2, prim_trace);
+
+    // Paths
+    addPrimOp("__toPath", 1, prim_toPath);
+    addPrimOp("__storePath", 1, prim_storePath);
+    addPrimOp("__pathExists", 1, prim_pathExists);
+    addPrimOp("baseNameOf", 1, prim_baseNameOf);
+    addPrimOp("dirOf", 1, prim_dirOf);
+    addPrimOp("__readFile", 1, prim_readFile);
+
+    // Creating files
+    addPrimOp("__toXML", 1, prim_toXML);
+    addPrimOp("__toJSON", 1, prim_toJSON);
+    addPrimOp("__toFile", 2, prim_toFile);
+    addPrimOp("__filterSource", 2, prim_filterSource);
+
+    // Sets
+    addPrimOp("__attrNames", 1, prim_attrNames);
+    addPrimOp("__getAttr", 2, prim_getAttr);
+    addPrimOp("__unsafeGetAttrPos", 2, prim_unsafeGetAttrPos);
+    addPrimOp("__hasAttr", 2, prim_hasAttr);
+    addPrimOp("__isAttrs", 1, prim_isAttrs);
+    addPrimOp("removeAttrs", 2, prim_removeAttrs);
+    addPrimOp("__listToAttrs", 1, prim_listToAttrs);
+    addPrimOp("__intersectAttrs", 2, prim_intersectAttrs);
+    addPrimOp("__functionArgs", 1, prim_functionArgs);
+
+    // Lists
+    addPrimOp("__isList", 1, prim_isList);
+    addPrimOp("__elemAt", 2, prim_elemAt);
+    addPrimOp("__head", 1, prim_head);
+    addPrimOp("__tail", 1, prim_tail);
+    addPrimOp("map", 2, prim_map);
+    addPrimOp("__filter", 2, prim_filter);
+    addPrimOp("__elem", 2, prim_elem);
+    addPrimOp("__concatLists", 1, prim_concatLists);
+    addPrimOp("__length", 1, prim_length);
+
+    // Integer arithmetic
+    addPrimOp("__add", 2, prim_add);
+    addPrimOp("__sub", 2, prim_sub);
+    addPrimOp("__mul", 2, prim_mul);
+    addPrimOp("__div", 2, prim_div);
+    addPrimOp("__lessThan", 2, prim_lessThan);
+
+    // String manipulation
+    addPrimOp("toString", 1, prim_toString);
+    addPrimOp("__substring", 3, prim_substring);
+    addPrimOp("__stringLength", 1, prim_stringLength);
+    addPrimOp("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
+    addPrimOp("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
+    addPrimOp("__hashString", 2, prim_hashString);
+
+    // Versions
+    addPrimOp("__parseDrvName", 1, prim_parseDrvName);
+    addPrimOp("__compareVersions", 2, prim_compareVersions);
+
+    // Derivations
+    addPrimOp("derivationStrict", 1, prim_derivationStrict);
+
+    /* Add a wrapper around the derivation primop that computes the
+       `drvPath' and `outPath' attributes lazily. */
+    string path = findFile("nix/derivation.nix");
+    assert(!path.empty());
+    sDerivationNix = symbols.create(path);
+    evalFile(path, v);
+    addConstant("derivation", v);
+
+    /* Now that we've added all primops, sort the `builtins' set,
+       because attribute lookups expect it to be sorted. */
+    baseEnv.values[0]->attrs->sort();
+}
+
+
+}
diff --git a/src/libexpr/symbol-table.hh b/src/libexpr/symbol-table.hh
new file mode 100644
index 000000000000..08e31d496585
--- /dev/null
+++ b/src/libexpr/symbol-table.hh
@@ -0,0 +1,95 @@
+#pragma once
+
+#include "config.h"
+
+#include <map>
+
+#if HAVE_TR1_UNORDERED_SET
+#include <tr1/unordered_set>
+#endif
+
+#include "types.hh"
+
+namespace nix {
+
+/* Symbol table used by the parser and evaluator to represent and look
+   up identifiers and attributes efficiently.  SymbolTable::create()
+   converts a string into a symbol.  Symbols have the property that
+   they can be compared efficiently (using a pointer equality test),
+   because the symbol table stores only one copy of each string. */
+
+class Symbol
+{
+private:
+    const string * s; // pointer into SymbolTable
+    Symbol(const string * s) : s(s) { };
+    friend class SymbolTable;
+
+public:
+    Symbol() : s(0) { };
+
+    bool operator == (const Symbol & s2) const
+    {
+        return s == s2.s;
+    }
+
+    bool operator != (const Symbol & s2) const
+    {
+        return s != s2.s;
+    }
+
+    bool operator < (const Symbol & s2) const
+    {
+        return s < s2.s;
+    }
+
+    operator const string & () const
+    {
+        return *s;
+    }
+
+    bool set() const
+    {
+        return s;
+    }
+
+    bool empty() const
+    {
+        return s->empty();
+    }
+
+    friend std::ostream & operator << (std::ostream & str, const Symbol & sym);
+};
+
+inline std::ostream & operator << (std::ostream & str, const Symbol & sym)
+{
+    str << *sym.s;
+    return str;
+}
+
+class SymbolTable
+{
+private:
+#if HAVE_TR1_UNORDERED_SET
+    typedef std::tr1::unordered_set<string> Symbols;
+#else
+    typedef std::set<string> Symbols;
+#endif
+    Symbols symbols;
+
+public:
+    Symbol create(const string & s)
+    {
+        std::pair<Symbols::iterator, bool> res = symbols.insert(s);
+        return Symbol(&*res.first);
+    }
+
+    unsigned int size() const
+    {
+        return symbols.size();
+    }
+
+    size_t totalSize() const;
+};
+
+}
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
new file mode 100644
index 000000000000..a2004df5c8c5
--- /dev/null
+++ b/src/libexpr/value-to-json.cc
@@ -0,0 +1,86 @@
+#include "value-to-json.hh"
+#include "eval-inline.hh"
+#include "util.hh"
+
+#include <cstdlib>
+
+
+namespace nix {
+
+
+void escapeJSON(std::ostream & str, const string & s)
+{
+    str << "\"";
+    foreach (string::const_iterator, i, s)
+        if (*i == '\"' || *i == '\\') str << "\\" << *i;
+        else if (*i == '\n') str << "\\n";
+        else if (*i == '\r') str << "\\r";
+        else if (*i == '\t') str << "\\t";
+        else str << *i;
+    str << "\"";
+}
+
+
+void printValueAsJSON(EvalState & state, bool strict,
+    Value & v, std::ostream & str, PathSet & context)
+{
+    checkInterrupt();
+
+    if (strict) state.forceValue(v);
+
+    switch (v.type) {
+
+        case tInt:
+            str << v.integer;
+            break;
+
+        case tBool:
+            str << (v.boolean ? "true" : "false");
+            break;
+
+        case tString:
+            copyContext(v, context);
+            escapeJSON(str, v.string.s);
+            break;
+
+        case tPath:
+            escapeJSON(str, state.copyPathToStore(context, v.path));
+            break;
+
+        case tNull:
+            str << "null";
+            break;
+
+        case tAttrs: {
+            Bindings::iterator i = v.attrs->find(state.sOutPath);
+            if (i == v.attrs->end()) {
+                JSONObject json(str);
+                StringSet names;
+                foreach (Bindings::iterator, i, *v.attrs)
+                    names.insert(i->name);
+                foreach (StringSet::iterator, i, names) {
+                    Attr & a(*v.attrs->find(state.symbols.create(*i)));
+                    json.attr(*i);
+                    printValueAsJSON(state, strict, *a.value, str, context);
+                }
+            } else
+                printValueAsJSON(state, strict, *i->value, str, context);
+            break;
+        }
+
+        case tList: {
+            JSONList json(str);
+            for (unsigned int n = 0; n < v.list.length; ++n) {
+                json.elem();
+                printValueAsJSON(state, strict, *v.list.elems[n], str, context);
+            }
+            break;
+        }
+
+        default:
+            throw TypeError(format("cannot convert %1% to JSON") % showType(v));
+    }
+}
+
+
+}
diff --git a/src/libexpr/value-to-json.hh b/src/libexpr/value-to-json.hh
new file mode 100644
index 000000000000..e3a97efe4269
--- /dev/null
+++ b/src/libexpr/value-to-json.hh
@@ -0,0 +1,64 @@
+#pragma once
+
+#include "nixexpr.hh"
+#include "eval.hh"
+
+#include <string>
+#include <map>
+
+namespace nix {
+
+void printValueAsJSON(EvalState & state, bool strict,
+    Value & v, std::ostream & out, PathSet & context);
+
+void escapeJSON(std::ostream & str, const string & s);
+
+struct JSONObject
+{
+    std::ostream & str;
+    bool first;
+    JSONObject(std::ostream & str) : str(str), first(true)
+    {
+        str << "{";
+    }
+    ~JSONObject()
+    {
+        str << "}";
+    }
+    void attr(const string & s)
+    {
+        if (!first) str << ","; else first = false;
+        escapeJSON(str, s);
+        str << ":";
+    }
+    void attr(const string & s, const string & t)
+    {
+        attr(s);
+        escapeJSON(str, t);
+    }
+};
+
+struct JSONList
+{
+    std::ostream & str;
+    bool first;
+    JSONList(std::ostream & str) : str(str), first(true)
+    {
+        str << "[";
+    }
+    ~JSONList()
+    {
+        str << "]";
+    }
+    void elem()
+    {
+        if (!first) str << ","; else first = false;
+    }
+    void elem(const string & s)
+    {
+        elem();
+        escapeJSON(str, s);
+    }
+};
+
+}
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
new file mode 100644
index 000000000000..3934a83eec25
--- /dev/null
+++ b/src/libexpr/value-to-xml.cc
@@ -0,0 +1,163 @@
+#include "value-to-xml.hh"
+#include "xml-writer.hh"
+#include "eval-inline.hh"
+#include "util.hh"
+
+#include <cstdlib>
+
+
+namespace nix {
+
+    
+static XMLAttrs singletonAttrs(const string & name, const string & value)
+{
+    XMLAttrs attrs;
+    attrs[name] = value;
+    return attrs;
+}
+
+
+static void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen);
+
+
+static void posToXML(XMLAttrs & xmlAttrs, const Pos & pos)
+{
+    xmlAttrs["path"] = pos.file;
+    xmlAttrs["line"] = (format("%1%") % pos.line).str();
+    xmlAttrs["column"] = (format("%1%") % pos.column).str();
+}
+
+
+static void showAttrs(EvalState & state, bool strict, bool location,
+    Bindings & attrs, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
+{
+    StringSet names;
+    
+    foreach (Bindings::iterator, i, attrs)
+        names.insert(i->name);
+    
+    foreach (StringSet::iterator, i, names) {
+        Attr & a(*attrs.find(state.symbols.create(*i)));
+        
+        XMLAttrs xmlAttrs;
+        xmlAttrs["name"] = *i;
+        if (location && a.pos != &noPos) posToXML(xmlAttrs, *a.pos);
+        
+        XMLOpenElement _(doc, "attr", xmlAttrs);
+        printValueAsXML(state, strict, location,
+            *a.value, doc, context, drvsSeen);
+    }
+}
+
+
+static void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
+{
+    checkInterrupt();
+
+    if (strict) state.forceValue(v);
+        
+    switch (v.type) {
+
+        case tInt:
+            doc.writeEmptyElement("int", singletonAttrs("value", (format("%1%") % v.integer).str()));
+            break;
+
+        case tBool:
+            doc.writeEmptyElement("bool", singletonAttrs("value", v.boolean ? "true" : "false"));
+            break;
+
+        case tString:
+            /* !!! show the context? */
+            copyContext(v, context);
+            doc.writeEmptyElement("string", singletonAttrs("value", v.string.s));
+            break;
+
+        case tPath:
+            doc.writeEmptyElement("path", singletonAttrs("value", v.path));
+            break;
+
+        case tNull:
+            doc.writeEmptyElement("null");
+            break;
+
+        case tAttrs:
+            if (state.isDerivation(v)) {
+                XMLAttrs xmlAttrs;
+            
+                Bindings::iterator a = v.attrs->find(state.symbols.create("derivation"));
+
+                Path drvPath;
+                a = v.attrs->find(state.sDrvPath);
+                if (a != v.attrs->end()) {
+                    if (strict) state.forceValue(*a->value);
+                    if (a->value->type == tString)
+                        xmlAttrs["drvPath"] = drvPath = a->value->string.s;
+                }
+        
+                a = v.attrs->find(state.sOutPath);
+                if (a != v.attrs->end()) {
+                    if (strict) state.forceValue(*a->value);
+                    if (a->value->type == tString)
+                        xmlAttrs["outPath"] = a->value->string.s;
+                }
+
+                XMLOpenElement _(doc, "derivation", xmlAttrs);
+
+                if (drvPath != "" && drvsSeen.find(drvPath) == drvsSeen.end()) {
+                    drvsSeen.insert(drvPath);
+                    showAttrs(state, strict, location, *v.attrs, doc, context, drvsSeen);
+                } else
+                    doc.writeEmptyElement("repeated");
+            }
+
+            else {
+                XMLOpenElement _(doc, "attrs");
+                showAttrs(state, strict, location, *v.attrs, doc, context, drvsSeen);
+            }
+            
+            break;
+
+        case tList: {
+            XMLOpenElement _(doc, "list");
+            for (unsigned int n = 0; n < v.list.length; ++n)
+                printValueAsXML(state, strict, location, *v.list.elems[n], doc, context, drvsSeen);
+            break;
+        }
+
+        case tLambda: {
+            XMLAttrs xmlAttrs;
+            if (location) posToXML(xmlAttrs, v.lambda.fun->pos);
+            XMLOpenElement _(doc, "function", xmlAttrs);
+            
+            if (v.lambda.fun->matchAttrs) {
+                XMLAttrs attrs;
+                if (!v.lambda.fun->arg.empty()) attrs["name"] = v.lambda.fun->arg;
+                if (v.lambda.fun->formals->ellipsis) attrs["ellipsis"] = "1";
+                XMLOpenElement _(doc, "attrspat", attrs);
+                foreach (Formals::Formals_::iterator, i, v.lambda.fun->formals->formals)
+                    doc.writeEmptyElement("attr", singletonAttrs("name", i->name));
+            } else
+                doc.writeEmptyElement("varpat", singletonAttrs("name", v.lambda.fun->arg));
+            
+            break;
+        }
+
+        default:
+            doc.writeEmptyElement("unevaluated");
+    }
+}
+
+
+void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, std::ostream & out, PathSet & context)
+{
+    XMLWriter doc(true, out);
+    XMLOpenElement root(doc, "expr");
+    PathSet drvsSeen;    
+    printValueAsXML(state, strict, location, v, doc, context, drvsSeen);
+}
+
+ 
+}
diff --git a/src/libexpr/value-to-xml.hh b/src/libexpr/value-to-xml.hh
new file mode 100644
index 000000000000..97657327edba
--- /dev/null
+++ b/src/libexpr/value-to-xml.hh
@@ -0,0 +1,14 @@
+#pragma once
+
+#include "nixexpr.hh"
+#include "eval.hh"
+
+#include <string>
+#include <map>
+
+namespace nix {
+
+void printValueAsXML(EvalState & state, bool strict, bool location,
+    Value & v, std::ostream & out, PathSet & context);
+    
+}
diff --git a/src/libexpr/value.hh b/src/libexpr/value.hh
new file mode 100644
index 000000000000..2feb2f9492ca
--- /dev/null
+++ b/src/libexpr/value.hh
@@ -0,0 +1,162 @@
+#pragma once
+
+#include "symbol-table.hh"
+
+namespace nix {
+
+
+typedef enum {
+    tInt = 1,
+    tBool,
+    tString,
+    tPath,
+    tNull,
+    tAttrs,
+    tList,
+    tThunk,
+    tApp,
+    tLambda,
+    tBlackhole,
+    tPrimOp,
+    tPrimOpApp,
+} ValueType;
+
+
+class Bindings;
+struct Env;
+struct Expr;
+struct ExprLambda;
+struct PrimOp;
+struct PrimOp;
+class Symbol;
+
+
+typedef long NixInt;
+
+
+struct Value
+{
+    ValueType type;
+    union
+    {
+        NixInt integer;
+        bool boolean;
+
+        /* Strings in the evaluator carry a so-called `context' which
+           is a list of strings representing store paths.  This is to
+           allow users to write things like
+
+             "--with-freetype2-library=" + freetype + "/lib"
+
+           where `freetype' is a derivation (or a source to be copied
+           to the store).  If we just concatenated the strings without
+           keeping track of the referenced store paths, then if the
+           string is used as a derivation attribute, the derivation
+           will not have the correct dependencies in its inputDrvs and
+           inputSrcs.
+
+           The semantics of the context is as follows: when a string
+           with context C is used as a derivation attribute, then the
+           derivations in C will be added to the inputDrvs of the
+           derivation, and the other store paths in C will be added to
+           the inputSrcs of the derivations.
+
+           For canonicity, the store paths should be in sorted order. */
+        struct {
+            const char * s;
+            const char * * context; // must be in sorted order
+        } string;
+
+        const char * path;
+        Bindings * attrs;
+        struct {
+            unsigned int length;
+            Value * * elems;
+        } list;
+        struct {
+            Env * env;
+            Expr * expr;
+        } thunk;
+        struct {
+            Value * left, * right;
+        } app;
+        struct {
+            Env * env;
+            ExprLambda * fun;
+        } lambda;
+        PrimOp * primOp;
+        struct {
+            Value * left, * right;
+        } primOpApp;
+    };
+};
+
+
+/* After overwriting an app node, be sure to clear pointers in the
+   Value to ensure that the target isn't kept alive unnecessarily. */
+static inline void clearValue(Value & v)
+{
+    v.app.right = 0;
+}
+
+
+static inline void mkInt(Value & v, NixInt n)
+{
+    clearValue(v);
+    v.type = tInt;
+    v.integer = n;
+}
+
+
+static inline void mkBool(Value & v, bool b)
+{
+    clearValue(v);
+    v.type = tBool;
+    v.boolean = b;
+}
+
+
+static inline void mkNull(Value & v)
+{
+    v.type = tNull;
+    v.app.left = v.app.right = 00; // scrub
+}
+
+
+static inline void mkApp(Value & v, Value & left, Value & right)
+{
+    v.type = tApp;
+    v.app.left = &left;
+    v.app.right = &right;
+}
+
+
+static inline void mkStringNoCopy(Value & v, const char * s)
+{
+    v.type = tString;
+    v.string.s = s;
+    v.string.context = 0;
+}
+
+
+static inline void mkString(Value & v, const Symbol & s)
+{
+    mkStringNoCopy(v, ((const string &) s).c_str());
+}
+
+
+void mkString(Value & v, const char * s);
+
+
+static inline void mkPathNoCopy(Value & v, const char * s)
+{
+    clearValue(v);
+    v.type = tPath;
+    v.path = s;
+}
+
+
+void mkPath(Value & v, const char * s);
+
+
+}
diff --git a/src/libmain/local.mk b/src/libmain/local.mk
new file mode 100644
index 000000000000..71a07d1979ab
--- /dev/null
+++ b/src/libmain/local.mk
@@ -0,0 +1,11 @@
+libraries += libmain
+
+libmain_NAME = libnixmain
+
+libmain_DIR := $(d)
+
+libmain_SOURCES := $(wildcard $(d)/*.cc)
+
+libmain_LIBS = libstore libutil libformat
+
+libmain_ALLOW_UNDEFINED = 1
diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
new file mode 100644
index 000000000000..fb70cb076732
--- /dev/null
+++ b/src/libmain/shared.cc
@@ -0,0 +1,297 @@
+#include "config.h"
+
+#include "shared.hh"
+#include "globals.hh"
+#include "store-api.hh"
+#include "util.hh"
+#include "misc.hh"
+
+#include <iostream>
+#include <cctype>
+#include <exception>
+
+#include <sys/time.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <signal.h>
+
+
+namespace nix {
+
+
+volatile sig_atomic_t blockInt = 0;
+
+
+static void sigintHandler(int signo)
+{
+    if (!blockInt) {
+        _isInterrupted = 1;
+        blockInt = 1;
+    }
+}
+
+
+static bool gcWarning = true;
+
+void printGCWarning()
+{
+    if (!gcWarning) return;
+    static bool haveWarned = false;
+    warnOnce(haveWarned,
+        "you did not specify `--add-root'; "
+        "the result might be removed by the garbage collector");
+}
+
+
+void printMissing(StoreAPI & store, const PathSet & paths)
+{
+    unsigned long long downloadSize, narSize;
+    PathSet willBuild, willSubstitute, unknown;
+    queryMissing(store, paths, willBuild, willSubstitute, unknown, downloadSize, narSize);
+    printMissing(willBuild, willSubstitute, unknown, downloadSize, narSize);
+}
+
+
+void printMissing(const PathSet & willBuild,
+    const PathSet & willSubstitute, const PathSet & unknown,
+    unsigned long long downloadSize, unsigned long long narSize)
+{
+    if (!willBuild.empty()) {
+        printMsg(lvlInfo, format("these derivations will be built:"));
+        foreach (PathSet::iterator, i, willBuild)
+            printMsg(lvlInfo, format("  %1%") % *i);
+    }
+
+    if (!willSubstitute.empty()) {
+        printMsg(lvlInfo, format("these paths will be fetched (%.2f MiB download, %.2f MiB unpacked):")
+            % (downloadSize / (1024.0 * 1024.0))
+            % (narSize / (1024.0 * 1024.0)));
+        foreach (PathSet::iterator, i, willSubstitute)
+            printMsg(lvlInfo, format("  %1%") % *i);
+    }
+
+    if (!unknown.empty()) {
+        printMsg(lvlInfo, format("don't know how to build these paths%1%:")
+            % (settings.readOnlyMode ? " (may be caused by read-only store access)" : ""));
+        foreach (PathSet::iterator, i, unknown)
+            printMsg(lvlInfo, format("  %1%") % *i);
+    }
+}
+
+
+static void setLogType(string lt)
+{
+    if (lt == "pretty") logType = ltPretty;
+    else if (lt == "escapes") logType = ltEscapes;
+    else if (lt == "flat") logType = ltFlat;
+    else throw UsageError("unknown log type");
+}
+
+
+string getArg(const string & opt,
+    Strings::iterator & i, const Strings::iterator & end)
+{
+    ++i;
+    if (i == end) throw UsageError(format("`%1%' requires an argument") % opt);
+    return *i;
+}
+
+
+void detectStackOverflow();
+
+
+/* Initialize and reorder arguments, then call the actual argument
+   processor. */
+static void initAndRun(int argc, char * * argv)
+{
+    settings.processEnvironment();
+    settings.loadConfFile();
+
+    /* Catch SIGINT. */
+    struct sigaction act;
+    act.sa_handler = sigintHandler;
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    if (sigaction(SIGINT, &act, 0))
+        throw SysError("installing handler for SIGINT");
+    if (sigaction(SIGTERM, &act, 0))
+        throw SysError("installing handler for SIGTERM");
+    if (sigaction(SIGHUP, &act, 0))
+        throw SysError("installing handler for SIGHUP");
+
+    /* Ignore SIGPIPE. */
+    act.sa_handler = SIG_IGN;
+    act.sa_flags = 0;
+    if (sigaction(SIGPIPE, &act, 0))
+        throw SysError("ignoring SIGPIPE");
+
+    /* Reset SIGCHLD to its default. */
+    act.sa_handler = SIG_DFL;
+    act.sa_flags = 0;
+    if (sigaction(SIGCHLD, &act, 0))
+        throw SysError("resetting SIGCHLD");
+
+    /* Register a SIGSEGV handler to detect stack overflows. */
+    detectStackOverflow();
+
+    /* There is no privacy in the Nix system ;-)  At least not for
+       now.  In particular, store objects should be readable by
+       everybody. */
+    umask(0022);
+
+    /* Initialise the PRNG. */
+    struct timeval tv;
+    gettimeofday(&tv, 0);
+    srandom(tv.tv_usec);
+
+    /* Process the NIX_LOG_TYPE environment variable. */
+    string lt = getEnv("NIX_LOG_TYPE");
+    if (lt != "") setLogType(lt);
+
+    /* Put the arguments in a vector. */
+    Strings args, remaining;
+    while (argc--) args.push_back(*argv++);
+    args.erase(args.begin());
+
+    /* Expand compound dash options (i.e., `-qlf' -> `-q -l -f'), and
+       ignore options for the ATerm library. */
+    for (Strings::iterator i = args.begin(); i != args.end(); ++i) {
+        string arg = *i;
+        if (arg.length() > 2 && arg[0] == '-' && arg[1] != '-' && !isdigit(arg[1])) {
+            for (unsigned int j = 1; j < arg.length(); j++)
+                if (isalpha(arg[j]))
+                    remaining.push_back((string) "-" + arg[j]);
+                else     {
+                    remaining.push_back(string(arg, j));
+                    break;
+                }
+        } else remaining.push_back(arg);
+    }
+    args = remaining;
+    remaining.clear();
+
+    /* Process default options. */
+    for (Strings::iterator i = args.begin(); i != args.end(); ++i) {
+        string arg = *i;
+        if (arg == "--verbose" || arg == "-v") verbosity = (Verbosity) (verbosity + 1);
+        else if (arg == "--quiet") verbosity = verbosity > lvlError ? (Verbosity) (verbosity - 1) : lvlError;
+        else if (arg == "--log-type") {
+            string s = getArg(arg, i, args.end());
+            setLogType(s);
+        }
+        else if (arg == "--no-build-output" || arg == "-Q")
+            settings.buildVerbosity = lvlVomit;
+        else if (arg == "--print-build-trace")
+            settings.printBuildTrace = true;
+        else if (arg == "--help") {
+            printHelp();
+            return;
+        }
+        else if (arg == "--version") {
+            std::cout << format("%1% (Nix) %2%") % programId % nixVersion << std::endl;
+            return;
+        }
+        else if (arg == "--keep-failed" || arg == "-K")
+            settings.keepFailed = true;
+        else if (arg == "--keep-going" || arg == "-k")
+            settings.keepGoing = true;
+        else if (arg == "--fallback")
+            settings.set("build-fallback", "true");
+        else if (arg == "--max-jobs" || arg == "-j")
+            settings.set("build-max-jobs", getArg(arg, i, args.end()));
+        else if (arg == "--cores")
+            settings.set("build-cores", getArg(arg, i, args.end()));
+        else if (arg == "--readonly-mode")
+            settings.readOnlyMode = true;
+        else if (arg == "--max-silent-time")
+            settings.set("build-max-silent-time", getArg(arg, i, args.end()));
+        else if (arg == "--timeout")
+            settings.set("build-timeout", getArg(arg, i, args.end()));
+        else if (arg == "--no-build-hook")
+            settings.useBuildHook = false;
+        else if (arg == "--show-trace")
+            settings.showTrace = true;
+        else if (arg == "--no-gc-warning")
+            gcWarning = false;
+        else if (arg == "--option") {
+            ++i; if (i == args.end()) throw UsageError("`--option' requires two arguments");
+            string name = *i;
+            ++i; if (i == args.end()) throw UsageError("`--option' requires two arguments");
+            string value = *i;
+            settings.set(name, value);
+        }
+        else remaining.push_back(arg);
+    }
+
+    settings.update();
+
+    run(remaining);
+
+    /* Close the Nix database. */
+    store.reset((StoreAPI *) 0);
+}
+
+
+void showManPage(const string & name)
+{
+    string cmd = "man " + name;
+    if (system(cmd.c_str()) != 0)
+        throw Error(format("command `%1%' failed") % cmd);
+}
+
+
+int exitCode = 0;
+char * * argvSaved = 0;
+
+}
+
+
+static char buf[1024];
+
+int main(int argc, char * * argv)
+{
+    using namespace nix;
+
+    argvSaved = argv;
+
+    /* Turn on buffering for cerr. */
+#if HAVE_PUBSETBUF
+    std::cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
+#endif
+
+    std::ios::sync_with_stdio(false);
+
+    try {
+        try {
+            initAndRun(argc, argv);
+        } catch (...) {
+            /* Subtle: we have to make sure that any `interrupted'
+               condition is discharged before we reach printMsg()
+               below, since otherwise it will throw an (uncaught)
+               exception. */
+            blockInt = 1; /* ignore further SIGINTs */
+            _isInterrupted = 0;
+            throw;
+        }
+    } catch (UsageError & e) {
+        printMsg(lvlError,
+            format(
+                "error: %1%\n"
+                "Try `%2% --help' for more information.")
+            % e.what() % programId);
+        return 1;
+    } catch (BaseError & e) {
+        printMsg(lvlError, format("error: %1%%2%") % (settings.showTrace ? e.prefix() : "") % e.msg());
+        if (e.prefix() != "" && !settings.showTrace)
+            printMsg(lvlError, "(use `--show-trace' to show detailed location information)");
+        return e.status;
+    } catch (std::bad_alloc & e) {
+        printMsg(lvlError, "error: out of memory");
+        return 1;
+    } catch (std::exception & e) {
+        printMsg(lvlError, format("error: %1%") % e.what());
+        return 1;
+    }
+
+    return exitCode;
+}
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
new file mode 100644
index 000000000000..ff89e86389c2
--- /dev/null
+++ b/src/libmain/shared.hh
@@ -0,0 +1,58 @@
+#pragma once
+
+#include "util.hh"
+
+#include <signal.h>
+
+
+/* These are not implemented here, but must be implemented by a
+   program linking against libmain. */
+
+/* Main program.  Called by main() after the ATerm library has been
+   initialised and some default arguments have been processed (and
+   removed from `args').  main() will catch all exceptions. */
+void run(nix::Strings args);
+
+/* Should print a help message to stdout and return. */
+void printHelp();
+
+extern std::string programId;
+
+
+namespace nix {
+
+MakeError(UsageError, nix::Error);
+
+class StoreAPI;
+
+/* Ugh.  No better place to put this. */
+void printGCWarning();
+
+void printMissing(StoreAPI & store, const PathSet & paths);
+
+void printMissing(const PathSet & willBuild,
+    const PathSet & willSubstitute, const PathSet & unknown,
+    unsigned long long downloadSize, unsigned long long narSize);
+
+template<class N> N getIntArg(const string & opt,
+    Strings::iterator & i, const Strings::iterator & end)
+{
+    ++i;
+    if (i == end) throw UsageError(format("`%1%' requires an argument") % opt);
+    N n;
+    if (!string2Int(*i, n))
+        throw UsageError(format("`%1%' requires an integer argument") % opt);
+    return n;
+}
+
+/* Show the manual page for the specified program. */
+void showManPage(const string & name);
+
+extern volatile ::sig_atomic_t blockInt;
+
+/* Exit code of the program. */
+extern int exitCode;
+
+extern char * * argvSaved;
+
+}
diff --git a/src/libmain/stack.cc b/src/libmain/stack.cc
new file mode 100644
index 000000000000..64df95547e0b
--- /dev/null
+++ b/src/libmain/stack.cc
@@ -0,0 +1,72 @@
+#include "config.h"
+
+#include "types.hh"
+
+#include <cstring>
+#include <cstddef>
+#include <cstdlib>
+
+#include <unistd.h>
+#include <signal.h>
+
+namespace nix {
+
+
+static void sigsegvHandler(int signo, siginfo_t * info, void * ctx)
+{
+    /* Detect stack overflows by comparing the faulting address with
+       the stack pointer.  Unfortunately, getting the stack pointer is
+       not portable. */
+    bool haveSP = true;
+    char * sp;
+#if defined(__x86_64__) && defined(REG_RSP)
+    sp = (char *) ((ucontext *) ctx)->uc_mcontext.gregs[REG_RSP];
+#elif defined(REG_ESP)
+    sp = (char *) ((ucontext *) ctx)->uc_mcontext.gregs[REG_ESP];
+#else
+    haveSP = false;
+#endif
+
+    if (haveSP) {
+        ptrdiff_t diff = (char *) info->si_addr - sp;
+        if (diff < 0) diff = -diff;
+        if (diff < 4096) {
+            char msg[] = "error: stack overflow (possible infinite recursion)\n";
+            write(2, msg, strlen(msg));
+            _exit(1); // maybe abort instead?
+        }
+    }
+
+    /* Restore default behaviour (i.e. segfault and dump core). */
+    struct sigaction act;
+    sigfillset(&act.sa_mask);
+    act.sa_handler = SIG_DFL;
+    act.sa_flags = 0;
+    if (sigaction(SIGSEGV, &act, 0)) abort();
+}
+
+
+void detectStackOverflow()
+{
+#if defined(SA_SIGINFO) && defined (SA_ONSTACK)
+    /* Install a SIGSEGV handler to detect stack overflows.  This
+       requires an alternative stack, otherwise the signal cannot be
+       delivered when we're out of stack space. */
+    stack_t stack;
+    stack.ss_size = 4096 * 4 + MINSIGSTKSZ;
+    stack.ss_sp = new char[stack.ss_size];
+    if (!stack.ss_sp) throw Error("cannot allocate alternative stack");
+    stack.ss_flags = 0;
+    if (sigaltstack(&stack, 0) == -1) throw SysError("cannot set alternative stack");
+
+    struct sigaction act;
+    sigfillset(&act.sa_mask);
+    act.sa_sigaction = sigsegvHandler;
+    act.sa_flags = SA_SIGINFO | SA_ONSTACK;
+    if (sigaction(SIGSEGV, &act, 0))
+        throw SysError("resetting SIGCHLD");
+#endif
+}
+
+
+}
diff --git a/src/libstore/build.cc b/src/libstore/build.cc
new file mode 100644
index 000000000000..1b379752fa0e
--- /dev/null
+++ b/src/libstore/build.cc
@@ -0,0 +1,3258 @@
+#include "config.h"
+
+#include "references.hh"
+#include "pathlocks.hh"
+#include "misc.hh"
+#include "globals.hh"
+#include "local-store.hh"
+#include "util.hh"
+#include "archive.hh"
+#include "affinity.hh"
+
+#include <map>
+#include <sstream>
+#include <algorithm>
+#include <boost/shared_ptr.hpp>
+#include <boost/weak_ptr.hpp>
+#include <boost/enable_shared_from_this.hpp>
+
+#include <time.h>
+#include <sys/time.h>
+#include <sys/wait.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/utsname.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <cstring>
+
+#include <pwd.h>
+#include <grp.h>
+
+#include <bzlib.h>
+
+
+/* Includes required for chroot support. */
+#if HAVE_SYS_PARAM_H
+#include <sys/param.h>
+#endif
+#if HAVE_SYS_MOUNT_H
+#include <sys/mount.h>
+#endif
+#if HAVE_SCHED_H
+#include <sched.h>
+#endif
+
+/* In GNU libc 2.11, <sys/mount.h> does not define `MS_PRIVATE', but
+   <linux/fs.h> does.  */
+#if !defined MS_PRIVATE && defined HAVE_LINUX_FS_H
+#include <linux/fs.h>
+#endif
+
+#define CHROOT_ENABLED HAVE_CHROOT && HAVE_UNSHARE && HAVE_SYS_MOUNT_H && defined(MS_BIND) && defined(MS_PRIVATE) && defined(CLONE_NEWNS)
+
+#if CHROOT_ENABLED
+#include <sys/socket.h>
+#include <sys/ioctl.h>
+#include <net/if.h>
+#include <netinet/ip.h>
+#endif
+
+
+#if HAVE_SYS_PERSONALITY_H
+#include <sys/personality.h>
+#define CAN_DO_LINUX32_BUILDS
+#endif
+
+
+namespace nix {
+
+using std::map;
+
+
+static string pathNullDevice = "/dev/null";
+
+
+/* Forward definition. */
+class Worker;
+struct HookInstance;
+
+
+/* A pointer to a goal. */
+class Goal;
+typedef boost::shared_ptr<Goal> GoalPtr;
+typedef boost::weak_ptr<Goal> WeakGoalPtr;
+
+/* Set of goals. */
+typedef set<GoalPtr> Goals;
+typedef set<WeakGoalPtr> WeakGoals;
+
+/* A map of paths to goals (and the other way around). */
+typedef map<Path, WeakGoalPtr> WeakGoalMap;
+
+
+
+class Goal : public boost::enable_shared_from_this<Goal>
+{
+public:
+    typedef enum {ecBusy, ecSuccess, ecFailed, ecNoSubstituters, ecIncompleteClosure} ExitCode;
+
+protected:
+
+    /* Backlink to the worker. */
+    Worker & worker;
+
+    /* Goals that this goal is waiting for. */
+    Goals waitees;
+
+    /* Goals waiting for this one to finish.  Must use weak pointers
+       here to prevent cycles. */
+    WeakGoals waiters;
+
+    /* Number of goals we are/were waiting for that have failed. */
+    unsigned int nrFailed;
+
+    /* Number of substitution goals we are/were waiting for that
+       failed because there are no substituters. */
+    unsigned int nrNoSubstituters;
+
+    /* Number of substitution goals we are/were waiting for that
+       failed because othey had unsubstitutable references. */
+    unsigned int nrIncompleteClosure;
+
+    /* Name of this goal for debugging purposes. */
+    string name;
+
+    /* Whether the goal is finished. */
+    ExitCode exitCode;
+
+    Goal(Worker & worker) : worker(worker)
+    {
+        nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
+        exitCode = ecBusy;
+    }
+
+    virtual ~Goal()
+    {
+        trace("goal destroyed");
+    }
+
+public:
+    virtual void work() = 0;
+
+    void addWaitee(GoalPtr waitee);
+
+    virtual void waiteeDone(GoalPtr waitee, ExitCode result);
+
+    virtual void handleChildOutput(int fd, const string & data)
+    {
+        abort();
+    }
+
+    virtual void handleEOF(int fd)
+    {
+        abort();
+    }
+
+    void trace(const format & f);
+
+    string getName()
+    {
+        return name;
+    }
+
+    ExitCode getExitCode()
+    {
+        return exitCode;
+    }
+
+    /* Cancel the goal.  It should wake up its waiters, get rid of any
+       running child processes that are being monitored by the worker
+       (important!), etc. */
+    virtual void cancel(bool timeout) = 0;
+
+protected:
+    void amDone(ExitCode result);
+};
+
+
+/* A mapping used to remember for each child process to what goal it
+   belongs, and file descriptors for receiving log data and output
+   path creation commands. */
+struct Child
+{
+    WeakGoalPtr goal;
+    set<int> fds;
+    bool respectTimeouts;
+    bool inBuildSlot;
+    time_t lastOutput; /* time we last got output on stdout/stderr */
+    time_t timeStarted;
+};
+
+typedef map<pid_t, Child> Children;
+
+
+/* The worker class. */
+class Worker
+{
+private:
+
+    /* Note: the worker should only have strong pointers to the
+       top-level goals. */
+
+    /* The top-level goals of the worker. */
+    Goals topGoals;
+
+    /* Goals that are ready to do some work. */
+    WeakGoals awake;
+
+    /* Goals waiting for a build slot. */
+    WeakGoals wantingToBuild;
+
+    /* Child processes currently running. */
+    Children children;
+
+    /* Number of build slots occupied.  This includes local builds and
+       substitutions but not remote builds via the build hook. */
+    unsigned int nrLocalBuilds;
+
+    /* Maps used to prevent multiple instantiations of a goal for the
+       same derivation / path. */
+    WeakGoalMap derivationGoals;
+    WeakGoalMap substitutionGoals;
+
+    /* Goals waiting for busy paths to be unlocked. */
+    WeakGoals waitingForAnyGoal;
+
+    /* Goals sleeping for a few seconds (polling a lock). */
+    WeakGoals waitingForAWhile;
+
+    /* Last time the goals in `waitingForAWhile' where woken up. */
+    time_t lastWokenUp;
+
+public:
+
+    /* Set if at least one derivation had a BuildError (i.e. permanent
+       failure). */
+    bool permanentFailure;
+
+    LocalStore & store;
+
+    boost::shared_ptr<HookInstance> hook;
+
+    Worker(LocalStore & store);
+    ~Worker();
+
+    /* Make a goal (with caching). */
+    GoalPtr makeDerivationGoal(const Path & drvPath, const StringSet & wantedOutputs, bool repair = false);
+    GoalPtr makeSubstitutionGoal(const Path & storePath, bool repair = false);
+
+    /* Remove a dead goal. */
+    void removeGoal(GoalPtr goal);
+
+    /* Wake up a goal (i.e., there is something for it to do). */
+    void wakeUp(GoalPtr goal);
+
+    /* Return the number of local build and substitution processes
+       currently running (but not remote builds via the build
+       hook). */
+    unsigned int getNrLocalBuilds();
+
+    /* Registers a running child process.  `inBuildSlot' means that
+       the process counts towards the jobs limit. */
+    void childStarted(GoalPtr goal, pid_t pid,
+        const set<int> & fds, bool inBuildSlot, bool respectTimeouts);
+
+    /* Unregisters a running child process.  `wakeSleepers' should be
+       false if there is no sense in waking up goals that are sleeping
+       because they can't run yet (e.g., there is no free build slot,
+       or the hook would still say `postpone'). */
+    void childTerminated(pid_t pid, bool wakeSleepers = true);
+
+    /* Put `goal' to sleep until a build slot becomes available (which
+       might be right away). */
+    void waitForBuildSlot(GoalPtr goal);
+
+    /* Wait for any goal to finish.  Pretty indiscriminate way to
+       wait for some resource that some other goal is holding. */
+    void waitForAnyGoal(GoalPtr goal);
+
+    /* Wait for a few seconds and then retry this goal.  Used when
+       waiting for a lock held by another process.  This kind of
+       polling is inefficient, but POSIX doesn't really provide a way
+       to wait for multiple locks in the main select() loop. */
+    void waitForAWhile(GoalPtr goal);
+
+    /* Loop until the specified top-level goals have finished. */
+    void run(const Goals & topGoals);
+
+    /* Wait for input to become available. */
+    void waitForInput();
+
+    unsigned int exitStatus();
+};
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+void Goal::addWaitee(GoalPtr waitee)
+{
+    waitees.insert(waitee);
+    waitee->waiters.insert(shared_from_this());
+}
+
+
+void Goal::waiteeDone(GoalPtr waitee, ExitCode result)
+{
+    assert(waitees.find(waitee) != waitees.end());
+    waitees.erase(waitee);
+
+    trace(format("waitee `%1%' done; %2% left") %
+        waitee->name % waitees.size());
+
+    if (result == ecFailed || result == ecNoSubstituters || result == ecIncompleteClosure) ++nrFailed;
+
+    if (result == ecNoSubstituters) ++nrNoSubstituters;
+
+    if (result == ecIncompleteClosure) ++nrIncompleteClosure;
+
+    if (waitees.empty() || (result == ecFailed && !settings.keepGoing)) {
+
+        /* If we failed and keepGoing is not set, we remove all
+           remaining waitees. */
+        foreach (Goals::iterator, i, waitees) {
+            GoalPtr goal = *i;
+            WeakGoals waiters2;
+            foreach (WeakGoals::iterator, j, goal->waiters)
+                if (j->lock() != shared_from_this()) waiters2.insert(*j);
+            goal->waiters = waiters2;
+        }
+        waitees.clear();
+
+        worker.wakeUp(shared_from_this());
+    }
+}
+
+
+void Goal::amDone(ExitCode result)
+{
+    trace("done");
+    assert(exitCode == ecBusy);
+    assert(result == ecSuccess || result == ecFailed || result == ecNoSubstituters || result == ecIncompleteClosure);
+    exitCode = result;
+    foreach (WeakGoals::iterator, i, waiters) {
+        GoalPtr goal = i->lock();
+        if (goal) goal->waiteeDone(shared_from_this(), result);
+    }
+    waiters.clear();
+    worker.removeGoal(shared_from_this());
+}
+
+
+void Goal::trace(const format & f)
+{
+    debug(format("%1%: %2%") % name % f);
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+/* Common initialisation performed in child processes. */
+static void commonChildInit(Pipe & logPipe)
+{
+    restoreAffinity();
+
+    /* Put the child in a separate session (and thus a separate
+       process group) so that it has no controlling terminal (meaning
+       that e.g. ssh cannot open /dev/tty) and it doesn't receive
+       terminal signals. */
+    if (setsid() == -1)
+        throw SysError(format("creating a new session"));
+
+    /* Dup the write side of the logger pipe into stderr. */
+    if (dup2(logPipe.writeSide, STDERR_FILENO) == -1)
+        throw SysError("cannot pipe standard error into log file");
+
+    /* Dup stderr to stdout. */
+    if (dup2(STDERR_FILENO, STDOUT_FILENO) == -1)
+        throw SysError("cannot dup stderr into stdout");
+
+    /* Reroute stdin to /dev/null. */
+    int fdDevNull = open(pathNullDevice.c_str(), O_RDWR);
+    if (fdDevNull == -1)
+        throw SysError(format("cannot open `%1%'") % pathNullDevice);
+    if (dup2(fdDevNull, STDIN_FILENO) == -1)
+        throw SysError("cannot dup null device into stdin");
+    close(fdDevNull);
+}
+
+
+/* Convert a string list to an array of char pointers.  Careful: the
+   string list should outlive the array. */
+const char * * strings2CharPtrs(const Strings & ss)
+{
+    const char * * arr = new const char * [ss.size() + 1];
+    const char * * p = arr;
+    foreach (Strings::const_iterator, i, ss) *p++ = i->c_str();
+    *p = 0;
+    return arr;
+}
+
+
+/* Restore default handling of SIGPIPE, otherwise some programs will
+   randomly say "Broken pipe". */
+static void restoreSIGPIPE()
+{
+    struct sigaction act, oact;
+    act.sa_handler = SIG_DFL;
+    act.sa_flags = 0;
+    if (sigaction(SIGPIPE, &act, &oact)) throw SysError("resetting SIGPIPE");
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+class UserLock
+{
+private:
+    /* POSIX locks suck.  If we have a lock on a file, and we open and
+       close that file again (without closing the original file
+       descriptor), we lose the lock.  So we have to be *very* careful
+       not to open a lock file on which we are holding a lock. */
+    static PathSet lockedPaths; /* !!! not thread-safe */
+
+    Path fnUserLock;
+    AutoCloseFD fdUserLock;
+
+    string user;
+    uid_t uid;
+    gid_t gid;
+
+public:
+    UserLock();
+    ~UserLock();
+
+    void acquire();
+    void release();
+
+    void kill();
+
+    string getUser() { return user; }
+    uid_t getUID() { return uid; }
+    uid_t getGID() { return gid; }
+
+    bool enabled() { return uid != 0; }
+
+};
+
+
+PathSet UserLock::lockedPaths;
+
+
+UserLock::UserLock()
+{
+    uid = gid = 0;
+}
+
+
+UserLock::~UserLock()
+{
+    release();
+}
+
+
+void UserLock::acquire()
+{
+    assert(uid == 0);
+
+    assert(settings.buildUsersGroup != "");
+
+    /* Get the members of the build-users-group. */
+    struct group * gr = getgrnam(settings.buildUsersGroup.c_str());
+    if (!gr)
+        throw Error(format("the group `%1%' specified in `build-users-group' does not exist")
+            % settings.buildUsersGroup);
+    gid = gr->gr_gid;
+
+    /* Copy the result of getgrnam. */
+    Strings users;
+    for (char * * p = gr->gr_mem; *p; ++p) {
+        debug(format("found build user `%1%'") % *p);
+        users.push_back(*p);
+    }
+
+    if (users.empty())
+        throw Error(format("the build users group `%1%' has no members")
+            % settings.buildUsersGroup);
+
+    /* Find a user account that isn't currently in use for another
+       build. */
+    foreach (Strings::iterator, i, users) {
+        debug(format("trying user `%1%'") % *i);
+
+        struct passwd * pw = getpwnam(i->c_str());
+        if (!pw)
+            throw Error(format("the user `%1%' in the group `%2%' does not exist")
+                % *i % settings.buildUsersGroup);
+
+        createDirs(settings.nixStateDir + "/userpool");
+
+        fnUserLock = (format("%1%/userpool/%2%") % settings.nixStateDir % pw->pw_uid).str();
+
+        if (lockedPaths.find(fnUserLock) != lockedPaths.end())
+            /* We already have a lock on this one. */
+            continue;
+
+        AutoCloseFD fd = open(fnUserLock.c_str(), O_RDWR | O_CREAT, 0600);
+        if (fd == -1)
+            throw SysError(format("opening user lock `%1%'") % fnUserLock);
+        closeOnExec(fd);
+
+        if (lockFile(fd, ltWrite, false)) {
+            fdUserLock = fd.borrow();
+            lockedPaths.insert(fnUserLock);
+            user = *i;
+            uid = pw->pw_uid;
+
+            /* Sanity check... */
+            if (uid == getuid() || uid == geteuid())
+                throw Error(format("the Nix user should not be a member of `%1%'")
+                    % settings.buildUsersGroup);
+
+            return;
+        }
+    }
+
+    throw Error(format("all build users are currently in use; "
+        "consider creating additional users and adding them to the `%1%' group")
+        % settings.buildUsersGroup);
+}
+
+
+void UserLock::release()
+{
+    if (uid == 0) return;
+    fdUserLock.close(); /* releases lock */
+    assert(lockedPaths.find(fnUserLock) != lockedPaths.end());
+    lockedPaths.erase(fnUserLock);
+    fnUserLock = "";
+    uid = 0;
+}
+
+
+void UserLock::kill()
+{
+    assert(enabled());
+    killUser(uid);
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+struct HookInstance
+{
+    /* Pipes for talking to the build hook. */
+    Pipe toHook;
+
+    /* Pipe for the hook's standard output/error. */
+    Pipe fromHook;
+
+    /* Pipe for the builder's standard output/error. */
+    Pipe builderOut;
+
+    /* The process ID of the hook. */
+    Pid pid;
+
+    HookInstance();
+
+    ~HookInstance();
+};
+
+
+HookInstance::HookInstance()
+{
+    debug("starting build hook");
+
+    Path buildHook = absPath(getEnv("NIX_BUILD_HOOK"));
+
+    /* Create a pipe to get the output of the child. */
+    fromHook.create();
+
+    /* Create the communication pipes. */
+    toHook.create();
+
+    /* Create a pipe to get the output of the builder. */
+    builderOut.create();
+
+    /* Fork the hook. */
+    pid = maybeVfork();
+    switch (pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0:
+        try { /* child */
+
+            commonChildInit(fromHook);
+
+            if (chdir("/") == -1) throw SysError("changing into `/");
+
+            /* Dup the communication pipes. */
+            if (dup2(toHook.readSide, STDIN_FILENO) == -1)
+                throw SysError("dupping to-hook read side");
+
+            /* Use fd 4 for the builder's stdout/stderr. */
+            if (dup2(builderOut.writeSide, 4) == -1)
+                throw SysError("dupping builder's stdout/stderr");
+
+            execl(buildHook.c_str(), buildHook.c_str(), settings.thisSystem.c_str(),
+                (format("%1%") % settings.maxSilentTime).str().c_str(),
+                (format("%1%") % settings.printBuildTrace).str().c_str(),
+                (format("%1%") % settings.buildTimeout).str().c_str(),
+                NULL);
+
+            throw SysError(format("executing `%1%'") % buildHook);
+
+        } catch (std::exception & e) {
+            writeToStderr("build hook error: " + string(e.what()) + "\n");
+        }
+        _exit(1);
+    }
+
+    /* parent */
+    pid.setSeparatePG(true);
+    pid.setKillSignal(SIGTERM);
+    fromHook.writeSide.close();
+    toHook.readSide.close();
+}
+
+
+HookInstance::~HookInstance()
+{
+    try {
+        pid.kill();
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+typedef map<string, string> HashRewrites;
+
+
+string rewriteHashes(string s, const HashRewrites & rewrites)
+{
+    foreach (HashRewrites::const_iterator, i, rewrites) {
+        assert(i->first.size() == i->second.size());
+        size_t j = 0;
+        while ((j = s.find(i->first, j)) != string::npos) {
+            debug(format("rewriting @ %1%") % j);
+            s.replace(j, i->second.size(), i->second);
+        }
+    }
+    return s;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+typedef enum {rpAccept, rpDecline, rpPostpone} HookReply;
+
+class SubstitutionGoal;
+
+class DerivationGoal : public Goal
+{
+private:
+    /* The path of the derivation. */
+    Path drvPath;
+
+    /* The specific outputs that we need to build.  Empty means all of
+       them. */
+    StringSet wantedOutputs;
+
+    /* Whether additional wanted outputs have been added. */
+    bool needRestart;
+
+    /* Whether to retry substituting the outputs after building the
+       inputs. */
+    bool retrySubstitution;
+
+    /* The derivation stored at drvPath. */
+    Derivation drv;
+
+    /* The remainder is state held during the build. */
+
+    /* Locks on the output paths. */
+    PathLocks outputLocks;
+
+    /* All input paths (that is, the union of FS closures of the
+       immediate input paths). */
+    PathSet inputPaths;
+
+    /* Referenceable paths (i.e., input and output paths). */
+    PathSet allPaths;
+
+    /* Outputs that are already valid. */
+    PathSet validPaths;
+
+    /* Outputs that are corrupt or not valid. */
+    PathSet missingPaths;
+
+    /* Paths that have been subject to hash rewriting. */
+    PathSet rewrittenPaths;
+
+    /* User selected for running the builder. */
+    UserLock buildUser;
+
+    /* The process ID of the builder. */
+    Pid pid;
+
+    /* The temporary directory. */
+    Path tmpDir;
+
+    /* File descriptor for the log file. */
+    FILE * fLogFile;
+    BZFILE * bzLogFile;
+    AutoCloseFD fdLogFile;
+
+    /* Number of bytes received from the builder's stdout/stderr. */
+    unsigned long logSize;
+
+    /* Pipe for the builder's standard output/error. */
+    Pipe builderOut;
+
+    /* The build hook. */
+    boost::shared_ptr<HookInstance> hook;
+
+    /* Whether we're currently doing a chroot build. */
+    bool useChroot;
+
+    Path chrootRootDir;
+
+    /* RAII object to delete the chroot directory. */
+    boost::shared_ptr<AutoDelete> autoDelChroot;
+
+    /* All inputs that are regular files. */
+    PathSet regularInputPaths;
+
+    /* Whether this is a fixed-output derivation. */
+    bool fixedOutput;
+
+    typedef void (DerivationGoal::*GoalState)();
+    GoalState state;
+
+    /* Stuff we need to pass to initChild(). */
+    typedef map<Path, Path> DirsInChroot; // maps target path to source path
+    DirsInChroot dirsInChroot;
+    typedef map<string, string> Environment;
+    Environment env;
+
+    /* Hash rewriting. */
+    HashRewrites rewritesToTmp, rewritesFromTmp;
+    PathSet redirectedOutputs;
+
+    /* Whether we're repairing.  If set, a derivation will be rebuilt
+       if its outputs are valid but corrupt or missing. */
+    bool repair;
+    map<Path, Path> redirectedBadOutputs;
+
+    /* Set of inodes seen during calls to canonicalisePathMetaData()
+       for this build's outputs.  This needs to be shared between
+       outputs to allow hard links between outputs. */
+    InodesSeen inodesSeen;
+
+    /* Magic exit code denoting that setting up the child environment
+       failed.  (It's possible that the child actually returns the
+       exit code, but ah well.) */
+    const static int childSetupFailed = 189;
+
+public:
+    DerivationGoal(const Path & drvPath, const StringSet & wantedOutputs, Worker & worker, bool repair = false);
+    ~DerivationGoal();
+
+    void cancel(bool timeout);
+
+    void work();
+
+    Path getDrvPath()
+    {
+        return drvPath;
+    }
+
+    /* Add wanted outputs to an already existing derivation goal. */
+    void addWantedOutputs(const StringSet & outputs);
+
+private:
+    /* The states. */
+    void init();
+    void haveDerivation();
+    void outputsSubstituted();
+    void closureRepaired();
+    void inputsRealised();
+    void tryToBuild();
+    void buildDone();
+
+    /* Is the build hook willing to perform the build? */
+    HookReply tryBuildHook();
+
+    /* Start building a derivation. */
+    void startBuilder();
+
+    /* Initialise the builder's process. */
+    void initChild();
+
+    friend int childEntry(void *);
+
+    /* Must be called after the output paths have become valid (either
+       due to a successful build or hook, or because they already
+       were). */
+    void computeClosure();
+
+    /* Open a log file and a pipe to it. */
+    Path openLogFile();
+
+    /* Close the log file. */
+    void closeLogFile();
+
+    /* Delete the temporary directory, if we have one. */
+    void deleteTmpDir(bool force);
+
+    /* Callback used by the worker to write to the log. */
+    void handleChildOutput(int fd, const string & data);
+    void handleEOF(int fd);
+
+    /* Return the set of (in)valid paths. */
+    PathSet checkPathValidity(bool returnValid, bool checkHash);
+
+    /* Abort the goal if `path' failed to build. */
+    bool pathFailed(const Path & path);
+
+    /* Forcibly kill the child process, if any. */
+    void killChild();
+
+    Path addHashRewrite(const Path & path);
+
+    void repairClosure();
+};
+
+
+DerivationGoal::DerivationGoal(const Path & drvPath, const StringSet & wantedOutputs, Worker & worker, bool repair)
+    : Goal(worker)
+    , wantedOutputs(wantedOutputs)
+    , needRestart(false)
+    , retrySubstitution(false)
+    , fLogFile(0)
+    , bzLogFile(0)
+    , useChroot(false)
+    , repair(repair)
+{
+    this->drvPath = drvPath;
+    state = &DerivationGoal::init;
+    name = (format("building of `%1%'") % drvPath).str();
+    trace("created");
+}
+
+
+DerivationGoal::~DerivationGoal()
+{
+    /* Careful: we should never ever throw an exception from a
+       destructor. */
+    try {
+        killChild();
+        deleteTmpDir(false);
+        closeLogFile();
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void DerivationGoal::killChild()
+{
+    if (pid != -1) {
+        worker.childTerminated(pid);
+
+        if (buildUser.enabled()) {
+            /* If we're using a build user, then there is a tricky
+               race condition: if we kill the build user before the
+               child has done its setuid() to the build user uid, then
+               it won't be killed, and we'll potentially lock up in
+               pid.wait().  So also send a conventional kill to the
+               child. */
+            ::kill(-pid, SIGKILL); /* ignore the result */
+            buildUser.kill();
+            pid.wait(true);
+        } else
+            pid.kill();
+
+        assert(pid == -1);
+    }
+
+    hook.reset();
+}
+
+
+void DerivationGoal::cancel(bool timeout)
+{
+    if (settings.printBuildTrace && timeout)
+        printMsg(lvlError, format("@ build-failed %1% - timeout") % drvPath);
+    killChild();
+    amDone(ecFailed);
+}
+
+
+void DerivationGoal::work()
+{
+    (this->*state)();
+}
+
+
+void DerivationGoal::addWantedOutputs(const StringSet & outputs)
+{
+    /* If we already want all outputs, there is nothing to do. */
+    if (wantedOutputs.empty()) return;
+
+    if (outputs.empty()) {
+        wantedOutputs.clear();
+        needRestart = true;
+    } else
+        foreach (StringSet::const_iterator, i, outputs)
+            if (wantedOutputs.find(*i) == wantedOutputs.end()) {
+                wantedOutputs.insert(*i);
+                needRestart = true;
+            }
+}
+
+
+void DerivationGoal::init()
+{
+    trace("init");
+
+    if (settings.readOnlyMode)
+        throw Error(format("cannot build derivation `%1%' - no write access to the Nix store") % drvPath);
+
+    /* The first thing to do is to make sure that the derivation
+       exists.  If it doesn't, it may be created through a
+       substitute. */
+    addWaitee(worker.makeSubstitutionGoal(drvPath));
+
+    state = &DerivationGoal::haveDerivation;
+}
+
+
+void DerivationGoal::haveDerivation()
+{
+    trace("loading derivation");
+
+    if (nrFailed != 0) {
+        printMsg(lvlError, format("cannot build missing derivation `%1%'") % drvPath);
+        amDone(ecFailed);
+        return;
+    }
+
+    /* `drvPath' should already be a root, but let's be on the safe
+       side: if the user forgot to make it a root, we wouldn't want
+       things being garbage collected while we're busy. */
+    worker.store.addTempRoot(drvPath);
+
+    assert(worker.store.isValidPath(drvPath));
+
+    /* Get the derivation. */
+    drv = derivationFromPath(worker.store, drvPath);
+
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        worker.store.addTempRoot(i->second.path);
+
+    /* Check what outputs paths are not already valid. */
+    PathSet invalidOutputs = checkPathValidity(false, repair);
+
+    /* If they are all valid, then we're done. */
+    if (invalidOutputs.size() == 0 && !repair) {
+        amDone(ecSuccess);
+        return;
+    }
+
+    /* Check whether any output previously failed to build.  If so,
+       don't bother. */
+    foreach (PathSet::iterator, i, invalidOutputs)
+        if (pathFailed(*i)) return;
+
+    /* We are first going to try to create the invalid output paths
+       through substitutes.  If that doesn't work, we'll build
+       them. */
+    if (settings.useSubstitutes && !willBuildLocally(drv))
+        foreach (PathSet::iterator, i, invalidOutputs)
+            addWaitee(worker.makeSubstitutionGoal(*i, repair));
+
+    if (waitees.empty()) /* to prevent hang (no wake-up event) */
+        outputsSubstituted();
+    else
+        state = &DerivationGoal::outputsSubstituted;
+}
+
+
+void DerivationGoal::outputsSubstituted()
+{
+    trace("all outputs substituted (maybe)");
+
+    if (nrFailed > 0 && nrFailed > nrNoSubstituters + nrIncompleteClosure && !settings.tryFallback)
+        throw Error(format("some substitutes for the outputs of derivation `%1%' failed (usually happens due to networking issues); try `--fallback' to build derivation from source ") % drvPath);
+
+    /*  If the substitutes form an incomplete closure, then we should
+        build the dependencies of this derivation, but after that, we
+        can still use the substitutes for this derivation itself. */
+    if (nrIncompleteClosure > 0 && !retrySubstitution) retrySubstitution = true;
+
+    nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
+
+    if (needRestart) {
+        needRestart = false;
+        haveDerivation();
+        return;
+    }
+
+    if (checkPathValidity(false, repair).size() == 0) {
+        if (repair) repairClosure(); else amDone(ecSuccess);
+        return;
+    }
+
+    /* Otherwise, at least one of the output paths could not be
+       produced using a substitute.  So we have to build instead. */
+
+    /* Make sure checkPathValidity() from now on checks all
+       outputs. */
+    wantedOutputs = PathSet();
+
+    /* The inputs must be built before we can build this goal. */
+    foreach (DerivationInputs::iterator, i, drv.inputDrvs)
+        addWaitee(worker.makeDerivationGoal(i->first, i->second, repair));
+
+    foreach (PathSet::iterator, i, drv.inputSrcs)
+        addWaitee(worker.makeSubstitutionGoal(*i));
+
+    if (waitees.empty()) /* to prevent hang (no wake-up event) */
+        inputsRealised();
+    else
+        state = &DerivationGoal::inputsRealised;
+}
+
+
+void DerivationGoal::repairClosure()
+{
+    /* If we're repairing, we now know that our own outputs are valid.
+       Now check whether the other paths in the outputs closure are
+       good.  If not, then start derivation goals for the derivations
+       that produced those outputs. */
+
+    /* Get the output closure. */
+    PathSet outputClosure;
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        computeFSClosure(worker.store, i->second.path, outputClosure);
+
+    /* Filter out our own outputs (which we have already checked). */
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        outputClosure.erase(i->second.path);
+
+    /* Get all dependencies of this derivation so that we know which
+       derivation is responsible for which path in the output
+       closure. */
+    PathSet inputClosure;
+    computeFSClosure(worker.store, drvPath, inputClosure);
+    std::map<Path, Path> outputsToDrv;
+    foreach (PathSet::iterator, i, inputClosure)
+        if (isDerivation(*i)) {
+            Derivation drv = derivationFromPath(worker.store, *i);
+            foreach (DerivationOutputs::iterator, j, drv.outputs)
+                outputsToDrv[j->second.path] = *i;
+        }
+
+    /* Check each path (slow!). */
+    PathSet broken;
+    foreach (PathSet::iterator, i, outputClosure) {
+        if (worker.store.pathContentsGood(*i)) continue;
+        printMsg(lvlError, format("found corrupted or missing path `%1%' in the output closure of `%2%'") % *i % drvPath);
+        Path drvPath2 = outputsToDrv[*i];
+        if (drvPath2 == "")
+            addWaitee(worker.makeSubstitutionGoal(*i, true));
+        else
+            addWaitee(worker.makeDerivationGoal(drvPath2, PathSet(), true));
+    }
+
+    if (waitees.empty()) {
+        amDone(ecSuccess);
+        return;
+    }
+
+    state = &DerivationGoal::closureRepaired;
+}
+
+
+void DerivationGoal::closureRepaired()
+{
+    trace("closure repaired");
+    if (nrFailed > 0)
+        throw Error(format("some paths in the output closure of derivation `%1%' could not be repaired") % drvPath);
+    amDone(ecSuccess);
+}
+
+
+void DerivationGoal::inputsRealised()
+{
+    trace("all inputs realised");
+
+    if (nrFailed != 0) {
+        printMsg(lvlError,
+            format("cannot build derivation `%1%': "
+                "%2% dependencies couldn't be built")
+            % drvPath % nrFailed);
+        amDone(ecFailed);
+        return;
+    }
+
+    if (retrySubstitution) {
+        haveDerivation();
+        return;
+    }
+
+    /* Gather information necessary for computing the closure and/or
+       running the build hook. */
+
+    /* The outputs are referenceable paths. */
+    foreach (DerivationOutputs::iterator, i, drv.outputs) {
+        debug(format("building path `%1%'") % i->second.path);
+        allPaths.insert(i->second.path);
+    }
+
+    /* Determine the full set of input paths. */
+
+    /* First, the input derivations. */
+    foreach (DerivationInputs::iterator, i, drv.inputDrvs) {
+        /* Add the relevant output closures of the input derivation
+           `*i' as input paths.  Only add the closures of output paths
+           that are specified as inputs. */
+        assert(worker.store.isValidPath(i->first));
+        Derivation inDrv = derivationFromPath(worker.store, i->first);
+        foreach (StringSet::iterator, j, i->second)
+            if (inDrv.outputs.find(*j) != inDrv.outputs.end())
+                computeFSClosure(worker.store, inDrv.outputs[*j].path, inputPaths);
+            else
+                throw Error(
+                    format("derivation `%1%' requires non-existent output `%2%' from input derivation `%3%'")
+                    % drvPath % *j % i->first);
+    }
+
+    /* Second, the input sources. */
+    foreach (PathSet::iterator, i, drv.inputSrcs)
+        computeFSClosure(worker.store, *i, inputPaths);
+
+    debug(format("added input paths %1%") % showPaths(inputPaths));
+
+    allPaths.insert(inputPaths.begin(), inputPaths.end());
+
+    /* Is this a fixed-output derivation? */
+    fixedOutput = true;
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        if (i->second.hash == "") fixedOutput = false;
+
+    /* Okay, try to build.  Note that here we don't wait for a build
+       slot to become available, since we don't need one if there is a
+       build hook. */
+    state = &DerivationGoal::tryToBuild;
+    worker.wakeUp(shared_from_this());
+}
+
+
+PathSet outputPaths(const DerivationOutputs & outputs)
+{
+    PathSet paths;
+    foreach (DerivationOutputs::const_iterator, i, outputs)
+        paths.insert(i->second.path);
+    return paths;
+}
+
+
+static string get(const StringPairs & map, const string & key)
+{
+    StringPairs::const_iterator i = map.find(key);
+    return i == map.end() ? (string) "" : i->second;
+}
+
+
+static bool canBuildLocally(const string & platform)
+{
+    return platform == settings.thisSystem
+#ifdef CAN_DO_LINUX32_BUILDS
+        || (platform == "i686-linux" && settings.thisSystem == "x86_64-linux")
+#endif
+        ;
+}
+
+
+bool willBuildLocally(const Derivation & drv)
+{
+    return get(drv.env, "preferLocalBuild") == "1" && canBuildLocally(drv.platform);
+}
+
+
+void DerivationGoal::tryToBuild()
+{
+    trace("trying to build");
+
+    /* Check for the possibility that some other goal in this process
+       has locked the output since we checked in haveDerivation().
+       (It can't happen between here and the lockPaths() call below
+       because we're not allowing multi-threading.)  If so, put this
+       goal to sleep until another goal finishes, then try again. */
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        if (pathIsLockedByMe(i->second.path)) {
+            debug(format("putting derivation `%1%' to sleep because `%2%' is locked by another goal")
+                % drvPath % i->second.path);
+            worker.waitForAnyGoal(shared_from_this());
+            return;
+        }
+
+    /* Obtain locks on all output paths.  The locks are automatically
+       released when we exit this function or Nix crashes.  If we
+       can't acquire the lock, then continue; hopefully some other
+       goal can start a build, and if not, the main loop will sleep a
+       few seconds and then retry this goal. */
+    if (!outputLocks.lockPaths(outputPaths(drv.outputs), "", false)) {
+        worker.waitForAWhile(shared_from_this());
+        return;
+    }
+
+    /* Now check again whether the outputs are valid.  This is because
+       another process may have started building in parallel.  After
+       it has finished and released the locks, we can (and should)
+       reuse its results.  (Strictly speaking the first check can be
+       omitted, but that would be less efficient.)  Note that since we
+       now hold the locks on the output paths, no other process can
+       build this derivation, so no further checks are necessary. */
+    validPaths = checkPathValidity(true, repair);
+    if (validPaths.size() == drv.outputs.size()) {
+        debug(format("skipping build of derivation `%1%', someone beat us to it")
+            % drvPath);
+        outputLocks.setDeletion(true);
+        amDone(ecSuccess);
+        return;
+    }
+
+    missingPaths = outputPaths(drv.outputs);
+    foreach (PathSet::iterator, i, validPaths) missingPaths.erase(*i);
+
+    /* If any of the outputs already exist but are not valid, delete
+       them. */
+    foreach (DerivationOutputs::iterator, i, drv.outputs) {
+        Path path = i->second.path;
+        if (worker.store.isValidPath(path)) continue;
+        if (!pathExists(path)) continue;
+        debug(format("removing unregistered path `%1%'") % path);
+        deletePath(path);
+    }
+
+    /* Check again whether any output previously failed to build,
+       because some other process may have tried and failed before we
+       acquired the lock. */
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        if (pathFailed(i->second.path)) return;
+
+    /* Don't do a remote build if the derivation has the attribute
+       `preferLocalBuild' set. */
+    bool buildLocally = willBuildLocally(drv);
+
+    /* Is the build hook willing to accept this job? */
+    if (!buildLocally) {
+        switch (tryBuildHook()) {
+            case rpAccept:
+                /* Yes, it has started doing so.  Wait until we get
+                   EOF from the hook. */
+                state = &DerivationGoal::buildDone;
+                return;
+            case rpPostpone:
+                /* Not now; wait until at least one child finishes or
+                   the wake-up timeout expires. */
+                worker.waitForAWhile(shared_from_this());
+                outputLocks.unlock();
+                return;
+            case rpDecline:
+                /* We should do it ourselves. */
+                break;
+        }
+    }
+
+    /* Make sure that we are allowed to start a build.  If this
+       derivation prefers to be done locally, do it even if
+       maxBuildJobs is 0. */
+    unsigned int curBuilds = worker.getNrLocalBuilds();
+    if (curBuilds >= settings.maxBuildJobs && !(buildLocally && curBuilds == 0)) {
+        worker.waitForBuildSlot(shared_from_this());
+        outputLocks.unlock();
+        return;
+    }
+
+    try {
+
+        /* Okay, we have to build. */
+        startBuilder();
+
+    } catch (BuildError & e) {
+        printMsg(lvlError, e.msg());
+        outputLocks.unlock();
+        buildUser.release();
+        if (settings.printBuildTrace)
+            printMsg(lvlError, format("@ build-failed %1% - %2% %3%")
+                % drvPath % 0 % e.msg());
+        worker.permanentFailure = true;
+        amDone(ecFailed);
+        return;
+    }
+
+    /* This state will be reached when we get EOF on the child's
+       log pipe. */
+    state = &DerivationGoal::buildDone;
+}
+
+
+void replaceValidPath(const Path & storePath, const Path tmpPath)
+{
+    /* We can't atomically replace storePath (the original) with
+       tmpPath (the replacement), so we have to move it out of the
+       way first.  We'd better not be interrupted here, because if
+       we're repairing (say) Glibc, we end up with a broken system. */
+    Path oldPath = (format("%1%.old-%2%-%3%") % storePath % getpid() % rand()).str();
+    if (pathExists(storePath))
+        rename(storePath.c_str(), oldPath.c_str());
+    if (rename(tmpPath.c_str(), storePath.c_str()) == -1)
+        throw SysError(format("moving `%1%' to `%2%'") % tmpPath % storePath);
+    if (pathExists(oldPath))
+        deletePath(oldPath);
+}
+
+
+void DerivationGoal::buildDone()
+{
+    trace("build done");
+
+    /* Since we got an EOF on the logger pipe, the builder is presumed
+       to have terminated.  In fact, the builder could also have
+       simply have closed its end of the pipe --- just don't do that
+       :-) */
+    int status;
+    pid_t savedPid;
+    if (hook) {
+        savedPid = hook->pid;
+        status = hook->pid.wait(true);
+    } else {
+        /* !!! this could block! security problem! solution: kill the
+           child */
+        savedPid = pid;
+        status = pid.wait(true);
+    }
+
+    debug(format("builder process for `%1%' finished") % drvPath);
+
+    /* So the child is gone now. */
+    worker.childTerminated(savedPid);
+
+    /* Close the read side of the logger pipe. */
+    if (hook) {
+        hook->builderOut.readSide.close();
+        hook->fromHook.readSide.close();
+    }
+    else builderOut.readSide.close();
+
+    /* Close the log file. */
+    closeLogFile();
+
+    /* When running under a build user, make sure that all processes
+       running under that uid are gone.  This is to prevent a
+       malicious user from leaving behind a process that keeps files
+       open and modifies them after they have been chown'ed to
+       root. */
+    if (buildUser.enabled()) buildUser.kill();
+
+    try {
+
+        /* Some cleanup per path.  We do this here and not in
+           computeClosure() for convenience when the build has
+           failed. */
+        foreach (PathSet::iterator, i, missingPaths) {
+            Path path = *i;
+
+            /* If the output was already valid, just skip (discard) it. */
+            if (validPaths.find(path) != validPaths.end()) continue;
+
+            if (useChroot && pathExists(chrootRootDir + path)) {
+                /* Move output paths from the chroot to the Nix store. */
+                if (repair)
+                    replaceValidPath(path, chrootRootDir + path);
+                else
+                    if (rename((chrootRootDir + path).c_str(), path.c_str()) == -1)
+                        throw SysError(format("moving build output `%1%' from the chroot to the Nix store") % path);
+            }
+
+            Path redirected;
+            if (repair && (redirected = redirectedBadOutputs[path]) != "" && pathExists(redirected))
+                replaceValidPath(path, redirected);
+
+            if (!pathExists(path)) continue;
+
+            struct stat st;
+            if (lstat(path.c_str(), &st) == -1)
+                throw SysError(format("getting attributes of path `%1%'") % path);
+
+#ifndef __CYGWIN__
+            /* Check that the output is not group or world writable,
+               as that means that someone else can have interfered
+               with the build.  Also, the output should be owned by
+               the build user. */
+            if ((!S_ISLNK(st.st_mode) && (st.st_mode & (S_IWGRP | S_IWOTH))) ||
+                (buildUser.enabled() && st.st_uid != buildUser.getUID()))
+                throw BuildError(format("suspicious ownership or permission on `%1%'; rejecting this build output") % path);
+#endif
+
+            /* Apply hash rewriting if necessary. */
+            if (!rewritesFromTmp.empty()) {
+                printMsg(lvlError, format("warning: rewriting hashes in `%1%'; cross fingers") % path);
+
+                /* Canonicalise first.  This ensures that the path
+                   we're rewriting doesn't contain a hard link to
+                   /etc/shadow or something like that. */
+                canonicalisePathMetaData(path, buildUser.enabled() ? buildUser.getUID() : -1, inodesSeen);
+
+                /* FIXME: this is in-memory. */
+                StringSink sink;
+                dumpPath(path, sink);
+                deletePath(path);
+                sink.s = rewriteHashes(sink.s, rewritesFromTmp);
+                StringSource source(sink.s);
+                restorePath(path, source);
+
+                rewrittenPaths.insert(path);
+            }
+        }
+
+        /* Check the exit status. */
+        if (!statusOk(status)) {
+            deleteTmpDir(false);
+            if (WIFEXITED(status) && WEXITSTATUS(status) == childSetupFailed)
+                throw Error(format("failed to set up the build environment for `%1%'") % drvPath);
+            throw BuildError(format("builder for `%1%' %2%")
+                % drvPath % statusToString(status));
+        }
+
+        /* Delete the chroot (if we were using one). */
+        autoDelChroot.reset(); /* this runs the destructor */
+
+        /* Delete redirected outputs (when doing hash rewriting). */
+        foreach (PathSet::iterator, i, redirectedOutputs)
+            deletePath(*i);
+
+        /* Compute the FS closure of the outputs and register them as
+           being valid. */
+        computeClosure();
+
+        deleteTmpDir(true);
+
+        /* It is now safe to delete the lock files, since all future
+           lockers will see that the output paths are valid; they will
+           not create new lock files with the same names as the old
+           (unlinked) lock files. */
+        outputLocks.setDeletion(true);
+        outputLocks.unlock();
+
+    } catch (BuildError & e) {
+        printMsg(lvlError, e.msg());
+        outputLocks.unlock();
+        buildUser.release();
+
+        /* When using a build hook, the hook will return a remote
+           build failure using exit code 100.  Anything else is a hook
+           problem. */
+        bool hookError = hook &&
+            (!WIFEXITED(status) || WEXITSTATUS(status) != 100);
+
+        if (settings.printBuildTrace) {
+            if (hook && hookError)
+                printMsg(lvlError, format("@ hook-failed %1% - %2% %3%")
+                    % drvPath % status % e.msg());
+            else
+                printMsg(lvlError, format("@ build-failed %1% - %2% %3%")
+                    % drvPath % 1 % e.msg());
+        }
+
+        /* Register the outputs of this build as "failed" so we won't
+           try to build them again (negative caching).  However, don't
+           do this for fixed-output derivations, since they're likely
+           to fail for transient reasons (e.g., fetchurl not being
+           able to access the network).  Hook errors (like
+           communication problems with the remote machine) shouldn't
+           be cached either. */
+        if (settings.cacheFailure && !hookError && !fixedOutput)
+            foreach (DerivationOutputs::iterator, i, drv.outputs)
+                worker.store.registerFailedPath(i->second.path);
+
+        worker.permanentFailure = !hookError && !fixedOutput;
+        amDone(ecFailed);
+        return;
+    }
+
+    /* Release the build user, if applicable. */
+    buildUser.release();
+
+    if (settings.printBuildTrace)
+        printMsg(lvlError, format("@ build-succeeded %1% -") % drvPath);
+
+    amDone(ecSuccess);
+}
+
+
+HookReply DerivationGoal::tryBuildHook()
+{
+    if (!settings.useBuildHook || getEnv("NIX_BUILD_HOOK") == "") return rpDecline;
+
+    if (!worker.hook)
+        worker.hook = boost::shared_ptr<HookInstance>(new HookInstance);
+
+    /* Tell the hook about system features (beyond the system type)
+       required from the build machine.  (The hook could parse the
+       drv file itself, but this is easier.) */
+    Strings features = tokenizeString<Strings>(get(drv.env, "requiredSystemFeatures"));
+    foreach (Strings::iterator, i, features) checkStoreName(*i); /* !!! abuse */
+
+    /* Send the request to the hook. */
+    writeLine(worker.hook->toHook.writeSide, (format("%1% %2% %3% %4%")
+        % (worker.getNrLocalBuilds() < settings.maxBuildJobs ? "1" : "0")
+        % drv.platform % drvPath % concatStringsSep(",", features)).str());
+
+    /* Read the first line of input, which should be a word indicating
+       whether the hook wishes to perform the build. */
+    string reply;
+    while (true) {
+        string s = readLine(worker.hook->fromHook.readSide);
+        if (string(s, 0, 2) == "# ") {
+            reply = string(s, 2);
+            break;
+        }
+        s += "\n";
+        writeToStderr(s);
+    }
+
+    debug(format("hook reply is `%1%'") % reply);
+
+    if (reply == "decline" || reply == "postpone")
+        return reply == "decline" ? rpDecline : rpPostpone;
+    else if (reply != "accept")
+        throw Error(format("bad hook reply `%1%'") % reply);
+
+    printMsg(lvlTalkative, format("using hook to build path(s) %1%")
+        % showPaths(outputPaths(drv.outputs)));
+
+    hook = worker.hook;
+    worker.hook.reset();
+
+    /* Tell the hook all the inputs that have to be copied to the
+       remote system.  This unfortunately has to contain the entire
+       derivation closure to ensure that the validity invariant holds
+       on the remote system.  (I.e., it's unfortunate that we have to
+       list it since the remote system *probably* already has it.) */
+    PathSet allInputs;
+    allInputs.insert(inputPaths.begin(), inputPaths.end());
+    computeFSClosure(worker.store, drvPath, allInputs);
+
+    string s;
+    foreach (PathSet::iterator, i, allInputs) s += *i + " ";
+    writeLine(hook->toHook.writeSide, s);
+
+    /* Tell the hooks the outputs that have to be copied back from the
+       remote system. */
+    s = "";
+    foreach (DerivationOutputs::iterator, i, drv.outputs)
+        s += i->second.path + " ";
+    writeLine(hook->toHook.writeSide, s);
+
+    hook->toHook.writeSide.close();
+
+    /* Create the log file and pipe. */
+    Path logFile = openLogFile();
+
+    set<int> fds;
+    fds.insert(hook->fromHook.readSide);
+    fds.insert(hook->builderOut.readSide);
+    worker.childStarted(shared_from_this(), hook->pid, fds, false, false);
+
+    if (settings.printBuildTrace)
+        printMsg(lvlError, format("@ build-started %1% - %2% %3%")
+            % drvPath % drv.platform % logFile);
+
+    return rpAccept;
+}
+
+
+void chmod_(const Path & path, mode_t mode)
+{
+    if (chmod(path.c_str(), mode) == -1)
+        throw SysError(format("setting permissions on `%1%'") % path);
+}
+
+
+int childEntry(void * arg)
+{
+    ((DerivationGoal *) arg)->initChild();
+    return 1;
+}
+
+
+void DerivationGoal::startBuilder()
+{
+    startNest(nest, lvlInfo, format(repair ? "repairing path(s) %1%" : "building path(s) %1%") % showPaths(missingPaths));
+
+    /* Right platform? */
+    if (!canBuildLocally(drv.platform)) {
+        if (settings.printBuildTrace)
+            printMsg(lvlError, format("@ unsupported-platform %1% %2%") % drvPath % drv.platform);
+        throw Error(
+            format("a `%1%' is required to build `%3%', but I am a `%2%'")
+            % drv.platform % settings.thisSystem % drvPath);
+    }
+
+    /* Construct the environment passed to the builder. */
+
+    /* Most shells initialise PATH to some default (/bin:/usr/bin:...) when
+       PATH is not set.  We don't want this, so we fill it in with some dummy
+       value. */
+    env["PATH"] = "/path-not-set";
+
+    /* Set HOME to a non-existing path to prevent certain programs from using
+       /etc/passwd (or NIS, or whatever) to locate the home directory (for
+       example, wget looks for ~/.wgetrc).  I.e., these tools use /etc/passwd
+       if HOME is not set, but they will just assume that the settings file
+       they are looking for does not exist if HOME is set but points to some
+       non-existing path. */
+    Path homeDir = "/homeless-shelter";
+    env["HOME"] = homeDir;
+
+    /* Tell the builder where the Nix store is.  Usually they
+       shouldn't care, but this is useful for purity checking (e.g.,
+       the compiler or linker might only want to accept paths to files
+       in the store or in the build directory). */
+    env["NIX_STORE"] = settings.nixStore;
+
+    /* The maximum number of cores to utilize for parallel building. */
+    env["NIX_BUILD_CORES"] = (format("%d") % settings.buildCores).str();
+
+    /* Add all bindings specified in the derivation. */
+    foreach (StringPairs::iterator, i, drv.env)
+        env[i->first] = i->second;
+
+    /* Create a temporary directory where the build will take
+       place. */
+    tmpDir = createTempDir("", "nix-build-" + storePathToName(drvPath), false, false, 0700);
+
+    /* For convenience, set an environment pointing to the top build
+       directory. */
+    env["NIX_BUILD_TOP"] = tmpDir;
+
+    /* Also set TMPDIR and variants to point to this directory. */
+    env["TMPDIR"] = env["TEMPDIR"] = env["TMP"] = env["TEMP"] = tmpDir;
+
+    /* Explicitly set PWD to prevent problems with chroot builds.  In
+       particular, dietlibc cannot figure out the cwd because the
+       inode of the current directory doesn't appear in .. (because
+       getdents returns the inode of the mount point). */
+    env["PWD"] = tmpDir;
+
+    /* Compatibility hack with Nix <= 0.7: if this is a fixed-output
+       derivation, tell the builder, so that for instance `fetchurl'
+       can skip checking the output.  On older Nixes, this environment
+       variable won't be set, so `fetchurl' will do the check. */
+    if (fixedOutput) env["NIX_OUTPUT_CHECKED"] = "1";
+
+    /* *Only* if this is a fixed-output derivation, propagate the
+       values of the environment variables specified in the
+       `impureEnvVars' attribute to the builder.  This allows for
+       instance environment variables for proxy configuration such as
+       `http_proxy' to be easily passed to downloaders like
+       `fetchurl'.  Passing such environment variables from the caller
+       to the builder is generally impure, but the output of
+       fixed-output derivations is by definition pure (since we
+       already know the cryptographic hash of the output). */
+    if (fixedOutput) {
+        Strings varNames = tokenizeString<Strings>(get(drv.env, "impureEnvVars"));
+        foreach (Strings::iterator, i, varNames) env[*i] = getEnv(*i);
+    }
+
+    /* The `exportReferencesGraph' feature allows the references graph
+       to be passed to a builder.  This attribute should be a list of
+       pairs [name1 path1 name2 path2 ...].  The references graph of
+       each `pathN' will be stored in a text file `nameN' in the
+       temporary build directory.  The text files have the format used
+       by `nix-store --register-validity'.  However, the deriver
+       fields are left empty. */
+    string s = get(drv.env, "exportReferencesGraph");
+    Strings ss = tokenizeString<Strings>(s);
+    if (ss.size() % 2 != 0)
+        throw BuildError(format("odd number of tokens in `exportReferencesGraph': `%1%'") % s);
+    for (Strings::iterator i = ss.begin(); i != ss.end(); ) {
+        string fileName = *i++;
+        checkStoreName(fileName); /* !!! abuse of this function */
+
+        /* Check that the store path is valid. */
+        Path storePath = *i++;
+        if (!isInStore(storePath))
+            throw BuildError(format("`exportReferencesGraph' contains a non-store path `%1%'")
+                % storePath);
+        storePath = toStorePath(storePath);
+        if (!worker.store.isValidPath(storePath))
+            throw BuildError(format("`exportReferencesGraph' contains an invalid path `%1%'")
+                % storePath);
+
+        /* If there are derivations in the graph, then include their
+           outputs as well.  This is useful if you want to do things
+           like passing all build-time dependencies of some path to a
+           derivation that builds a NixOS DVD image. */
+        PathSet paths, paths2;
+        computeFSClosure(worker.store, storePath, paths);
+        paths2 = paths;
+
+        foreach (PathSet::iterator, j, paths2) {
+            if (isDerivation(*j)) {
+                Derivation drv = derivationFromPath(worker.store, *j);
+                foreach (DerivationOutputs::iterator, k, drv.outputs)
+                    computeFSClosure(worker.store, k->second.path, paths);
+            }
+        }
+
+        /* Write closure info to `fileName'. */
+        writeFile(tmpDir + "/" + fileName,
+            worker.store.makeValidityRegistration(paths, false, false));
+    }
+
+
+    /* If `build-users-group' is not empty, then we have to build as
+       one of the members of that group. */
+    if (settings.buildUsersGroup != "") {
+        buildUser.acquire();
+        assert(buildUser.getUID() != 0);
+        assert(buildUser.getGID() != 0);
+
+        /* Make sure that no other processes are executing under this
+           uid. */
+        buildUser.kill();
+
+        /* Change ownership of the temporary build directory. */
+        if (chown(tmpDir.c_str(), buildUser.getUID(), buildUser.getGID()) == -1)
+            throw SysError(format("cannot change ownership of `%1%'") % tmpDir);
+
+        /* Check that the Nix store has the appropriate permissions,
+           i.e., owned by root and mode 1775 (sticky bit on so that
+           the builder can create its output but not mess with the
+           outputs of other processes). */
+        struct stat st;
+        if (stat(settings.nixStore.c_str(), &st) == -1)
+            throw SysError(format("cannot stat `%1%'") % settings.nixStore);
+        if (!(st.st_mode & S_ISVTX) ||
+            ((st.st_mode & S_IRWXG) != S_IRWXG) ||
+            (st.st_gid != buildUser.getGID()))
+            throw Error(format(
+                "builder does not have write permission to `%2%'; "
+                "try `chgrp %1% %2%; chmod 1775 %2%'")
+                % buildUser.getGID() % settings.nixStore);
+    }
+
+
+    /* Are we doing a chroot build?  Note that fixed-output
+       derivations are never done in a chroot, mainly so that
+       functions like fetchurl (which needs a proper /etc/resolv.conf)
+       work properly.  Purity checking for fixed-output derivations
+       is somewhat pointless anyway. */
+    useChroot = settings.useChroot;
+
+    if (fixedOutput) useChroot = false;
+
+    /* Hack to allow derivations to disable chroot builds. */
+    if (get(drv.env, "__noChroot") == "1") useChroot = false;
+
+    if (useChroot) {
+#if CHROOT_ENABLED
+        /* Create a temporary directory in which we set up the chroot
+           environment using bind-mounts.  We put it in the Nix store
+           to ensure that we can create hard-links to non-directory
+           inputs in the fake Nix store in the chroot (see below). */
+        chrootRootDir = drvPath + ".chroot";
+        if (pathExists(chrootRootDir)) deletePath(chrootRootDir);
+
+        /* Clean up the chroot directory automatically. */
+        autoDelChroot = boost::shared_ptr<AutoDelete>(new AutoDelete(chrootRootDir));
+
+        printMsg(lvlChatty, format("setting up chroot environment in `%1%'") % chrootRootDir);
+
+        /* Create a writable /tmp in the chroot.  Many builders need
+           this.  (Of course they should really respect $TMPDIR
+           instead.) */
+        Path chrootTmpDir = chrootRootDir + "/tmp";
+        createDirs(chrootTmpDir);
+        chmod_(chrootTmpDir, 01777);
+
+        /* Create a /etc/passwd with entries for the build user and the
+           nobody account.  The latter is kind of a hack to support
+           Samba-in-QEMU. */
+        createDirs(chrootRootDir + "/etc");
+
+        writeFile(chrootRootDir + "/etc/passwd",
+            (format(
+                "nixbld:x:%1%:%2%:Nix build user:/:/noshell\n"
+                "nobody:x:65534:65534:Nobody:/:/noshell\n")
+                % (buildUser.enabled() ? buildUser.getUID() : getuid())
+                % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
+
+        /* Declare the build user's group so that programs get a consistent
+           view of the system (e.g., "id -gn"). */
+        writeFile(chrootRootDir + "/etc/group",
+            (format("nixbld:!:%1%:\n")
+                % (buildUser.enabled() ? buildUser.getGID() : getgid())).str());
+
+        /* Create /etc/hosts with localhost entry. */
+        writeFile(chrootRootDir + "/etc/hosts", "127.0.0.1 localhost\n");
+
+        /* Bind-mount a user-configurable set of directories from the
+           host file system. */
+        foreach (StringSet::iterator, i, settings.dirsInChroot) {
+            size_t p = i->find('=');
+            if (p == string::npos)
+                dirsInChroot[*i] = *i;
+            else
+                dirsInChroot[string(*i, 0, p)] = string(*i, p + 1);
+        }
+        dirsInChroot[tmpDir] = tmpDir;
+
+        /* Make the closure of the inputs available in the chroot,
+           rather than the whole Nix store.  This prevents any access
+           to undeclared dependencies.  Directories are bind-mounted,
+           while other inputs are hard-linked (since only directories
+           can be bind-mounted).  !!! As an extra security
+           precaution, make the fake Nix store only writable by the
+           build user. */
+        createDirs(chrootRootDir + settings.nixStore);
+        chmod_(chrootRootDir + settings.nixStore, 01777);
+
+        foreach (PathSet::iterator, i, inputPaths) {
+            struct stat st;
+            if (lstat(i->c_str(), &st))
+                throw SysError(format("getting attributes of path `%1%'") % *i);
+            if (S_ISDIR(st.st_mode))
+                dirsInChroot[*i] = *i;
+            else {
+                Path p = chrootRootDir + *i;
+                if (link(i->c_str(), p.c_str()) == -1) {
+                    /* Hard-linking fails if we exceed the maximum
+                       link count on a file (e.g. 32000 of ext3),
+                       which is quite possible after a `nix-store
+                       --optimise'. */
+                    if (errno != EMLINK)
+                        throw SysError(format("linking `%1%' to `%2%'") % p % *i);
+                    StringSink sink;
+                    dumpPath(*i, sink);
+                    StringSource source(sink.s);
+                    restorePath(p, source);
+                }
+
+                regularInputPaths.insert(*i);
+            }
+        }
+
+        /* If we're repairing, it's possible that we're rebuilding a
+           path that is in settings.dirsInChroot (typically the
+           dependencies of /bin/sh).  Throw them out. */
+        if (repair)
+            foreach (DerivationOutputs::iterator, i, drv.outputs)
+                dirsInChroot.erase(i->second.path);
+
+#else
+        throw Error("chroot builds are not supported on this platform");
+#endif
+    }
+
+    else {
+
+        if (pathExists(homeDir))
+            throw Error(format("directory `%1%' exists; please remove it") % homeDir);
+
+        /* We're not doing a chroot build, but we have some valid
+           output paths.  Since we can't just overwrite or delete
+           them, we have to do hash rewriting: i.e. in the
+           environment/arguments passed to the build, we replace the
+           hashes of the valid outputs with unique dummy strings;
+           after the build, we discard the redirected outputs
+           corresponding to the valid outputs, and rewrite the
+           contents of the new outputs to replace the dummy strings
+           with the actual hashes. */
+        if (validPaths.size() > 0)
+            //throw Error(format("derivation `%1%' is blocked by its output path(s) %2%") % drvPath % showPaths(validPaths));
+            foreach (PathSet::iterator, i, validPaths)
+                redirectedOutputs.insert(addHashRewrite(*i));
+
+        /* If we're repairing, then we don't want to delete the
+           corrupt outputs in advance.  So rewrite them as well. */
+        if (repair)
+            foreach (PathSet::iterator, i, missingPaths)
+                if (worker.store.isValidPath(*i) && pathExists(*i))
+                    redirectedBadOutputs[*i] = addHashRewrite(*i);
+    }
+
+
+    /* Run the builder. */
+    printMsg(lvlChatty, format("executing builder `%1%'") %
+        drv.builder);
+
+    /* Create the log file. */
+    Path logFile = openLogFile();
+
+    /* Create a pipe to get the output of the builder. */
+    builderOut.create();
+
+    /* Fork a child to build the package.  Note that while we
+       currently use forks to run and wait for the children, it
+       shouldn't be hard to use threads for this on systems where
+       fork() is unavailable or inefficient.
+
+       If we're building in a chroot, then also set up private
+       namespaces for the build:
+
+       - The PID namespace causes the build to start as PID 1.
+         Processes outside of the chroot are not visible to those on
+         the inside, but processes inside the chroot are visible from
+         the outside (though with different PIDs).
+
+       - The private mount namespace ensures that all the bind mounts
+         we do will only show up in this process and its children, and
+         will disappear automatically when we're done.
+
+       - The private network namespace ensures that the builder cannot
+         talk to the outside world (or vice versa).  It only has a
+         private loopback interface.
+
+       - The IPC namespace prevents the builder from communicating
+         with outside processes using SysV IPC mechanisms (shared
+         memory, message queues, semaphores).  It also ensures that
+         all IPC objects are destroyed when the builder exits.
+
+       - The UTS namespace ensures that builders see a hostname of
+         localhost rather than the actual hostname.
+    */
+#if CHROOT_ENABLED
+    if (useChroot) {
+        char stack[32 * 1024];
+        pid = clone(childEntry, stack + sizeof(stack) - 8,
+            CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWNET | CLONE_NEWIPC | CLONE_NEWUTS | SIGCHLD, this);
+    } else
+#endif
+    {
+        pid = fork();
+        if (pid == 0) initChild();
+    }
+
+    if (pid == -1) throw SysError("unable to fork");
+
+    /* parent */
+    pid.setSeparatePG(true);
+    builderOut.writeSide.close();
+    worker.childStarted(shared_from_this(), pid,
+        singleton<set<int> >(builderOut.readSide), true, true);
+
+    if (settings.printBuildTrace) {
+        printMsg(lvlError, format("@ build-started %1% - %2% %3%")
+            % drvPath % drv.platform % logFile);
+    }
+}
+
+
+void DerivationGoal::initChild()
+{
+    /* Warning: in the child we should absolutely not make any SQLite
+       calls! */
+
+    bool inSetup = true;
+
+    try { /* child */
+
+#if CHROOT_ENABLED
+        if (useChroot) {
+            /* Initialise the loopback interface. */
+            AutoCloseFD fd(socket(PF_INET, SOCK_DGRAM, IPPROTO_IP));
+            if (fd == -1) throw SysError("cannot open IP socket");
+
+            struct ifreq ifr;
+            strcpy(ifr.ifr_name, "lo");
+            ifr.ifr_flags = IFF_UP | IFF_LOOPBACK | IFF_RUNNING;
+            if (ioctl(fd, SIOCSIFFLAGS, &ifr) == -1)
+                throw SysError("cannot set loopback interface flags");
+
+            fd.close();
+
+            /* Set the hostname etc. to fixed values. */
+            char hostname[] = "localhost";
+            sethostname(hostname, sizeof(hostname));
+            char domainname[] = "(none)"; // kernel default
+            setdomainname(domainname, sizeof(domainname));
+
+            /* Make all filesystems private.  This is necessary
+               because subtrees may have been mounted as "shared"
+               (MS_SHARED).  (Systemd does this, for instance.)  Even
+               though we have a private mount namespace, mounting
+               filesystems on top of a shared subtree still propagates
+               outside of the namespace.  Making a subtree private is
+               local to the namespace, though, so setting MS_PRIVATE
+               does not affect the outside world. */
+            Strings mounts = tokenizeString<Strings>(readFile("/proc/self/mountinfo", true), "\n");
+            foreach (Strings::iterator, i, mounts) {
+                vector<string> fields = tokenizeString<vector<string> >(*i, " ");
+                string fs = decodeOctalEscaped(fields.at(4));
+                if (mount(0, fs.c_str(), 0, MS_PRIVATE, 0) == -1)
+                    throw SysError(format("unable to make filesystem `%1%' private") % fs);
+            }
+
+            /* Bind-mount all the directories from the "host"
+               filesystem that we want in the chroot
+               environment. */
+            foreach (DirsInChroot::iterator, i, dirsInChroot) {
+                struct stat st;
+                Path source = i->second;
+                Path target = chrootRootDir + i->first;
+                if (source == "/proc") continue; // backwards compatibility
+                debug(format("bind mounting `%1%' to `%2%'") % source % target);
+                if (stat(source.c_str(), &st) == -1)
+                    throw SysError(format("getting attributes of path `%1%'") % source);
+                if (S_ISDIR(st.st_mode))
+                    createDirs(target);
+                else {
+                    createDirs(dirOf(target));
+                    writeFile(target, "");
+                }
+                if (mount(source.c_str(), target.c_str(), "", MS_BIND, 0) == -1)
+                    throw SysError(format("bind mount from `%1%' to `%2%' failed") % source % target);
+            }
+
+            /* Bind a new instance of procfs on /proc to reflect our
+               private PID namespace. */
+            createDirs(chrootRootDir + "/proc");
+            if (mount("none", (chrootRootDir + "/proc").c_str(), "proc", 0, 0) == -1)
+                throw SysError("mounting /proc");
+
+            /* Mount a new tmpfs on /dev/shm to ensure that whatever
+               the builder puts in /dev/shm is cleaned up automatically. */
+            if (pathExists("/dev/shm"))
+                if (mount("none", (chrootRootDir + "/dev/shm").c_str(), "tmpfs", 0, 0) == -1)
+                    throw SysError("mounting /dev/shm");
+
+            /* Do the chroot().  Below we do a chdir() to the
+               temporary build directory to make sure the current
+               directory is in the chroot.  (Actually the order
+               doesn't matter, since due to the bind mount tmpDir and
+               tmpRootDit/tmpDir are the same directories.) */
+            if (chroot(chrootRootDir.c_str()) == -1)
+                throw SysError(format("cannot change root directory to `%1%'") % chrootRootDir);
+        }
+#endif
+
+        commonChildInit(builderOut);
+
+        if (chdir(tmpDir.c_str()) == -1)
+            throw SysError(format("changing into `%1%'") % tmpDir);
+
+        /* Close all other file descriptors. */
+        closeMostFDs(set<int>());
+
+#ifdef CAN_DO_LINUX32_BUILDS
+        /* Change the personality to 32-bit if we're doing an
+           i686-linux build on an x86_64-linux machine. */
+        struct utsname utsbuf;
+        uname(&utsbuf);
+        if (drv.platform == "i686-linux" &&
+            (settings.thisSystem == "x86_64-linux" ||
+             (!strcmp(utsbuf.sysname, "Linux") && !strcmp(utsbuf.machine, "x86_64")))) {
+            if (personality(0x0008 | 0x8000000 /* == PER_LINUX32_3GB */) == -1)
+                throw SysError("cannot set i686-linux personality");
+        }
+
+        /* Impersonate a Linux 2.6 machine to get some determinism in
+           builds that depend on the kernel version. */
+        if ((drv.platform == "i686-linux" || drv.platform == "x86_64-linux") && settings.impersonateLinux26) {
+            int cur = personality(0xffffffff);
+            if (cur != -1) personality(cur | 0x0020000 /* == UNAME26 */);
+        }
+#endif
+
+        /* Fill in the environment. */
+        Strings envStrs;
+        foreach (Environment::const_iterator, i, env)
+            envStrs.push_back(rewriteHashes(i->first + "=" + i->second, rewritesToTmp));
+        const char * * envArr = strings2CharPtrs(envStrs);
+
+        Path program = drv.builder.c_str();
+        std::vector<const char *> args; /* careful with c_str()! */
+        string user; /* must be here for its c_str()! */
+
+        /* If we are running in `build-users' mode, then switch to the
+           user we allocated above.  Make sure that we drop all root
+           privileges.  Note that above we have closed all file
+           descriptors except std*, so that's safe.  Also note that
+           setuid() when run as root sets the real, effective and
+           saved UIDs. */
+        if (buildUser.enabled()) {
+            printMsg(lvlChatty, format("switching to user `%1%'") % buildUser.getUser());
+
+            if (setgroups(0, 0) == -1)
+                throw SysError("cannot clear the set of supplementary groups");
+
+            if (setgid(buildUser.getGID()) == -1 ||
+                getgid() != buildUser.getGID() ||
+                getegid() != buildUser.getGID())
+                throw SysError("setgid failed");
+
+            if (setuid(buildUser.getUID()) == -1 ||
+                getuid() != buildUser.getUID() ||
+                geteuid() != buildUser.getUID())
+                throw SysError("setuid failed");
+        }
+
+        /* Fill in the arguments. */
+        string builderBasename = baseNameOf(drv.builder);
+        args.push_back(builderBasename.c_str());
+        foreach (Strings::iterator, i, drv.args)
+            args.push_back(rewriteHashes(*i, rewritesToTmp).c_str());
+        args.push_back(0);
+
+        restoreSIGPIPE();
+
+        /* Execute the program.  This should not return. */
+        inSetup = false;
+        execve(program.c_str(), (char * *) &args[0], (char * *) envArr);
+
+        throw SysError(format("executing `%1%'") % drv.builder);
+
+    } catch (std::exception & e) {
+        writeToStderr("build error: " + string(e.what()) + "\n");
+        _exit(inSetup ? childSetupFailed : 1);
+    }
+
+    abort(); /* never reached */
+}
+
+
+/* Parse a list of reference specifiers.  Each element must either be
+   a store path, or the symbolic name of the output of the derivation
+   (such as `out'). */
+PathSet parseReferenceSpecifiers(const Derivation & drv, string attr)
+{
+    PathSet result;
+    Paths paths = tokenizeString<Paths>(attr);
+    foreach (Strings::iterator, i, paths) {
+        if (isStorePath(*i))
+            result.insert(*i);
+        else if (drv.outputs.find(*i) != drv.outputs.end())
+            result.insert(drv.outputs.find(*i)->second.path);
+        else throw BuildError(
+            format("derivation contains an illegal reference specifier `%1%'")
+            % *i);
+    }
+    return result;
+}
+
+
+void DerivationGoal::computeClosure()
+{
+    map<Path, PathSet> allReferences;
+    map<Path, HashResult> contentHashes;
+
+    /* When using a build hook, the build hook can register the output
+       as valid (by doing `nix-store --import').  If so we don't have
+       to do anything here. */
+    if (hook) {
+        bool allValid = true;
+        foreach (DerivationOutputs::iterator, i, drv.outputs)
+            if (!worker.store.isValidPath(i->second.path)) allValid = false;
+        if (allValid) return;
+    }
+
+    /* Check whether the output paths were created, and grep each
+       output path to determine what other paths it references.  Also make all
+       output paths read-only. */
+    foreach (DerivationOutputs::iterator, i, drv.outputs) {
+        Path path = i->second.path;
+        if (missingPaths.find(path) == missingPaths.end()) continue;
+
+        if (!pathExists(path)) {
+            throw BuildError(
+                format("builder for `%1%' failed to produce output path `%2%'")
+                % drvPath % path);
+        }
+
+        struct stat st;
+        if (lstat(path.c_str(), &st) == -1)
+            throw SysError(format("getting attributes of path `%1%'") % path);
+
+        startNest(nest, lvlTalkative,
+            format("scanning for references inside `%1%'") % path);
+
+        /* Check that fixed-output derivations produced the right
+           outputs (i.e., the content hash should match the specified
+           hash). */
+        if (i->second.hash != "") {
+
+            bool recursive; HashType ht; Hash h;
+            i->second.parseHashInfo(recursive, ht, h);
+
+            if (!recursive) {
+                /* The output path should be a regular file without
+                   execute permission. */
+                if (!S_ISREG(st.st_mode) || (st.st_mode & S_IXUSR) != 0)
+                    throw BuildError(
+                        format("output path `%1% should be a non-executable regular file")
+                        % path);
+            }
+
+            /* Check the hash. */
+            Hash h2 = recursive ? hashPath(ht, path).first : hashFile(ht, path);
+            if (h != h2)
+                throw BuildError(
+                    format("output path `%1%' should have %2% hash `%3%', instead has `%4%'")
+                    % path % i->second.hashAlgo % printHash16or32(h) % printHash16or32(h2));
+        }
+
+        /* Get rid of all weird permissions.  This also checks that
+           all files are owned by the build user, if applicable. */
+        canonicalisePathMetaData(path,
+            buildUser.enabled() && rewrittenPaths.find(path) == rewrittenPaths.end() ? buildUser.getUID() : -1, inodesSeen);
+
+        /* For this output path, find the references to other paths
+           contained in it.  Compute the SHA-256 NAR hash at the same
+           time.  The hash is stored in the database so that we can
+           verify later on whether nobody has messed with the store. */
+        HashResult hash;
+        PathSet references = scanForReferences(path, allPaths, hash);
+        contentHashes[path] = hash;
+
+        /* For debugging, print out the referenced and unreferenced
+           paths. */
+        foreach (PathSet::iterator, i, inputPaths) {
+            PathSet::iterator j = references.find(*i);
+            if (j == references.end())
+                debug(format("unreferenced input: `%1%'") % *i);
+            else
+                debug(format("referenced input: `%1%'") % *i);
+        }
+
+        allReferences[path] = references;
+
+        /* If the derivation specifies an `allowedReferences'
+           attribute (containing a list of paths that the output may
+           refer to), check that all references are in that list.  !!!
+           allowedReferences should really be per-output. */
+        if (drv.env.find("allowedReferences") != drv.env.end()) {
+            PathSet allowed = parseReferenceSpecifiers(drv, get(drv.env, "allowedReferences"));
+            foreach (PathSet::iterator, i, references)
+                if (allowed.find(*i) == allowed.end())
+                    throw BuildError(format("output is not allowed to refer to path `%1%'") % *i);
+        }
+
+        worker.store.optimisePath(path); // FIXME: combine with scanForReferences()
+
+        worker.store.markContentsGood(path);
+    }
+
+    /* Register each output path as valid, and register the sets of
+       paths referenced by each of them.  If there are cycles in the
+       outputs, this will fail. */
+    ValidPathInfos infos;
+    foreach (PathSet::iterator, i, missingPaths) {
+        ValidPathInfo info;
+        info.path = *i;
+        info.hash = contentHashes[*i].first;
+        info.narSize = contentHashes[*i].second;
+        info.references = allReferences[*i];
+        info.deriver = drvPath;
+        infos.push_back(info);
+    }
+    worker.store.registerValidPaths(infos);
+}
+
+
+string drvsLogDir = "drvs";
+
+
+Path DerivationGoal::openLogFile()
+{
+    logSize = 0;
+
+    if (!settings.keepLog) return "";
+
+    string baseName = baseNameOf(drvPath);
+
+    /* Create a log file. */
+    Path dir = (format("%1%/%2%/%3%/") % settings.nixLogDir % drvsLogDir % string(baseName, 0, 2)).str();
+    createDirs(dir);
+
+    if (settings.compressLog) {
+
+        Path logFileName = (format("%1%/%2%.bz2") % dir % string(baseName, 2)).str();
+        AutoCloseFD fd = open(logFileName.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
+        if (fd == -1) throw SysError(format("creating log file `%1%'") % logFileName);
+        closeOnExec(fd);
+
+        if (!(fLogFile = fdopen(fd.borrow(), "w")))
+            throw SysError(format("opening file `%1%'") % logFileName);
+
+        int err;
+        if (!(bzLogFile = BZ2_bzWriteOpen(&err, fLogFile, 9, 0, 0)))
+            throw Error(format("cannot open compressed log file `%1%'") % logFileName);
+
+        return logFileName;
+
+    } else {
+        Path logFileName = (format("%1%/%2%") % dir % string(baseName, 2)).str();
+        fdLogFile = open(logFileName.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
+        if (fdLogFile == -1) throw SysError(format("creating log file `%1%'") % logFileName);
+        closeOnExec(fdLogFile);
+        return logFileName;
+    }
+}
+
+
+void DerivationGoal::closeLogFile()
+{
+    if (bzLogFile) {
+        int err;
+        BZ2_bzWriteClose(&err, bzLogFile, 0, 0, 0);
+        bzLogFile = 0;
+        if (err != BZ_OK) throw Error(format("cannot close compressed log file (BZip2 error = %1%)") % err);
+    }
+
+    if (fLogFile) {
+        fclose(fLogFile);
+        fLogFile = 0;
+    }
+
+    fdLogFile.close();
+}
+
+
+void DerivationGoal::deleteTmpDir(bool force)
+{
+    if (tmpDir != "") {
+        if (settings.keepFailed && !force) {
+            printMsg(lvlError,
+                format("note: keeping build directory `%2%'")
+                % drvPath % tmpDir);
+            chmod(tmpDir.c_str(), 0755);
+        }
+        else
+            deletePath(tmpDir);
+        tmpDir = "";
+    }
+}
+
+
+void DerivationGoal::handleChildOutput(int fd, const string & data)
+{
+    if ((hook && fd == hook->builderOut.readSide) ||
+        (!hook && fd == builderOut.readSide))
+    {
+        logSize += data.size();
+        if (settings.maxLogSize && logSize > settings.maxLogSize) {
+            printMsg(lvlError,
+                format("%1% killed after writing more than %2% bytes of log output")
+                % getName() % settings.maxLogSize);
+            cancel(true); // not really a timeout, but close enough
+            return;
+        }
+        if (verbosity >= settings.buildVerbosity)
+            writeToStderr(data);
+        if (bzLogFile) {
+            int err;
+            BZ2_bzWrite(&err, bzLogFile, (unsigned char *) data.data(), data.size());
+            if (err != BZ_OK) throw Error(format("cannot write to compressed log file (BZip2 error = %1%)") % err);
+        } else if (fdLogFile != -1)
+            writeFull(fdLogFile, (unsigned char *) data.data(), data.size());
+    }
+
+    if (hook && fd == hook->fromHook.readSide)
+        writeToStderr(data);
+}
+
+
+void DerivationGoal::handleEOF(int fd)
+{
+    worker.wakeUp(shared_from_this());
+}
+
+
+PathSet DerivationGoal::checkPathValidity(bool returnValid, bool checkHash)
+{
+    PathSet result;
+    foreach (DerivationOutputs::iterator, i, drv.outputs) {
+        if (!wantOutput(i->first, wantedOutputs)) continue;
+        bool good =
+            worker.store.isValidPath(i->second.path) &&
+            (!checkHash || worker.store.pathContentsGood(i->second.path));
+        if (good == returnValid) result.insert(i->second.path);
+    }
+    return result;
+}
+
+
+bool DerivationGoal::pathFailed(const Path & path)
+{
+    if (!settings.cacheFailure) return false;
+
+    if (!worker.store.hasPathFailed(path)) return false;
+
+    printMsg(lvlError, format("builder for `%1%' failed previously (cached)") % path);
+
+    if (settings.printBuildTrace)
+        printMsg(lvlError, format("@ build-failed %1% - cached") % drvPath);
+
+    worker.permanentFailure = true;
+    amDone(ecFailed);
+
+    return true;
+}
+
+
+Path DerivationGoal::addHashRewrite(const Path & path)
+{
+    string h1 = string(path, settings.nixStore.size() + 1, 32);
+    string h2 = string(printHash32(hashString(htSHA256, "rewrite:" + drvPath + ":" + path)), 0, 32);
+    Path p = settings.nixStore + "/" + h2 + string(path, settings.nixStore.size() + 33);
+    if (pathExists(p)) deletePath(p);
+    assert(path.size() == p.size());
+    rewritesToTmp[h1] = h2;
+    rewritesFromTmp[h2] = h1;
+    return p;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+class SubstitutionGoal : public Goal
+{
+    friend class Worker;
+
+private:
+    /* The store path that should be realised through a substitute. */
+    Path storePath;
+
+    /* The remaining substituters. */
+    Paths subs;
+
+    /* The current substituter. */
+    Path sub;
+
+    /* Whether any substituter can realise this path */
+    bool hasSubstitute;
+
+    /* Path info returned by the substituter's query info operation. */
+    SubstitutablePathInfo info;
+
+    /* Pipe for the substituter's standard output. */
+    Pipe outPipe;
+
+    /* Pipe for the substituter's standard error. */
+    Pipe logPipe;
+
+    /* The process ID of the builder. */
+    Pid pid;
+
+    /* Lock on the store path. */
+    boost::shared_ptr<PathLocks> outputLock;
+
+    /* Whether to try to repair a valid path. */
+    bool repair;
+
+    /* Location where we're downloading the substitute.  Differs from
+       storePath when doing a repair. */
+    Path destPath;
+
+    typedef void (SubstitutionGoal::*GoalState)();
+    GoalState state;
+
+public:
+    SubstitutionGoal(const Path & storePath, Worker & worker, bool repair = false);
+    ~SubstitutionGoal();
+
+    void cancel(bool timeout);
+
+    void work();
+
+    /* The states. */
+    void init();
+    void tryNext();
+    void gotInfo();
+    void referencesValid();
+    void tryToRun();
+    void finished();
+
+    /* Callback used by the worker to write to the log. */
+    void handleChildOutput(int fd, const string & data);
+    void handleEOF(int fd);
+
+    Path getStorePath() { return storePath; }
+};
+
+
+SubstitutionGoal::SubstitutionGoal(const Path & storePath, Worker & worker, bool repair)
+    : Goal(worker)
+    , hasSubstitute(false)
+    , repair(repair)
+{
+    this->storePath = storePath;
+    state = &SubstitutionGoal::init;
+    name = (format("substitution of `%1%'") % storePath).str();
+    trace("created");
+}
+
+
+SubstitutionGoal::~SubstitutionGoal()
+{
+    if (pid != -1) worker.childTerminated(pid);
+}
+
+
+void SubstitutionGoal::cancel(bool timeout)
+{
+    if (settings.printBuildTrace && timeout)
+        printMsg(lvlError, format("@ substituter-failed %1% timeout") % storePath);
+    if (pid != -1) {
+        pid_t savedPid = pid;
+        pid.kill();
+        worker.childTerminated(savedPid);
+    }
+    amDone(ecFailed);
+}
+
+
+void SubstitutionGoal::work()
+{
+    (this->*state)();
+}
+
+
+void SubstitutionGoal::init()
+{
+    trace("init");
+
+    worker.store.addTempRoot(storePath);
+
+    /* If the path already exists we're done. */
+    if (!repair && worker.store.isValidPath(storePath)) {
+        amDone(ecSuccess);
+        return;
+    }
+
+    if (settings.readOnlyMode)
+        throw Error(format("cannot substitute path `%1%' - no write access to the Nix store") % storePath);
+
+    subs = settings.substituters;
+
+    tryNext();
+}
+
+
+void SubstitutionGoal::tryNext()
+{
+    trace("trying next substituter");
+
+    if (subs.size() == 0) {
+        /* None left.  Terminate this goal and let someone else deal
+           with it. */
+        debug(format("path `%1%' is required, but there is no substituter that can build it") % storePath);
+        /* Hack: don't indicate failure if there were no substituters.
+           In that case the calling derivation should just do a
+           build. */
+        amDone(hasSubstitute ? ecFailed : ecNoSubstituters);
+        return;
+    }
+
+    sub = subs.front();
+    subs.pop_front();
+
+    SubstitutablePathInfos infos;
+    PathSet dummy(singleton<PathSet>(storePath));
+    worker.store.querySubstitutablePathInfos(sub, dummy, infos);
+    SubstitutablePathInfos::iterator k = infos.find(storePath);
+    if (k == infos.end()) { tryNext(); return; }
+    info = k->second;
+    hasSubstitute = true;
+
+    /* To maintain the closure invariant, we first have to realise the
+       paths referenced by this one. */
+    foreach (PathSet::iterator, i, info.references)
+        if (*i != storePath) /* ignore self-references */
+            addWaitee(worker.makeSubstitutionGoal(*i));
+
+    if (waitees.empty()) /* to prevent hang (no wake-up event) */
+        referencesValid();
+    else
+        state = &SubstitutionGoal::referencesValid;
+}
+
+
+void SubstitutionGoal::referencesValid()
+{
+    trace("all references realised");
+
+    if (nrFailed > 0) {
+        debug(format("some references of path `%1%' could not be realised") % storePath);
+        amDone(nrNoSubstituters > 0 || nrIncompleteClosure > 0 ? ecIncompleteClosure : ecFailed);
+        return;
+    }
+
+    foreach (PathSet::iterator, i, info.references)
+        if (*i != storePath) /* ignore self-references */
+            assert(worker.store.isValidPath(*i));
+
+    state = &SubstitutionGoal::tryToRun;
+    worker.wakeUp(shared_from_this());
+}
+
+
+void SubstitutionGoal::tryToRun()
+{
+    trace("trying to run");
+
+    /* Make sure that we are allowed to start a build.  Note that even
+       is maxBuildJobs == 0 (no local builds allowed), we still allow
+       a substituter to run.  This is because substitutions cannot be
+       distributed to another machine via the build hook. */
+    if (worker.getNrLocalBuilds() >= (settings.maxBuildJobs == 0 ? 1 : settings.maxBuildJobs)) {
+        worker.waitForBuildSlot(shared_from_this());
+        return;
+    }
+
+    /* Maybe a derivation goal has already locked this path
+       (exceedingly unlikely, since it should have used a substitute
+       first, but let's be defensive). */
+    outputLock.reset(); // make sure this goal's lock is gone
+    if (pathIsLockedByMe(storePath)) {
+        debug(format("restarting substitution of `%1%' because it's locked by another goal")
+            % storePath);
+        worker.waitForAnyGoal(shared_from_this());
+        return; /* restart in the tryToRun() state when another goal finishes */
+    }
+
+    /* Acquire a lock on the output path. */
+    outputLock = boost::shared_ptr<PathLocks>(new PathLocks);
+    if (!outputLock->lockPaths(singleton<PathSet>(storePath), "", false)) {
+        worker.waitForAWhile(shared_from_this());
+        return;
+    }
+
+    /* Check again whether the path is invalid. */
+    if (!repair && worker.store.isValidPath(storePath)) {
+        debug(format("store path `%1%' has become valid") % storePath);
+        outputLock->setDeletion(true);
+        amDone(ecSuccess);
+        return;
+    }
+
+    printMsg(lvlInfo, format("fetching path `%1%'...") % storePath);
+
+    outPipe.create();
+    logPipe.create();
+
+    destPath = repair ? storePath + ".tmp" : storePath;
+
+    /* Remove the (stale) output path if it exists. */
+    if (pathExists(destPath))
+        deletePath(destPath);
+
+    worker.store.setSubstituterEnv();
+
+    /* Fill in the arguments. */
+    Strings args;
+    args.push_back(baseNameOf(sub));
+    args.push_back("--substitute");
+    args.push_back(storePath);
+    args.push_back(destPath);
+    const char * * argArr = strings2CharPtrs(args);
+
+    /* Fork the substitute program. */
+    pid = maybeVfork();
+
+    switch (pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0:
+        try { /* child */
+
+            commonChildInit(logPipe);
+
+            if (dup2(outPipe.writeSide, STDOUT_FILENO) == -1)
+                throw SysError("cannot dup output pipe into stdout");
+
+            execv(sub.c_str(), (char * *) argArr);
+
+            throw SysError(format("executing `%1%'") % sub);
+
+        } catch (std::exception & e) {
+            writeToStderr("substitute error: " + string(e.what()) + "\n");
+        }
+        _exit(1);
+    }
+
+    /* parent */
+    pid.setSeparatePG(true);
+    pid.setKillSignal(SIGTERM);
+    outPipe.writeSide.close();
+    logPipe.writeSide.close();
+    worker.childStarted(shared_from_this(),
+        pid, singleton<set<int> >(logPipe.readSide), true, true);
+
+    state = &SubstitutionGoal::finished;
+
+    if (settings.printBuildTrace)
+        printMsg(lvlError, format("@ substituter-started %1% %2%") % storePath % sub);
+}
+
+
+void SubstitutionGoal::finished()
+{
+    trace("substitute finished");
+
+    /* Since we got an EOF on the logger pipe, the substitute is
+       presumed to have terminated.  */
+    pid_t savedPid = pid;
+    int status = pid.wait(true);
+
+    /* So the child is gone now. */
+    worker.childTerminated(savedPid);
+
+    /* Close the read side of the logger pipe. */
+    logPipe.readSide.close();
+
+    /* Get the hash info from stdout. */
+    string dummy = readLine(outPipe.readSide);
+    string expectedHashStr = statusOk(status) ? readLine(outPipe.readSide) : "";
+    outPipe.readSide.close();
+
+    /* Check the exit status and the build result. */
+    HashResult hash;
+    try {
+
+        if (!statusOk(status))
+            throw SubstError(format("fetching path `%1%' %2%")
+                % storePath % statusToString(status));
+
+        if (!pathExists(destPath))
+            throw SubstError(format("substitute did not produce path `%1%'") % destPath);
+
+        hash = hashPath(htSHA256, destPath);
+
+        /* Verify the expected hash we got from the substituer. */
+        if (expectedHashStr != "") {
+            size_t n = expectedHashStr.find(':');
+            if (n == string::npos)
+                throw Error(format("bad hash from substituter: %1%") % expectedHashStr);
+            HashType hashType = parseHashType(string(expectedHashStr, 0, n));
+            if (hashType == htUnknown)
+                throw Error(format("unknown hash algorithm in `%1%'") % expectedHashStr);
+            Hash expectedHash = parseHash16or32(hashType, string(expectedHashStr, n + 1));
+            Hash actualHash = hashType == htSHA256 ? hash.first : hashPath(hashType, destPath).first;
+            if (expectedHash != actualHash)
+                throw SubstError(format("hash mismatch in downloaded path `%1%': expected %2%, got %3%")
+                    % storePath % printHash(expectedHash) % printHash(actualHash));
+        }
+
+    } catch (SubstError & e) {
+
+        printMsg(lvlInfo, e.msg());
+
+        if (settings.printBuildTrace) {
+            printMsg(lvlError, format("@ substituter-failed %1% %2% %3%")
+                % storePath % status % e.msg());
+        }
+
+        /* Try the next substitute. */
+        state = &SubstitutionGoal::tryNext;
+        worker.wakeUp(shared_from_this());
+        return;
+    }
+
+    canonicalisePathMetaData(destPath, -1);
+
+    worker.store.optimisePath(destPath); // FIXME: combine with hashPath()
+
+    if (repair) replaceValidPath(storePath, destPath);
+
+    ValidPathInfo info2;
+    info2.path = storePath;
+    info2.hash = hash.first;
+    info2.narSize = hash.second;
+    info2.references = info.references;
+    info2.deriver = info.deriver;
+    worker.store.registerValidPath(info2);
+
+    outputLock->setDeletion(true);
+
+    worker.store.markContentsGood(storePath);
+
+    printMsg(lvlChatty,
+        format("substitution of path `%1%' succeeded") % storePath);
+
+    if (settings.printBuildTrace)
+        printMsg(lvlError, format("@ substituter-succeeded %1%") % storePath);
+
+    amDone(ecSuccess);
+}
+
+
+void SubstitutionGoal::handleChildOutput(int fd, const string & data)
+{
+    assert(fd == logPipe.readSide);
+    if (verbosity >= settings.buildVerbosity) writeToStderr(data);
+    /* Don't write substitution output to a log file for now.  We
+       probably should, though. */
+}
+
+
+void SubstitutionGoal::handleEOF(int fd)
+{
+    if (fd == logPipe.readSide) worker.wakeUp(shared_from_this());
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+static bool working = false;
+
+
+Worker::Worker(LocalStore & store)
+    : store(store)
+{
+    /* Debugging: prevent recursive workers. */
+    if (working) abort();
+    working = true;
+    nrLocalBuilds = 0;
+    lastWokenUp = 0;
+    permanentFailure = false;
+}
+
+
+Worker::~Worker()
+{
+    working = false;
+
+    /* Explicitly get rid of all strong pointers now.  After this all
+       goals that refer to this worker should be gone.  (Otherwise we
+       are in trouble, since goals may call childTerminated() etc. in
+       their destructors). */
+    topGoals.clear();
+}
+
+
+GoalPtr Worker::makeDerivationGoal(const Path & path, const StringSet & wantedOutputs, bool repair)
+{
+    GoalPtr goal = derivationGoals[path].lock();
+    if (!goal) {
+        goal = GoalPtr(new DerivationGoal(path, wantedOutputs, *this, repair));
+        derivationGoals[path] = goal;
+        wakeUp(goal);
+    } else
+        (dynamic_cast<DerivationGoal *>(goal.get()))->addWantedOutputs(wantedOutputs);
+    return goal;
+}
+
+
+GoalPtr Worker::makeSubstitutionGoal(const Path & path, bool repair)
+{
+    GoalPtr goal = substitutionGoals[path].lock();
+    if (!goal) {
+        goal = GoalPtr(new SubstitutionGoal(path, *this, repair));
+        substitutionGoals[path] = goal;
+        wakeUp(goal);
+    }
+    return goal;
+}
+
+
+static void removeGoal(GoalPtr goal, WeakGoalMap & goalMap)
+{
+    /* !!! inefficient */
+    for (WeakGoalMap::iterator i = goalMap.begin();
+         i != goalMap.end(); )
+        if (i->second.lock() == goal) {
+            WeakGoalMap::iterator j = i; ++j;
+            goalMap.erase(i);
+            i = j;
+        }
+        else ++i;
+}
+
+
+void Worker::removeGoal(GoalPtr goal)
+{
+    nix::removeGoal(goal, derivationGoals);
+    nix::removeGoal(goal, substitutionGoals);
+    if (topGoals.find(goal) != topGoals.end()) {
+        topGoals.erase(goal);
+        /* If a top-level goal failed, then kill all other goals
+           (unless keepGoing was set). */
+        if (goal->getExitCode() == Goal::ecFailed && !settings.keepGoing)
+            topGoals.clear();
+    }
+
+    /* Wake up goals waiting for any goal to finish. */
+    foreach (WeakGoals::iterator, i, waitingForAnyGoal) {
+        GoalPtr goal = i->lock();
+        if (goal) wakeUp(goal);
+    }
+
+    waitingForAnyGoal.clear();
+}
+
+
+void Worker::wakeUp(GoalPtr goal)
+{
+    goal->trace("woken up");
+    awake.insert(goal);
+}
+
+
+unsigned Worker::getNrLocalBuilds()
+{
+    return nrLocalBuilds;
+}
+
+
+void Worker::childStarted(GoalPtr goal,
+    pid_t pid, const set<int> & fds, bool inBuildSlot,
+    bool respectTimeouts)
+{
+    Child child;
+    child.goal = goal;
+    child.fds = fds;
+    child.timeStarted = child.lastOutput = time(0);
+    child.inBuildSlot = inBuildSlot;
+    child.respectTimeouts = respectTimeouts;
+    children[pid] = child;
+    if (inBuildSlot) nrLocalBuilds++;
+}
+
+
+void Worker::childTerminated(pid_t pid, bool wakeSleepers)
+{
+    assert(pid != -1); /* common mistake */
+
+    Children::iterator i = children.find(pid);
+    assert(i != children.end());
+
+    if (i->second.inBuildSlot) {
+        assert(nrLocalBuilds > 0);
+        nrLocalBuilds--;
+    }
+
+    children.erase(pid);
+
+    if (wakeSleepers) {
+
+        /* Wake up goals waiting for a build slot. */
+        foreach (WeakGoals::iterator, i, wantingToBuild) {
+            GoalPtr goal = i->lock();
+            if (goal) wakeUp(goal);
+        }
+
+        wantingToBuild.clear();
+    }
+}
+
+
+void Worker::waitForBuildSlot(GoalPtr goal)
+{
+    debug("wait for build slot");
+    if (getNrLocalBuilds() < settings.maxBuildJobs)
+        wakeUp(goal); /* we can do it right away */
+    else
+        wantingToBuild.insert(goal);
+}
+
+
+void Worker::waitForAnyGoal(GoalPtr goal)
+{
+    debug("wait for any goal");
+    waitingForAnyGoal.insert(goal);
+}
+
+
+void Worker::waitForAWhile(GoalPtr goal)
+{
+    debug("wait for a while");
+    waitingForAWhile.insert(goal);
+}
+
+
+void Worker::run(const Goals & _topGoals)
+{
+    foreach (Goals::iterator, i,  _topGoals) topGoals.insert(*i);
+
+    startNest(nest, lvlDebug, format("entered goal loop"));
+
+    while (1) {
+
+        checkInterrupt();
+
+        /* Call every wake goal. */
+        while (!awake.empty() && !topGoals.empty()) {
+            WeakGoals awake2(awake);
+            awake.clear();
+            foreach (WeakGoals::iterator, i, awake2) {
+                checkInterrupt();
+                GoalPtr goal = i->lock();
+                if (goal) goal->work();
+                if (topGoals.empty()) break;
+            }
+        }
+
+        if (topGoals.empty()) break;
+
+        /* Wait for input. */
+        if (!children.empty() || !waitingForAWhile.empty())
+            waitForInput();
+        else {
+            if (awake.empty() && settings.maxBuildJobs == 0) throw Error(
+                "unable to start any build; either increase `--max-jobs' "
+                "or enable distributed builds");
+            assert(!awake.empty());
+        }
+    }
+
+    /* If --keep-going is not set, it's possible that the main goal
+       exited while some of its subgoals were still active.  But if
+       --keep-going *is* set, then they must all be finished now. */
+    assert(!settings.keepGoing || awake.empty());
+    assert(!settings.keepGoing || wantingToBuild.empty());
+    assert(!settings.keepGoing || children.empty());
+}
+
+
+void Worker::waitForInput()
+{
+    printMsg(lvlVomit, "waiting for children");
+
+    /* Process output from the file descriptors attached to the
+       children, namely log output and output path creation commands.
+       We also use this to detect child termination: if we get EOF on
+       the logger pipe of a build, we assume that the builder has
+       terminated. */
+
+    bool useTimeout = false;
+    struct timeval timeout;
+    timeout.tv_usec = 0;
+    time_t before = time(0);
+
+    /* If we're monitoring for silence on stdout/stderr, or if there
+       is a build timeout, then wait for input until the first
+       deadline for any child. */
+    assert(sizeof(time_t) >= sizeof(long));
+    time_t nearest = LONG_MAX; // nearest deadline
+    foreach (Children::iterator, i, children) {
+        if (!i->second.respectTimeouts) continue;
+        if (settings.maxSilentTime != 0)
+            nearest = std::min(nearest, i->second.lastOutput + settings.maxSilentTime);
+        if (settings.buildTimeout != 0)
+            nearest = std::min(nearest, i->second.timeStarted + settings.buildTimeout);
+    }
+    if (nearest != LONG_MAX) {
+        timeout.tv_sec = std::max((time_t) 1, nearest - before);
+        useTimeout = true;
+        printMsg(lvlVomit, format("sleeping %1% seconds") % timeout.tv_sec);
+    }
+
+    /* If we are polling goals that are waiting for a lock, then wake
+       up after a few seconds at most. */
+    if (!waitingForAWhile.empty()) {
+        useTimeout = true;
+        if (lastWokenUp == 0)
+            printMsg(lvlError, "waiting for locks or build slots...");
+        if (lastWokenUp == 0 || lastWokenUp > before) lastWokenUp = before;
+        timeout.tv_sec = std::max((time_t) 1, (time_t) (lastWokenUp + settings.pollInterval - before));
+    } else lastWokenUp = 0;
+
+    using namespace std;
+    /* Use select() to wait for the input side of any logger pipe to
+       become `available'.  Note that `available' (i.e., non-blocking)
+       includes EOF. */
+    fd_set fds;
+    FD_ZERO(&fds);
+    int fdMax = 0;
+    foreach (Children::iterator, i, children) {
+        foreach (set<int>::iterator, j, i->second.fds) {
+            FD_SET(*j, &fds);
+            if (*j >= fdMax) fdMax = *j + 1;
+        }
+    }
+
+    if (select(fdMax, &fds, 0, 0, useTimeout ? &timeout : 0) == -1) {
+        if (errno == EINTR) return;
+        throw SysError("waiting for input");
+    }
+
+    time_t after = time(0);
+
+    /* Process all available file descriptors. */
+
+    /* Since goals may be canceled from inside the loop below (causing
+       them go be erased from the `children' map), we have to be
+       careful that we don't keep iterators alive across calls to
+       cancel(). */
+    set<pid_t> pids;
+    foreach (Children::iterator, i, children) pids.insert(i->first);
+
+    foreach (set<pid_t>::iterator, i, pids) {
+        checkInterrupt();
+        Children::iterator j = children.find(*i);
+        if (j == children.end()) continue; // child destroyed
+        GoalPtr goal = j->second.goal.lock();
+        assert(goal);
+
+        set<int> fds2(j->second.fds);
+        foreach (set<int>::iterator, k, fds2) {
+            if (FD_ISSET(*k, &fds)) {
+                unsigned char buffer[4096];
+                ssize_t rd = read(*k, buffer, sizeof(buffer));
+                if (rd == -1) {
+                    if (errno != EINTR)
+                        throw SysError(format("reading from %1%")
+                            % goal->getName());
+                } else if (rd == 0) {
+                    debug(format("%1%: got EOF") % goal->getName());
+                    goal->handleEOF(*k);
+                    j->second.fds.erase(*k);
+                } else {
+                    printMsg(lvlVomit, format("%1%: read %2% bytes")
+                        % goal->getName() % rd);
+                    string data((char *) buffer, rd);
+                    goal->handleChildOutput(*k, data);
+                    j->second.lastOutput = after;
+                }
+            }
+        }
+
+        if (settings.maxSilentTime != 0 &&
+            j->second.respectTimeouts &&
+            after - j->second.lastOutput >= (time_t) settings.maxSilentTime)
+        {
+            printMsg(lvlError,
+                format("%1% timed out after %2% seconds of silence")
+                % goal->getName() % settings.maxSilentTime);
+            goal->cancel(true);
+        }
+
+        if (settings.buildTimeout != 0 &&
+            j->second.respectTimeouts &&
+            after - j->second.timeStarted >= (time_t) settings.buildTimeout)
+        {
+            printMsg(lvlError,
+                format("%1% timed out after %2% seconds")
+                % goal->getName() % settings.buildTimeout);
+            goal->cancel(true);
+        }
+    }
+
+    if (!waitingForAWhile.empty() && lastWokenUp + settings.pollInterval <= after) {
+        lastWokenUp = after;
+        foreach (WeakGoals::iterator, i, waitingForAWhile) {
+            GoalPtr goal = i->lock();
+            if (goal) wakeUp(goal);
+        }
+        waitingForAWhile.clear();
+    }
+}
+
+
+unsigned int Worker::exitStatus()
+{
+    return permanentFailure ? 100 : 1;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+void LocalStore::buildPaths(const PathSet & drvPaths, bool repair)
+{
+    startNest(nest, lvlDebug,
+        format("building %1%") % showPaths(drvPaths));
+
+    Worker worker(*this);
+
+    Goals goals;
+    foreach (PathSet::const_iterator, i, drvPaths) {
+        DrvPathWithOutputs i2 = parseDrvPathWithOutputs(*i);
+        if (isDerivation(i2.first))
+            goals.insert(worker.makeDerivationGoal(i2.first, i2.second, repair));
+        else
+            goals.insert(worker.makeSubstitutionGoal(*i, repair));
+    }
+
+    worker.run(goals);
+
+    PathSet failed;
+    foreach (Goals::iterator, i, goals)
+        if ((*i)->getExitCode() == Goal::ecFailed) {
+            DerivationGoal * i2 = dynamic_cast<DerivationGoal *>(i->get());
+            if (i2) failed.insert(i2->getDrvPath());
+            else failed.insert(dynamic_cast<SubstitutionGoal *>(i->get())->getStorePath());
+        }
+
+    if (!failed.empty())
+        throw Error(format("build of %1% failed") % showPaths(failed), worker.exitStatus());
+}
+
+
+void LocalStore::ensurePath(const Path & path)
+{
+    /* If the path is already valid, we're done. */
+    if (isValidPath(path)) return;
+
+    Worker worker(*this);
+    GoalPtr goal = worker.makeSubstitutionGoal(path);
+    Goals goals = singleton<Goals>(goal);
+
+    worker.run(goals);
+
+    if (goal->getExitCode() != Goal::ecSuccess)
+        throw Error(format("path `%1%' does not exist and cannot be created") % path, worker.exitStatus());
+}
+
+
+void LocalStore::repairPath(const Path & path)
+{
+    Worker worker(*this);
+    GoalPtr goal = worker.makeSubstitutionGoal(path, true);
+    Goals goals = singleton<Goals>(goal);
+
+    worker.run(goals);
+
+    if (goal->getExitCode() != Goal::ecSuccess)
+        throw Error(format("cannot repair path `%1%'") % path, worker.exitStatus());
+}
+
+
+}
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
new file mode 100644
index 000000000000..d91e42784ca5
--- /dev/null
+++ b/src/libstore/derivations.cc
@@ -0,0 +1,278 @@
+#include "derivations.hh"
+#include "store-api.hh"
+#include "globals.hh"
+#include "util.hh"
+#include "misc.hh"
+
+
+namespace nix {
+
+
+void DerivationOutput::parseHashInfo(bool & recursive, HashType & hashType, Hash & hash) const
+{
+    recursive = false;
+    string algo = hashAlgo;
+
+    if (string(algo, 0, 2) == "r:") {
+        recursive = true;
+        algo = string(algo, 2);
+    }
+
+    hashType = parseHashType(algo);
+    if (hashType == htUnknown)
+        throw Error(format("unknown hash algorithm `%1%'") % algo);
+
+    hash = parseHash(hashType, this->hash);
+}
+
+
+Path writeDerivation(StoreAPI & store,
+    const Derivation & drv, const string & name, bool repair)
+{
+    PathSet references;
+    references.insert(drv.inputSrcs.begin(), drv.inputSrcs.end());
+    foreach (DerivationInputs::const_iterator, i, drv.inputDrvs)
+        references.insert(i->first);
+    /* Note that the outputs of a derivation are *not* references
+       (that can be missing (of course) and should not necessarily be
+       held during a garbage collection). */
+    string suffix = name + drvExtension;
+    string contents = unparseDerivation(drv);
+    return settings.readOnlyMode
+        ? computeStorePathForText(suffix, contents, references)
+        : store.addTextToStore(suffix, contents, references, repair);
+}
+
+
+static Path parsePath(std::istream & str)
+{
+    string s = parseString(str);
+    if (s.size() == 0 || s[0] != '/')
+        throw Error(format("bad path `%1%' in derivation") % s);
+    return s;
+}
+
+
+static StringSet parseStrings(std::istream & str, bool arePaths)
+{
+    StringSet res;
+    while (!endOfList(str))
+        res.insert(arePaths ? parsePath(str) : parseString(str));
+    return res;
+}
+
+
+Derivation parseDerivation(const string & s)
+{
+    Derivation drv;
+    std::istringstream str(s);
+    expect(str, "Derive([");
+
+    /* Parse the list of outputs. */
+    while (!endOfList(str)) {
+        DerivationOutput out;
+        expect(str, "("); string id = parseString(str);
+        expect(str, ","); out.path = parsePath(str);
+        expect(str, ","); out.hashAlgo = parseString(str);
+        expect(str, ","); out.hash = parseString(str);
+        expect(str, ")");
+        drv.outputs[id] = out;
+    }
+
+    /* Parse the list of input derivations. */
+    expect(str, ",[");
+    while (!endOfList(str)) {
+        expect(str, "(");
+        Path drvPath = parsePath(str);
+        expect(str, ",[");
+        drv.inputDrvs[drvPath] = parseStrings(str, false);
+        expect(str, ")");
+    }
+
+    expect(str, ",["); drv.inputSrcs = parseStrings(str, true);
+    expect(str, ","); drv.platform = parseString(str);
+    expect(str, ","); drv.builder = parseString(str);
+
+    /* Parse the builder arguments. */
+    expect(str, ",[");
+    while (!endOfList(str))
+        drv.args.push_back(parseString(str));
+
+    /* Parse the environment variables. */
+    expect(str, ",[");
+    while (!endOfList(str)) {
+        expect(str, "("); string name = parseString(str);
+        expect(str, ","); string value = parseString(str);
+        expect(str, ")");
+        drv.env[name] = value;
+    }
+
+    expect(str, ")");
+    return drv;
+}
+
+
+static void printString(string & res, const string & s)
+{
+    res += '"';
+    for (const char * i = s.c_str(); *i; i++)
+        if (*i == '\"' || *i == '\\') { res += "\\"; res += *i; }
+        else if (*i == '\n') res += "\\n";
+        else if (*i == '\r') res += "\\r";
+        else if (*i == '\t') res += "\\t";
+        else res += *i;
+    res += '"';
+}
+
+
+template<class ForwardIterator>
+static void printStrings(string & res, ForwardIterator i, ForwardIterator j)
+{
+    res += '[';
+    bool first = true;
+    for ( ; i != j; ++i) {
+        if (first) first = false; else res += ',';
+        printString(res, *i);
+    }
+    res += ']';
+}
+
+
+string unparseDerivation(const Derivation & drv)
+{
+    string s;
+    s.reserve(65536);
+    s += "Derive([";
+
+    bool first = true;
+    foreach (DerivationOutputs::const_iterator, i, drv.outputs) {
+        if (first) first = false; else s += ',';
+        s += '('; printString(s, i->first);
+        s += ','; printString(s, i->second.path);
+        s += ','; printString(s, i->second.hashAlgo);
+        s += ','; printString(s, i->second.hash);
+        s += ')';
+    }
+
+    s += "],[";
+    first = true;
+    foreach (DerivationInputs::const_iterator, i, drv.inputDrvs) {
+        if (first) first = false; else s += ',';
+        s += '('; printString(s, i->first);
+        s += ','; printStrings(s, i->second.begin(), i->second.end());
+        s += ')';
+    }
+
+    s += "],";
+    printStrings(s, drv.inputSrcs.begin(), drv.inputSrcs.end());
+
+    s += ','; printString(s, drv.platform);
+    s += ','; printString(s, drv.builder);
+    s += ','; printStrings(s, drv.args.begin(), drv.args.end());
+
+    s += ",[";
+    first = true;
+    foreach (StringPairs::const_iterator, i, drv.env) {
+        if (first) first = false; else s += ',';
+        s += '('; printString(s, i->first);
+        s += ','; printString(s, i->second);
+        s += ')';
+    }
+
+    s += "])";
+
+    return s;
+}
+
+
+bool isDerivation(const string & fileName)
+{
+    return hasSuffix(fileName, drvExtension);
+}
+
+
+bool isFixedOutputDrv(const Derivation & drv)
+{
+    return drv.outputs.size() == 1 &&
+        drv.outputs.begin()->first == "out" &&
+        drv.outputs.begin()->second.hash != "";
+}
+
+
+DrvHashes drvHashes;
+
+
+/* Returns the hash of a derivation modulo fixed-output
+   subderivations.  A fixed-output derivation is a derivation with one
+   output (`out') for which an expected hash and hash algorithm are
+   specified (using the `outputHash' and `outputHashAlgo'
+   attributes).  We don't want changes to such derivations to
+   propagate upwards through the dependency graph, changing output
+   paths everywhere.
+
+   For instance, if we change the url in a call to the `fetchurl'
+   function, we do not want to rebuild everything depending on it
+   (after all, (the hash of) the file being downloaded is unchanged).
+   So the *output paths* should not change.  On the other hand, the
+   *derivation paths* should change to reflect the new dependency
+   graph.
+
+   That's what this function does: it returns a hash which is just the
+   hash of the derivation ATerm, except that any input derivation
+   paths have been replaced by the result of a recursive call to this
+   function, and that for fixed-output derivations we return a hash of
+   its output path. */
+Hash hashDerivationModulo(StoreAPI & store, Derivation drv)
+{
+    /* Return a fixed hash for fixed-output derivations. */
+    if (isFixedOutputDrv(drv)) {
+        DerivationOutputs::const_iterator i = drv.outputs.begin();
+        return hashString(htSHA256, "fixed:out:"
+            + i->second.hashAlgo + ":"
+            + i->second.hash + ":"
+            + i->second.path);
+    }
+
+    /* For other derivations, replace the inputs paths with recursive
+       calls to this function.*/
+    DerivationInputs inputs2;
+    foreach (DerivationInputs::const_iterator, i, drv.inputDrvs) {
+        Hash h = drvHashes[i->first];
+        if (h.type == htUnknown) {
+            assert(store.isValidPath(i->first));
+            Derivation drv2 = parseDerivation(readFile(i->first));
+            h = hashDerivationModulo(store, drv2);
+            drvHashes[i->first] = h;
+        }
+        inputs2[printHash(h)] = i->second;
+    }
+    drv.inputDrvs = inputs2;
+
+    return hashString(htSHA256, unparseDerivation(drv));
+}
+
+
+DrvPathWithOutputs parseDrvPathWithOutputs(const string & s)
+{
+    size_t n = s.find("!");
+    return n == s.npos
+        ? DrvPathWithOutputs(s, std::set<string>())
+        : DrvPathWithOutputs(string(s, 0, n), tokenizeString<std::set<string> >(string(s, n + 1), ","));
+}
+
+
+Path makeDrvPathWithOutputs(const Path & drvPath, const std::set<string> & outputs)
+{
+    return outputs.empty()
+        ? drvPath
+        : drvPath + "!" + concatStringsSep(",", outputs);
+}
+
+
+bool wantOutput(const string & output, const std::set<string> & wanted)
+{
+    return wanted.empty() || wanted.find(output) != wanted.end();
+}
+
+
+}
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
new file mode 100644
index 000000000000..703410b92552
--- /dev/null
+++ b/src/libstore/derivations.hh
@@ -0,0 +1,93 @@
+#pragma once
+
+#include "types.hh"
+#include "hash.hh"
+
+#include <map>
+
+
+namespace nix {
+
+
+/* Extension of derivations in the Nix store. */
+const string drvExtension = ".drv";
+
+
+/* Abstract syntax of derivations. */
+
+struct DerivationOutput
+{
+    Path path;
+    string hashAlgo; /* hash used for expected hash computation */
+    string hash; /* expected hash, may be null */
+    DerivationOutput()
+    {
+    }
+    DerivationOutput(Path path, string hashAlgo, string hash)
+    {
+        this->path = path;
+        this->hashAlgo = hashAlgo;
+        this->hash = hash;
+    }
+    void parseHashInfo(bool & recursive, HashType & hashType, Hash & hash) const;
+};
+
+typedef std::map<string, DerivationOutput> DerivationOutputs;
+
+/* For inputs that are sub-derivations, we specify exactly which
+   output IDs we are interested in. */
+typedef std::map<Path, StringSet> DerivationInputs;
+
+typedef std::map<string, string> StringPairs;
+
+struct Derivation
+{
+    DerivationOutputs outputs; /* keyed on symbolic IDs */
+    DerivationInputs inputDrvs; /* inputs that are sub-derivations */
+    PathSet inputSrcs; /* inputs that are sources */
+    string platform;
+    Path builder;
+    Strings args;
+    StringPairs env;
+};
+
+
+class StoreAPI;
+
+
+/* Write a derivation to the Nix store, and return its path. */
+Path writeDerivation(StoreAPI & store,
+    const Derivation & drv, const string & name, bool repair = false);
+
+/* Parse a derivation. */
+Derivation parseDerivation(const string & s);
+
+/* Print a derivation. */
+string unparseDerivation(const Derivation & drv);
+
+/* Check whether a file name ends with the extensions for
+   derivations. */
+bool isDerivation(const string & fileName);
+
+/* Return true iff this is a fixed-output derivation. */
+bool isFixedOutputDrv(const Derivation & drv);
+
+Hash hashDerivationModulo(StoreAPI & store, Derivation drv);
+
+/* Memoisation of hashDerivationModulo(). */
+typedef std::map<Path, Hash> DrvHashes;
+
+extern DrvHashes drvHashes;
+
+/* Split a string specifying a derivation and a set of outputs
+   (/nix/store/hash-foo!out1,out2,...) into the derivation path and
+   the outputs. */
+typedef std::pair<string, std::set<string> > DrvPathWithOutputs;
+DrvPathWithOutputs parseDrvPathWithOutputs(const string & s);
+
+Path makeDrvPathWithOutputs(const Path & drvPath, const std::set<string> & outputs);
+
+bool wantOutput(const string & output, const std::set<string> & wanted);
+
+
+}
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
new file mode 100644
index 000000000000..79bd7d56b3fe
--- /dev/null
+++ b/src/libstore/gc.cc
@@ -0,0 +1,752 @@
+#include "globals.hh"
+#include "misc.hh"
+#include "local-store.hh"
+
+#include <boost/shared_ptr.hpp>
+
+#include <functional>
+#include <queue>
+#include <algorithm>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+
+namespace nix {
+
+
+static string gcLockName = "gc.lock";
+static string tempRootsDir = "temproots";
+static string gcRootsDir = "gcroots";
+
+
+/* Acquire the global GC lock.  This is used to prevent new Nix
+   processes from starting after the temporary root files have been
+   read.  To be precise: when they try to create a new temporary root
+   file, they will block until the garbage collector has finished /
+   yielded the GC lock. */
+int LocalStore::openGCLock(LockType lockType)
+{
+    Path fnGCLock = (format("%1%/%2%")
+        % settings.nixStateDir % gcLockName).str();
+
+    debug(format("acquiring global GC lock `%1%'") % fnGCLock);
+
+    AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT, 0600);
+    if (fdGCLock == -1)
+        throw SysError(format("opening global GC lock `%1%'") % fnGCLock);
+    closeOnExec(fdGCLock);
+
+    if (!lockFile(fdGCLock, lockType, false)) {
+        printMsg(lvlError, format("waiting for the big garbage collector lock..."));
+        lockFile(fdGCLock, lockType, true);
+    }
+
+    /* !!! Restrict read permission on the GC root.  Otherwise any
+       process that can open the file for reading can DoS the
+       collector. */
+
+    return fdGCLock.borrow();
+}
+
+
+void createSymlink(const Path & link, const Path & target)
+{
+    /* Create directories up to `gcRoot'. */
+    createDirs(dirOf(link));
+
+    /* Create the new symlink. */
+    Path tempLink = (format("%1%.tmp-%2%-%3%")
+        % link % getpid() % rand()).str();
+    if (symlink(target.c_str(), tempLink.c_str()) == -1)
+        throw SysError(format("symlinking `%1%' to `%2%'")
+            % tempLink % target);
+
+    /* Atomically replace the old one. */
+    if (rename(tempLink.c_str(), link.c_str()) == -1)
+        throw SysError(format("cannot rename `%1%' to `%2%'")
+            % tempLink % link);
+}
+
+
+void LocalStore::syncWithGC()
+{
+    AutoCloseFD fdGCLock = openGCLock(ltRead);
+}
+
+
+void LocalStore::addIndirectRoot(const Path & path)
+{
+    string hash = printHash32(hashString(htSHA1, path));
+    Path realRoot = canonPath((format("%1%/%2%/auto/%3%")
+        % settings.nixStateDir % gcRootsDir % hash).str());
+    createSymlink(realRoot, path);
+}
+
+
+Path addPermRoot(StoreAPI & store, const Path & _storePath,
+    const Path & _gcRoot, bool indirect, bool allowOutsideRootsDir)
+{
+    Path storePath(canonPath(_storePath));
+    Path gcRoot(canonPath(_gcRoot));
+    assertStorePath(storePath);
+
+    if (isInStore(gcRoot))
+        throw Error(format(
+                "creating a garbage collector root (%1%) in the Nix store is forbidden "
+                "(are you running nix-build inside the store?)") % gcRoot);
+
+    if (indirect) {
+        /* Don't clobber the the link if it already exists and doesn't
+           point to the Nix store. */
+        if (pathExists(gcRoot) && (!isLink(gcRoot) || !isInStore(readLink(gcRoot))))
+            throw Error(format("cannot create symlink `%1%'; already exists") % gcRoot);
+        createSymlink(gcRoot, storePath);
+        store.addIndirectRoot(gcRoot);
+    }
+
+    else {
+        if (!allowOutsideRootsDir) {
+            Path rootsDir = canonPath((format("%1%/%2%") % settings.nixStateDir % gcRootsDir).str());
+
+            if (string(gcRoot, 0, rootsDir.size() + 1) != rootsDir + "/")
+                throw Error(format(
+                    "path `%1%' is not a valid garbage collector root; "
+                    "it's not in the directory `%2%'")
+                    % gcRoot % rootsDir);
+        }
+
+        createSymlink(gcRoot, storePath);
+    }
+
+    /* Check that the root can be found by the garbage collector.
+       !!! This can be very slow on machines that have many roots.
+       Instead of reading all the roots, it would be more efficient to
+       check if the root is in a directory in or linked from the
+       gcroots directory. */
+    if (settings.checkRootReachability) {
+        Roots roots = store.findRoots();
+        if (roots.find(gcRoot) == roots.end())
+            printMsg(lvlError,
+                format(
+                    "warning: `%1%' is not in a directory where the garbage collector looks for roots; "
+                    "therefore, `%2%' might be removed by the garbage collector")
+                % gcRoot % storePath);
+    }
+
+    /* Grab the global GC root, causing us to block while a GC is in
+       progress.  This prevents the set of permanent roots from
+       increasing while a GC is in progress. */
+    store.syncWithGC();
+
+    return gcRoot;
+}
+
+
+/* The file to which we write our temporary roots. */
+static Path fnTempRoots;
+static AutoCloseFD fdTempRoots;
+
+
+void LocalStore::addTempRoot(const Path & path)
+{
+    /* Create the temporary roots file for this process. */
+    if (fdTempRoots == -1) {
+
+        while (1) {
+            Path dir = (format("%1%/%2%") % settings.nixStateDir % tempRootsDir).str();
+            createDirs(dir);
+
+            fnTempRoots = (format("%1%/%2%")
+                % dir % getpid()).str();
+
+            AutoCloseFD fdGCLock = openGCLock(ltRead);
+
+            if (pathExists(fnTempRoots))
+                /* It *must* be stale, since there can be no two
+                   processes with the same pid. */
+                unlink(fnTempRoots.c_str());
+
+            fdTempRoots = openLockFile(fnTempRoots, true);
+
+            fdGCLock.close();
+
+            debug(format("acquiring read lock on `%1%'") % fnTempRoots);
+            lockFile(fdTempRoots, ltRead, true);
+
+            /* Check whether the garbage collector didn't get in our
+               way. */
+            struct stat st;
+            if (fstat(fdTempRoots, &st) == -1)
+                throw SysError(format("statting `%1%'") % fnTempRoots);
+            if (st.st_size == 0) break;
+
+            /* The garbage collector deleted this file before we could
+               get a lock.  (It won't delete the file after we get a
+               lock.)  Try again. */
+        }
+
+    }
+
+    /* Upgrade the lock to a write lock.  This will cause us to block
+       if the garbage collector is holding our lock. */
+    debug(format("acquiring write lock on `%1%'") % fnTempRoots);
+    lockFile(fdTempRoots, ltWrite, true);
+
+    string s = path + '\0';
+    writeFull(fdTempRoots, (const unsigned char *) s.data(), s.size());
+
+    /* Downgrade to a read lock. */
+    debug(format("downgrading to read lock on `%1%'") % fnTempRoots);
+    lockFile(fdTempRoots, ltRead, true);
+}
+
+
+void removeTempRoots()
+{
+    if (fdTempRoots != -1) {
+        fdTempRoots.close();
+        unlink(fnTempRoots.c_str());
+    }
+}
+
+
+/* Automatically clean up the temporary roots file when we exit. */
+struct RemoveTempRoots
+{
+    ~RemoveTempRoots()
+    {
+        removeTempRoots();
+    }
+};
+
+static RemoveTempRoots autoRemoveTempRoots __attribute__((unused));
+
+
+typedef boost::shared_ptr<AutoCloseFD> FDPtr;
+typedef list<FDPtr> FDs;
+
+
+static void readTempRoots(PathSet & tempRoots, FDs & fds)
+{
+    /* Read the `temproots' directory for per-process temporary root
+       files. */
+    Strings tempRootFiles = readDirectory(
+        (format("%1%/%2%") % settings.nixStateDir % tempRootsDir).str());
+
+    foreach (Strings::iterator, i, tempRootFiles) {
+        Path path = (format("%1%/%2%/%3%") % settings.nixStateDir % tempRootsDir % *i).str();
+
+        debug(format("reading temporary root file `%1%'") % path);
+        FDPtr fd(new AutoCloseFD(open(path.c_str(), O_RDWR, 0666)));
+        if (*fd == -1) {
+            /* It's okay if the file has disappeared. */
+            if (errno == ENOENT) continue;
+            throw SysError(format("opening temporary roots file `%1%'") % path);
+        }
+
+        /* This should work, but doesn't, for some reason. */
+        //FDPtr fd(new AutoCloseFD(openLockFile(path, false)));
+        //if (*fd == -1) continue;
+
+        /* Try to acquire a write lock without blocking.  This can
+           only succeed if the owning process has died.  In that case
+           we don't care about its temporary roots. */
+        if (lockFile(*fd, ltWrite, false)) {
+            printMsg(lvlError, format("removing stale temporary roots file `%1%'") % path);
+            unlink(path.c_str());
+            writeFull(*fd, (const unsigned char *) "d", 1);
+            continue;
+        }
+
+        /* Acquire a read lock.  This will prevent the owning process
+           from upgrading to a write lock, therefore it will block in
+           addTempRoot(). */
+        debug(format("waiting for read lock on `%1%'") % path);
+        lockFile(*fd, ltRead, true);
+
+        /* Read the entire file. */
+        string contents = readFile(*fd);
+
+        /* Extract the roots. */
+        string::size_type pos = 0, end;
+
+        while ((end = contents.find((char) 0, pos)) != string::npos) {
+            Path root(contents, pos, end - pos);
+            debug(format("got temporary root `%1%'") % root);
+            assertStorePath(root);
+            tempRoots.insert(root);
+            pos = end + 1;
+        }
+
+        fds.push_back(fd); /* keep open */
+    }
+}
+
+
+static void foundRoot(StoreAPI & store,
+    const Path & path, const Path & target, Roots & roots)
+{
+    Path storePath = toStorePath(target);
+    if (store.isValidPath(storePath))
+        roots[path] = storePath;
+    else
+        printMsg(lvlInfo, format("skipping invalid root from `%1%' to `%2%'") % path % storePath);
+}
+
+
+static void findRoots(StoreAPI & store, const Path & path, Roots & roots)
+{
+    try {
+
+        struct stat st = lstat(path);
+
+        if (S_ISDIR(st.st_mode)) {
+            Strings names = readDirectory(path);
+            foreach (Strings::iterator, i, names)
+                findRoots(store, path + "/" + *i, roots);
+        }
+
+        else if (S_ISLNK(st.st_mode)) {
+            Path target = readLink(path);
+            if (isInStore(target))
+                foundRoot(store, path, target, roots);
+
+            /* Handle indirect roots. */
+            else {
+                target = absPath(target, dirOf(path));
+                if (!pathExists(target)) {
+                    if (isInDir(path, settings.nixStateDir + "/" + gcRootsDir + "/auto")) {
+                        printMsg(lvlInfo, format("removing stale link from `%1%' to `%2%'") % path % target);
+                        unlink(path.c_str());
+                    }
+                } else {
+                    struct stat st2 = lstat(target);
+                    if (!S_ISLNK(st2.st_mode)) return;
+                    Path target2 = readLink(target);
+                    if (isInStore(target2)) foundRoot(store, target, target2, roots);
+                }
+            }
+        }
+
+    }
+
+    catch (SysError & e) {
+        /* We only ignore permanent failures. */
+        if (e.errNo == EACCES || e.errNo == ENOENT || e.errNo == ENOTDIR)
+            printMsg(lvlInfo, format("cannot read potential root `%1%'") % path);
+        else
+            throw;
+    }
+}
+
+
+Roots LocalStore::findRoots()
+{
+    Roots roots;
+
+    /* Process direct roots in {gcroots,manifests,profiles}. */
+    nix::findRoots(*this, settings.nixStateDir + "/" + gcRootsDir, roots);
+    nix::findRoots(*this, settings.nixStateDir + "/manifests", roots);
+    nix::findRoots(*this, settings.nixStateDir + "/profiles", roots);
+
+    return roots;
+}
+
+
+static void addAdditionalRoots(StoreAPI & store, PathSet & roots)
+{
+    Path rootFinder = getEnv("NIX_ROOT_FINDER",
+        settings.nixLibexecDir + "/nix/find-runtime-roots.pl");
+
+    if (rootFinder.empty()) return;
+
+    debug(format("executing `%1%' to find additional roots") % rootFinder);
+
+    string result = runProgram(rootFinder);
+
+    StringSet paths = tokenizeString<StringSet>(result, "\n");
+
+    foreach (StringSet::iterator, i, paths) {
+        if (isInStore(*i)) {
+            Path path = toStorePath(*i);
+            if (roots.find(path) == roots.end() && store.isValidPath(path)) {
+                debug(format("got additional root `%1%'") % path);
+                roots.insert(path);
+            }
+        }
+    }
+}
+
+
+struct GCLimitReached { };
+
+
+struct LocalStore::GCState
+{
+    GCOptions options;
+    GCResults & results;
+    PathSet roots;
+    PathSet tempRoots;
+    PathSet dead;
+    PathSet alive;
+    bool gcKeepOutputs;
+    bool gcKeepDerivations;
+    unsigned long long bytesInvalidated;
+    Path trashDir;
+    bool shouldDelete;
+    GCState(GCResults & results_) : results(results_), bytesInvalidated(0) { }
+};
+
+
+bool LocalStore::isActiveTempFile(const GCState & state,
+    const Path & path, const string & suffix)
+{
+    return hasSuffix(path, suffix)
+        && state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end();
+}
+
+
+void LocalStore::deleteGarbage(GCState & state, const Path & path)
+{
+    unsigned long long bytesFreed;
+    deletePath(path, bytesFreed);
+    state.results.bytesFreed += bytesFreed;
+}
+
+
+void LocalStore::deletePathRecursive(GCState & state, const Path & path)
+{
+    checkInterrupt();
+
+    unsigned long long size = 0;
+
+    if (isValidPath(path)) {
+        PathSet referrers;
+        queryReferrers(path, referrers);
+        foreach (PathSet::iterator, i, referrers)
+            if (*i != path) deletePathRecursive(state, *i);
+        size = queryPathInfo(path).narSize;
+        invalidatePathChecked(path);
+    }
+
+    struct stat st;
+    if (lstat(path.c_str(), &st)) {
+        if (errno == ENOENT) return;
+        throw SysError(format("getting status of %1%") % path);
+    }
+
+    printMsg(lvlInfo, format("deleting `%1%'") % path);
+
+    state.results.paths.insert(path);
+
+    /* If the path is not a regular file or symlink, move it to the
+       trash directory.  The move is to ensure that later (when we're
+       not holding the global GC lock) we can delete the path without
+       being afraid that the path has become alive again.  Otherwise
+       delete it right away. */
+    if (S_ISDIR(st.st_mode)) {
+        // Estimate the amount freed using the narSize field.  FIXME:
+        // if the path was not valid, need to determine the actual
+        // size.
+        state.bytesInvalidated += size;
+        // Mac OS X cannot rename directories if they are read-only.
+        if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
+            throw SysError(format("making `%1%' writable") % path);
+        Path tmp = state.trashDir + "/" + baseNameOf(path);
+        if (rename(path.c_str(), tmp.c_str()))
+            throw SysError(format("unable to rename `%1%' to `%2%'") % path % tmp);
+    } else
+        deleteGarbage(state, path);
+
+    if (state.results.bytesFreed + state.bytesInvalidated > state.options.maxFreed) {
+        printMsg(lvlInfo, format("deleted or invalidated more than %1% bytes; stopping") % state.options.maxFreed);
+        throw GCLimitReached();
+    }
+}
+
+
+bool LocalStore::canReachRoot(GCState & state, PathSet & visited, const Path & path)
+{
+    if (visited.find(path) != visited.end()) return false;
+
+    if (state.alive.find(path) != state.alive.end()) {
+        return true;
+    }
+
+    if (state.dead.find(path) != state.dead.end()) {
+        return false;
+    }
+
+    if (state.roots.find(path) != state.roots.end()) {
+        printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % path);
+        state.alive.insert(path);
+        return true;
+    }
+
+    visited.insert(path);
+
+    if (!isValidPath(path)) return false;
+
+    PathSet incoming;
+
+    /* Don't delete this path if any of its referrers are alive. */
+    queryReferrers(path, incoming);
+
+    /* If gc-keep-derivations is set and this is a derivation, then
+       don't delete the derivation if any of the outputs are alive. */
+    if (state.gcKeepDerivations && isDerivation(path)) {
+        PathSet outputs = queryDerivationOutputs(path);
+        foreach (PathSet::iterator, i, outputs)
+            if (isValidPath(*i) && queryDeriver(*i) == path)
+                incoming.insert(*i);
+    }
+
+    /* If gc-keep-outputs is set, then don't delete this path if there
+       are derivers of this path that are not garbage. */
+    if (state.gcKeepOutputs) {
+        PathSet derivers = queryValidDerivers(path);
+        foreach (PathSet::iterator, i, derivers)
+            incoming.insert(*i);
+    }
+
+    foreach (PathSet::iterator, i, incoming)
+        if (*i != path)
+            if (canReachRoot(state, visited, *i)) {
+                state.alive.insert(path);
+                return true;
+            }
+
+    return false;
+}
+
+
+void LocalStore::tryToDelete(GCState & state, const Path & path)
+{
+    checkInterrupt();
+
+    if (path == linksDir || path == state.trashDir) return;
+
+    startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path);
+
+    if (!isValidPath(path)) {
+        /* A lock file belonging to a path that we're building right
+           now isn't garbage. */
+        if (isActiveTempFile(state, path, ".lock")) return;
+
+        /* Don't delete .chroot directories for derivations that are
+           currently being built. */
+        if (isActiveTempFile(state, path, ".chroot")) return;
+    }
+
+    PathSet visited;
+
+    if (canReachRoot(state, visited, path)) {
+        printMsg(lvlDebug, format("cannot delete `%1%' because it's still reachable") % path);
+    } else {
+        /* No path we visited was a root, so everything is garbage.
+           But we only delete ‘path’ and its referrers here so that
+           ‘nix-store --delete’ doesn't have the unexpected effect of
+           recursing into derivations and outputs. */
+        state.dead.insert(visited.begin(), visited.end());
+        if (state.shouldDelete)
+            deletePathRecursive(state, path);
+    }
+}
+
+
+/* Unlink all files in /nix/store/.links that have a link count of 1,
+   which indicates that there are no other links and so they can be
+   safely deleted.  FIXME: race condition with optimisePath(): we
+   might see a link count of 1 just before optimisePath() increases
+   the link count. */
+void LocalStore::removeUnusedLinks(const GCState & state)
+{
+    AutoCloseDir dir = opendir(linksDir.c_str());
+    if (!dir) throw SysError(format("opening directory `%1%'") % linksDir);
+
+    long long actualSize = 0, unsharedSize = 0;
+
+    struct dirent * dirent;
+    while (errno = 0, dirent = readdir(dir)) {
+        checkInterrupt();
+        string name = dirent->d_name;
+        if (name == "." || name == "..") continue;
+        Path path = linksDir + "/" + name;
+
+        struct stat st;
+        if (lstat(path.c_str(), &st) == -1)
+            throw SysError(format("statting `%1%'") % path);
+
+        if (st.st_nlink != 1) {
+            unsigned long long size = st.st_blocks * 512ULL;
+            actualSize += size;
+            unsharedSize += (st.st_nlink - 1) * size;
+            continue;
+        }
+
+        printMsg(lvlTalkative, format("deleting unused link `%1%'") % path);
+
+        if (unlink(path.c_str()) == -1)
+            throw SysError(format("deleting `%1%'") % path);
+
+        state.results.bytesFreed += st.st_blocks * 512;
+    }
+
+    struct stat st;
+    if (stat(linksDir.c_str(), &st) == -1)
+        throw SysError(format("statting `%1%'") % linksDir);
+    long long overhead = st.st_blocks * 512ULL;
+
+    printMsg(lvlInfo, format("note: currently hard linking saves %.2f MiB")
+        % ((unsharedSize - actualSize - overhead) / (1024.0 * 1024.0)));
+}
+
+
+void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
+{
+    GCState state(results);
+    state.options = options;
+    state.trashDir = settings.nixStore + "/trash";
+    state.gcKeepOutputs = settings.gcKeepOutputs;
+    state.gcKeepDerivations = settings.gcKeepDerivations;
+
+    /* Using `--ignore-liveness' with `--delete' can have unintended
+       consequences if `gc-keep-outputs' or `gc-keep-derivations' are
+       true (the garbage collector will recurse into deleting the
+       outputs or derivers, respectively).  So disable them. */
+    if (options.action == GCOptions::gcDeleteSpecific && options.ignoreLiveness) {
+        state.gcKeepOutputs = false;
+        state.gcKeepDerivations = false;
+    }
+
+    state.shouldDelete = options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific;
+
+    /* Acquire the global GC root.  This prevents
+       a) New roots from being added.
+       b) Processes from creating new temporary root files. */
+    AutoCloseFD fdGCLock = openGCLock(ltWrite);
+
+    /* Find the roots.  Since we've grabbed the GC lock, the set of
+       permanent roots cannot increase now. */
+    printMsg(lvlError, format("finding garbage collector roots..."));
+    Roots rootMap = options.ignoreLiveness ? Roots() : findRoots();
+
+    foreach (Roots::iterator, i, rootMap) state.roots.insert(i->second);
+
+    /* Add additional roots returned by the program specified by the
+       NIX_ROOT_FINDER environment variable.  This is typically used
+       to add running programs to the set of roots (to prevent them
+       from being garbage collected). */
+    if (!options.ignoreLiveness)
+        addAdditionalRoots(*this, state.roots);
+
+    /* Read the temporary roots.  This acquires read locks on all
+       per-process temporary root files.  So after this point no paths
+       can be added to the set of temporary roots. */
+    FDs fds;
+    readTempRoots(state.tempRoots, fds);
+    state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());
+
+    /* After this point the set of roots or temporary roots cannot
+       increase, since we hold locks on everything.  So everything
+       that is not reachable from `roots'. */
+
+    if (state.shouldDelete) {
+        if (pathExists(state.trashDir)) deleteGarbage(state, state.trashDir);
+        createDirs(state.trashDir);
+    }
+
+    /* Now either delete all garbage paths, or just the specified
+       paths (for gcDeleteSpecific). */
+
+    if (options.action == GCOptions::gcDeleteSpecific) {
+
+        foreach (PathSet::iterator, i, options.pathsToDelete) {
+            assertStorePath(*i);
+            tryToDelete(state, *i);
+            if (state.dead.find(*i) == state.dead.end())
+                throw Error(format("cannot delete path `%1%' since it is still alive") % *i);
+        }
+
+    } else if (options.maxFreed > 0) {
+
+        if (state.shouldDelete)
+            printMsg(lvlError, format("deleting garbage..."));
+        else
+            printMsg(lvlError, format("determining live/dead paths..."));
+
+        try {
+
+            AutoCloseDir dir = opendir(settings.nixStore.c_str());
+            if (!dir) throw SysError(format("opening directory `%1%'") % settings.nixStore);
+
+            /* Read the store and immediately delete all paths that
+               aren't valid.  When using --max-freed etc., deleting
+               invalid paths is preferred over deleting unreachable
+               paths, since unreachable paths could become reachable
+               again.  We don't use readDirectory() here so that GCing
+               can start faster. */
+            Paths entries;
+            struct dirent * dirent;
+            while (errno = 0, dirent = readdir(dir)) {
+                checkInterrupt();
+                string name = dirent->d_name;
+                if (name == "." || name == "..") continue;
+                Path path = settings.nixStore + "/" + name;
+                if (isValidPath(path))
+                    entries.push_back(path);
+                else
+                    tryToDelete(state, path);
+            }
+
+            dir.close();
+
+            /* Now delete the unreachable valid paths.  Randomise the
+               order in which we delete entries to make the collector
+               less biased towards deleting paths that come
+               alphabetically first (e.g. /nix/store/000...).  This
+               matters when using --max-freed etc. */
+            vector<Path> entries_(entries.begin(), entries.end());
+            random_shuffle(entries_.begin(), entries_.end());
+
+            foreach (vector<Path>::iterator, i, entries_)
+                tryToDelete(state, *i);
+
+        } catch (GCLimitReached & e) {
+        }
+    }
+
+    if (state.options.action == GCOptions::gcReturnLive) {
+        state.results.paths = state.alive;
+        return;
+    }
+
+    if (state.options.action == GCOptions::gcReturnDead) {
+        state.results.paths = state.dead;
+        return;
+    }
+
+    /* Allow other processes to add to the store from here on. */
+    fdGCLock.close();
+    fds.clear();
+
+    /* Delete the trash directory. */
+    printMsg(lvlInfo, format("deleting `%1%'") % state.trashDir);
+    deleteGarbage(state, state.trashDir);
+
+    /* Clean up the links directory. */
+    if (options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific) {
+        printMsg(lvlError, format("deleting unused links..."));
+        removeUnusedLinks(state);
+    }
+
+    /* While we're at it, vacuum the database. */
+    if (options.action == GCOptions::gcDeleteDead) vacuumDB();
+}
+
+
+}
diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
new file mode 100644
index 000000000000..68add1982f43
--- /dev/null
+++ b/src/libstore/globals.cc
@@ -0,0 +1,218 @@
+#include "config.h"
+
+#include "globals.hh"
+#include "util.hh"
+
+#include <map>
+#include <algorithm>
+
+
+namespace nix {
+
+
+/* The default location of the daemon socket, relative to nixStateDir.
+   The socket is in a directory to allow you to control access to the
+   Nix daemon by setting the mode/ownership of the directory
+   appropriately.  (This wouldn't work on the socket itself since it
+   must be deleted and recreated on startup.) */
+#define DEFAULT_SOCKET_PATH "/daemon-socket/socket"
+
+
+Settings settings;
+
+
+Settings::Settings()
+{
+    keepFailed = false;
+    keepGoing = false;
+    tryFallback = false;
+    buildVerbosity = lvlError;
+    maxBuildJobs = 1;
+    buildCores = 1;
+    readOnlyMode = false;
+    thisSystem = SYSTEM;
+    maxSilentTime = 0;
+    buildTimeout = 0;
+    useBuildHook = true;
+    printBuildTrace = false;
+    reservedSize = 1024 * 1024;
+    fsyncMetadata = true;
+    useSQLiteWAL = true;
+    syncBeforeRegistering = false;
+    useSubstitutes = true;
+    useChroot = false;
+    dirsInChroot.insert("/dev");
+    dirsInChroot.insert("/dev/pts");
+    impersonateLinux26 = false;
+    keepLog = true;
+    compressLog = true;
+    maxLogSize = 0;
+    cacheFailure = false;
+    pollInterval = 5;
+    checkRootReachability = false;
+    gcKeepOutputs = false;
+    gcKeepDerivations = true;
+    autoOptimiseStore = false;
+    envKeepDerivations = false;
+    lockCPU = getEnv("NIX_AFFINITY_HACK", "1") == "1";
+    showTrace = false;
+}
+
+
+void Settings::processEnvironment()
+{
+    nixStore = canonPath(getEnv("NIX_STORE_DIR", getEnv("NIX_STORE", NIX_STORE_DIR)));
+    nixDataDir = canonPath(getEnv("NIX_DATA_DIR", NIX_DATA_DIR));
+    nixLogDir = canonPath(getEnv("NIX_LOG_DIR", NIX_LOG_DIR));
+    nixStateDir = canonPath(getEnv("NIX_STATE_DIR", NIX_STATE_DIR));
+    nixDBPath = getEnv("NIX_DB_DIR", nixStateDir + "/db");
+    nixConfDir = canonPath(getEnv("NIX_CONF_DIR", NIX_CONF_DIR));
+    nixLibexecDir = canonPath(getEnv("NIX_LIBEXEC_DIR", NIX_LIBEXEC_DIR));
+    nixBinDir = canonPath(getEnv("NIX_BIN_DIR", NIX_BIN_DIR));
+    nixDaemonSocketFile = canonPath(nixStateDir + DEFAULT_SOCKET_PATH);
+
+    string subs = getEnv("NIX_SUBSTITUTERS", "default");
+    if (subs == "default") {
+#if 0
+        if (getEnv("NIX_OTHER_STORES") != "")
+            substituters.push_back(nixLibexecDir + "/nix/substituters/copy-from-other-stores.pl");
+#endif
+        substituters.push_back(nixLibexecDir + "/nix/substituters/download-using-manifests.pl");
+        substituters.push_back(nixLibexecDir + "/nix/substituters/download-from-binary-cache.pl");
+    } else
+        substituters = tokenizeString<Strings>(subs, ":");
+}
+
+
+void Settings::loadConfFile()
+{
+    Path settingsFile = (format("%1%/%2%") % nixConfDir % "nix.conf").str();
+    if (!pathExists(settingsFile)) return;
+    string contents = readFile(settingsFile);
+
+    unsigned int pos = 0;
+
+    while (pos < contents.size()) {
+        string line;
+        while (pos < contents.size() && contents[pos] != '\n')
+            line += contents[pos++];
+        pos++;
+
+        string::size_type hash = line.find('#');
+        if (hash != string::npos)
+            line = string(line, 0, hash);
+
+        vector<string> tokens = tokenizeString<vector<string> >(line);
+        if (tokens.empty()) continue;
+
+        if (tokens.size() < 2 || tokens[1] != "=")
+            throw Error(format("illegal configuration line `%1%' in `%2%'") % line % settingsFile);
+
+        string name = tokens[0];
+
+        vector<string>::iterator i = tokens.begin();
+        advance(i, 2);
+        settings[name] = concatStringsSep(" ", Strings(i, tokens.end())); // FIXME: slow
+    };
+}
+
+
+void Settings::set(const string & name, const string & value)
+{
+    settings[name] = value;
+    overrides[name] = value;
+}
+
+
+void Settings::update()
+{
+    get(tryFallback, "build-fallback");
+    get(maxBuildJobs, "build-max-jobs");
+    get(buildCores, "build-cores");
+    get(thisSystem, "system");
+    get(maxSilentTime, "build-max-silent-time");
+    get(buildTimeout, "build-timeout");
+    get(reservedSize, "gc-reserved-space");
+    get(fsyncMetadata, "fsync-metadata");
+    get(useSQLiteWAL, "use-sqlite-wal");
+    get(syncBeforeRegistering, "sync-before-registering");
+    get(useSubstitutes, "build-use-substitutes");
+    get(buildUsersGroup, "build-users-group");
+    get(useChroot, "build-use-chroot");
+    get(dirsInChroot, "build-chroot-dirs");
+    get(impersonateLinux26, "build-impersonate-linux-26");
+    get(keepLog, "build-keep-log");
+    get(compressLog, "build-compress-log");
+    get(maxLogSize, "build-max-log-size");
+    get(cacheFailure, "build-cache-failure");
+    get(pollInterval, "build-poll-interval");
+    get(checkRootReachability, "gc-check-reachability");
+    get(gcKeepOutputs, "gc-keep-outputs");
+    get(gcKeepDerivations, "gc-keep-derivations");
+    get(autoOptimiseStore, "auto-optimise-store");
+    get(envKeepDerivations, "env-keep-derivations");
+}
+
+
+void Settings::get(string & res, const string & name)
+{
+    SettingsMap::iterator i = settings.find(name);
+    if (i == settings.end()) return;
+    res = i->second;
+}
+
+
+void Settings::get(bool & res, const string & name)
+{
+    SettingsMap::iterator i = settings.find(name);
+    if (i == settings.end()) return;
+    if (i->second == "true") res = true;
+    else if (i->second == "false") res = false;
+    else throw Error(format("configuration option `%1%' should be either `true' or `false', not `%2%'")
+        % name % i->second);
+}
+
+
+void Settings::get(StringSet & res, const string & name)
+{
+    SettingsMap::iterator i = settings.find(name);
+    if (i == settings.end()) return;
+    res.clear();
+    Strings ss = tokenizeString<Strings>(i->second);
+    res.insert(ss.begin(), ss.end());
+}
+
+
+template<class N> void Settings::get(N & res, const string & name)
+{
+    SettingsMap::iterator i = settings.find(name);
+    if (i == settings.end()) return;
+    if (!string2Int(i->second, res))
+        throw Error(format("configuration setting `%1%' should have an integer value") % name);
+}
+
+
+string Settings::pack()
+{
+    string s;
+    foreach (SettingsMap::iterator, i, settings) {
+        if (i->first.find('\n') != string::npos ||
+            i->first.find('=') != string::npos ||
+            i->second.find('\n') != string::npos)
+            throw Error("illegal option name/value");
+        s += i->first; s += '='; s += i->second; s += '\n';
+    }
+    return s;
+}
+
+
+Settings::SettingsMap Settings::getOverrides()
+{
+    return overrides;
+}
+
+
+const string nixVersion = PACKAGE_VERSION;
+
+
+}
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
new file mode 100644
index 000000000000..9300edbe9615
--- /dev/null
+++ b/src/libstore/globals.hh
@@ -0,0 +1,209 @@
+#pragma once
+
+#include "types.hh"
+
+#include <map>
+#include <sys/types.h>
+
+
+namespace nix {
+
+
+struct Settings {
+
+    typedef std::map<string, string> SettingsMap;
+
+    Settings();
+
+    void processEnvironment();
+
+    void loadConfFile();
+
+    void set(const string & name, const string & value);
+
+    void update();
+
+    string pack();
+
+    SettingsMap getOverrides();
+
+    /* The directory where we store sources and derived files. */
+    Path nixStore;
+
+    Path nixDataDir; /* !!! fix */
+
+    /* The directory where we log various operations. */
+    Path nixLogDir;
+
+    /* The directory where state is stored. */
+    Path nixStateDir;
+
+    /* The directory where we keep the SQLite database. */
+    Path nixDBPath;
+
+    /* The directory where configuration files are stored. */
+    Path nixConfDir;
+
+    /* The directory where internal helper programs are stored. */
+    Path nixLibexecDir;
+
+    /* The directory where the main programs are stored. */
+    Path nixBinDir;
+
+    /* File name of the socket the daemon listens to.  */
+    Path nixDaemonSocketFile;
+
+    /* Whether to keep temporary directories of failed builds. */
+    bool keepFailed;
+
+    /* Whether to keep building subgoals when a sibling (another
+       subgoal of the same goal) fails. */
+    bool keepGoing;
+
+    /* Whether, if we cannot realise the known closure corresponding
+       to a derivation, we should try to normalise the derivation
+       instead. */
+    bool tryFallback;
+
+    /* Verbosity level for build output. */
+    Verbosity buildVerbosity;
+
+    /* Maximum number of parallel build jobs.  0 means unlimited. */
+    unsigned int maxBuildJobs;
+
+    /* Number of CPU cores to utilize in parallel within a build,
+       i.e. by passing this number to Make via '-j'. 0 means that the
+       number of actual CPU cores on the local host ought to be
+       auto-detected. */
+    unsigned int buildCores;
+
+    /* Read-only mode.  Don't copy stuff to the store, don't change
+       the database. */
+    bool readOnlyMode;
+
+    /* The canonical system name, as returned by config.guess. */
+    string thisSystem;
+
+    /* The maximum time in seconds that a builer can go without
+       producing any output on stdout/stderr before it is killed.  0
+       means infinity. */
+    time_t maxSilentTime;
+
+    /* The maximum duration in seconds that a builder can run.  0
+       means infinity.  */
+    time_t buildTimeout;
+
+    /* The substituters.  There are programs that can somehow realise
+       a store path without building, e.g., by downloading it or
+       copying it from a CD. */
+    Paths substituters;
+
+    /* Whether to use build hooks (for distributed builds).  Sometimes
+       users want to disable this from the command-line. */
+    bool useBuildHook;
+
+    /* Whether buildDerivations() should print out lines on stderr in
+       a fixed format to allow its progress to be monitored.  Each
+       line starts with a "@".  The following are defined:
+
+       @ build-started <drvpath> <outpath> <system> <logfile>
+       @ build-failed <drvpath> <outpath> <exitcode> <error text>
+       @ build-succeeded <drvpath> <outpath>
+       @ substituter-started <outpath> <substituter>
+       @ substituter-failed <outpath> <exitcode> <error text>
+       @ substituter-succeeded <outpath>
+
+       Best combined with --no-build-output, otherwise stderr might
+       conceivably contain lines in this format printed by the
+       builders. */
+    bool printBuildTrace;
+
+    /* Amount of reserved space for the garbage collector
+       (/nix/var/nix/db/reserved). */
+    off_t reservedSize;
+
+    /* Whether SQLite should use fsync. */
+    bool fsyncMetadata;
+
+    /* Whether SQLite should use WAL mode. */
+    bool useSQLiteWAL;
+
+    /* Whether to call sync() before registering a path as valid. */
+    bool syncBeforeRegistering;
+
+    /* Whether to use substitutes. */
+    bool useSubstitutes;
+
+    /* The Unix group that contains the build users. */
+    string buildUsersGroup;
+
+    /* Whether to build in chroot. */
+    bool useChroot;
+
+    /* The directories from the host filesystem to be included in the
+       chroot. */
+    StringSet dirsInChroot;
+
+    /* Whether to impersonate a Linux 2.6 machine on newer kernels. */
+    bool impersonateLinux26;
+
+    /* Whether to store build logs. */
+    bool keepLog;
+
+    /* Whether to compress logs. */
+    bool compressLog;
+
+    /* Maximum number of bytes a builder can write to stdout/stderr
+       before being killed (0 means no limit). */
+    unsigned long maxLogSize;
+
+    /* Whether to cache build failures. */
+    bool cacheFailure;
+
+    /* How often (in seconds) to poll for locks. */
+    unsigned int pollInterval;
+
+    /* Whether to check if new GC roots can in fact be found by the
+       garbage collector. */
+    bool checkRootReachability;
+
+    /* Whether the garbage collector should keep outputs of live
+       derivations. */
+    bool gcKeepOutputs;
+
+    /* Whether the garbage collector should keep derivers of live
+       paths. */
+    bool gcKeepDerivations;
+
+    /* Whether to automatically replace files with identical contents
+       with hard links. */
+    bool autoOptimiseStore;
+
+    /* Whether to add derivations as a dependency of user environments
+       (to prevent them from being GCed). */
+    bool envKeepDerivations;
+
+    /* Whether to lock the Nix client and worker to the same CPU. */
+    bool lockCPU;
+
+    /* Whether to show a stack trace if Nix evaluation fails. */
+    bool showTrace;
+
+private:
+    SettingsMap settings, overrides;
+
+    void get(string & res, const string & name);
+    void get(bool & res, const string & name);
+    void get(StringSet & res, const string & name);
+    template<class N> void get(N & res, const string & name);
+};
+
+
+// FIXME: don't use a global variable.
+extern Settings settings;
+
+
+extern const string nixVersion;
+
+
+}
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
new file mode 100644
index 000000000000..3c367c080815
--- /dev/null
+++ b/src/libstore/local-store.cc
@@ -0,0 +1,1996 @@
+#include "config.h"
+#include "local-store.hh"
+#include "globals.hh"
+#include "archive.hh"
+#include "pathlocks.hh"
+#include "worker-protocol.hh"
+#include "derivations.hh"
+#include "affinity.hh"
+
+#include <iostream>
+#include <algorithm>
+#include <cstring>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <utime.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdio.h>
+#include <time.h>
+
+#if HAVE_UNSHARE && HAVE_STATVFS && HAVE_SYS_MOUNT_H
+#include <sched.h>
+#include <sys/statvfs.h>
+#include <sys/mount.h>
+#endif
+
+#if HAVE_LINUX_FS_H
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#include <errno.h>
+#endif
+
+#include <sqlite3.h>
+
+
+namespace nix {
+
+
+MakeError(SQLiteError, Error);
+MakeError(SQLiteBusy, SQLiteError);
+
+
+static void throwSQLiteError(sqlite3 * db, const format & f)
+    __attribute__ ((noreturn));
+
+static void throwSQLiteError(sqlite3 * db, const format & f)
+{
+    int err = sqlite3_errcode(db);
+    if (err == SQLITE_BUSY || err == SQLITE_PROTOCOL) {
+        if (err == SQLITE_PROTOCOL)
+            printMsg(lvlError, "warning: SQLite database is busy (SQLITE_PROTOCOL)");
+        else {
+            static bool warned = false;
+            if (!warned) {
+                printMsg(lvlError, "warning: SQLite database is busy");
+                warned = true;
+            }
+        }
+        /* Sleep for a while since retrying the transaction right away
+           is likely to fail again. */
+#if HAVE_NANOSLEEP
+        struct timespec t;
+        t.tv_sec = 0;
+        t.tv_nsec = (random() % 100) * 1000 * 1000; /* <= 0.1s */
+        nanosleep(&t, 0);
+#else
+        sleep(1);
+#endif
+        throw SQLiteBusy(format("%1%: %2%") % f.str() % sqlite3_errmsg(db));
+    }
+    else
+        throw SQLiteError(format("%1%: %2%") % f.str() % sqlite3_errmsg(db));
+}
+
+
+/* Convenience macros for retrying a SQLite transaction. */
+#define retry_sqlite while (1) { try {
+#define end_retry_sqlite break; } catch (SQLiteBusy & e) { } }
+
+
+SQLite::~SQLite()
+{
+    try {
+        if (db && sqlite3_close(db) != SQLITE_OK)
+            throwSQLiteError(db, "closing database");
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void SQLiteStmt::create(sqlite3 * db, const string & s)
+{
+    checkInterrupt();
+    assert(!stmt);
+    if (sqlite3_prepare_v2(db, s.c_str(), -1, &stmt, 0) != SQLITE_OK)
+        throwSQLiteError(db, "creating statement");
+    this->db = db;
+}
+
+
+void SQLiteStmt::reset()
+{
+    assert(stmt);
+    /* Note: sqlite3_reset() returns the error code for the most
+       recent call to sqlite3_step().  So ignore it. */
+    sqlite3_reset(stmt);
+    curArg = 1;
+}
+
+
+SQLiteStmt::~SQLiteStmt()
+{
+    try {
+        if (stmt && sqlite3_finalize(stmt) != SQLITE_OK)
+            throwSQLiteError(db, "finalizing statement");
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void SQLiteStmt::bind(const string & value)
+{
+    if (sqlite3_bind_text(stmt, curArg++, value.c_str(), -1, SQLITE_TRANSIENT) != SQLITE_OK)
+        throwSQLiteError(db, "binding argument");
+}
+
+
+void SQLiteStmt::bind(int value)
+{
+    if (sqlite3_bind_int(stmt, curArg++, value) != SQLITE_OK)
+        throwSQLiteError(db, "binding argument");
+}
+
+
+void SQLiteStmt::bind64(long long value)
+{
+    if (sqlite3_bind_int64(stmt, curArg++, value) != SQLITE_OK)
+        throwSQLiteError(db, "binding argument");
+}
+
+
+void SQLiteStmt::bind()
+{
+    if (sqlite3_bind_null(stmt, curArg++) != SQLITE_OK)
+        throwSQLiteError(db, "binding argument");
+}
+
+
+/* Helper class to ensure that prepared statements are reset when
+   leaving the scope that uses them.  Unfinished prepared statements
+   prevent transactions from being aborted, and can cause locks to be
+   kept when they should be released. */
+struct SQLiteStmtUse
+{
+    SQLiteStmt & stmt;
+    SQLiteStmtUse(SQLiteStmt & stmt) : stmt(stmt)
+    {
+        stmt.reset();
+    }
+    ~SQLiteStmtUse()
+    {
+        try {
+            stmt.reset();
+        } catch (...) {
+            ignoreException();
+        }
+    }
+};
+
+
+struct SQLiteTxn
+{
+    bool active;
+    sqlite3 * db;
+
+    SQLiteTxn(sqlite3 * db) : active(false) {
+        this->db = db;
+        if (sqlite3_exec(db, "begin;", 0, 0, 0) != SQLITE_OK)
+            throwSQLiteError(db, "starting transaction");
+        active = true;
+    }
+
+    void commit()
+    {
+        if (sqlite3_exec(db, "commit;", 0, 0, 0) != SQLITE_OK)
+            throwSQLiteError(db, "committing transaction");
+        active = false;
+    }
+
+    ~SQLiteTxn()
+    {
+        try {
+            if (active && sqlite3_exec(db, "rollback;", 0, 0, 0) != SQLITE_OK)
+                throwSQLiteError(db, "aborting transaction");
+        } catch (...) {
+            ignoreException();
+        }
+    }
+};
+
+
+void checkStoreNotSymlink()
+{
+    if (getEnv("NIX_IGNORE_SYMLINK_STORE") == "1") return;
+    Path path = settings.nixStore;
+    struct stat st;
+    while (path != "/") {
+        if (lstat(path.c_str(), &st))
+            throw SysError(format("getting status of `%1%'") % path);
+        if (S_ISLNK(st.st_mode))
+            throw Error(format(
+                "the path `%1%' is a symlink; "
+                "this is not allowed for the Nix store and its parent directories")
+                % path);
+        path = dirOf(path);
+    }
+}
+
+
+LocalStore::LocalStore(bool reserveSpace)
+    : didSetSubstituterEnv(false)
+{
+    schemaPath = settings.nixDBPath + "/schema";
+
+    if (settings.readOnlyMode) {
+        openDB(false);
+        return;
+    }
+
+    /* Create missing state directories if they don't already exist. */
+    createDirs(settings.nixStore);
+    makeStoreWritable();
+    createDirs(linksDir = settings.nixStore + "/.links");
+    Path profilesDir = settings.nixStateDir + "/profiles";
+    createDirs(settings.nixStateDir + "/profiles");
+    createDirs(settings.nixStateDir + "/temproots");
+    createDirs(settings.nixDBPath);
+    Path gcRootsDir = settings.nixStateDir + "/gcroots";
+    if (!pathExists(gcRootsDir)) {
+        createDirs(gcRootsDir);
+        if (symlink(profilesDir.c_str(), (gcRootsDir + "/profiles").c_str()) == -1)
+            throw SysError(format("creating symlink to `%1%'") % profilesDir);
+    }
+
+    checkStoreNotSymlink();
+
+    /* We can't open a SQLite database if the disk is full.  Since
+       this prevents the garbage collector from running when it's most
+       needed, we reserve some dummy space that we can free just
+       before doing a garbage collection. */
+    try {
+        Path reservedPath = settings.nixDBPath + "/reserved";
+        if (reserveSpace) {
+            struct stat st;
+            if (stat(reservedPath.c_str(), &st) == -1 ||
+                st.st_size != settings.reservedSize)
+                writeFile(reservedPath, string(settings.reservedSize, 'X'));
+        }
+        else
+            deletePath(reservedPath);
+    } catch (SysError & e) { /* don't care about errors */
+    }
+
+    /* Acquire the big fat lock in shared mode to make sure that no
+       schema upgrade is in progress. */
+    try {
+        Path globalLockPath = settings.nixDBPath + "/big-lock";
+        globalLock = openLockFile(globalLockPath.c_str(), true);
+    } catch (SysError & e) {
+        if (e.errNo != EACCES) throw;
+        settings.readOnlyMode = true;
+        openDB(false);
+        return;
+    }
+
+    if (!lockFile(globalLock, ltRead, false)) {
+        printMsg(lvlError, "waiting for the big Nix store lock...");
+        lockFile(globalLock, ltRead, true);
+    }
+
+    /* Check the current database schema and if necessary do an
+       upgrade.  */
+    int curSchema = getSchema();
+    if (curSchema > nixSchemaVersion)
+        throw Error(format("current Nix store schema is version %1%, but I only support %2%")
+            % curSchema % nixSchemaVersion);
+
+    else if (curSchema == 0) { /* new store */
+        curSchema = nixSchemaVersion;
+        openDB(true);
+        writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
+    }
+
+    else if (curSchema < nixSchemaVersion) {
+        if (curSchema < 5)
+            throw Error(
+                "Your Nix store has a database in Berkeley DB format,\n"
+                "which is no longer supported. To convert to the new format,\n"
+                "please upgrade Nix to version 0.12 first.");
+
+        if (!lockFile(globalLock, ltWrite, false)) {
+            printMsg(lvlError, "waiting for exclusive access to the Nix store...");
+            lockFile(globalLock, ltWrite, true);
+        }
+
+        /* Get the schema version again, because another process may
+           have performed the upgrade already. */
+        curSchema = getSchema();
+
+        if (curSchema < 6) upgradeStore6();
+        else if (curSchema < 7) { upgradeStore7(); openDB(true); }
+
+        writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
+
+        lockFile(globalLock, ltRead, true);
+    }
+
+    else openDB(false);
+}
+
+
+LocalStore::~LocalStore()
+{
+    try {
+        foreach (RunningSubstituters::iterator, i, runningSubstituters) {
+            if (i->second.disabled) continue;
+            i->second.to.close();
+            i->second.from.close();
+            i->second.error.close();
+            i->second.pid.wait(true);
+        }
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+int LocalStore::getSchema()
+{
+    int curSchema = 0;
+    if (pathExists(schemaPath)) {
+        string s = readFile(schemaPath);
+        if (!string2Int(s, curSchema))
+            throw Error(format("`%1%' is corrupt") % schemaPath);
+    }
+    return curSchema;
+}
+
+
+void LocalStore::openDB(bool create)
+{
+    /* Open the Nix database. */
+    if (sqlite3_open_v2((settings.nixDBPath + "/db.sqlite").c_str(), &db.db,
+            SQLITE_OPEN_READWRITE | (create ? SQLITE_OPEN_CREATE : 0), 0) != SQLITE_OK)
+        throw Error("cannot open SQLite database");
+
+    if (sqlite3_busy_timeout(db, 60 * 60 * 1000) != SQLITE_OK)
+        throwSQLiteError(db, "setting timeout");
+
+    if (sqlite3_exec(db, "pragma foreign_keys = 1;", 0, 0, 0) != SQLITE_OK)
+        throwSQLiteError(db, "enabling foreign keys");
+
+    /* !!! check whether sqlite has been built with foreign key
+       support */
+
+    /* Whether SQLite should fsync().  "Normal" synchronous mode
+       should be safe enough.  If the user asks for it, don't sync at
+       all.  This can cause database corruption if the system
+       crashes. */
+    string syncMode = settings.fsyncMetadata ? "normal" : "off";
+    if (sqlite3_exec(db, ("pragma synchronous = " + syncMode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
+        throwSQLiteError(db, "setting synchronous mode");
+
+    /* Set the SQLite journal mode.  WAL mode is fastest, so it's the
+       default. */
+    string mode = settings.useSQLiteWAL ? "wal" : "truncate";
+    string prevMode;
+    {
+        SQLiteStmt stmt;
+        stmt.create(db, "pragma main.journal_mode;");
+        if (sqlite3_step(stmt) != SQLITE_ROW)
+            throwSQLiteError(db, "querying journal mode");
+        prevMode = string((const char *) sqlite3_column_text(stmt, 0));
+    }
+    if (prevMode != mode &&
+        sqlite3_exec(db, ("pragma main.journal_mode = " + mode + ";").c_str(), 0, 0, 0) != SQLITE_OK)
+        throwSQLiteError(db, "setting journal mode");
+
+    /* Increase the auto-checkpoint interval to 40000 pages.  This
+       seems enough to ensure that instantiating the NixOS system
+       derivation is done in a single fsync(). */
+    if (mode == "wal" && sqlite3_exec(db, "pragma wal_autocheckpoint = 40000;", 0, 0, 0) != SQLITE_OK)
+        throwSQLiteError(db, "setting autocheckpoint interval");
+
+    /* Initialise the database schema, if necessary. */
+    if (create) {
+        const char * schema =
+#include "schema.sql.hh"
+            ;
+        if (sqlite3_exec(db, (const char *) schema, 0, 0, 0) != SQLITE_OK)
+            throwSQLiteError(db, "initialising database schema");
+    }
+
+    /* Prepare SQL statements. */
+    stmtRegisterValidPath.create(db,
+        "insert into ValidPaths (path, hash, registrationTime, deriver, narSize) values (?, ?, ?, ?, ?);");
+    stmtUpdatePathInfo.create(db,
+        "update ValidPaths set narSize = ?, hash = ? where path = ?;");
+    stmtAddReference.create(db,
+        "insert or replace into Refs (referrer, reference) values (?, ?);");
+    stmtQueryPathInfo.create(db,
+        "select id, hash, registrationTime, deriver, narSize from ValidPaths where path = ?;");
+    stmtQueryReferences.create(db,
+        "select path from Refs join ValidPaths on reference = id where referrer = ?;");
+    stmtQueryReferrers.create(db,
+        "select path from Refs join ValidPaths on referrer = id where reference = (select id from ValidPaths where path = ?);");
+    stmtInvalidatePath.create(db,
+        "delete from ValidPaths where path = ?;");
+    stmtRegisterFailedPath.create(db,
+        "insert or ignore into FailedPaths (path, time) values (?, ?);");
+    stmtHasPathFailed.create(db,
+        "select time from FailedPaths where path = ?;");
+    stmtQueryFailedPaths.create(db,
+        "select path from FailedPaths;");
+    // If the path is a derivation, then clear its outputs.
+    stmtClearFailedPath.create(db,
+        "delete from FailedPaths where ?1 = '*' or path = ?1 "
+        "or path in (select d.path from DerivationOutputs d join ValidPaths v on d.drv = v.id where v.path = ?1);");
+    stmtAddDerivationOutput.create(db,
+        "insert or replace into DerivationOutputs (drv, id, path) values (?, ?, ?);");
+    stmtQueryValidDerivers.create(db,
+        "select v.id, v.path from DerivationOutputs d join ValidPaths v on d.drv = v.id where d.path = ?;");
+    stmtQueryDerivationOutputs.create(db,
+        "select id, path from DerivationOutputs where drv = ?;");
+    // Use "path >= ?" with limit 1 rather than "path like '?%'" to
+    // ensure efficient lookup.
+    stmtQueryPathFromHashPart.create(db,
+        "select path from ValidPaths where path >= ? limit 1;");
+}
+
+
+/* To improve purity, users may want to make the Nix store a read-only
+   bind mount.  So make the Nix store writable for this process. */
+void LocalStore::makeStoreWritable()
+{
+#if HAVE_UNSHARE && HAVE_STATVFS && HAVE_SYS_MOUNT_H && defined(MS_BIND) && defined(MS_REMOUNT)
+    if (getuid() != 0) return;
+    /* Check if /nix/store is on a read-only mount. */
+    struct statvfs stat;
+    if (statvfs(settings.nixStore.c_str(), &stat) !=0)
+        throw SysError("Getting info of nix store mountpoint");
+
+    if (stat.f_flag & ST_RDONLY) {
+        if (unshare(CLONE_NEWNS) == -1)
+            throw SysError("setting up a private mount namespace");
+
+        if (mount(0, settings.nixStore.c_str(), 0, MS_REMOUNT | MS_BIND, 0) == -1)
+            throw SysError(format("remounting %1% writable") % settings.nixStore);
+    }
+#endif
+}
+
+
+const time_t mtimeStore = 1; /* 1 second into the epoch */
+
+
+static void canonicaliseTimestampAndPermissions(const Path & path, const struct stat & st)
+{
+    if (!S_ISLNK(st.st_mode)) {
+
+        /* Mask out all type related bits. */
+        mode_t mode = st.st_mode & ~S_IFMT;
+
+        if (mode != 0444 && mode != 0555) {
+            mode = (st.st_mode & S_IFMT)
+                 | 0444
+                 | (st.st_mode & S_IXUSR ? 0111 : 0);
+            if (chmod(path.c_str(), mode) == -1)
+                throw SysError(format("changing mode of `%1%' to %2$o") % path % mode);
+        }
+
+    }
+
+    if (st.st_mtime != mtimeStore) {
+        struct timeval times[2];
+        times[0].tv_sec = st.st_atime;
+        times[0].tv_usec = 0;
+        times[1].tv_sec = mtimeStore;
+        times[1].tv_usec = 0;
+#if HAVE_LUTIMES
+        if (lutimes(path.c_str(), times) == -1)
+            if (errno != ENOSYS ||
+                (!S_ISLNK(st.st_mode) && utimes(path.c_str(), times) == -1))
+#else
+        if (!S_ISLNK(st.st_mode) && utimes(path.c_str(), times) == -1)
+#endif
+            throw SysError(format("changing modification time of `%1%'") % path);
+    }
+}
+
+
+void canonicaliseTimestampAndPermissions(const Path & path)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+    canonicaliseTimestampAndPermissions(path, st);
+}
+
+
+static void canonicalisePathMetaData_(const Path & path, uid_t fromUid, InodesSeen & inodesSeen)
+{
+    checkInterrupt();
+
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+
+    /* Really make sure that the path is of a supported type.  This
+       has already been checked in dumpPath(). */
+    assert(S_ISREG(st.st_mode) || S_ISDIR(st.st_mode) || S_ISLNK(st.st_mode));
+
+    /* Fail if the file is not owned by the build user.  This prevents
+       us from messing up the ownership/permissions of files
+       hard-linked into the output (e.g. "ln /etc/shadow $out/foo").
+       However, ignore files that we chown'ed ourselves previously to
+       ensure that we don't fail on hard links within the same build
+       (i.e. "touch $out/foo; ln $out/foo $out/bar"). */
+    if (fromUid != (uid_t) -1 && st.st_uid != fromUid) {
+        assert(!S_ISDIR(st.st_mode));
+        if (inodesSeen.find(Inode(st.st_dev, st.st_ino)) == inodesSeen.end())
+            throw BuildError(format("invalid ownership on file `%1%'") % path);
+        mode_t mode = st.st_mode & ~S_IFMT;
+        assert(S_ISLNK(st.st_mode) || (st.st_uid == geteuid() && (mode == 0444 || mode == 0555) && st.st_mtime == mtimeStore));
+        return;
+    }
+
+    inodesSeen.insert(Inode(st.st_dev, st.st_ino));
+
+    canonicaliseTimestampAndPermissions(path, st);
+
+    /* Change ownership to the current uid.  If it's a symlink, use
+       lchown if available, otherwise don't bother.  Wrong ownership
+       of a symlink doesn't matter, since the owning user can't change
+       the symlink and can't delete it because the directory is not
+       writable.  The only exception is top-level paths in the Nix
+       store (since that directory is group-writable for the Nix build
+       users group); we check for this case below. */
+    if (st.st_uid != geteuid()) {
+#if HAVE_LCHOWN
+        if (lchown(path.c_str(), geteuid(), (gid_t) -1) == -1)
+#else
+        if (!S_ISLNK(st.st_mode) &&
+            chown(path.c_str(), geteuid(), (gid_t) -1) == -1)
+#endif
+            throw SysError(format("changing owner of `%1%' to %2%")
+                % path % geteuid());
+    }
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+        foreach (Strings::iterator, i, names)
+            canonicalisePathMetaData_(path + "/" + *i, fromUid, inodesSeen);
+    }
+}
+
+
+void canonicalisePathMetaData(const Path & path, uid_t fromUid, InodesSeen & inodesSeen)
+{
+    canonicalisePathMetaData_(path, fromUid, inodesSeen);
+
+    /* On platforms that don't have lchown(), the top-level path can't
+       be a symlink, since we can't change its ownership. */
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+
+    if (st.st_uid != geteuid()) {
+        assert(S_ISLNK(st.st_mode));
+        throw Error(format("wrong ownership of top-level store path `%1%'") % path);
+    }
+}
+
+
+void canonicalisePathMetaData(const Path & path, uid_t fromUid)
+{
+    InodesSeen inodesSeen;
+    canonicalisePathMetaData(path, fromUid, inodesSeen);
+}
+
+
+void LocalStore::checkDerivationOutputs(const Path & drvPath, const Derivation & drv)
+{
+    string drvName = storePathToName(drvPath);
+    assert(isDerivation(drvName));
+    drvName = string(drvName, 0, drvName.size() - drvExtension.size());
+
+    if (isFixedOutputDrv(drv)) {
+        DerivationOutputs::const_iterator out = drv.outputs.find("out");
+        if (out == drv.outputs.end())
+            throw Error(format("derivation `%1%' does not have an output named `out'") % drvPath);
+
+        bool recursive; HashType ht; Hash h;
+        out->second.parseHashInfo(recursive, ht, h);
+        Path outPath = makeFixedOutputPath(recursive, ht, h, drvName);
+
+        StringPairs::const_iterator j = drv.env.find("out");
+        if (out->second.path != outPath || j == drv.env.end() || j->second != outPath)
+            throw Error(format("derivation `%1%' has incorrect output `%2%', should be `%3%'")
+                % drvPath % out->second.path % outPath);
+    }
+
+    else {
+        Derivation drvCopy(drv);
+        foreach (DerivationOutputs::iterator, i, drvCopy.outputs) {
+            i->second.path = "";
+            drvCopy.env[i->first] = "";
+        }
+
+        Hash h = hashDerivationModulo(*this, drvCopy);
+
+        foreach (DerivationOutputs::const_iterator, i, drv.outputs) {
+            Path outPath = makeOutputPath(i->first, h, drvName);
+            StringPairs::const_iterator j = drv.env.find(i->first);
+            if (i->second.path != outPath || j == drv.env.end() || j->second != outPath)
+                throw Error(format("derivation `%1%' has incorrect output `%2%', should be `%3%'")
+                    % drvPath % i->second.path % outPath);
+        }
+    }
+}
+
+
+unsigned long long LocalStore::addValidPath(const ValidPathInfo & info, bool checkOutputs)
+{
+    SQLiteStmtUse use(stmtRegisterValidPath);
+    stmtRegisterValidPath.bind(info.path);
+    stmtRegisterValidPath.bind("sha256:" + printHash(info.hash));
+    stmtRegisterValidPath.bind(info.registrationTime == 0 ? time(0) : info.registrationTime);
+    if (info.deriver != "")
+        stmtRegisterValidPath.bind(info.deriver);
+    else
+        stmtRegisterValidPath.bind(); // null
+    if (info.narSize != 0)
+        stmtRegisterValidPath.bind64(info.narSize);
+    else
+        stmtRegisterValidPath.bind(); // null
+    if (sqlite3_step(stmtRegisterValidPath) != SQLITE_DONE)
+        throwSQLiteError(db, format("registering valid path `%1%' in database") % info.path);
+    unsigned long long id = sqlite3_last_insert_rowid(db);
+
+    /* If this is a derivation, then store the derivation outputs in
+       the database.  This is useful for the garbage collector: it can
+       efficiently query whether a path is an output of some
+       derivation. */
+    if (isDerivation(info.path)) {
+        Derivation drv = parseDerivation(readFile(info.path));
+
+        /* Verify that the output paths in the derivation are correct
+           (i.e., follow the scheme for computing output paths from
+           derivations).  Note that if this throws an error, then the
+           DB transaction is rolled back, so the path validity
+           registration above is undone. */
+        if (checkOutputs) checkDerivationOutputs(info.path, drv);
+
+        foreach (DerivationOutputs::iterator, i, drv.outputs) {
+            SQLiteStmtUse use(stmtAddDerivationOutput);
+            stmtAddDerivationOutput.bind(id);
+            stmtAddDerivationOutput.bind(i->first);
+            stmtAddDerivationOutput.bind(i->second.path);
+            if (sqlite3_step(stmtAddDerivationOutput) != SQLITE_DONE)
+                throwSQLiteError(db, format("adding derivation output for `%1%' in database") % info.path);
+        }
+    }
+
+    return id;
+}
+
+
+void LocalStore::addReference(unsigned long long referrer, unsigned long long reference)
+{
+    SQLiteStmtUse use(stmtAddReference);
+    stmtAddReference.bind(referrer);
+    stmtAddReference.bind(reference);
+    if (sqlite3_step(stmtAddReference) != SQLITE_DONE)
+        throwSQLiteError(db, "adding reference to database");
+}
+
+
+void LocalStore::registerFailedPath(const Path & path)
+{
+    retry_sqlite {
+        SQLiteStmtUse use(stmtRegisterFailedPath);
+        stmtRegisterFailedPath.bind(path);
+        stmtRegisterFailedPath.bind(time(0));
+        if (sqlite3_step(stmtRegisterFailedPath) != SQLITE_DONE)
+            throwSQLiteError(db, format("registering failed path `%1%'") % path);
+    } end_retry_sqlite;
+}
+
+
+bool LocalStore::hasPathFailed(const Path & path)
+{
+    retry_sqlite {
+        SQLiteStmtUse use(stmtHasPathFailed);
+        stmtHasPathFailed.bind(path);
+        int res = sqlite3_step(stmtHasPathFailed);
+        if (res != SQLITE_DONE && res != SQLITE_ROW)
+            throwSQLiteError(db, "querying whether path failed");
+        return res == SQLITE_ROW;
+    } end_retry_sqlite;
+}
+
+
+PathSet LocalStore::queryFailedPaths()
+{
+    retry_sqlite {
+        SQLiteStmtUse use(stmtQueryFailedPaths);
+
+        PathSet res;
+        int r;
+        while ((r = sqlite3_step(stmtQueryFailedPaths)) == SQLITE_ROW) {
+            const char * s = (const char *) sqlite3_column_text(stmtQueryFailedPaths, 0);
+            assert(s);
+            res.insert(s);
+        }
+
+        if (r != SQLITE_DONE)
+            throwSQLiteError(db, "error querying failed paths");
+
+        return res;
+    } end_retry_sqlite;
+}
+
+
+void LocalStore::clearFailedPaths(const PathSet & paths)
+{
+    retry_sqlite {
+        SQLiteTxn txn(db);
+
+        foreach (PathSet::const_iterator, i, paths) {
+            SQLiteStmtUse use(stmtClearFailedPath);
+            stmtClearFailedPath.bind(*i);
+            if (sqlite3_step(stmtClearFailedPath) != SQLITE_DONE)
+                throwSQLiteError(db, format("clearing failed path `%1%' in database") % *i);
+        }
+
+        txn.commit();
+    } end_retry_sqlite;
+}
+
+
+Hash parseHashField(const Path & path, const string & s)
+{
+    string::size_type colon = s.find(':');
+    if (colon == string::npos)
+        throw Error(format("corrupt hash `%1%' in valid-path entry for `%2%'")
+            % s % path);
+    HashType ht = parseHashType(string(s, 0, colon));
+    if (ht == htUnknown)
+        throw Error(format("unknown hash type `%1%' in valid-path entry for `%2%'")
+            % string(s, 0, colon) % path);
+    return parseHash(ht, string(s, colon + 1));
+}
+
+
+ValidPathInfo LocalStore::queryPathInfo(const Path & path)
+{
+    ValidPathInfo info;
+    info.path = path;
+
+    assertStorePath(path);
+
+    retry_sqlite {
+
+        /* Get the path info. */
+        SQLiteStmtUse use1(stmtQueryPathInfo);
+
+        stmtQueryPathInfo.bind(path);
+
+        int r = sqlite3_step(stmtQueryPathInfo);
+        if (r == SQLITE_DONE) throw Error(format("path `%1%' is not valid") % path);
+        if (r != SQLITE_ROW) throwSQLiteError(db, "querying path in database");
+
+        info.id = sqlite3_column_int(stmtQueryPathInfo, 0);
+
+        const char * s = (const char *) sqlite3_column_text(stmtQueryPathInfo, 1);
+        assert(s);
+        info.hash = parseHashField(path, s);
+
+        info.registrationTime = sqlite3_column_int(stmtQueryPathInfo, 2);
+
+        s = (const char *) sqlite3_column_text(stmtQueryPathInfo, 3);
+        if (s) info.deriver = s;
+
+        /* Note that narSize = NULL yields 0. */
+        info.narSize = sqlite3_column_int64(stmtQueryPathInfo, 4);
+
+        /* Get the references. */
+        SQLiteStmtUse use2(stmtQueryReferences);
+
+        stmtQueryReferences.bind(info.id);
+
+        while ((r = sqlite3_step(stmtQueryReferences)) == SQLITE_ROW) {
+            s = (const char *) sqlite3_column_text(stmtQueryReferences, 0);
+            assert(s);
+            info.references.insert(s);
+        }
+
+        if (r != SQLITE_DONE)
+            throwSQLiteError(db, format("error getting references of `%1%'") % path);
+
+        return info;
+    } end_retry_sqlite;
+}
+
+
+/* Update path info in the database.  Currently only updates the
+   narSize field. */
+void LocalStore::updatePathInfo(const ValidPathInfo & info)
+{
+    SQLiteStmtUse use(stmtUpdatePathInfo);
+    if (info.narSize != 0)
+        stmtUpdatePathInfo.bind64(info.narSize);
+    else
+        stmtUpdatePathInfo.bind(); // null
+    stmtUpdatePathInfo.bind("sha256:" + printHash(info.hash));
+    stmtUpdatePathInfo.bind(info.path);
+    if (sqlite3_step(stmtUpdatePathInfo) != SQLITE_DONE)
+        throwSQLiteError(db, format("updating info of path `%1%' in database") % info.path);
+}
+
+
+unsigned long long LocalStore::queryValidPathId(const Path & path)
+{
+    SQLiteStmtUse use(stmtQueryPathInfo);
+    stmtQueryPathInfo.bind(path);
+    int res = sqlite3_step(stmtQueryPathInfo);
+    if (res == SQLITE_ROW) return sqlite3_column_int(stmtQueryPathInfo, 0);
+    if (res == SQLITE_DONE) throw Error(format("path `%1%' is not valid") % path);
+    throwSQLiteError(db, "querying path in database");
+}
+
+
+bool LocalStore::isValidPath_(const Path & path)
+{
+    SQLiteStmtUse use(stmtQueryPathInfo);
+    stmtQueryPathInfo.bind(path);
+    int res = sqlite3_step(stmtQueryPathInfo);
+    if (res != SQLITE_DONE && res != SQLITE_ROW)
+        throwSQLiteError(db, "querying path in database");
+    return res == SQLITE_ROW;
+}
+
+
+bool LocalStore::isValidPath(const Path & path)
+{
+    retry_sqlite {
+        return isValidPath_(path);
+    } end_retry_sqlite;
+}
+
+
+PathSet LocalStore::queryValidPaths(const PathSet & paths)
+{
+    retry_sqlite {
+        PathSet res;
+        foreach (PathSet::const_iterator, i, paths)
+            if (isValidPath_(*i)) res.insert(*i);
+        return res;
+    } end_retry_sqlite;
+}
+
+
+PathSet LocalStore::queryAllValidPaths()
+{
+    retry_sqlite {
+        SQLiteStmt stmt;
+        stmt.create(db, "select path from ValidPaths");
+
+        PathSet res;
+        int r;
+        while ((r = sqlite3_step(stmt)) == SQLITE_ROW) {
+            const char * s = (const char *) sqlite3_column_text(stmt, 0);
+            assert(s);
+            res.insert(s);
+        }
+
+        if (r != SQLITE_DONE)
+            throwSQLiteError(db, "error getting valid paths");
+
+        return res;
+    } end_retry_sqlite;
+}
+
+
+void LocalStore::queryReferences(const Path & path,
+    PathSet & references)
+{
+    ValidPathInfo info = queryPathInfo(path);
+    references.insert(info.references.begin(), info.references.end());
+}
+
+
+void LocalStore::queryReferrers_(const Path & path, PathSet & referrers)
+{
+    SQLiteStmtUse use(stmtQueryReferrers);
+
+    stmtQueryReferrers.bind(path);
+
+    int r;
+    while ((r = sqlite3_step(stmtQueryReferrers)) == SQLITE_ROW) {
+        const char * s = (const char *) sqlite3_column_text(stmtQueryReferrers, 0);
+        assert(s);
+        referrers.insert(s);
+    }
+
+    if (r != SQLITE_DONE)
+        throwSQLiteError(db, format("error getting references of `%1%'") % path);
+}
+
+
+void LocalStore::queryReferrers(const Path & path, PathSet & referrers)
+{
+    assertStorePath(path);
+    retry_sqlite {
+        queryReferrers_(path, referrers);
+    } end_retry_sqlite;
+}
+
+
+Path LocalStore::queryDeriver(const Path & path)
+{
+    return queryPathInfo(path).deriver;
+}
+
+
+PathSet LocalStore::queryValidDerivers(const Path & path)
+{
+    assertStorePath(path);
+
+    retry_sqlite {
+        SQLiteStmtUse use(stmtQueryValidDerivers);
+        stmtQueryValidDerivers.bind(path);
+
+        PathSet derivers;
+        int r;
+        while ((r = sqlite3_step(stmtQueryValidDerivers)) == SQLITE_ROW) {
+            const char * s = (const char *) sqlite3_column_text(stmtQueryValidDerivers, 1);
+            assert(s);
+            derivers.insert(s);
+        }
+
+        if (r != SQLITE_DONE)
+            throwSQLiteError(db, format("error getting valid derivers of `%1%'") % path);
+
+        return derivers;
+    } end_retry_sqlite;
+}
+
+
+PathSet LocalStore::queryDerivationOutputs(const Path & path)
+{
+    retry_sqlite {
+        SQLiteStmtUse use(stmtQueryDerivationOutputs);
+        stmtQueryDerivationOutputs.bind(queryValidPathId(path));
+
+        PathSet outputs;
+        int r;
+        while ((r = sqlite3_step(stmtQueryDerivationOutputs)) == SQLITE_ROW) {
+            const char * s = (const char *) sqlite3_column_text(stmtQueryDerivationOutputs, 1);
+            assert(s);
+            outputs.insert(s);
+        }
+
+        if (r != SQLITE_DONE)
+            throwSQLiteError(db, format("error getting outputs of `%1%'") % path);
+
+        return outputs;
+    } end_retry_sqlite;
+}
+
+
+StringSet LocalStore::queryDerivationOutputNames(const Path & path)
+{
+    retry_sqlite {
+        SQLiteStmtUse use(stmtQueryDerivationOutputs);
+        stmtQueryDerivationOutputs.bind(queryValidPathId(path));
+
+        StringSet outputNames;
+        int r;
+        while ((r = sqlite3_step(stmtQueryDerivationOutputs)) == SQLITE_ROW) {
+            const char * s = (const char *) sqlite3_column_text(stmtQueryDerivationOutputs, 0);
+            assert(s);
+            outputNames.insert(s);
+        }
+
+        if (r != SQLITE_DONE)
+            throwSQLiteError(db, format("error getting output names of `%1%'") % path);
+
+        return outputNames;
+    } end_retry_sqlite;
+}
+
+
+Path LocalStore::queryPathFromHashPart(const string & hashPart)
+{
+    if (hashPart.size() != 32) throw Error("invalid hash part");
+
+    Path prefix = settings.nixStore + "/" + hashPart;
+
+    retry_sqlite {
+        SQLiteStmtUse use(stmtQueryPathFromHashPart);
+        stmtQueryPathFromHashPart.bind(prefix);
+
+        int res = sqlite3_step(stmtQueryPathFromHashPart);
+        if (res == SQLITE_DONE) return "";
+        if (res != SQLITE_ROW) throwSQLiteError(db, "finding path in database");
+
+        const char * s = (const char *) sqlite3_column_text(stmtQueryPathFromHashPart, 0);
+        return s && prefix.compare(0, prefix.size(), s, prefix.size()) == 0 ? s : "";
+    } end_retry_sqlite;
+}
+
+
+void LocalStore::setSubstituterEnv()
+{
+    if (didSetSubstituterEnv) return;
+
+    /* Pass configuration options (including those overridden with
+       --option) to substituters. */
+    setenv("_NIX_OPTIONS", settings.pack().c_str(), 1);
+
+    didSetSubstituterEnv = true;
+}
+
+
+void LocalStore::startSubstituter(const Path & substituter, RunningSubstituter & run)
+{
+    if (run.disabled || run.pid != -1) return;
+
+    debug(format("starting substituter program `%1%'") % substituter);
+
+    Pipe toPipe, fromPipe, errorPipe;
+
+    toPipe.create();
+    fromPipe.create();
+    errorPipe.create();
+
+    setSubstituterEnv();
+
+    run.pid = maybeVfork();
+
+    switch (run.pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0: /* child */
+        try {
+            restoreAffinity();
+            if (dup2(toPipe.readSide, STDIN_FILENO) == -1)
+                throw SysError("dupping stdin");
+            if (dup2(fromPipe.writeSide, STDOUT_FILENO) == -1)
+                throw SysError("dupping stdout");
+            if (dup2(errorPipe.writeSide, STDERR_FILENO) == -1)
+                throw SysError("dupping stderr");
+            execl(substituter.c_str(), substituter.c_str(), "--query", NULL);
+            throw SysError(format("executing `%1%'") % substituter);
+        } catch (std::exception & e) {
+            std::cerr << "error: " << e.what() << std::endl;
+        }
+        _exit(1);
+    }
+
+    /* Parent. */
+
+    run.program = baseNameOf(substituter);
+    run.to = toPipe.writeSide.borrow();
+    run.from = run.fromBuf.fd = fromPipe.readSide.borrow();
+    run.error = errorPipe.readSide.borrow();
+
+    toPipe.readSide.close();
+    fromPipe.writeSide.close();
+    errorPipe.writeSide.close();
+
+    /* The substituter may exit right away if it's disabled in any way
+       (e.g. copy-from-other-stores.pl will exit if no other stores
+       are configured). */
+    try {
+        getLineFromSubstituter(run);
+    } catch (EndOfFile & e) {
+        run.to.close();
+        run.from.close();
+        run.error.close();
+        run.disabled = true;
+        if (run.pid.wait(true) != 0) throw;
+    }
+}
+
+
+/* Read a line from the substituter's stdout, while also processing
+   its stderr. */
+string LocalStore::getLineFromSubstituter(RunningSubstituter & run)
+{
+    string res, err;
+
+    /* We might have stdout data left over from the last time. */
+    if (run.fromBuf.hasData()) goto haveData;
+
+    while (1) {
+        checkInterrupt();
+
+        fd_set fds;
+        FD_ZERO(&fds);
+        FD_SET(run.from, &fds);
+        FD_SET(run.error, &fds);
+
+        /* Wait for data to appear on the substituter's stdout or
+           stderr. */
+        if (select(run.from > run.error ? run.from + 1 : run.error + 1, &fds, 0, 0, 0) == -1) {
+            if (errno == EINTR) continue;
+            throw SysError("waiting for input from the substituter");
+        }
+
+        /* Completely drain stderr before dealing with stdout. */
+        if (FD_ISSET(run.error, &fds)) {
+            char buf[4096];
+            ssize_t n = read(run.error, (unsigned char *) buf, sizeof(buf));
+            if (n == -1) {
+                if (errno == EINTR) continue;
+                throw SysError("reading from substituter's stderr");
+            }
+            if (n == 0) throw EndOfFile(format("substituter `%1%' died unexpectedly") % run.program);
+            err.append(buf, n);
+            string::size_type p;
+            while ((p = err.find('\n')) != string::npos) {
+                printMsg(lvlError, run.program + ": " + string(err, 0, p));
+                err = string(err, p + 1);
+            }
+        }
+
+        /* Read from stdout until we get a newline or the buffer is empty. */
+        else if (run.fromBuf.hasData() || FD_ISSET(run.from, &fds)) {
+        haveData:
+            do {
+                unsigned char c;
+                run.fromBuf(&c, 1);
+                if (c == '\n') {
+                    if (!err.empty()) printMsg(lvlError, run.program + ": " + err);
+                    return res;
+                }
+                res += c;
+            } while (run.fromBuf.hasData());
+        }
+    }
+}
+
+
+template<class T> T LocalStore::getIntLineFromSubstituter(RunningSubstituter & run)
+{
+    string s = getLineFromSubstituter(run);
+    T res;
+    if (!string2Int(s, res)) throw Error("integer expected from stream");
+    return res;
+}
+
+
+PathSet LocalStore::querySubstitutablePaths(const PathSet & paths)
+{
+    PathSet res;
+    foreach (Paths::iterator, i, settings.substituters) {
+        if (res.size() == paths.size()) break;
+        RunningSubstituter & run(runningSubstituters[*i]);
+        startSubstituter(*i, run);
+        if (run.disabled) continue;
+        string s = "have ";
+        foreach (PathSet::const_iterator, j, paths)
+            if (res.find(*j) == res.end()) { s += *j; s += " "; }
+        writeLine(run.to, s);
+        while (true) {
+            /* FIXME: we only read stderr when an error occurs, so
+               substituters should only write (short) messages to
+               stderr when they fail.  I.e. they shouldn't write debug
+               output. */
+            Path path = getLineFromSubstituter(run);
+            if (path == "") break;
+            res.insert(path);
+        }
+    }
+    return res;
+}
+
+
+void LocalStore::querySubstitutablePathInfos(const Path & substituter,
+    PathSet & paths, SubstitutablePathInfos & infos)
+{
+    RunningSubstituter & run(runningSubstituters[substituter]);
+    startSubstituter(substituter, run);
+    if (run.disabled) return;
+
+    string s = "info ";
+    foreach (PathSet::const_iterator, i, paths)
+        if (infos.find(*i) == infos.end()) { s += *i; s += " "; }
+    writeLine(run.to, s);
+
+    while (true) {
+        Path path = getLineFromSubstituter(run);
+        if (path == "") break;
+        if (paths.find(path) == paths.end())
+            throw Error(format("got unexpected path `%1%' from substituter") % path);
+        paths.erase(path);
+        SubstitutablePathInfo & info(infos[path]);
+        info.deriver = getLineFromSubstituter(run);
+        if (info.deriver != "") assertStorePath(info.deriver);
+        int nrRefs = getIntLineFromSubstituter<int>(run);
+        while (nrRefs--) {
+            Path p = getLineFromSubstituter(run);
+            assertStorePath(p);
+            info.references.insert(p);
+        }
+        info.downloadSize = getIntLineFromSubstituter<long long>(run);
+        info.narSize = getIntLineFromSubstituter<long long>(run);
+    }
+}
+
+
+void LocalStore::querySubstitutablePathInfos(const PathSet & paths,
+    SubstitutablePathInfos & infos)
+{
+    PathSet todo = paths;
+    foreach (Paths::iterator, i, settings.substituters) {
+        if (todo.empty()) break;
+        querySubstitutablePathInfos(*i, todo, infos);
+    }
+}
+
+
+Hash LocalStore::queryPathHash(const Path & path)
+{
+    return queryPathInfo(path).hash;
+}
+
+
+void LocalStore::registerValidPath(const ValidPathInfo & info)
+{
+    ValidPathInfos infos;
+    infos.push_back(info);
+    registerValidPaths(infos);
+}
+
+
+void LocalStore::registerValidPaths(const ValidPathInfos & infos)
+{
+    /* SQLite will fsync by default, but the new valid paths may not be fsync-ed.
+     * So some may want to fsync them before registering the validity, at the
+     * expense of some speed of the path registering operation. */
+    if (settings.syncBeforeRegistering) sync();
+
+    retry_sqlite {
+        SQLiteTxn txn(db);
+        PathSet paths;
+
+        foreach (ValidPathInfos::const_iterator, i, infos) {
+            assert(i->hash.type == htSHA256);
+            if (isValidPath_(i->path))
+                updatePathInfo(*i);
+            else
+                addValidPath(*i);
+            paths.insert(i->path);
+        }
+
+        foreach (ValidPathInfos::const_iterator, i, infos) {
+            unsigned long long referrer = queryValidPathId(i->path);
+            foreach (PathSet::iterator, j, i->references)
+                addReference(referrer, queryValidPathId(*j));
+        }
+
+        /* Do a topological sort of the paths.  This will throw an
+           error if a cycle is detected and roll back the
+           transaction.  Cycles can only occur when a derivation
+           has multiple outputs. */
+        topoSortPaths(*this, paths);
+
+        txn.commit();
+    } end_retry_sqlite;
+}
+
+
+/* Invalidate a path.  The caller is responsible for checking that
+   there are no referrers. */
+void LocalStore::invalidatePath(const Path & path)
+{
+    debug(format("invalidating path `%1%'") % path);
+
+    drvHashes.erase(path);
+
+    SQLiteStmtUse use(stmtInvalidatePath);
+
+    stmtInvalidatePath.bind(path);
+
+    if (sqlite3_step(stmtInvalidatePath) != SQLITE_DONE)
+        throwSQLiteError(db, format("invalidating path `%1%' in database") % path);
+
+    /* Note that the foreign key constraints on the Refs table take
+       care of deleting the references entries for `path'. */
+}
+
+
+Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
+    bool recursive, HashType hashAlgo, bool repair)
+{
+    Hash h = hashString(hashAlgo, dump);
+
+    Path dstPath = makeFixedOutputPath(recursive, hashAlgo, h, name);
+
+    addTempRoot(dstPath);
+
+    if (repair || !isValidPath(dstPath)) {
+
+        /* The first check above is an optimisation to prevent
+           unnecessary lock acquisition. */
+
+        PathLocks outputLock(singleton<PathSet, Path>(dstPath));
+
+        if (repair || !isValidPath(dstPath)) {
+
+            if (pathExists(dstPath)) deletePath(dstPath);
+
+            if (recursive) {
+                StringSource source(dump);
+                restorePath(dstPath, source);
+            } else
+                writeFile(dstPath, dump);
+
+            canonicalisePathMetaData(dstPath, -1);
+
+            /* Register the SHA-256 hash of the NAR serialisation of
+               the path in the database.  We may just have computed it
+               above (if called with recursive == true and hashAlgo ==
+               sha256); otherwise, compute it here. */
+            HashResult hash;
+            if (recursive) {
+                hash.first = hashAlgo == htSHA256 ? h : hashString(htSHA256, dump);
+                hash.second = dump.size();
+            } else
+                hash = hashPath(htSHA256, dstPath);
+
+            optimisePath(dstPath); // FIXME: combine with hashPath()
+
+            ValidPathInfo info;
+            info.path = dstPath;
+            info.hash = hash.first;
+            info.narSize = hash.second;
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+Path LocalStore::addToStore(const Path & _srcPath,
+    bool recursive, HashType hashAlgo, PathFilter & filter, bool repair)
+{
+    Path srcPath(absPath(_srcPath));
+    debug(format("adding `%1%' to the store") % srcPath);
+
+    /* Read the whole path into memory. This is not a very scalable
+       method for very large paths, but `copyPath' is mainly used for
+       small files. */
+    StringSink sink;
+    if (recursive)
+        dumpPath(srcPath, sink, filter);
+    else
+        sink.s = readFile(srcPath);
+
+    return addToStoreFromDump(sink.s, baseNameOf(srcPath), recursive, hashAlgo, repair);
+}
+
+
+Path LocalStore::addTextToStore(const string & name, const string & s,
+    const PathSet & references, bool repair)
+{
+    Path dstPath = computeStorePathForText(name, s, references);
+
+    addTempRoot(dstPath);
+
+    if (repair || !isValidPath(dstPath)) {
+
+        PathLocks outputLock(singleton<PathSet, Path>(dstPath));
+
+        if (repair || !isValidPath(dstPath)) {
+
+            if (pathExists(dstPath)) deletePath(dstPath);
+
+            writeFile(dstPath, s);
+
+            canonicalisePathMetaData(dstPath, -1);
+
+            HashResult hash = hashPath(htSHA256, dstPath);
+
+            optimisePath(dstPath);
+
+            ValidPathInfo info;
+            info.path = dstPath;
+            info.hash = hash.first;
+            info.narSize = hash.second;
+            info.references = references;
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+struct HashAndWriteSink : Sink
+{
+    Sink & writeSink;
+    HashSink hashSink;
+    HashAndWriteSink(Sink & writeSink) : writeSink(writeSink), hashSink(htSHA256)
+    {
+    }
+    virtual void operator () (const unsigned char * data, size_t len)
+    {
+        writeSink(data, len);
+        hashSink(data, len);
+    }
+    Hash currentHash()
+    {
+        return hashSink.currentHash().first;
+    }
+};
+
+
+#define EXPORT_MAGIC 0x4558494e
+
+
+static void checkSecrecy(const Path & path)
+{
+    struct stat st;
+    if (stat(path.c_str(), &st))
+        throw SysError(format("getting status of `%1%'") % path);
+    if ((st.st_mode & (S_IRWXG | S_IRWXO)) != 0)
+        throw Error(format("file `%1%' should be secret (inaccessible to everybody else)!") % path);
+}
+
+
+void LocalStore::exportPath(const Path & path, bool sign,
+    Sink & sink)
+{
+    assertStorePath(path);
+
+    addTempRoot(path);
+    if (!isValidPath(path))
+        throw Error(format("path `%1%' is not valid") % path);
+
+    HashAndWriteSink hashAndWriteSink(sink);
+
+    dumpPath(path, hashAndWriteSink);
+
+    /* Refuse to export paths that have changed.  This prevents
+       filesystem corruption from spreading to other machines.
+       Don't complain if the stored hash is zero (unknown). */
+    Hash hash = hashAndWriteSink.currentHash();
+    Hash storedHash = queryPathHash(path);
+    if (hash != storedHash && storedHash != Hash(storedHash.type))
+        throw Error(format("hash of path `%1%' has changed from `%2%' to `%3%'!") % path
+            % printHash(storedHash) % printHash(hash));
+
+    writeInt(EXPORT_MAGIC, hashAndWriteSink);
+
+    writeString(path, hashAndWriteSink);
+
+    PathSet references;
+    queryReferences(path, references);
+    writeStrings(references, hashAndWriteSink);
+
+    Path deriver = queryDeriver(path);
+    writeString(deriver, hashAndWriteSink);
+
+    if (sign) {
+        Hash hash = hashAndWriteSink.currentHash();
+
+        writeInt(1, hashAndWriteSink);
+
+        Path tmpDir = createTempDir();
+        AutoDelete delTmp(tmpDir);
+        Path hashFile = tmpDir + "/hash";
+        writeFile(hashFile, printHash(hash));
+
+        Path secretKey = settings.nixConfDir + "/signing-key.sec";
+        checkSecrecy(secretKey);
+
+        Strings args;
+        args.push_back("rsautl");
+        args.push_back("-sign");
+        args.push_back("-inkey");
+        args.push_back(secretKey);
+        args.push_back("-in");
+        args.push_back(hashFile);
+        string signature = runProgram(OPENSSL_PATH, true, args);
+
+        writeString(signature, hashAndWriteSink);
+
+    } else
+        writeInt(0, hashAndWriteSink);
+}
+
+
+struct HashAndReadSource : Source
+{
+    Source & readSource;
+    HashSink hashSink;
+    bool hashing;
+    HashAndReadSource(Source & readSource) : readSource(readSource), hashSink(htSHA256)
+    {
+        hashing = true;
+    }
+    size_t read(unsigned char * data, size_t len)
+    {
+        size_t n = readSource.read(data, len);
+        if (hashing) hashSink(data, n);
+        return n;
+    }
+};
+
+
+/* Create a temporary directory in the store that won't be
+   garbage-collected. */
+Path LocalStore::createTempDirInStore()
+{
+    Path tmpDir;
+    do {
+        /* There is a slight possibility that `tmpDir' gets deleted by
+           the GC between createTempDir() and addTempRoot(), so repeat
+           until `tmpDir' exists. */
+        tmpDir = createTempDir(settings.nixStore);
+        addTempRoot(tmpDir);
+    } while (!pathExists(tmpDir));
+    return tmpDir;
+}
+
+
+Path LocalStore::importPath(bool requireSignature, Source & source)
+{
+    HashAndReadSource hashAndReadSource(source);
+
+    /* We don't yet know what store path this archive contains (the
+       store path follows the archive data proper), and besides, we
+       don't know yet whether the signature is valid. */
+    Path tmpDir = createTempDirInStore();
+    AutoDelete delTmp(tmpDir);
+    Path unpacked = tmpDir + "/unpacked";
+
+    restorePath(unpacked, hashAndReadSource);
+
+    unsigned int magic = readInt(hashAndReadSource);
+    if (magic != EXPORT_MAGIC)
+        throw Error("Nix archive cannot be imported; wrong format");
+
+    Path dstPath = readStorePath(hashAndReadSource);
+
+    printMsg(lvlInfo, format("importing path `%1%'") % dstPath);
+
+    PathSet references = readStorePaths<PathSet>(hashAndReadSource);
+
+    Path deriver = readString(hashAndReadSource);
+    if (deriver != "") assertStorePath(deriver);
+
+    Hash hash = hashAndReadSource.hashSink.finish().first;
+    hashAndReadSource.hashing = false;
+
+    bool haveSignature = readInt(hashAndReadSource) == 1;
+
+    if (requireSignature && !haveSignature)
+        throw Error(format("imported archive of `%1%' lacks a signature") % dstPath);
+
+    if (haveSignature) {
+        string signature = readString(hashAndReadSource);
+
+        if (requireSignature) {
+            Path sigFile = tmpDir + "/sig";
+            writeFile(sigFile, signature);
+
+            Strings args;
+            args.push_back("rsautl");
+            args.push_back("-verify");
+            args.push_back("-inkey");
+            args.push_back(settings.nixConfDir + "/signing-key.pub");
+            args.push_back("-pubin");
+            args.push_back("-in");
+            args.push_back(sigFile);
+            string hash2 = runProgram(OPENSSL_PATH, true, args);
+
+            /* Note: runProgram() throws an exception if the signature
+               is invalid. */
+
+            if (printHash(hash) != hash2)
+                throw Error(
+                    "signed hash doesn't match actual contents of imported "
+                    "archive; archive could be corrupt, or someone is trying "
+                    "to import a Trojan horse");
+        }
+    }
+
+    /* Do the actual import. */
+
+    /* !!! way too much code duplication with addTextToStore() etc. */
+    addTempRoot(dstPath);
+
+    if (!isValidPath(dstPath)) {
+
+        PathLocks outputLock;
+
+        /* Lock the output path.  But don't lock if we're being called
+           from a build hook (whose parent process already acquired a
+           lock on this path). */
+        Strings locksHeld = tokenizeString<Strings>(getEnv("NIX_HELD_LOCKS"));
+        if (find(locksHeld.begin(), locksHeld.end(), dstPath) == locksHeld.end())
+            outputLock.lockPaths(singleton<PathSet, Path>(dstPath));
+
+        if (!isValidPath(dstPath)) {
+
+            if (pathExists(dstPath)) deletePath(dstPath);
+
+            if (rename(unpacked.c_str(), dstPath.c_str()) == -1)
+                throw SysError(format("cannot move `%1%' to `%2%'")
+                    % unpacked % dstPath);
+
+            canonicalisePathMetaData(dstPath, -1);
+
+            /* !!! if we were clever, we could prevent the hashPath()
+               here. */
+            HashResult hash = hashPath(htSHA256, dstPath);
+
+            optimisePath(dstPath); // FIXME: combine with hashPath()
+
+            ValidPathInfo info;
+            info.path = dstPath;
+            info.hash = hash.first;
+            info.narSize = hash.second;
+            info.references = references;
+            info.deriver = deriver != "" && isValidPath(deriver) ? deriver : "";
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+Paths LocalStore::importPaths(bool requireSignature, Source & source)
+{
+    Paths res;
+    while (true) {
+        unsigned long long n = readLongLong(source);
+        if (n == 0) break;
+        if (n != 1) throw Error("input doesn't look like something created by `nix-store --export'");
+        res.push_back(importPath(requireSignature, source));
+    }
+    return res;
+}
+
+
+void LocalStore::invalidatePathChecked(const Path & path)
+{
+    assertStorePath(path);
+
+    retry_sqlite {
+        SQLiteTxn txn(db);
+
+        if (isValidPath_(path)) {
+            PathSet referrers; queryReferrers_(path, referrers);
+            referrers.erase(path); /* ignore self-references */
+            if (!referrers.empty())
+                throw PathInUse(format("cannot delete path `%1%' because it is in use by %2%")
+                    % path % showPaths(referrers));
+            invalidatePath(path);
+        }
+
+        txn.commit();
+    } end_retry_sqlite;
+}
+
+
+bool LocalStore::verifyStore(bool checkContents, bool repair)
+{
+    printMsg(lvlError, format("reading the Nix store..."));
+
+    bool errors = false;
+
+    /* Acquire the global GC lock to prevent a garbage collection. */
+    AutoCloseFD fdGCLock = openGCLock(ltWrite);
+
+    Paths entries = readDirectory(settings.nixStore);
+    PathSet store(entries.begin(), entries.end());
+
+    /* Check whether all valid paths actually exist. */
+    printMsg(lvlInfo, "checking path existence...");
+
+    PathSet validPaths2 = queryAllValidPaths(), validPaths, done;
+
+    foreach (PathSet::iterator, i, validPaths2)
+        verifyPath(*i, store, done, validPaths, repair, errors);
+
+    /* Release the GC lock so that checking content hashes (which can
+       take ages) doesn't block the GC or builds. */
+    fdGCLock.close();
+
+    /* Optionally, check the content hashes (slow). */
+    if (checkContents) {
+        printMsg(lvlInfo, "checking hashes...");
+
+        Hash nullHash(htSHA256);
+
+        foreach (PathSet::iterator, i, validPaths) {
+            try {
+                ValidPathInfo info = queryPathInfo(*i);
+
+                /* Check the content hash (optionally - slow). */
+                printMsg(lvlTalkative, format("checking contents of `%1%'") % *i);
+                HashResult current = hashPath(info.hash.type, *i);
+
+                if (info.hash != nullHash && info.hash != current.first) {
+                    printMsg(lvlError, format("path `%1%' was modified! "
+                            "expected hash `%2%', got `%3%'")
+                        % *i % printHash(info.hash) % printHash(current.first));
+                    if (repair) repairPath(*i); else errors = true;
+                } else {
+
+                    bool update = false;
+
+                    /* Fill in missing hashes. */
+                    if (info.hash == nullHash) {
+                        printMsg(lvlError, format("fixing missing hash on `%1%'") % *i);
+                        info.hash = current.first;
+                        update = true;
+                    }
+
+                    /* Fill in missing narSize fields (from old stores). */
+                    if (info.narSize == 0) {
+                        printMsg(lvlError, format("updating size field on `%1%' to %2%") % *i % current.second);
+                        info.narSize = current.second;
+                        update = true;
+                    }
+
+                    if (update) updatePathInfo(info);
+
+                }
+
+            } catch (Error & e) {
+                /* It's possible that the path got GC'ed, so ignore
+                   errors on invalid paths. */
+                if (isValidPath(*i))
+                    printMsg(lvlError, format("error: %1%") % e.msg());
+                else
+                    printMsg(lvlError, format("warning: %1%") % e.msg());
+                errors = true;
+            }
+        }
+    }
+
+    return errors;
+}
+
+
+void LocalStore::verifyPath(const Path & path, const PathSet & store,
+    PathSet & done, PathSet & validPaths, bool repair, bool & errors)
+{
+    checkInterrupt();
+
+    if (done.find(path) != done.end()) return;
+    done.insert(path);
+
+    if (!isStorePath(path)) {
+        printMsg(lvlError, format("path `%1%' is not in the Nix store") % path);
+        invalidatePath(path);
+        return;
+    }
+
+    if (store.find(baseNameOf(path)) == store.end()) {
+        /* Check any referrers first.  If we can invalidate them
+           first, then we can invalidate this path as well. */
+        bool canInvalidate = true;
+        PathSet referrers; queryReferrers(path, referrers);
+        foreach (PathSet::iterator, i, referrers)
+            if (*i != path) {
+                verifyPath(*i, store, done, validPaths, repair, errors);
+                if (validPaths.find(*i) != validPaths.end())
+                    canInvalidate = false;
+            }
+
+        if (canInvalidate) {
+            printMsg(lvlError, format("path `%1%' disappeared, removing from database...") % path);
+            invalidatePath(path);
+        } else {
+            printMsg(lvlError, format("path `%1%' disappeared, but it still has valid referrers!") % path);
+            if (repair)
+                try {
+                    repairPath(path);
+                } catch (Error & e) {
+                    printMsg(lvlError, format("warning: %1%") % e.msg());
+                    errors = true;
+                }
+            else errors = true;
+        }
+
+        return;
+    }
+
+    validPaths.insert(path);
+}
+
+
+bool LocalStore::pathContentsGood(const Path & path)
+{
+    std::map<Path, bool>::iterator i = pathContentsGoodCache.find(path);
+    if (i != pathContentsGoodCache.end()) return i->second;
+    printMsg(lvlInfo, format("checking path `%1%'...") % path);
+    ValidPathInfo info = queryPathInfo(path);
+    bool res;
+    if (!pathExists(path))
+        res = false;
+    else {
+        HashResult current = hashPath(info.hash.type, path);
+        Hash nullHash(htSHA256);
+        res = info.hash == nullHash || info.hash == current.first;
+    }
+    pathContentsGoodCache[path] = res;
+    if (!res) printMsg(lvlError, format("path `%1%' is corrupted or missing!") % path);
+    return res;
+}
+
+
+void LocalStore::markContentsGood(const Path & path)
+{
+    pathContentsGoodCache[path] = true;
+}
+
+
+/* Functions for upgrading from the pre-SQLite database. */
+
+PathSet LocalStore::queryValidPathsOld()
+{
+    PathSet paths;
+    Strings entries = readDirectory(settings.nixDBPath + "/info");
+    foreach (Strings::iterator, i, entries)
+        if (i->at(0) != '.') paths.insert(settings.nixStore + "/" + *i);
+    return paths;
+}
+
+
+ValidPathInfo LocalStore::queryPathInfoOld(const Path & path)
+{
+    ValidPathInfo res;
+    res.path = path;
+
+    /* Read the info file. */
+    string baseName = baseNameOf(path);
+    Path infoFile = (format("%1%/info/%2%") % settings.nixDBPath % baseName).str();
+    if (!pathExists(infoFile))
+        throw Error(format("path `%1%' is not valid") % path);
+    string info = readFile(infoFile);
+
+    /* Parse it. */
+    Strings lines = tokenizeString<Strings>(info, "\n");
+
+    foreach (Strings::iterator, i, lines) {
+        string::size_type p = i->find(':');
+        if (p == string::npos)
+            throw Error(format("corrupt line in `%1%': %2%") % infoFile % *i);
+        string name(*i, 0, p);
+        string value(*i, p + 2);
+        if (name == "References") {
+            Strings refs = tokenizeString<Strings>(value, " ");
+            res.references = PathSet(refs.begin(), refs.end());
+        } else if (name == "Deriver") {
+            res.deriver = value;
+        } else if (name == "Hash") {
+            res.hash = parseHashField(path, value);
+        } else if (name == "Registered-At") {
+            int n = 0;
+            string2Int(value, n);
+            res.registrationTime = n;
+        }
+    }
+
+    return res;
+}
+
+
+/* Upgrade from schema 5 (Nix 0.12) to schema 6 (Nix >= 0.15). */
+void LocalStore::upgradeStore6()
+{
+    printMsg(lvlError, "upgrading Nix store to new schema (this may take a while)...");
+
+    openDB(true);
+
+    PathSet validPaths = queryValidPathsOld();
+
+    SQLiteTxn txn(db);
+
+    foreach (PathSet::iterator, i, validPaths) {
+        addValidPath(queryPathInfoOld(*i), false);
+        std::cerr << ".";
+    }
+
+    std::cerr << "|";
+
+    foreach (PathSet::iterator, i, validPaths) {
+        ValidPathInfo info = queryPathInfoOld(*i);
+        unsigned long long referrer = queryValidPathId(*i);
+        foreach (PathSet::iterator, j, info.references)
+            addReference(referrer, queryValidPathId(*j));
+        std::cerr << ".";
+    }
+
+    std::cerr << "\n";
+
+    txn.commit();
+}
+
+
+#if defined(FS_IOC_SETFLAGS) && defined(FS_IOC_GETFLAGS) && defined(FS_IMMUTABLE_FL)
+
+static void makeMutable(const Path & path)
+{
+    checkInterrupt();
+
+    struct stat st = lstat(path);
+
+    if (!S_ISDIR(st.st_mode) && !S_ISREG(st.st_mode)) return;
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+        foreach (Strings::iterator, i, names)
+            makeMutable(path + "/" + *i);
+    }
+
+    /* The O_NOFOLLOW is important to prevent us from changing the
+       mutable bit on the target of a symlink (which would be a
+       security hole). */
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_NOFOLLOW);
+    if (fd == -1) {
+        if (errno == ELOOP) return; // it's a symlink
+        throw SysError(format("opening file `%1%'") % path);
+    }
+
+    unsigned int flags = 0, old;
+
+    /* Silently ignore errors getting/setting the immutable flag so
+       that we work correctly on filesystems that don't support it. */
+    if (ioctl(fd, FS_IOC_GETFLAGS, &flags)) return;
+    old = flags;
+    flags &= ~FS_IMMUTABLE_FL;
+    if (old == flags) return;
+    if (ioctl(fd, FS_IOC_SETFLAGS, &flags)) return;
+}
+
+/* Upgrade from schema 6 (Nix 0.15) to schema 7 (Nix >= 1.3). */
+void LocalStore::upgradeStore7()
+{
+    if (getuid() != 0) return;
+    printMsg(lvlError, "removing immutable bits from the Nix store (this may take a while)...");
+    makeMutable(settings.nixStore);
+}
+
+#else
+
+void LocalStore::upgradeStore7()
+{
+}
+
+#endif
+
+
+void LocalStore::vacuumDB()
+{
+    if (sqlite3_exec(db, "vacuum;", 0, 0, 0) != SQLITE_OK)
+        throwSQLiteError(db, "vacuuming SQLite database");
+}
+
+
+}
diff --git a/src/libstore/local-store.hh b/src/libstore/local-store.hh
new file mode 100644
index 000000000000..1ace7cec996b
--- /dev/null
+++ b/src/libstore/local-store.hh
@@ -0,0 +1,333 @@
+#pragma once
+
+#include <string>
+
+#include "store-api.hh"
+#include "util.hh"
+#include "pathlocks.hh"
+
+
+class sqlite3;
+class sqlite3_stmt;
+
+
+namespace nix {
+
+
+/* Nix store and database schema version.  Version 1 (or 0) was Nix <=
+   0.7.  Version 2 was Nix 0.8 and 0.9.  Version 3 is Nix 0.10.
+   Version 4 is Nix 0.11.  Version 5 is Nix 0.12-0.16.  Version 6 is
+   Nix 1.0.  Version 7 is Nix 1.3. */
+const int nixSchemaVersion = 7;
+
+
+extern string drvsLogDir;
+
+
+struct Derivation;
+
+
+struct OptimiseStats
+{
+    unsigned long totalFiles;
+    unsigned long sameContents;
+    unsigned long filesLinked;
+    unsigned long long bytesFreed;
+    unsigned long long blocksFreed;
+    OptimiseStats()
+    {
+        totalFiles = sameContents = filesLinked = 0;
+        bytesFreed = blocksFreed = 0;
+    }
+};
+
+
+struct RunningSubstituter
+{
+    Path program;
+    Pid pid;
+    AutoCloseFD to, from, error;
+    FdSource fromBuf;
+    bool disabled;
+    RunningSubstituter() : disabled(false) { };
+};
+
+
+/* Wrapper object to close the SQLite database automatically. */
+struct SQLite
+{
+    sqlite3 * db;
+    SQLite() { db = 0; }
+    ~SQLite();
+    operator sqlite3 * () { return db; }
+};
+
+
+/* Wrapper object to create and destroy SQLite prepared statements. */
+struct SQLiteStmt
+{
+    sqlite3 * db;
+    sqlite3_stmt * stmt;
+    unsigned int curArg;
+    SQLiteStmt() { stmt = 0; }
+    void create(sqlite3 * db, const string & s);
+    void reset();
+    ~SQLiteStmt();
+    operator sqlite3_stmt * () { return stmt; }
+    void bind(const string & value);
+    void bind(int value);
+    void bind64(long long value);
+    void bind();
+};
+
+
+class LocalStore : public StoreAPI
+{
+private:
+    typedef std::map<Path, RunningSubstituter> RunningSubstituters;
+    RunningSubstituters runningSubstituters;
+
+    Path linksDir;
+
+public:
+
+    /* Initialise the local store, upgrading the schema if
+       necessary. */
+    LocalStore(bool reserveSpace = true);
+
+    ~LocalStore();
+
+    /* Implementations of abstract store API methods. */
+
+    bool isValidPath(const Path & path);
+
+    PathSet queryValidPaths(const PathSet & paths);
+
+    PathSet queryAllValidPaths();
+
+    ValidPathInfo queryPathInfo(const Path & path);
+
+    Hash queryPathHash(const Path & path);
+
+    void queryReferences(const Path & path, PathSet & references);
+
+    void queryReferrers(const Path & path, PathSet & referrers);
+
+    Path queryDeriver(const Path & path);
+
+    PathSet queryValidDerivers(const Path & path);
+
+    PathSet queryDerivationOutputs(const Path & path);
+
+    StringSet queryDerivationOutputNames(const Path & path);
+
+    Path queryPathFromHashPart(const string & hashPart);
+
+    PathSet querySubstitutablePaths(const PathSet & paths);
+
+    void querySubstitutablePathInfos(const Path & substituter,
+        PathSet & paths, SubstitutablePathInfos & infos);
+
+    void querySubstitutablePathInfos(const PathSet & paths,
+        SubstitutablePathInfos & infos);
+
+    Path addToStore(const Path & srcPath,
+        bool recursive = true, HashType hashAlgo = htSHA256,
+        PathFilter & filter = defaultPathFilter, bool repair = false);
+
+    /* Like addToStore(), but the contents of the path are contained
+       in `dump', which is either a NAR serialisation (if recursive ==
+       true) or simply the contents of a regular file (if recursive ==
+       false). */
+    Path addToStoreFromDump(const string & dump, const string & name,
+        bool recursive = true, HashType hashAlgo = htSHA256, bool repair = false);
+
+    Path addTextToStore(const string & name, const string & s,
+        const PathSet & references, bool repair = false);
+
+    void exportPath(const Path & path, bool sign,
+        Sink & sink);
+
+    Paths importPaths(bool requireSignature, Source & source);
+
+    void buildPaths(const PathSet & paths, bool repair = false);
+
+    void ensurePath(const Path & path);
+
+    void addTempRoot(const Path & path);
+
+    void addIndirectRoot(const Path & path);
+
+    void syncWithGC();
+
+    Roots findRoots();
+
+    void collectGarbage(const GCOptions & options, GCResults & results);
+
+    /* Optimise the disk space usage of the Nix store by hard-linking
+       files with the same contents. */
+    void optimiseStore(OptimiseStats & stats);
+
+    /* Optimise a single store path. */
+    void optimisePath(const Path & path);
+
+    /* Check the integrity of the Nix store.  Returns true if errors
+       remain. */
+    bool verifyStore(bool checkContents, bool repair);
+
+    /* Register the validity of a path, i.e., that `path' exists, that
+       the paths referenced by it exists, and in the case of an output
+       path of a derivation, that it has been produced by a successful
+       execution of the derivation (or something equivalent).  Also
+       register the hash of the file system contents of the path.  The
+       hash must be a SHA-256 hash. */
+    void registerValidPath(const ValidPathInfo & info);
+
+    void registerValidPaths(const ValidPathInfos & infos);
+
+    /* Register that the build of a derivation with output `path' has
+       failed. */
+    void registerFailedPath(const Path & path);
+
+    /* Query whether `path' previously failed to build. */
+    bool hasPathFailed(const Path & path);
+
+    PathSet queryFailedPaths();
+
+    void clearFailedPaths(const PathSet & paths);
+
+    void vacuumDB();
+
+    /* Repair the contents of the given path by redownloading it using
+       a substituter (if available). */
+    void repairPath(const Path & path);
+
+    /* Check whether the given valid path exists and has the right
+       contents. */
+    bool pathContentsGood(const Path & path);
+
+    void markContentsGood(const Path & path);
+
+    void setSubstituterEnv();
+
+private:
+
+    Path schemaPath;
+
+    /* Lock file used for upgrading. */
+    AutoCloseFD globalLock;
+
+    /* The SQLite database object. */
+    SQLite db;
+
+    /* Some precompiled SQLite statements. */
+    SQLiteStmt stmtRegisterValidPath;
+    SQLiteStmt stmtUpdatePathInfo;
+    SQLiteStmt stmtAddReference;
+    SQLiteStmt stmtQueryPathInfo;
+    SQLiteStmt stmtQueryReferences;
+    SQLiteStmt stmtQueryReferrers;
+    SQLiteStmt stmtInvalidatePath;
+    SQLiteStmt stmtRegisterFailedPath;
+    SQLiteStmt stmtHasPathFailed;
+    SQLiteStmt stmtQueryFailedPaths;
+    SQLiteStmt stmtClearFailedPath;
+    SQLiteStmt stmtAddDerivationOutput;
+    SQLiteStmt stmtQueryValidDerivers;
+    SQLiteStmt stmtQueryDerivationOutputs;
+    SQLiteStmt stmtQueryPathFromHashPart;
+
+    /* Cache for pathContentsGood(). */
+    std::map<Path, bool> pathContentsGoodCache;
+
+    bool didSetSubstituterEnv;
+
+    int getSchema();
+
+    void openDB(bool create);
+
+    void makeStoreWritable();
+
+    unsigned long long queryValidPathId(const Path & path);
+
+    unsigned long long addValidPath(const ValidPathInfo & info, bool checkOutputs = true);
+
+    void addReference(unsigned long long referrer, unsigned long long reference);
+
+    void appendReferrer(const Path & from, const Path & to, bool lock);
+
+    void rewriteReferrers(const Path & path, bool purge, PathSet referrers);
+
+    void invalidatePath(const Path & path);
+
+    /* Delete a path from the Nix store. */
+    void invalidatePathChecked(const Path & path);
+
+    void verifyPath(const Path & path, const PathSet & store,
+        PathSet & done, PathSet & validPaths, bool repair, bool & errors);
+
+    void updatePathInfo(const ValidPathInfo & info);
+
+    void upgradeStore6();
+    void upgradeStore7();
+    PathSet queryValidPathsOld();
+    ValidPathInfo queryPathInfoOld(const Path & path);
+
+    struct GCState;
+
+    void deleteGarbage(GCState & state, const Path & path);
+
+    void tryToDelete(GCState & state, const Path & path);
+
+    bool canReachRoot(GCState & state, PathSet & visited, const Path & path);
+
+    void deletePathRecursive(GCState & state, const Path & path);
+
+    bool isActiveTempFile(const GCState & state,
+        const Path & path, const string & suffix);
+
+    int openGCLock(LockType lockType);
+
+    void removeUnusedLinks(const GCState & state);
+
+    void startSubstituter(const Path & substituter,
+        RunningSubstituter & runningSubstituter);
+
+    string getLineFromSubstituter(RunningSubstituter & run);
+
+    template<class T> T getIntLineFromSubstituter(RunningSubstituter & run);
+
+    Path createTempDirInStore();
+
+    Path importPath(bool requireSignature, Source & source);
+
+    void checkDerivationOutputs(const Path & drvPath, const Derivation & drv);
+
+    void optimisePath_(OptimiseStats & stats, const Path & path);
+
+    // Internal versions that are not wrapped in retry_sqlite.
+    bool isValidPath_(const Path & path);
+    void queryReferrers_(const Path & path, PathSet & referrers);
+};
+
+
+typedef std::pair<dev_t, ino_t> Inode;
+typedef set<Inode> InodesSeen;
+
+
+/* "Fix", or canonicalise, the meta-data of the files in a store path
+   after it has been built.  In particular:
+   - the last modification date on each file is set to 1 (i.e.,
+     00:00:01 1/1/1970 UTC)
+   - the permissions are set of 444 or 555 (i.e., read-only with or
+     without execute permission; setuid bits etc. are cleared)
+   - the owner and group are set to the Nix user and group, if we're
+     running as root. */
+void canonicalisePathMetaData(const Path & path, uid_t fromUid, InodesSeen & inodesSeen);
+void canonicalisePathMetaData(const Path & path, uid_t fromUid);
+
+void canonicaliseTimestampAndPermissions(const Path & path);
+
+MakeError(PathInUse, Error);
+
+}
diff --git a/src/libstore/local.mk b/src/libstore/local.mk
new file mode 100644
index 000000000000..2dddce740dcc
--- /dev/null
+++ b/src/libstore/local.mk
@@ -0,0 +1,28 @@
+libraries += libstore
+
+libstore_NAME = libnixstore
+
+libstore_DIR := $(d)
+
+libstore_SOURCES := $(wildcard $(d)/*.cc)
+
+libstore_LIBS = libutil libformat
+
+libstore_LDFLAGS = -lsqlite3 -lbz2
+
+libstore_CXXFLAGS = \
+ -DNIX_STORE_DIR=\"$(storedir)\" \
+ -DNIX_DATA_DIR=\"$(datadir)\" \
+ -DNIX_STATE_DIR=\"$(localstatedir)/nix\" \
+ -DNIX_LOG_DIR=\"$(localstatedir)/log/nix\" \
+ -DNIX_CONF_DIR=\"$(sysconfdir)/nix\" \
+ -DNIX_LIBEXEC_DIR=\"$(libexecdir)\" \
+ -DNIX_BIN_DIR=\"$(bindir)\" \
+ -DPACKAGE_VERSION=\"$(PACKAGE_VERSION)\"
+
+$(d)/local-store.cc: $(d)/schema.sql.hh
+
+%.sql.hh: %.sql
+	$(trace-gen) sed -e 's/"/\\"/g' -e 's/\(.*\)/"\1\\n"/' < $< > $@ || (rm $@ && exit 1)
+
+clean-files += $(d)/schema.sql.hh
diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
new file mode 100644
index 000000000000..1bf3f9378245
--- /dev/null
+++ b/src/libstore/misc.cc
@@ -0,0 +1,220 @@
+#include "misc.hh"
+#include "store-api.hh"
+#include "local-store.hh"
+#include "globals.hh"
+
+
+namespace nix {
+
+
+Derivation derivationFromPath(StoreAPI & store, const Path & drvPath)
+{
+    assertStorePath(drvPath);
+    store.ensurePath(drvPath);
+    return parseDerivation(readFile(drvPath));
+}
+
+
+void computeFSClosure(StoreAPI & store, const Path & path,
+    PathSet & paths, bool flipDirection, bool includeOutputs, bool includeDerivers)
+{
+    if (paths.find(path) != paths.end()) return;
+    paths.insert(path);
+
+    PathSet edges;
+
+    if (flipDirection) {
+        store.queryReferrers(path, edges);
+
+        if (includeOutputs) {
+            PathSet derivers = store.queryValidDerivers(path);
+            foreach (PathSet::iterator, i, derivers)
+                edges.insert(*i);
+        }
+
+        if (includeDerivers && isDerivation(path)) {
+            PathSet outputs = store.queryDerivationOutputs(path);
+            foreach (PathSet::iterator, i, outputs)
+                if (store.isValidPath(*i) && store.queryDeriver(*i) == path)
+                    edges.insert(*i);
+        }
+
+    } else {
+        store.queryReferences(path, edges);
+
+        if (includeOutputs && isDerivation(path)) {
+            PathSet outputs = store.queryDerivationOutputs(path);
+            foreach (PathSet::iterator, i, outputs)
+                if (store.isValidPath(*i)) edges.insert(*i);
+        }
+
+        if (includeDerivers) {
+            Path deriver = store.queryDeriver(path);
+            if (store.isValidPath(deriver)) edges.insert(deriver);
+        }
+    }
+
+    foreach (PathSet::iterator, i, edges)
+        computeFSClosure(store, *i, paths, flipDirection, includeOutputs, includeDerivers);
+}
+
+
+Path findOutput(const Derivation & drv, string id)
+{
+    foreach (DerivationOutputs::const_iterator, i, drv.outputs)
+        if (i->first == id) return i->second.path;
+    throw Error(format("derivation has no output `%1%'") % id);
+}
+
+
+void queryMissing(StoreAPI & store, const PathSet & targets,
+    PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
+    unsigned long long & downloadSize, unsigned long long & narSize)
+{
+    downloadSize = narSize = 0;
+
+    PathSet todo(targets.begin(), targets.end()), done;
+
+    /* Getting substitute info has high latency when using the binary
+       cache substituter.  Thus it's essential to do substitute
+       queries in parallel as much as possible.  To accomplish this
+       we do the following:
+
+       - For all paths still to be processed (‘todo’), we add all
+         paths for which we need info to the set ‘query’.  For an
+         unbuilt derivation this is the output paths; otherwise, it's
+         the path itself.
+
+       - We get info about all paths in ‘query’ in parallel.
+
+       - We process the results and add new items to ‘todo’ if
+         necessary.  E.g. if a path is substitutable, then we need to
+         get info on its references.
+
+       - Repeat until ‘todo’ is empty.
+    */
+
+    while (!todo.empty()) {
+
+        PathSet query, todoDrv, todoNonDrv;
+
+        foreach (PathSet::iterator, i, todo) {
+            if (done.find(*i) != done.end()) continue;
+            done.insert(*i);
+
+            DrvPathWithOutputs i2 = parseDrvPathWithOutputs(*i);
+
+            if (isDerivation(i2.first)) {
+                if (!store.isValidPath(i2.first)) {
+                    // FIXME: we could try to substitute p.
+                    unknown.insert(*i);
+                    continue;
+                }
+                Derivation drv = derivationFromPath(store, i2.first);
+
+                PathSet invalid;
+                foreach (DerivationOutputs::iterator, j, drv.outputs)
+                    if (wantOutput(j->first, i2.second)
+                        && !store.isValidPath(j->second.path))
+                        invalid.insert(j->second.path);
+                if (invalid.empty()) continue;
+
+                todoDrv.insert(*i);
+                if (settings.useSubstitutes && !willBuildLocally(drv))
+                    query.insert(invalid.begin(), invalid.end());
+            }
+
+            else {
+                if (store.isValidPath(*i)) continue;
+                query.insert(*i);
+                todoNonDrv.insert(*i);
+            }
+        }
+
+        todo.clear();
+
+        SubstitutablePathInfos infos;
+        store.querySubstitutablePathInfos(query, infos);
+
+        foreach (PathSet::iterator, i, todoDrv) {
+            DrvPathWithOutputs i2 = parseDrvPathWithOutputs(*i);
+
+            // FIXME: cache this
+            Derivation drv = derivationFromPath(store, i2.first);
+
+            PathSet outputs;
+            bool mustBuild = false;
+            if (settings.useSubstitutes && !willBuildLocally(drv)) {
+                foreach (DerivationOutputs::iterator, j, drv.outputs) {
+                    if (!wantOutput(j->first, i2.second)) continue;
+                    if (!store.isValidPath(j->second.path)) {
+                        if (infos.find(j->second.path) == infos.end())
+                            mustBuild = true;
+                        else
+                            outputs.insert(j->second.path);
+                    }
+                }
+            } else
+                mustBuild = true;
+
+            if (mustBuild) {
+                willBuild.insert(i2.first);
+                todo.insert(drv.inputSrcs.begin(), drv.inputSrcs.end());
+                foreach (DerivationInputs::iterator, j, drv.inputDrvs)
+                    todo.insert(makeDrvPathWithOutputs(j->first, j->second));
+            } else
+                todoNonDrv.insert(outputs.begin(), outputs.end());
+        }
+
+        foreach (PathSet::iterator, i, todoNonDrv) {
+            done.insert(*i);
+            SubstitutablePathInfos::iterator info = infos.find(*i);
+            if (info != infos.end()) {
+                willSubstitute.insert(*i);
+                downloadSize += info->second.downloadSize;
+                narSize += info->second.narSize;
+                todo.insert(info->second.references.begin(), info->second.references.end());
+            } else
+                unknown.insert(*i);
+        }
+    }
+}
+
+
+static void dfsVisit(StoreAPI & store, const PathSet & paths,
+    const Path & path, PathSet & visited, Paths & sorted,
+    PathSet & parents)
+{
+    if (parents.find(path) != parents.end())
+        throw BuildError(format("cycle detected in the references of `%1%'") % path);
+
+    if (visited.find(path) != visited.end()) return;
+    visited.insert(path);
+    parents.insert(path);
+
+    PathSet references;
+    if (store.isValidPath(path))
+        store.queryReferences(path, references);
+
+    foreach (PathSet::iterator, i, references)
+        /* Don't traverse into paths that don't exist.  That can
+           happen due to substitutes for non-existent paths. */
+        if (*i != path && paths.find(*i) != paths.end())
+            dfsVisit(store, paths, *i, visited, sorted, parents);
+
+    sorted.push_front(path);
+    parents.erase(path);
+}
+
+
+Paths topoSortPaths(StoreAPI & store, const PathSet & paths)
+{
+    Paths sorted;
+    PathSet visited, parents;
+    foreach (PathSet::const_iterator, i, paths)
+        dfsVisit(store, paths, *i, visited, sorted, parents);
+    return sorted;
+}
+
+
+}
diff --git a/src/libstore/misc.hh b/src/libstore/misc.hh
new file mode 100644
index 000000000000..144cb7f457cd
--- /dev/null
+++ b/src/libstore/misc.hh
@@ -0,0 +1,38 @@
+#pragma once
+
+#include "derivations.hh"
+
+
+namespace nix {
+
+
+/* Read a derivation, after ensuring its existence through
+   ensurePath(). */
+Derivation derivationFromPath(StoreAPI & store, const Path & drvPath);
+
+/* Place in `paths' the set of all store paths in the file system
+   closure of `storePath'; that is, all paths than can be directly or
+   indirectly reached from it.  `paths' is not cleared.  If
+   `flipDirection' is true, the set of paths that can reach
+   `storePath' is returned; that is, the closures under the
+   `referrers' relation instead of the `references' relation is
+   returned. */
+void computeFSClosure(StoreAPI & store, const Path & path,
+    PathSet & paths, bool flipDirection = false,
+    bool includeOutputs = false, bool includeDerivers = false);
+
+/* Return the path corresponding to the output identifier `id' in the
+   given derivation. */
+Path findOutput(const Derivation & drv, string id);
+
+/* Given a set of paths that are to be built, return the set of
+   derivations that will be built, and the set of output paths that
+   will be substituted. */
+void queryMissing(StoreAPI & store, const PathSet & targets,
+    PathSet & willBuild, PathSet & willSubstitute, PathSet & unknown,
+    unsigned long long & downloadSize, unsigned long long & narSize);
+
+bool willBuildLocally(const Derivation & drv);
+
+
+}
diff --git a/src/libstore/optimise-store.cc b/src/libstore/optimise-store.cc
new file mode 100644
index 000000000000..d833f3aa05b5
--- /dev/null
+++ b/src/libstore/optimise-store.cc
@@ -0,0 +1,180 @@
+#include "config.h"
+
+#include "util.hh"
+#include "local-store.hh"
+#include "globals.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+
+
+namespace nix {
+
+
+static void makeWritable(const Path & path)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+    if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
+        throw SysError(format("changing writability of `%1%'") % path);
+}
+
+
+struct MakeReadOnly
+{
+    Path path;
+    MakeReadOnly(const Path & path) : path(path) { }
+    ~MakeReadOnly()
+    {
+        try {
+            /* This will make the path read-only. */
+            if (path != "") canonicaliseTimestampAndPermissions(path);
+        } catch (...) {
+            ignoreException();
+        }
+    }
+};
+
+
+void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path)
+{
+    checkInterrupt();
+    
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+        foreach (Strings::iterator, i, names)
+            optimisePath_(stats, path + "/" + *i);
+        return;
+    }
+
+    /* We can hard link regular files and maybe symlinks. */
+    if (!S_ISREG(st.st_mode)
+#if CAN_LINK_SYMLINK
+        && !S_ISLNK(st.st_mode)
+#endif
+        ) return;
+
+    /* Sometimes SNAFUs can cause files in the Nix store to be
+       modified, in particular when running programs as root under
+       NixOS (example: $fontconfig/var/cache being modified).  Skip
+       those files.  FIXME: check the modification time. */
+    if (S_ISREG(st.st_mode) && (st.st_mode & S_IWUSR)) {
+        printMsg(lvlError, format("skipping suspicious writable file `%1%'") % path);
+        return;
+    }
+
+    /* Hash the file.  Note that hashPath() returns the hash over the
+       NAR serialisation, which includes the execute bit on the file.
+       Thus, executable and non-executable files with the same
+       contents *won't* be linked (which is good because otherwise the
+       permissions would be screwed up).
+
+       Also note that if `path' is a symlink, then we're hashing the
+       contents of the symlink (i.e. the result of readlink()), not
+       the contents of the target (which may not even exist). */
+    Hash hash = hashPath(htSHA256, path).first;
+    stats.totalFiles++;
+    printMsg(lvlDebug, format("`%1%' has hash `%2%'") % path % printHash(hash));
+
+    /* Check if this is a known hash. */
+    Path linkPath = linksDir + "/" + printHash32(hash);
+
+    if (!pathExists(linkPath)) {
+        /* Nope, create a hard link in the links directory. */
+        if (link(path.c_str(), linkPath.c_str()) == 0) return;
+        if (errno != EEXIST)
+            throw SysError(format("cannot link `%1%' to `%2%'") % linkPath % path);
+        /* Fall through if another process created ‘linkPath’ before
+           we did. */
+    }
+
+    /* Yes!  We've seen a file with the same contents.  Replace the
+       current file with a hard link to that file. */
+    struct stat stLink;
+    if (lstat(linkPath.c_str(), &stLink))
+        throw SysError(format("getting attributes of path `%1%'") % linkPath);
+
+    stats.sameContents++;
+    if (st.st_ino == stLink.st_ino) {
+        printMsg(lvlDebug, format("`%1%' is already linked to `%2%'") % path % linkPath);
+        return;
+    }
+
+    printMsg(lvlTalkative, format("linking `%1%' to `%2%'") % path % linkPath);
+
+    /* Make the containing directory writable, but only if it's not
+       the store itself (we don't want or need to mess with its
+       permissions). */
+    bool mustToggle = !isStorePath(path);
+    if (mustToggle) makeWritable(dirOf(path));
+
+    /* When we're done, make the directory read-only again and reset
+       its timestamp back to 0. */
+    MakeReadOnly makeReadOnly(mustToggle ? dirOf(path) : "");
+
+    Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
+        % settings.nixStore % getpid() % rand()).str();
+
+    if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
+        if (errno == EMLINK) {
+            /* Too many links to the same file (>= 32000 on most file
+               systems).  This is likely to happen with empty files.
+               Just shrug and ignore. */
+            if (st.st_size)
+                printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
+            return;
+        }
+        throw SysError(format("cannot link `%1%' to `%2%'") % tempLink % linkPath);
+    }
+
+    /* Atomically replace the old file with the new hard link. */
+    if (rename(tempLink.c_str(), path.c_str()) == -1) {
+        if (unlink(tempLink.c_str()) == -1)
+            printMsg(lvlError, format("unable to unlink `%1%'") % tempLink);
+        if (errno == EMLINK) {
+            /* Some filesystems generate too many links on the rename,
+               rather than on the original link.  (Probably it
+               temporarily increases the st_nlink field before
+               decreasing it again.) */
+            if (st.st_size)
+                printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
+            return;
+        }
+        throw SysError(format("cannot rename `%1%' to `%2%'") % tempLink % path);
+    }
+
+    stats.filesLinked++;
+    stats.bytesFreed += st.st_size;
+    stats.blocksFreed += st.st_blocks;
+}
+
+
+void LocalStore::optimiseStore(OptimiseStats & stats)
+{
+    PathSet paths = queryAllValidPaths();
+
+    foreach (PathSet::iterator, i, paths) {
+        addTempRoot(*i);
+        if (!isValidPath(*i)) continue; /* path was GC'ed, probably */
+        startNest(nest, lvlChatty, format("hashing files in `%1%'") % *i);
+        optimisePath_(stats, *i);
+    }
+}
+
+
+void LocalStore::optimisePath(const Path & path)
+{
+    OptimiseStats stats;
+    if (settings.autoOptimiseStore) optimisePath_(stats, path);
+}
+
+
+}
diff --git a/src/libstore/pathlocks.cc b/src/libstore/pathlocks.cc
new file mode 100644
index 000000000000..b858ed238de0
--- /dev/null
+++ b/src/libstore/pathlocks.cc
@@ -0,0 +1,199 @@
+#include "pathlocks.hh"
+#include "util.hh"
+
+#include <cerrno>
+#include <cstdlib>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+
+namespace nix {
+
+
+int openLockFile(const Path & path, bool create)
+{
+    AutoCloseFD fd;
+
+    fd = open(path.c_str(), O_RDWR | (create ? O_CREAT : 0), 0600);
+    if (fd == -1 && (create || errno != ENOENT))
+        throw SysError(format("opening lock file `%1%'") % path);
+
+    closeOnExec(fd);
+
+    return fd.borrow();
+}
+
+
+void deleteLockFile(const Path & path, int fd)
+{
+    /* Get rid of the lock file.  Have to be careful not to introduce
+       races.  Write a (meaningless) token to the file to indicate to
+       other processes waiting on this lock that the lock is stale
+       (deleted). */
+    unlink(path.c_str());
+    writeFull(fd, (const unsigned char *) "d", 1);
+    /* Note that the result of unlink() is ignored; removing the lock
+       file is an optimisation, not a necessity. */
+}
+
+
+bool lockFile(int fd, LockType lockType, bool wait)
+{
+    struct flock lock;
+    if (lockType == ltRead) lock.l_type = F_RDLCK;
+    else if (lockType == ltWrite) lock.l_type = F_WRLCK;
+    else if (lockType == ltNone) lock.l_type = F_UNLCK;
+    else abort();
+    lock.l_whence = SEEK_SET;
+    lock.l_start = 0;
+    lock.l_len = 0; /* entire file */
+
+    if (wait) {
+        while (fcntl(fd, F_SETLKW, &lock) != 0) {
+            checkInterrupt();
+            if (errno != EINTR)
+                throw SysError(format("acquiring/releasing lock"));
+        }
+    } else {
+        while (fcntl(fd, F_SETLK, &lock) != 0) {
+            checkInterrupt();
+            if (errno == EACCES || errno == EAGAIN) return false;
+            if (errno != EINTR) 
+                throw SysError(format("acquiring/releasing lock"));
+        }
+    }
+
+    return true;
+}
+
+
+/* This enables us to check whether are not already holding a lock on
+   a file ourselves.  POSIX locks (fcntl) suck in this respect: if we
+   close a descriptor, the previous lock will be closed as well.  And
+   there is no way to query whether we already have a lock (F_GETLK
+   only works on locks held by other processes). */
+static StringSet lockedPaths; /* !!! not thread-safe */
+
+
+PathLocks::PathLocks()
+    : deletePaths(false)
+{
+}
+
+
+PathLocks::PathLocks(const PathSet & paths, const string & waitMsg)
+    : deletePaths(false)
+{
+    lockPaths(paths, waitMsg);
+}
+
+
+bool PathLocks::lockPaths(const PathSet & _paths,
+    const string & waitMsg, bool wait)
+{
+    assert(fds.empty());
+    
+    /* Note that `fds' is built incrementally so that the destructor
+       will only release those locks that we have already acquired. */
+
+    /* Sort the paths.  This assures that locks are always acquired in
+       the same order, thus preventing deadlocks. */
+    Paths paths(_paths.begin(), _paths.end());
+    paths.sort();
+    
+    /* Acquire the lock for each path. */
+    foreach (Paths::iterator, i, paths) {
+        checkInterrupt();
+        Path path = *i;
+        Path lockPath = path + ".lock";
+
+        debug(format("locking path `%1%'") % path);
+
+        if (lockedPaths.find(lockPath) != lockedPaths.end())
+            throw Error("deadlock: trying to re-acquire self-held lock");
+
+        AutoCloseFD fd;
+        
+        while (1) {
+
+            /* Open/create the lock file. */
+	    fd = openLockFile(lockPath, true);
+
+            /* Acquire an exclusive lock. */
+            if (!lockFile(fd, ltWrite, false)) {
+                if (wait) {
+                    if (waitMsg != "") printMsg(lvlError, waitMsg);
+                    lockFile(fd, ltWrite, true);
+                } else {
+                    /* Failed to lock this path; release all other
+                       locks. */
+                    unlock();
+                    return false;
+                }
+            }
+
+            debug(format("lock acquired on `%1%'") % lockPath);
+
+            /* Check that the lock file hasn't become stale (i.e.,
+               hasn't been unlinked). */
+            struct stat st;
+            if (fstat(fd, &st) == -1)
+                throw SysError(format("statting lock file `%1%'") % lockPath);
+            if (st.st_size != 0)
+                /* This lock file has been unlinked, so we're holding
+                   a lock on a deleted file.  This means that other
+                   processes may create and acquire a lock on
+                   `lockPath', and proceed.  So we must retry. */
+                debug(format("open lock file `%1%' has become stale") % lockPath);
+            else
+                break;
+        }
+
+        /* Use borrow so that the descriptor isn't closed. */
+        fds.push_back(FDPair(fd.borrow(), lockPath));
+        lockedPaths.insert(lockPath);
+    }
+
+    return true;
+}
+
+
+PathLocks::~PathLocks()
+{
+    unlock();
+}
+
+
+void PathLocks::unlock()
+{
+    foreach (list<FDPair>::iterator, i, fds) {
+        if (deletePaths) deleteLockFile(i->second, i->first);
+
+        lockedPaths.erase(i->second);
+        if (close(i->first) == -1)
+            printMsg(lvlError,
+                format("error (ignored): cannot close lock file on `%1%'") % i->second);
+
+        debug(format("lock released on `%1%'") % i->second);
+    }
+
+    fds.clear();
+}
+
+
+void PathLocks::setDeletion(bool deletePaths)
+{
+    this->deletePaths = deletePaths;
+}
+
+
+bool pathIsLockedByMe(const Path & path)
+{
+    Path lockPath = path + ".lock";
+    return lockedPaths.find(lockPath) != lockedPaths.end();
+}
+
+ 
+}
diff --git a/src/libstore/pathlocks.hh b/src/libstore/pathlocks.hh
new file mode 100644
index 000000000000..8a6b1450da2a
--- /dev/null
+++ b/src/libstore/pathlocks.hh
@@ -0,0 +1,45 @@
+#pragma once
+
+#include "types.hh"
+
+
+namespace nix {
+
+
+/* Open (possibly create) a lock file and return the file descriptor.
+   -1 is returned if create is false and the lock could not be opened
+   because it doesn't exist.  Any other error throws an exception. */
+int openLockFile(const Path & path, bool create);
+
+/* Delete an open lock file. */
+void deleteLockFile(const Path & path, int fd);
+
+enum LockType { ltRead, ltWrite, ltNone };
+
+bool lockFile(int fd, LockType lockType, bool wait);
+
+
+class PathLocks 
+{
+private:
+    typedef std::pair<int, Path> FDPair;
+    list<FDPair> fds;
+    bool deletePaths;
+
+public:
+    PathLocks();
+    PathLocks(const PathSet & paths,
+        const string & waitMsg = "");
+    bool lockPaths(const PathSet & _paths,
+        const string & waitMsg = "",
+        bool wait = true);
+    ~PathLocks();
+    void unlock();
+    void setDeletion(bool deletePaths);
+};
+
+
+bool pathIsLockedByMe(const Path & path);
+
+
+}
diff --git a/src/libstore/references.cc b/src/libstore/references.cc
new file mode 100644
index 000000000000..282b848938b3
--- /dev/null
+++ b/src/libstore/references.cc
@@ -0,0 +1,122 @@
+#include "references.hh"
+#include "hash.hh"
+#include "util.hh"
+#include "archive.hh"
+
+#include <map>
+#include <cstdlib>
+
+
+namespace nix {
+
+
+static unsigned int refLength = 32; /* characters */
+
+
+static void search(const unsigned char * s, unsigned int len, 
+    StringSet & hashes, StringSet & seen)
+{
+    static bool initialised = false;
+    static bool isBase32[256];
+    if (!initialised) {
+        for (unsigned int i = 0; i < 256; ++i) isBase32[i] = false;
+        for (unsigned int i = 0; i < base32Chars.size(); ++i)
+            isBase32[(unsigned char) base32Chars[i]] = true;
+        initialised = true;
+    }
+    
+    for (unsigned int i = 0; i + refLength <= len; ) {
+        int j;
+        bool match = true;
+        for (j = refLength - 1; j >= 0; --j)
+            if (!isBase32[(unsigned char) s[i + j]]) {
+                i += j + 1;
+                match = false;
+                break;
+            }
+        if (!match) continue;
+        string ref((const char *) s + i, refLength);
+        if (hashes.find(ref) != hashes.end()) {
+            debug(format("found reference to `%1%' at offset `%2%'")
+                  % ref % i);
+            seen.insert(ref);
+            hashes.erase(ref);
+        }
+        ++i;
+    }
+}
+
+
+struct RefScanSink : Sink
+{
+    HashSink hashSink;
+    StringSet hashes;
+    StringSet seen;
+
+    string tail;
+
+    RefScanSink() : hashSink(htSHA256) { }
+    
+    void operator () (const unsigned char * data, size_t len);
+};
+
+
+void RefScanSink::operator () (const unsigned char * data, size_t len)
+{
+    hashSink(data, len);
+
+    /* It's possible that a reference spans the previous and current
+       fragment, so search in the concatenation of the tail of the
+       previous fragment and the start of the current fragment. */
+    string s = tail + string((const char *) data, len > refLength ? refLength : len);
+    search((const unsigned char *) s.data(), s.size(), hashes, seen);
+
+    search(data, len, hashes, seen);
+
+    unsigned int tailLen = len <= refLength ? len : refLength;
+    tail =
+        string(tail, tail.size() < refLength - tailLen ? 0 : tail.size() - (refLength - tailLen)) +
+        string((const char *) data + len - tailLen, tailLen);
+}
+
+
+PathSet scanForReferences(const string & path,
+    const PathSet & refs, HashResult & hash)
+{
+    RefScanSink sink;
+    std::map<string, Path> backMap;
+
+    /* For efficiency (and a higher hit rate), just search for the
+       hash part of the file name.  (This assumes that all references
+       have the form `HASH-bla'). */
+    foreach (PathSet::const_iterator, i, refs) {
+        string baseName = baseNameOf(*i);
+        string::size_type pos = baseName.find('-');
+        if (pos == string::npos)
+            throw Error(format("bad reference `%1%'") % *i);
+        string s = string(baseName, 0, pos);
+        assert(s.size() == refLength);
+        assert(backMap.find(s) == backMap.end());
+        // parseHash(htSHA256, s);
+        sink.hashes.insert(s);
+        backMap[s] = *i;
+    }
+
+    /* Look for the hashes in the NAR dump of the path. */
+    dumpPath(path, sink);
+
+    /* Map the hashes found back to their store paths. */
+    PathSet found;
+    foreach (StringSet::iterator, i, sink.seen) {
+        std::map<string, Path>::iterator j;
+        if ((j = backMap.find(*i)) == backMap.end()) abort();
+        found.insert(j->second);
+    }
+
+    hash = sink.hashSink.finish();
+        
+    return found;
+}
+
+
+}
diff --git a/src/libstore/references.hh b/src/libstore/references.hh
new file mode 100644
index 000000000000..013809d122f3
--- /dev/null
+++ b/src/libstore/references.hh
@@ -0,0 +1,11 @@
+#pragma once
+
+#include "types.hh"
+#include "hash.hh"
+
+namespace nix {
+
+PathSet scanForReferences(const Path & path, const PathSet & refs,
+    HashResult & hash);
+    
+}
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
new file mode 100644
index 000000000000..3017254baf3b
--- /dev/null
+++ b/src/libstore/remote-store.cc
@@ -0,0 +1,602 @@
+#include "serialise.hh"
+#include "util.hh"
+#include "remote-store.hh"
+#include "worker-protocol.hh"
+#include "archive.hh"
+#include "affinity.hh"
+#include "globals.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <fcntl.h>
+
+#include <iostream>
+#include <unistd.h>
+#include <cstring>
+
+namespace nix {
+
+
+Path readStorePath(Source & from)
+{
+    Path path = readString(from);
+    assertStorePath(path);
+    return path;
+}
+
+
+template<class T> T readStorePaths(Source & from)
+{
+    T paths = readStrings<T>(from);
+    foreach (typename T::iterator, i, paths) assertStorePath(*i);
+    return paths;
+}
+
+template PathSet readStorePaths(Source & from);
+
+
+RemoteStore::RemoteStore()
+{
+    initialised = false;
+}
+
+
+void RemoteStore::openConnection(bool reserveSpace)
+{
+    if (initialised) return;
+    initialised = true;
+
+    string remoteMode = getEnv("NIX_REMOTE");
+
+    if (remoteMode == "daemon")
+        /* Connect to a daemon that does the privileged work for
+           us. */
+        connectToDaemon();
+    else
+        throw Error(format("invalid setting for NIX_REMOTE, `%1%'") % remoteMode);
+
+    from.fd = fdSocket;
+    to.fd = fdSocket;
+
+    /* Send the magic greeting, check for the reply. */
+    try {
+        writeInt(WORKER_MAGIC_1, to);
+        to.flush();
+        unsigned int magic = readInt(from);
+        if (magic != WORKER_MAGIC_2) throw Error("protocol mismatch");
+
+        daemonVersion = readInt(from);
+        if (GET_PROTOCOL_MAJOR(daemonVersion) != GET_PROTOCOL_MAJOR(PROTOCOL_VERSION))
+            throw Error("Nix daemon protocol version not supported");
+        writeInt(PROTOCOL_VERSION, to);
+
+        if (GET_PROTOCOL_MINOR(daemonVersion) >= 14) {
+            int cpu = settings.lockCPU ? lockToCurrentCPU() : -1;
+            if (cpu != -1) {
+                writeInt(1, to);
+                writeInt(cpu, to);
+            } else
+                writeInt(0, to);
+        }
+
+        if (GET_PROTOCOL_MINOR(daemonVersion) >= 11)
+            writeInt(reserveSpace, to);
+
+        processStderr();
+    }
+    catch (Error & e) {
+        throw Error(format("cannot start worker (%1%)")
+            % e.msg());
+    }
+
+    setOptions();
+}
+
+
+void RemoteStore::connectToDaemon()
+{
+    fdSocket = socket(PF_UNIX, SOCK_STREAM, 0);
+    if (fdSocket == -1)
+        throw SysError("cannot create Unix domain socket");
+    closeOnExec(fdSocket);
+
+    string socketPath = settings.nixDaemonSocketFile;
+
+    /* Urgh, sockaddr_un allows path names of only 108 characters.  So
+       chdir to the socket directory so that we can pass a relative
+       path name.  !!! this is probably a bad idea in multi-threaded
+       applications... */
+    AutoCloseFD fdPrevDir = open(".", O_RDONLY);
+    if (fdPrevDir == -1) throw SysError("couldn't open current directory");
+    chdir(dirOf(socketPath).c_str());
+    Path socketPathRel = "./" + baseNameOf(socketPath);
+
+    struct sockaddr_un addr;
+    addr.sun_family = AF_UNIX;
+    if (socketPathRel.size() >= sizeof(addr.sun_path))
+        throw Error(format("socket path `%1%' is too long") % socketPathRel);
+    using namespace std;
+    strcpy(addr.sun_path, socketPathRel.c_str());
+
+    if (connect(fdSocket, (struct sockaddr *) &addr, sizeof(addr)) == -1)
+        throw SysError(format("cannot connect to daemon at `%1%'") % socketPath);
+
+    if (fchdir(fdPrevDir) == -1)
+        throw SysError("couldn't change back to previous directory");
+}
+
+
+RemoteStore::~RemoteStore()
+{
+    try {
+        to.flush();
+        fdSocket.close();
+        if (child != -1)
+            child.wait(true);
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void RemoteStore::setOptions()
+{
+    writeInt(wopSetOptions, to);
+
+    writeInt(settings.keepFailed, to);
+    writeInt(settings.keepGoing, to);
+    writeInt(settings.tryFallback, to);
+    writeInt(verbosity, to);
+    writeInt(settings.maxBuildJobs, to);
+    writeInt(settings.maxSilentTime, to);
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 2)
+        writeInt(settings.useBuildHook, to);
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 4) {
+        writeInt(settings.buildVerbosity, to);
+        writeInt(logType, to);
+        writeInt(settings.printBuildTrace, to);
+    }
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 6)
+        writeInt(settings.buildCores, to);
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 10)
+        writeInt(settings.useSubstitutes, to);
+
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 12) {
+        Settings::SettingsMap overrides = settings.getOverrides();
+        writeInt(overrides.size(), to);
+        foreach (Settings::SettingsMap::iterator, i, overrides) {
+            writeString(i->first, to);
+            writeString(i->second, to);
+        }
+    }
+
+    processStderr();
+}
+
+
+bool RemoteStore::isValidPath(const Path & path)
+{
+    openConnection();
+    writeInt(wopIsValidPath, to);
+    writeString(path, to);
+    processStderr();
+    unsigned int reply = readInt(from);
+    return reply != 0;
+}
+
+
+PathSet RemoteStore::queryValidPaths(const PathSet & paths)
+{
+    openConnection();
+    if (GET_PROTOCOL_MINOR(daemonVersion) < 12) {
+        PathSet res;
+        foreach (PathSet::const_iterator, i, paths)
+            if (isValidPath(*i)) res.insert(*i);
+        return res;
+    } else {
+        writeInt(wopQueryValidPaths, to);
+        writeStrings(paths, to);
+        processStderr();
+        return readStorePaths<PathSet>(from);
+    }
+}
+
+
+PathSet RemoteStore::queryAllValidPaths()
+{
+    openConnection();
+    writeInt(wopQueryAllValidPaths, to);
+    processStderr();
+    return readStorePaths<PathSet>(from);
+}
+
+
+PathSet RemoteStore::querySubstitutablePaths(const PathSet & paths)
+{
+    openConnection();
+    if (GET_PROTOCOL_MINOR(daemonVersion) < 12) {
+        PathSet res;
+        foreach (PathSet::const_iterator, i, paths) {
+            writeInt(wopHasSubstitutes, to);
+            writeString(*i, to);
+            processStderr();
+            if (readInt(from)) res.insert(*i);
+        }
+        return res;
+    } else {
+        writeInt(wopQuerySubstitutablePaths, to);
+        writeStrings(paths, to);
+        processStderr();
+        return readStorePaths<PathSet>(from);
+    }
+}
+
+
+void RemoteStore::querySubstitutablePathInfos(const PathSet & paths,
+    SubstitutablePathInfos & infos)
+{
+    if (paths.empty()) return;
+
+    openConnection();
+
+    if (GET_PROTOCOL_MINOR(daemonVersion) < 3) return;
+
+    if (GET_PROTOCOL_MINOR(daemonVersion) < 12) {
+
+        foreach (PathSet::const_iterator, i, paths) {
+            SubstitutablePathInfo info;
+            writeInt(wopQuerySubstitutablePathInfo, to);
+            writeString(*i, to);
+            processStderr();
+            unsigned int reply = readInt(from);
+            if (reply == 0) continue;
+            info.deriver = readString(from);
+            if (info.deriver != "") assertStorePath(info.deriver);
+            info.references = readStorePaths<PathSet>(from);
+            info.downloadSize = readLongLong(from);
+            info.narSize = GET_PROTOCOL_MINOR(daemonVersion) >= 7 ? readLongLong(from) : 0;
+            infos[*i] = info;
+        }
+
+    } else {
+
+        writeInt(wopQuerySubstitutablePathInfos, to);
+        writeStrings(paths, to);
+        processStderr();
+        unsigned int count = readInt(from);
+        for (unsigned int n = 0; n < count; n++) {
+            Path path = readStorePath(from);
+            SubstitutablePathInfo & info(infos[path]);
+            info.deriver = readString(from);
+            if (info.deriver != "") assertStorePath(info.deriver);
+            info.references = readStorePaths<PathSet>(from);
+            info.downloadSize = readLongLong(from);
+            info.narSize = readLongLong(from);
+        }
+
+    }
+}
+
+
+ValidPathInfo RemoteStore::queryPathInfo(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryPathInfo, to);
+    writeString(path, to);
+    processStderr();
+    ValidPathInfo info;
+    info.path = path;
+    info.deriver = readString(from);
+    if (info.deriver != "") assertStorePath(info.deriver);
+    info.hash = parseHash(htSHA256, readString(from));
+    info.references = readStorePaths<PathSet>(from);
+    info.registrationTime = readInt(from);
+    info.narSize = readLongLong(from);
+    return info;
+}
+
+
+Hash RemoteStore::queryPathHash(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryPathHash, to);
+    writeString(path, to);
+    processStderr();
+    string hash = readString(from);
+    return parseHash(htSHA256, hash);
+}
+
+
+void RemoteStore::queryReferences(const Path & path,
+    PathSet & references)
+{
+    openConnection();
+    writeInt(wopQueryReferences, to);
+    writeString(path, to);
+    processStderr();
+    PathSet references2 = readStorePaths<PathSet>(from);
+    references.insert(references2.begin(), references2.end());
+}
+
+
+void RemoteStore::queryReferrers(const Path & path,
+    PathSet & referrers)
+{
+    openConnection();
+    writeInt(wopQueryReferrers, to);
+    writeString(path, to);
+    processStderr();
+    PathSet referrers2 = readStorePaths<PathSet>(from);
+    referrers.insert(referrers2.begin(), referrers2.end());
+}
+
+
+Path RemoteStore::queryDeriver(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryDeriver, to);
+    writeString(path, to);
+    processStderr();
+    Path drvPath = readString(from);
+    if (drvPath != "") assertStorePath(drvPath);
+    return drvPath;
+}
+
+
+PathSet RemoteStore::queryValidDerivers(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryValidDerivers, to);
+    writeString(path, to);
+    processStderr();
+    return readStorePaths<PathSet>(from);
+}
+
+
+PathSet RemoteStore::queryDerivationOutputs(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryDerivationOutputs, to);
+    writeString(path, to);
+    processStderr();
+    return readStorePaths<PathSet>(from);
+}
+
+
+PathSet RemoteStore::queryDerivationOutputNames(const Path & path)
+{
+    openConnection();
+    writeInt(wopQueryDerivationOutputNames, to);
+    writeString(path, to);
+    processStderr();
+    return readStrings<PathSet>(from);
+}
+
+
+Path RemoteStore::queryPathFromHashPart(const string & hashPart)
+{
+    openConnection();
+    writeInt(wopQueryPathFromHashPart, to);
+    writeString(hashPart, to);
+    processStderr();
+    Path path = readString(from);
+    if (!path.empty()) assertStorePath(path);
+    return path;
+}
+
+
+Path RemoteStore::addToStore(const Path & _srcPath,
+    bool recursive, HashType hashAlgo, PathFilter & filter, bool repair)
+{
+    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
+
+    openConnection();
+
+    Path srcPath(absPath(_srcPath));
+
+    writeInt(wopAddToStore, to);
+    writeString(baseNameOf(srcPath), to);
+    /* backwards compatibility hack */
+    writeInt((hashAlgo == htSHA256 && recursive) ? 0 : 1, to);
+    writeInt(recursive ? 1 : 0, to);
+    writeString(printHashType(hashAlgo), to);
+    dumpPath(srcPath, to, filter);
+    processStderr();
+    return readStorePath(from);
+}
+
+
+Path RemoteStore::addTextToStore(const string & name, const string & s,
+    const PathSet & references, bool repair)
+{
+    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
+
+    openConnection();
+    writeInt(wopAddTextToStore, to);
+    writeString(name, to);
+    writeString(s, to);
+    writeStrings(references, to);
+
+    processStderr();
+    return readStorePath(from);
+}
+
+
+void RemoteStore::exportPath(const Path & path, bool sign,
+    Sink & sink)
+{
+    openConnection();
+    writeInt(wopExportPath, to);
+    writeString(path, to);
+    writeInt(sign ? 1 : 0, to);
+    processStderr(&sink); /* sink receives the actual data */
+    readInt(from);
+}
+
+
+Paths RemoteStore::importPaths(bool requireSignature, Source & source)
+{
+    openConnection();
+    writeInt(wopImportPaths, to);
+    /* We ignore requireSignature, since the worker forces it to true
+       anyway. */
+    processStderr(0, &source);
+    return readStorePaths<Paths>(from);
+}
+
+
+void RemoteStore::buildPaths(const PathSet & drvPaths, bool repair)
+{
+    if (repair) throw Error("repairing is not supported when building through the Nix daemon");
+    openConnection();
+    writeInt(wopBuildPaths, to);
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 13)
+        writeStrings(drvPaths, to);
+    else {
+        /* For backwards compatibility with old daemons, strip output
+           identifiers. */
+        PathSet drvPaths2;
+        foreach (PathSet::const_iterator, i, drvPaths)
+            drvPaths2.insert(string(*i, 0, i->find('!')));
+        writeStrings(drvPaths2, to);
+    }
+    processStderr();
+    readInt(from);
+}
+
+
+void RemoteStore::ensurePath(const Path & path)
+{
+    openConnection();
+    writeInt(wopEnsurePath, to);
+    writeString(path, to);
+    processStderr();
+    readInt(from);
+}
+
+
+void RemoteStore::addTempRoot(const Path & path)
+{
+    openConnection();
+    writeInt(wopAddTempRoot, to);
+    writeString(path, to);
+    processStderr();
+    readInt(from);
+}
+
+
+void RemoteStore::addIndirectRoot(const Path & path)
+{
+    openConnection();
+    writeInt(wopAddIndirectRoot, to);
+    writeString(path, to);
+    processStderr();
+    readInt(from);
+}
+
+
+void RemoteStore::syncWithGC()
+{
+    openConnection();
+    writeInt(wopSyncWithGC, to);
+    processStderr();
+    readInt(from);
+}
+
+
+Roots RemoteStore::findRoots()
+{
+    openConnection();
+    writeInt(wopFindRoots, to);
+    processStderr();
+    unsigned int count = readInt(from);
+    Roots result;
+    while (count--) {
+        Path link = readString(from);
+        Path target = readStorePath(from);
+        result[link] = target;
+    }
+    return result;
+}
+
+
+void RemoteStore::collectGarbage(const GCOptions & options, GCResults & results)
+{
+    openConnection(false);
+
+    writeInt(wopCollectGarbage, to);
+    writeInt(options.action, to);
+    writeStrings(options.pathsToDelete, to);
+    writeInt(options.ignoreLiveness, to);
+    writeLongLong(options.maxFreed, to);
+    writeInt(0, to);
+    if (GET_PROTOCOL_MINOR(daemonVersion) >= 5) {
+        /* removed options */
+        writeInt(0, to);
+        writeInt(0, to);
+    }
+
+    processStderr();
+
+    results.paths = readStrings<PathSet>(from);
+    results.bytesFreed = readLongLong(from);
+    readLongLong(from); // obsolete
+}
+
+
+PathSet RemoteStore::queryFailedPaths()
+{
+    openConnection();
+    writeInt(wopQueryFailedPaths, to);
+    processStderr();
+    return readStorePaths<PathSet>(from);
+}
+
+
+void RemoteStore::clearFailedPaths(const PathSet & paths)
+{
+    openConnection();
+    writeInt(wopClearFailedPaths, to);
+    writeStrings(paths, to);
+    processStderr();
+    readInt(from);
+}
+
+
+void RemoteStore::processStderr(Sink * sink, Source * source)
+{
+    to.flush();
+    unsigned int msg;
+    while ((msg = readInt(from)) == STDERR_NEXT
+        || msg == STDERR_READ || msg == STDERR_WRITE) {
+        if (msg == STDERR_WRITE) {
+            string s = readString(from);
+            if (!sink) throw Error("no sink");
+            (*sink)((const unsigned char *) s.data(), s.size());
+        }
+        else if (msg == STDERR_READ) {
+            if (!source) throw Error("no source");
+            size_t len = readInt(from);
+            unsigned char * buf = new unsigned char[len];
+            AutoDeleteArray<unsigned char> d(buf);
+            writeString(buf, source->read(buf, len), to);
+            to.flush();
+        }
+        else {
+            string s = readString(from);
+            writeToStderr(s);
+        }
+    }
+    if (msg == STDERR_ERROR) {
+        string error = readString(from);
+        unsigned int status = GET_PROTOCOL_MINOR(daemonVersion) >= 8 ? readInt(from) : 1;
+        throw Error(format("%1%") % error, status);
+    }
+    else if (msg != STDERR_LAST)
+        throw Error("protocol error processing standard error");
+}
+
+
+}
diff --git a/src/libstore/remote-store.hh b/src/libstore/remote-store.hh
new file mode 100644
index 000000000000..14253b92cd0e
--- /dev/null
+++ b/src/libstore/remote-store.hh
@@ -0,0 +1,104 @@
+#pragma once
+
+#include <string>
+
+#include "store-api.hh"
+
+
+namespace nix {
+
+
+class Pipe;
+class Pid;
+struct FdSink;
+struct FdSource;
+
+
+class RemoteStore : public StoreAPI
+{
+public:
+
+    RemoteStore();
+
+    ~RemoteStore();
+    
+    /* Implementations of abstract store API methods. */
+    
+    bool isValidPath(const Path & path);
+
+    PathSet queryValidPaths(const PathSet & paths);
+    
+    PathSet queryAllValidPaths();
+    
+    ValidPathInfo queryPathInfo(const Path & path);
+
+    Hash queryPathHash(const Path & path);
+
+    void queryReferences(const Path & path, PathSet & references);
+
+    void queryReferrers(const Path & path, PathSet & referrers);
+
+    Path queryDeriver(const Path & path);
+    
+    PathSet queryValidDerivers(const Path & path);
+
+    PathSet queryDerivationOutputs(const Path & path);
+    
+    StringSet queryDerivationOutputNames(const Path & path);
+
+    Path queryPathFromHashPart(const string & hashPart);
+    
+    PathSet querySubstitutablePaths(const PathSet & paths);
+    
+    void querySubstitutablePathInfos(const PathSet & paths,
+        SubstitutablePathInfos & infos);
+    
+    Path addToStore(const Path & srcPath,
+        bool recursive = true, HashType hashAlgo = htSHA256,
+        PathFilter & filter = defaultPathFilter, bool repair = false);
+
+    Path addTextToStore(const string & name, const string & s,
+        const PathSet & references, bool repair = false);
+
+    void exportPath(const Path & path, bool sign,
+        Sink & sink);
+
+    Paths importPaths(bool requireSignature, Source & source);
+    
+    void buildPaths(const PathSet & paths, bool repair = false);
+
+    void ensurePath(const Path & path);
+
+    void addTempRoot(const Path & path);
+
+    void addIndirectRoot(const Path & path);
+    
+    void syncWithGC();
+    
+    Roots findRoots();
+
+    void collectGarbage(const GCOptions & options, GCResults & results);
+    
+    PathSet queryFailedPaths();
+
+    void clearFailedPaths(const PathSet & paths);
+    
+private:
+    AutoCloseFD fdSocket;
+    FdSink to;
+    FdSource from;
+    Pid child;
+    unsigned int daemonVersion;
+    bool initialised;
+
+    void openConnection(bool reserveSpace = true);
+
+    void processStderr(Sink * sink = 0, Source * source = 0);
+
+    void connectToDaemon();
+
+    void setOptions();
+};
+
+
+}
diff --git a/src/libstore/schema.sql b/src/libstore/schema.sql
new file mode 100644
index 000000000000..c1b4a689afcb
--- /dev/null
+++ b/src/libstore/schema.sql
@@ -0,0 +1,44 @@
+create table if not exists ValidPaths (
+    id               integer primary key autoincrement not null,
+    path             text unique not null,
+    hash             text not null,
+    registrationTime integer not null,
+    deriver          text,
+    narSize          integer
+);
+
+create table if not exists Refs (
+    referrer  integer not null,
+    reference integer not null,
+    primary key (referrer, reference),
+    foreign key (referrer) references ValidPaths(id) on delete cascade,
+    foreign key (reference) references ValidPaths(id) on delete restrict
+);
+
+create index if not exists IndexReferrer on Refs(referrer);
+create index if not exists IndexReference on Refs(reference);
+
+-- Paths can refer to themselves, causing a tuple (N, N) in the Refs
+-- table.  This causes a deletion of the corresponding row in
+-- ValidPaths to cause a foreign key constraint violation (due to `on
+-- delete restrict' on the `reference' column).  Therefore, explicitly
+-- get rid of self-references.
+create trigger if not exists DeleteSelfRefs before delete on ValidPaths
+  begin
+    delete from Refs where referrer = old.id and reference = old.id;
+  end;
+
+create table if not exists DerivationOutputs (
+    drv  integer not null,
+    id   text not null, -- symbolic output id, usually "out"
+    path text not null,
+    primary key (drv, id),
+    foreign key (drv) references ValidPaths(id) on delete cascade
+);
+
+create index if not exists IndexDerivationOutputs on DerivationOutputs(path);
+
+create table if not exists FailedPaths (
+    path text primary key not null,
+    time integer not null
+);
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
new file mode 100644
index 000000000000..0f250a3c7c04
--- /dev/null
+++ b/src/libstore/store-api.cc
@@ -0,0 +1,331 @@
+#include "store-api.hh"
+#include "globals.hh"
+#include "util.hh"
+
+#include <climits>
+
+
+namespace nix {
+
+
+GCOptions::GCOptions()
+{
+    action = gcDeleteDead;
+    ignoreLiveness = false;
+    maxFreed = ULLONG_MAX;
+}
+
+
+bool isInStore(const Path & path)
+{
+    return isInDir(path, settings.nixStore);
+}
+
+
+bool isStorePath(const Path & path)
+{
+    return isInStore(path)
+        && path.find('/', settings.nixStore.size() + 1) == Path::npos;
+}
+
+
+void assertStorePath(const Path & path)
+{
+    if (!isStorePath(path))
+        throw Error(format("path `%1%' is not in the Nix store") % path);
+}
+
+
+Path toStorePath(const Path & path)
+{
+    if (!isInStore(path))
+        throw Error(format("path `%1%' is not in the Nix store") % path);
+    Path::size_type slash = path.find('/', settings.nixStore.size() + 1);
+    if (slash == Path::npos)
+        return path;
+    else
+        return Path(path, 0, slash);
+}
+
+
+Path followLinksToStore(const Path & _path)
+{
+    Path path = absPath(_path);
+    while (!isInStore(path)) {
+        if (!isLink(path)) break;
+        string target = readLink(path);
+        path = absPath(target, dirOf(path));
+    }
+    if (!isInStore(path))
+        throw Error(format("path `%1%' is not in the Nix store") % path);
+    return path;
+}
+
+
+Path followLinksToStorePath(const Path & path)
+{
+    return toStorePath(followLinksToStore(path));
+}
+
+
+string storePathToName(const Path & path)
+{
+    assertStorePath(path);
+    return string(path, settings.nixStore.size() + 34);
+}
+
+
+void checkStoreName(const string & name)
+{
+    string validChars = "+-._?=";
+    /* Disallow names starting with a dot for possible security
+       reasons (e.g., "." and ".."). */
+    if (string(name, 0, 1) == ".")
+        throw Error(format("illegal name: `%1%'") % name);
+    foreach (string::const_iterator, i, name)
+        if (!((*i >= 'A' && *i <= 'Z') ||
+              (*i >= 'a' && *i <= 'z') ||
+              (*i >= '0' && *i <= '9') ||
+              validChars.find(*i) != string::npos))
+        {
+            throw Error(format("invalid character `%1%' in name `%2%'")
+                % *i % name);
+        }
+}
+
+
+/* Store paths have the following form:
+
+   <store>/<h>-<name>
+
+   where
+
+   <store> = the location of the Nix store, usually /nix/store
+   
+   <name> = a human readable name for the path, typically obtained
+     from the name attribute of the derivation, or the name of the
+     source file from which the store path is created.  For derivation
+     outputs other than the default "out" output, the string "-<id>"
+     is suffixed to <name>.
+     
+   <h> = base-32 representation of the first 160 bits of a SHA-256
+     hash of <s>; the hash part of the store name
+     
+   <s> = the string "<type>:sha256:<h2>:<store>:<name>";
+     note that it includes the location of the store as well as the
+     name to make sure that changes to either of those are reflected
+     in the hash (e.g. you won't get /nix/store/<h>-name1 and
+     /nix/store/<h>-name2 with equal hash parts).
+     
+   <type> = one of:
+     "text:<r1>:<r2>:...<rN>"
+       for plain text files written to the store using
+       addTextToStore(); <r1> ... <rN> are the references of the
+       path.
+     "source"
+       for paths copied to the store using addToStore() when recursive
+       = true and hashAlgo = "sha256"
+     "output:<id>"
+       for either the outputs created by derivations, OR paths copied
+       to the store using addToStore() with recursive != true or
+       hashAlgo != "sha256" (in that case "source" is used; it's
+       silly, but it's done that way for compatibility).  <id> is the
+       name of the output (usually, "out").
+
+   <h2> = base-16 representation of a SHA-256 hash of:
+     if <type> = "text:...":
+       the string written to the resulting store path
+     if <type> = "source":
+       the serialisation of the path from which this store path is
+       copied, as returned by hashPath()
+     if <type> = "output:out":
+       for non-fixed derivation outputs:
+         the derivation (see hashDerivationModulo() in
+         primops.cc)
+       for paths copied by addToStore() or produced by fixed-output
+       derivations:
+         the string "fixed:out:<rec><algo>:<hash>:", where
+           <rec> = "r:" for recursive (path) hashes, or "" or flat
+             (file) hashes
+           <algo> = "md5", "sha1" or "sha256"
+           <hash> = base-16 representation of the path or flat hash of
+             the contents of the path (or expected contents of the
+             path for fixed-output derivations)
+
+   It would have been nicer to handle fixed-output derivations under
+   "source", e.g. have something like "source:<rec><algo>", but we're
+   stuck with this for now...
+
+   The main reason for this way of computing names is to prevent name
+   collisions (for security).  For instance, it shouldn't be feasible
+   to come up with a derivation whose output path collides with the
+   path for a copied source.  The former would have a <s> starting with
+   "output:out:", while the latter would have a <2> starting with
+   "source:".
+*/
+
+
+Path makeStorePath(const string & type,
+    const Hash & hash, const string & name)
+{
+    /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
+    string s = type + ":sha256:" + printHash(hash) + ":"
+        + settings.nixStore + ":" + name;
+
+    checkStoreName(name);
+
+    return settings.nixStore + "/"
+        + printHash32(compressHash(hashString(htSHA256, s), 20))
+        + "-" + name;
+}
+
+
+Path makeOutputPath(const string & id,
+    const Hash & hash, const string & name)
+{
+    return makeStorePath("output:" + id, hash,
+        name + (id == "out" ? "" : "-" + id));
+}
+
+
+Path makeFixedOutputPath(bool recursive,
+    HashType hashAlgo, Hash hash, string name)
+{
+    return hashAlgo == htSHA256 && recursive
+        ? makeStorePath("source", hash, name)
+        : makeStorePath("output:out", hashString(htSHA256,
+                "fixed:out:" + (recursive ? (string) "r:" : "") +
+                printHashType(hashAlgo) + ":" + printHash(hash) + ":"),
+            name);
+}
+
+
+std::pair<Path, Hash> computeStorePathForPath(const Path & srcPath,
+    bool recursive, HashType hashAlgo, PathFilter & filter)
+{
+    HashType ht(hashAlgo);
+    Hash h = recursive ? hashPath(ht, srcPath, filter).first : hashFile(ht, srcPath);
+    string name = baseNameOf(srcPath);
+    Path dstPath = makeFixedOutputPath(recursive, hashAlgo, h, name);
+    return std::pair<Path, Hash>(dstPath, h);
+}
+
+
+Path computeStorePathForText(const string & name, const string & s,
+    const PathSet & references)
+{
+    Hash hash = hashString(htSHA256, s);
+    /* Stuff the references (if any) into the type.  This is a bit
+       hacky, but we can't put them in `s' since that would be
+       ambiguous. */
+    string type = "text";
+    foreach (PathSet::const_iterator, i, references) {
+        type += ":";
+        type += *i;
+    }
+    return makeStorePath(type, hash, name);
+}
+
+
+/* Return a string accepted by decodeValidPathInfo() that
+   registers the specified paths as valid.  Note: it's the
+   responsibility of the caller to provide a closure. */
+string StoreAPI::makeValidityRegistration(const PathSet & paths,
+    bool showDerivers, bool showHash)
+{
+    string s = "";
+    
+    foreach (PathSet::iterator, i, paths) {
+        s += *i + "\n";
+
+        ValidPathInfo info = queryPathInfo(*i);
+
+        if (showHash) {
+            s += printHash(info.hash) + "\n";
+            s += (format("%1%\n") % info.narSize).str();
+        }
+
+        Path deriver = showDerivers ? info.deriver : "";
+        s += deriver + "\n";
+
+        s += (format("%1%\n") % info.references.size()).str();
+
+        foreach (PathSet::iterator, j, info.references)
+            s += *j + "\n";
+    }
+
+    return s;
+}
+
+
+ValidPathInfo decodeValidPathInfo(std::istream & str, bool hashGiven)
+{
+    ValidPathInfo info;
+    getline(str, info.path);
+    if (str.eof()) { info.path = ""; return info; }
+    if (hashGiven) {
+        string s;
+        getline(str, s);
+        info.hash = parseHash(htSHA256, s);
+        getline(str, s);
+        if (!string2Int(s, info.narSize)) throw Error("number expected");
+    }
+    getline(str, info.deriver);
+    string s; int n;
+    getline(str, s);
+    if (!string2Int(s, n)) throw Error("number expected");
+    while (n--) {
+        getline(str, s);
+        info.references.insert(s);
+    }
+    if (!str || str.eof()) throw Error("missing input");
+    return info;
+}
+
+
+string showPaths(const PathSet & paths)
+{
+    string s;
+    foreach (PathSet::const_iterator, i, paths) {
+        if (s.size() != 0) s += ", ";
+        s += "`" + *i + "'";
+    }
+    return s;
+}
+
+
+void exportPaths(StoreAPI & store, const Paths & paths,
+    bool sign, Sink & sink)
+{
+    foreach (Paths::const_iterator, i, paths) {
+        writeInt(1, sink);
+        store.exportPath(*i, sign, sink);
+    }
+    writeInt(0, sink);
+}
+
+
+}
+
+
+#include "local-store.hh"
+#include "serialise.hh"
+#include "remote-store.hh"
+
+
+namespace nix {
+
+
+boost::shared_ptr<StoreAPI> store;
+
+
+boost::shared_ptr<StoreAPI> openStore(bool reserveSpace)
+{
+    if (getEnv("NIX_REMOTE") == "")
+        return boost::shared_ptr<StoreAPI>(new LocalStore(reserveSpace));
+    else
+        return boost::shared_ptr<StoreAPI>(new RemoteStore());
+}
+
+
+}
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
new file mode 100644
index 000000000000..a82fe3221639
--- /dev/null
+++ b/src/libstore/store-api.hh
@@ -0,0 +1,364 @@
+#pragma once
+
+#include "hash.hh"
+#include "serialise.hh"
+
+#include <string>
+#include <map>
+
+#include <boost/shared_ptr.hpp>
+
+
+namespace nix {
+
+
+typedef std::map<Path, Path> Roots;
+
+
+struct GCOptions
+{
+    /* Garbage collector operation:
+
+       - `gcReturnLive': return the set of paths reachable from
+         (i.e. in the closure of) the roots.
+
+       - `gcReturnDead': return the set of paths not reachable from
+         the roots.
+
+       - `gcDeleteDead': actually delete the latter set.
+
+       - `gcDeleteSpecific': delete the paths listed in
+          `pathsToDelete', insofar as they are not reachable.
+    */
+    typedef enum {
+        gcReturnLive,
+        gcReturnDead,
+        gcDeleteDead,
+        gcDeleteSpecific,
+    } GCAction;
+
+    GCAction action;
+
+    /* If `ignoreLiveness' is set, then reachability from the roots is
+       ignored (dangerous!).  However, the paths must still be
+       unreferenced *within* the store (i.e., there can be no other
+       store paths that depend on them). */
+    bool ignoreLiveness;
+
+    /* For `gcDeleteSpecific', the paths to delete. */
+    PathSet pathsToDelete;
+
+    /* Stop after at least `maxFreed' bytes have been freed. */
+    unsigned long long maxFreed;
+
+    GCOptions();
+};
+
+
+struct GCResults 
+{
+    /* Depending on the action, the GC roots, or the paths that would
+       be or have been deleted. */
+    PathSet paths;
+
+    /* For `gcReturnDead', `gcDeleteDead' and `gcDeleteSpecific', the
+       number of bytes that would be or was freed. */
+    unsigned long long bytesFreed;
+
+    GCResults()
+    {
+        bytesFreed = 0;
+    }
+};
+
+
+struct SubstitutablePathInfo
+{
+    Path deriver;
+    PathSet references;
+    unsigned long long downloadSize; /* 0 = unknown or inapplicable */
+    unsigned long long narSize; /* 0 = unknown */
+};
+
+typedef std::map<Path, SubstitutablePathInfo> SubstitutablePathInfos;
+
+
+struct ValidPathInfo 
+{
+    Path path;
+    Path deriver;
+    Hash hash;
+    PathSet references;
+    time_t registrationTime;
+    unsigned long long narSize; // 0 = unknown
+    unsigned long long id; // internal use only
+    ValidPathInfo() : registrationTime(0), narSize(0) { }
+};
+
+typedef list<ValidPathInfo> ValidPathInfos;
+
+
+class StoreAPI 
+{
+public:
+
+    virtual ~StoreAPI() { }
+
+    /* Check whether a path is valid. */ 
+    virtual bool isValidPath(const Path & path) = 0;
+
+    /* Query which of the given paths is valid. */
+    virtual PathSet queryValidPaths(const PathSet & paths) = 0;
+
+    /* Query the set of all valid paths. */
+    virtual PathSet queryAllValidPaths() = 0;
+
+    /* Query information about a valid path. */
+    virtual ValidPathInfo queryPathInfo(const Path & path) = 0;
+
+    /* Query the hash of a valid path. */ 
+    virtual Hash queryPathHash(const Path & path) = 0;
+
+    /* Query the set of outgoing FS references for a store path.  The
+       result is not cleared. */
+    virtual void queryReferences(const Path & path,
+        PathSet & references) = 0;
+
+    /* Queries the set of incoming FS references for a store path.
+       The result is not cleared. */
+    virtual void queryReferrers(const Path & path,
+        PathSet & referrers) = 0;
+
+    /* Query the deriver of a store path.  Return the empty string if
+       no deriver has been set. */
+    virtual Path queryDeriver(const Path & path) = 0;
+
+    /* Return all currently valid derivations that have `path' as an
+       output.  (Note that the result of `queryDeriver()' is the
+       derivation that was actually used to produce `path', which may
+       not exist anymore.) */
+    virtual PathSet queryValidDerivers(const Path & path) = 0;
+
+    /* Query the outputs of the derivation denoted by `path'. */
+    virtual PathSet queryDerivationOutputs(const Path & path) = 0;
+
+    /* Query the output names of the derivation denoted by `path'. */
+    virtual StringSet queryDerivationOutputNames(const Path & path) = 0;
+
+    /* Query the full store path given the hash part of a valid store
+       path, or "" if the path doesn't exist. */
+    virtual Path queryPathFromHashPart(const string & hashPart) = 0;
+    
+    /* Query which of the given paths have substitutes. */
+    virtual PathSet querySubstitutablePaths(const PathSet & paths) = 0;
+
+    /* Query substitute info (i.e. references, derivers and download
+       sizes) of a set of paths.  If a path does not have substitute
+       info, it's omitted from the resulting ‘infos’ map. */
+    virtual void querySubstitutablePathInfos(const PathSet & paths,
+        SubstitutablePathInfos & infos) = 0;
+    
+    /* Copy the contents of a path to the store and register the
+       validity the resulting path.  The resulting path is returned.
+       The function object `filter' can be used to exclude files (see
+       libutil/archive.hh). */
+    virtual Path addToStore(const Path & srcPath,
+        bool recursive = true, HashType hashAlgo = htSHA256,
+        PathFilter & filter = defaultPathFilter, bool repair = false) = 0;
+
+    /* Like addToStore, but the contents written to the output path is
+       a regular file containing the given string. */
+    virtual Path addTextToStore(const string & name, const string & s,
+        const PathSet & references, bool repair = false) = 0;
+
+    /* Export a store path, that is, create a NAR dump of the store
+       path and append its references and its deriver.  Optionally, a
+       cryptographic signature (created by OpenSSL) of the preceding
+       data is attached. */
+    virtual void exportPath(const Path & path, bool sign,
+        Sink & sink) = 0;
+
+    /* Import a sequence of NAR dumps created by exportPaths() into
+       the Nix store. */
+    virtual Paths importPaths(bool requireSignature, Source & source) = 0;
+
+    /* For each path, if it's a derivation, build it.  Building a
+       derivation means ensuring that the output paths are valid.  If
+       they are already valid, this is a no-op.  Otherwise, validity
+       can be reached in two ways.  First, if the output paths is
+       substitutable, then build the path that way.  Second, the
+       output paths can be created by running the builder, after
+       recursively building any sub-derivations. For inputs that are
+       not derivations, substitute them. */
+    virtual void buildPaths(const PathSet & paths, bool repair = false) = 0;
+
+    /* Ensure that a path is valid.  If it is not currently valid, it
+       may be made valid by running a substitute (if defined for the
+       path). */
+    virtual void ensurePath(const Path & path) = 0;
+
+    /* Add a store path as a temporary root of the garbage collector.
+       The root disappears as soon as we exit. */
+    virtual void addTempRoot(const Path & path) = 0;
+
+    /* Add an indirect root, which is merely a symlink to `path' from
+       /nix/var/nix/gcroots/auto/<hash of `path'>.  `path' is supposed
+       to be a symlink to a store path.  The garbage collector will
+       automatically remove the indirect root when it finds that
+       `path' has disappeared. */
+    virtual void addIndirectRoot(const Path & path) = 0;
+
+    /* Acquire the global GC lock, then immediately release it.  This
+       function must be called after registering a new permanent root,
+       but before exiting.  Otherwise, it is possible that a running
+       garbage collector doesn't see the new root and deletes the
+       stuff we've just built.  By acquiring the lock briefly, we
+       ensure that either:
+
+       - The collector is already running, and so we block until the
+         collector is finished.  The collector will know about our
+         *temporary* locks, which should include whatever it is we
+         want to register as a permanent lock.
+
+       - The collector isn't running, or it's just started but hasn't
+         acquired the GC lock yet.  In that case we get and release
+         the lock right away, then exit.  The collector scans the
+         permanent root and sees our's.
+
+       In either case the permanent root is seen by the collector. */
+    virtual void syncWithGC() = 0;
+
+    /* Find the roots of the garbage collector.  Each root is a pair
+       (link, storepath) where `link' is the path of the symlink
+       outside of the Nix store that point to `storePath'.  */
+    virtual Roots findRoots() = 0;
+
+    /* Perform a garbage collection. */
+    virtual void collectGarbage(const GCOptions & options, GCResults & results) = 0;
+
+    /* Return the set of paths that have failed to build.*/
+    virtual PathSet queryFailedPaths() = 0;
+
+    /* Clear the "failed" status of the given paths.  The special
+       value `*' causes all failed paths to be cleared. */
+    virtual void clearFailedPaths(const PathSet & paths) = 0;
+
+    /* Return a string representing information about the path that
+       can be loaded into the database using `nix-store --load-db' or
+       `nix-store --register-validity'. */
+    string makeValidityRegistration(const PathSet & paths,
+        bool showDerivers, bool showHash);
+};
+
+
+/* !!! These should be part of the store API, I guess. */
+
+/* Throw an exception if `path' is not directly in the Nix store. */
+void assertStorePath(const Path & path);
+
+bool isInStore(const Path & path);
+bool isStorePath(const Path & path);
+
+/* Extract the name part of the given store path. */
+string storePathToName(const Path & path);
+    
+void checkStoreName(const string & name);
+
+
+/* Chop off the parts after the top-level store name, e.g.,
+   /nix/store/abcd-foo/bar => /nix/store/abcd-foo. */
+Path toStorePath(const Path & path);
+
+
+/* Follow symlinks until we end up with a path in the Nix store. */
+Path followLinksToStore(const Path & path);
+
+
+/* Same as followLinksToStore(), but apply toStorePath() to the
+   result. */
+Path followLinksToStorePath(const Path & path);
+
+
+/* Constructs a unique store path name. */
+Path makeStorePath(const string & type,
+    const Hash & hash, const string & name);
+    
+Path makeOutputPath(const string & id,
+    const Hash & hash, const string & name);
+
+Path makeFixedOutputPath(bool recursive,
+    HashType hashAlgo, Hash hash, string name);
+
+
+/* This is the preparatory part of addToStore() and addToStoreFixed();
+   it computes the store path to which srcPath is to be copied.
+   Returns the store path and the cryptographic hash of the
+   contents of srcPath. */
+std::pair<Path, Hash> computeStorePathForPath(const Path & srcPath,
+    bool recursive = true, HashType hashAlgo = htSHA256,
+    PathFilter & filter = defaultPathFilter);
+
+/* Preparatory part of addTextToStore().
+
+   !!! Computation of the path should take the references given to
+   addTextToStore() into account, otherwise we have a (relatively
+   minor) security hole: a caller can register a source file with
+   bogus references.  If there are too many references, the path may
+   not be garbage collected when it has to be (not really a problem,
+   the caller could create a root anyway), or it may be garbage
+   collected when it shouldn't be (more serious).
+
+   Hashing the references would solve this (bogus references would
+   simply yield a different store path, so other users wouldn't be
+   affected), but it has some backwards compatibility issues (the
+   hashing scheme changes), so I'm not doing that for now. */
+Path computeStorePathForText(const string & name, const string & s,
+    const PathSet & references);
+
+
+/* Remove the temporary roots file for this process.  Any temporary
+   root becomes garbage after this point unless it has been registered
+   as a (permanent) root. */
+void removeTempRoots();
+
+
+/* Register a permanent GC root. */
+Path addPermRoot(StoreAPI & store, const Path & storePath,
+    const Path & gcRoot, bool indirect, bool allowOutsideRootsDir = false);
+
+
+/* Sort a set of paths topologically under the references relation.
+   If p refers to q, then p preceeds q in this list. */
+Paths topoSortPaths(StoreAPI & store, const PathSet & paths);
+
+
+/* For now, there is a single global store API object, but we'll
+   purify that in the future. */
+extern boost::shared_ptr<StoreAPI> store;
+
+
+/* Factory method: open the Nix database, either through the local or
+   remote implementation. */
+boost::shared_ptr<StoreAPI> openStore(bool reserveSpace = true);
+
+
+/* Display a set of paths in human-readable form (i.e., between quotes
+   and separated by commas). */
+string showPaths(const PathSet & paths);
+
+
+ValidPathInfo decodeValidPathInfo(std::istream & str,
+    bool hashGiven = false);
+
+
+/* Export multiple paths in the format expected by ‘nix-store
+   --import’. */
+void exportPaths(StoreAPI & store, const Paths & paths,
+    bool sign, Sink & sink);
+
+
+MakeError(SubstError, Error)
+MakeError(BuildError, Error) /* denotes a permanent build failure */
+
+
+}
diff --git a/src/libstore/worker-protocol.hh b/src/libstore/worker-protocol.hh
new file mode 100644
index 000000000000..9317f89c3763
--- /dev/null
+++ b/src/libstore/worker-protocol.hh
@@ -0,0 +1,60 @@
+#pragma once
+
+namespace nix {
+
+
+#define WORKER_MAGIC_1 0x6e697863
+#define WORKER_MAGIC_2 0x6478696f
+
+#define PROTOCOL_VERSION 0x10e
+#define GET_PROTOCOL_MAJOR(x) ((x) & 0xff00)
+#define GET_PROTOCOL_MINOR(x) ((x) & 0x00ff)
+
+
+typedef enum {
+    wopQuit = 0,
+    wopIsValidPath = 1,
+    wopHasSubstitutes = 3,
+    wopQueryPathHash = 4,
+    wopQueryReferences = 5,
+    wopQueryReferrers = 6,
+    wopAddToStore = 7,
+    wopAddTextToStore = 8,
+    wopBuildPaths = 9,
+    wopEnsurePath = 10,
+    wopAddTempRoot = 11,
+    wopAddIndirectRoot = 12,
+    wopSyncWithGC = 13,
+    wopFindRoots = 14,
+    wopExportPath = 16,
+    wopQueryDeriver = 18,
+    wopSetOptions = 19,
+    wopCollectGarbage = 20,
+    wopQuerySubstitutablePathInfo = 21,
+    wopQueryDerivationOutputs = 22,
+    wopQueryAllValidPaths = 23,
+    wopQueryFailedPaths = 24,
+    wopClearFailedPaths = 25,
+    wopQueryPathInfo = 26,
+    wopImportPaths = 27,
+    wopQueryDerivationOutputNames = 28,
+    wopQueryPathFromHashPart = 29,
+    wopQuerySubstitutablePathInfos = 30,
+    wopQueryValidPaths = 31,
+    wopQuerySubstitutablePaths = 32,
+    wopQueryValidDerivers = 33,
+} WorkerOp;
+
+
+#define STDERR_NEXT  0x6f6c6d67
+#define STDERR_READ  0x64617461 // data needed from source
+#define STDERR_WRITE 0x64617416 // data for sink
+#define STDERR_LAST  0x616c7473
+#define STDERR_ERROR 0x63787470
+
+
+Path readStorePath(Source & from);
+template<class T> T readStorePaths(Source & from);
+
+
+}
diff --git a/src/libutil/affinity.cc b/src/libutil/affinity.cc
new file mode 100644
index 000000000000..3e21f43a2e9d
--- /dev/null
+++ b/src/libutil/affinity.cc
@@ -0,0 +1,55 @@
+#include "types.hh"
+#include "util.hh"
+#include "affinity.hh"
+
+#if HAVE_SCHED_H
+#include <sched.h>
+#endif
+
+namespace nix {
+
+
+#if HAVE_SCHED_SETAFFINITY
+static bool didSaveAffinity = false;
+static cpu_set_t savedAffinity;
+#endif
+
+
+void setAffinityTo(int cpu)
+{
+#if HAVE_SCHED_SETAFFINITY
+    if (sched_getaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1) return;
+    didSaveAffinity = true;
+    printMsg(lvlDebug, format("locking this thread to CPU %1%") % cpu);
+    cpu_set_t newAffinity;
+    CPU_ZERO(&newAffinity);
+    CPU_SET(cpu, &newAffinity);
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &newAffinity) == -1)
+        printMsg(lvlError, format("failed to lock thread to CPU %1%") % cpu);
+#endif
+}
+
+
+int lockToCurrentCPU()
+{
+#if HAVE_SCHED_SETAFFINITY
+    int cpu = sched_getcpu();
+    if (cpu != -1) setAffinityTo(cpu);
+    return cpu;
+#else
+    return -1;
+#endif
+}
+
+
+void restoreAffinity()
+{
+#if HAVE_SCHED_SETAFFINITY
+    if (!didSaveAffinity) return;
+    if (sched_setaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1)
+        printMsg(lvlError, "failed to restore affinity %1%");
+#endif
+}
+
+
+}
diff --git a/src/libutil/affinity.hh b/src/libutil/affinity.hh
new file mode 100644
index 000000000000..c1bd28e1367a
--- /dev/null
+++ b/src/libutil/affinity.hh
@@ -0,0 +1,9 @@
+#pragma once
+
+namespace nix {
+
+void setAffinityTo(int cpu);
+int lockToCurrentCPU();
+void restoreAffinity();
+
+}
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
new file mode 100644
index 000000000000..b19ff4bf99a1
--- /dev/null
+++ b/src/libutil/archive.cc
@@ -0,0 +1,336 @@
+#include "config.h"
+
+#include <cerrno>
+#include <algorithm>
+#include <vector>
+
+#define _XOPEN_SOURCE 600
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <fcntl.h>
+
+#include "archive.hh"
+#include "util.hh"
+
+
+namespace nix {
+
+
+static string archiveVersion1 = "nix-archive-1";
+
+
+PathFilter defaultPathFilter;
+
+
+static void dump(const string & path, Sink & sink, PathFilter & filter);
+
+
+static void dumpEntries(const Path & path, Sink & sink, PathFilter & filter)
+{
+    Strings names = readDirectory(path);
+    vector<string> names2(names.begin(), names.end());
+    sort(names2.begin(), names2.end());
+
+    for (vector<string>::iterator i = names2.begin();
+         i != names2.end(); ++i)
+    {
+        Path entry = path + "/" + *i;
+        if (filter(entry)) {
+            writeString("entry", sink);
+            writeString("(", sink);
+            writeString("name", sink);
+            writeString(*i, sink);
+            writeString("node", sink);
+            dump(entry, sink, filter);
+            writeString(")", sink);
+        }
+    }
+}
+
+
+static void dumpContents(const Path & path, size_t size, 
+    Sink & sink)
+{
+    writeString("contents", sink);
+    writeLongLong(size, sink);
+
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1) throw SysError(format("opening file `%1%'") % path);
+    
+    unsigned char buf[65536];
+    size_t left = size;
+
+    while (left > 0) {
+        size_t n = left > sizeof(buf) ? sizeof(buf) : left;
+        readFull(fd, buf, n);
+        left -= n;
+        sink(buf, n);
+    }
+
+    writePadding(size, sink);
+}
+
+
+static void dump(const Path & path, Sink & sink, PathFilter & filter)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting attributes of path `%1%'") % path);
+
+    writeString("(", sink);
+
+    if (S_ISREG(st.st_mode)) {
+        writeString("type", sink);
+        writeString("regular", sink);
+        if (st.st_mode & S_IXUSR) {
+            writeString("executable", sink);
+            writeString("", sink);
+        }
+        dumpContents(path, (size_t) st.st_size, sink);
+    } 
+
+    else if (S_ISDIR(st.st_mode)) {
+        writeString("type", sink);
+        writeString("directory", sink);
+        dumpEntries(path, sink, filter);
+    }
+
+    else if (S_ISLNK(st.st_mode)) {
+        writeString("type", sink);
+        writeString("symlink", sink);
+        writeString("target", sink);
+        writeString(readLink(path), sink);
+    }
+
+    else throw Error(format("file `%1%' has an unknown type") % path);
+
+    writeString(")", sink);
+}
+
+
+void dumpPath(const Path & path, Sink & sink, PathFilter & filter)
+{
+    writeString(archiveVersion1, sink);
+    dump(path, sink, filter);
+}
+
+
+static SerialisationError badArchive(string s)
+{
+    return SerialisationError("bad archive: " + s);
+}
+
+
+static void skipGeneric(Source & source)
+{
+    if (readString(source) == "(") {
+        while (readString(source) != ")")
+            skipGeneric(source);
+    }
+}
+
+
+static void parse(ParseSink & sink, Source & source, const Path & path);
+
+
+
+static void parseEntry(ParseSink & sink, Source & source, const Path & path)
+{
+    string s, name;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    while (1) {
+        checkInterrupt();
+
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        } else if (s == "name") {
+            name = readString(source);
+        } else if (s == "node") {
+            if (s == "") throw badArchive("entry name missing");
+            parse(sink, source, path + "/" + name);
+        } else {
+            throw badArchive("unknown field " + s);
+            skipGeneric(source);
+        }
+    }
+}
+
+
+static void parseContents(ParseSink & sink, Source & source, const Path & path)
+{
+    unsigned long long size = readLongLong(source);
+    
+    sink.preallocateContents(size);
+
+    unsigned long long left = size;
+    unsigned char buf[65536];
+
+    while (left) {
+        checkInterrupt();
+        unsigned int n = sizeof(buf);
+        if ((unsigned long long) n > left) n = left;
+        source(buf, n);
+        sink.receiveContents(buf, n);
+        left -= n;
+    }
+
+    readPadding(size, source);
+}
+
+
+static void parse(ParseSink & sink, Source & source, const Path & path)
+{
+    string s;
+
+    s = readString(source);
+    if (s != "(") throw badArchive("expected open tag");
+
+    enum { tpUnknown, tpRegular, tpDirectory, tpSymlink } type = tpUnknown;
+
+    while (1) {
+        checkInterrupt();
+
+        s = readString(source);
+
+        if (s == ")") {
+            break;
+        }
+
+        else if (s == "type") {
+            if (type != tpUnknown)
+                throw badArchive("multiple type fields");
+            string t = readString(source);
+
+            if (t == "regular") {
+                type = tpRegular;
+                sink.createRegularFile(path);
+            }
+
+            else if (t == "directory") {
+                sink.createDirectory(path);
+                type = tpDirectory;
+            }
+
+            else if (t == "symlink") {
+                type = tpSymlink;
+            }
+            
+            else throw badArchive("unknown file type " + t);
+            
+        }
+
+        else if (s == "contents" && type == tpRegular) {
+            parseContents(sink, source, path);
+        }
+
+        else if (s == "executable" && type == tpRegular) {
+            readString(source);
+            sink.isExecutable();
+        }
+
+        else if (s == "entry" && type == tpDirectory) {
+            parseEntry(sink, source, path);
+        }
+
+        else if (s == "target" && type == tpSymlink) {
+            string target = readString(source);
+            sink.createSymlink(path, target);
+        }
+
+        else {
+            throw badArchive("unknown field " + s);
+            skipGeneric(source);
+        }
+    }
+}
+
+
+void parseDump(ParseSink & sink, Source & source)
+{
+    string version;    
+    try {
+        version = readString(source);
+    } catch (SerialisationError & e) {
+        /* This generally means the integer at the start couldn't be
+           decoded.  Ignore and throw the exception below. */
+    }
+    if (version != archiveVersion1)
+        throw badArchive("input doesn't look like a Nix archive");
+    parse(sink, source, "");
+}
+
+
+struct RestoreSink : ParseSink
+{
+    Path dstPath;
+    AutoCloseFD fd;
+
+    void createDirectory(const Path & path)
+    {
+        Path p = dstPath + path;
+        if (mkdir(p.c_str(), 0777) == -1)
+            throw SysError(format("creating directory `%1%'") % p);
+    };
+
+    void createRegularFile(const Path & path)
+    {
+        Path p = dstPath + path;
+        fd.close();
+        fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY, 0666);
+        if (fd == -1) throw SysError(format("creating file `%1%'") % p);
+    }
+
+    void isExecutable()
+    {
+        struct stat st;
+        if (fstat(fd, &st) == -1)
+            throw SysError("fstat");
+        if (fchmod(fd, st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
+            throw SysError("fchmod");
+    }
+
+    void preallocateContents(unsigned long long len)
+    {
+#if HAVE_POSIX_FALLOCATE
+        if (len) {
+            errno = posix_fallocate(fd, 0, len);
+            /* Note that EINVAL may indicate that the underlying
+               filesystem doesn't support preallocation (e.g. on
+               OpenSolaris).  Since preallocation is just an
+               optimisation, ignore it. */
+            if (errno && errno != EINVAL)
+                throw SysError(format("preallocating file of %1% bytes") % len);
+        }
+#endif
+    }
+
+    void receiveContents(unsigned char * data, unsigned int len)
+    {
+        writeFull(fd, data, len);
+    }
+
+    void createSymlink(const Path & path, const string & target)
+    {
+        Path p = dstPath + path;
+        if (symlink(target.c_str(), p.c_str()) == -1)
+            throw SysError(format("creating symlink `%1%'") % p);
+    }
+};
+
+ 
+void restorePath(const Path & path, Source & source)
+{
+    RestoreSink sink;
+    sink.dstPath = path;
+    parseDump(sink, source);
+}
+
+ 
+}
diff --git a/src/libutil/archive.hh b/src/libutil/archive.hh
new file mode 100644
index 000000000000..ccac92074d54
--- /dev/null
+++ b/src/libutil/archive.hh
@@ -0,0 +1,75 @@
+#pragma once
+
+#include "types.hh"
+#include "serialise.hh"
+
+
+namespace nix {
+
+
+/* dumpPath creates a Nix archive of the specified path.  The format
+   is as follows:
+
+   IF path points to a REGULAR FILE:
+     dump(path) = attrs(
+       [ ("type", "regular")
+       , ("contents", contents(path))
+       ])
+
+   IF path points to a DIRECTORY:
+     dump(path) = attrs(
+       [ ("type", "directory")
+       , ("entries", concat(map(f, sort(entries(path)))))
+       ])
+       where f(fn) = attrs(
+         [ ("name", fn)
+         , ("file", dump(path + "/" + fn))
+         ])
+
+   where:
+
+     attrs(as) = concat(map(attr, as)) + encN(0) 
+     attrs((a, b)) = encS(a) + encS(b)
+
+     encS(s) = encN(len(s)) + s + (padding until next 64-bit boundary)
+
+     encN(n) = 64-bit little-endian encoding of n.
+
+     contents(path) = the contents of a regular file.
+
+     sort(strings) = lexicographic sort by 8-bit value (strcmp).
+
+     entries(path) = the entries of a directory, without `.' and
+     `..'.
+
+     `+' denotes string concatenation. */
+
+struct PathFilter
+{
+    virtual ~PathFilter() { }
+    virtual bool operator () (const Path & path) { return true; }
+};
+
+extern PathFilter defaultPathFilter;
+
+void dumpPath(const Path & path, Sink & sink,
+    PathFilter & filter = defaultPathFilter);
+
+struct ParseSink
+{
+    virtual void createDirectory(const Path & path) { };
+    
+    virtual void createRegularFile(const Path & path) { };
+    virtual void isExecutable() { };
+    virtual void preallocateContents(unsigned long long size) { };
+    virtual void receiveContents(unsigned char * data, unsigned int len) { };
+
+    virtual void createSymlink(const Path & path, const string & target) { };
+};
+    
+void parseDump(ParseSink & sink, Source & source);
+
+void restorePath(const Path & path, Source & source);
+
+ 
+}
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
new file mode 100644
index 000000000000..de2c1ebd724f
--- /dev/null
+++ b/src/libutil/hash.cc
@@ -0,0 +1,382 @@
+#include "config.h"
+
+#include <iostream>
+#include <cstring>
+
+#ifdef HAVE_OPENSSL
+#include <openssl/md5.h>
+#include <openssl/sha.h>
+#else
+extern "C" {
+#include "md5.h"
+#include "sha1.h"
+#include "sha256.h"
+}
+#endif
+
+#include "hash.hh"
+#include "archive.hh"
+#include "util.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+
+namespace nix {
+
+
+Hash::Hash()
+{
+    type = htUnknown;
+    hashSize = 0;
+    memset(hash, 0, maxHashSize);
+}
+
+
+Hash::Hash(HashType type)
+{
+    this->type = type;
+    if (type == htMD5) hashSize = md5HashSize;
+    else if (type == htSHA1) hashSize = sha1HashSize;
+    else if (type == htSHA256) hashSize = sha256HashSize;
+    else throw Error("unknown hash type");
+    assert(hashSize <= maxHashSize);
+    memset(hash, 0, maxHashSize);
+}
+
+
+bool Hash::operator == (const Hash & h2) const
+{
+    if (hashSize != h2.hashSize) return false;
+    for (unsigned int i = 0; i < hashSize; i++)
+        if (hash[i] != h2.hash[i]) return false;
+    return true;
+}
+
+
+bool Hash::operator != (const Hash & h2) const
+{
+    return !(*this == h2);
+}
+
+
+bool Hash::operator < (const Hash & h) const
+{
+    for (unsigned int i = 0; i < hashSize; i++) {
+        if (hash[i] < h.hash[i]) return true;
+        if (hash[i] > h.hash[i]) return false;
+    }
+    return false;
+}
+
+
+const string base16Chars = "0123456789abcdef";
+
+
+string printHash(const Hash & hash)
+{
+    char buf[hash.hashSize * 2];
+    for (unsigned int i = 0; i < hash.hashSize; i++) {
+        buf[i * 2] = base16Chars[hash.hash[i] >> 4];
+        buf[i * 2 + 1] = base16Chars[hash.hash[i] & 0x0f];
+    }
+    return string(buf, hash.hashSize * 2);
+}
+
+    
+Hash parseHash(HashType ht, const string & s)
+{
+    Hash hash(ht);
+    if (s.length() != hash.hashSize * 2)
+        throw Error(format("invalid hash `%1%'") % s);
+    for (unsigned int i = 0; i < hash.hashSize; i++) {
+        string s2(s, i * 2, 2);
+        if (!isxdigit(s2[0]) || !isxdigit(s2[1])) 
+            throw Error(format("invalid hash `%1%'") % s);
+        std::istringstream str(s2);
+        int n;
+        str >> std::hex >> n;
+        hash.hash[i] = n;
+    }
+    return hash;
+}
+
+
+static unsigned char divMod(unsigned char * bytes, unsigned char y)
+{
+    unsigned int borrow = 0;
+
+    int pos = Hash::maxHashSize - 1;
+    while (pos >= 0 && !bytes[pos]) --pos;
+
+    for ( ; pos >= 0; --pos) {
+        unsigned int s = bytes[pos] + (borrow << 8);
+        unsigned int d = s / y;
+        borrow = s % y;
+        bytes[pos] = d;
+    }
+
+    return borrow;
+}
+
+
+unsigned int hashLength32(const Hash & hash)
+{
+    return (hash.hashSize * 8 - 1) / 5 + 1;
+}
+
+
+// omitted: E O U T
+const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";
+
+
+string printHash32(const Hash & hash)
+{
+    Hash hash2(hash);
+    unsigned int len = hashLength32(hash);
+
+    const char * chars = base32Chars.data();
+    
+    string s(len, '0');
+
+    int pos = len - 1;
+    while (pos >= 0) {
+        unsigned char digit = divMod(hash2.hash, 32);
+        s[pos--] = chars[digit];
+    }
+
+    for (unsigned int i = 0; i < hash2.maxHashSize; ++i)
+        assert(hash2.hash[i] == 0);
+
+    return s;
+}
+
+
+string printHash16or32(const Hash & hash)
+{
+    return hash.type == htMD5 ? printHash(hash) : printHash32(hash);
+}
+
+
+static bool mul(unsigned char * bytes, unsigned char y, int maxSize)
+{
+    unsigned char carry = 0;
+
+    for (int pos = 0; pos < maxSize; ++pos) {
+        unsigned int m = bytes[pos] * y + carry;
+        bytes[pos] = m & 0xff;
+        carry = m >> 8;
+    }
+
+    return carry;
+}
+
+
+static bool add(unsigned char * bytes, unsigned char y, int maxSize)
+{
+    unsigned char carry = y;
+
+    for (int pos = 0; pos < maxSize; ++pos) {
+        unsigned int m = bytes[pos] + carry;
+        bytes[pos] = m & 0xff;
+        carry = m >> 8;
+        if (carry == 0) break;
+    }
+
+    return carry;
+}
+
+
+Hash parseHash32(HashType ht, const string & s)
+{
+    Hash hash(ht);
+
+    const char * chars = base32Chars.data();
+
+    for (unsigned int i = 0; i < s.length(); ++i) {
+        char c = s[i];
+        unsigned char digit;
+        for (digit = 0; digit < base32Chars.size(); ++digit) /* !!! slow */
+            if (chars[digit] == c) break;
+        if (digit >= 32)
+            throw Error(format("invalid base-32 hash `%1%'") % s);
+        if (mul(hash.hash, 32, hash.hashSize) ||
+            add(hash.hash, digit, hash.hashSize))
+            throw Error(format("base-32 hash `%1%' is too large") % s);
+    }
+
+    return hash;
+}
+
+
+Hash parseHash16or32(HashType ht, const string & s)
+{
+    Hash hash(ht);
+    if (s.size() == hash.hashSize * 2)
+        /* hexadecimal representation */
+        hash = parseHash(ht, s);
+    else if (s.size() == hashLength32(hash))
+        /* base-32 representation */
+        hash = parseHash32(ht, s);
+    else
+        throw Error(format("hash `%1%' has wrong length for hash type `%2%'")
+            % s % printHashType(ht));
+    return hash;
+}
+
+
+bool isHash(const string & s)
+{
+    if (s.length() != 32) return false;
+    for (int i = 0; i < 32; i++) {
+        char c = s[i];
+        if (!((c >= '0' && c <= '9') ||
+              (c >= 'a' && c <= 'f')))
+            return false;
+    }
+    return true;
+}
+
+
+union Ctx
+{
+    MD5_CTX md5;
+    SHA_CTX sha1;
+    SHA256_CTX sha256;
+};
+
+
+static void start(HashType ht, Ctx & ctx)
+{
+    if (ht == htMD5) MD5_Init(&ctx.md5);
+    else if (ht == htSHA1) SHA1_Init(&ctx.sha1);
+    else if (ht == htSHA256) SHA256_Init(&ctx.sha256);
+}
+
+
+static void update(HashType ht, Ctx & ctx,
+    const unsigned char * bytes, unsigned int len)
+{
+    if (ht == htMD5) MD5_Update(&ctx.md5, bytes, len);
+    else if (ht == htSHA1) SHA1_Update(&ctx.sha1, bytes, len);
+    else if (ht == htSHA256) SHA256_Update(&ctx.sha256, bytes, len);
+}
+
+
+static void finish(HashType ht, Ctx & ctx, unsigned char * hash)
+{
+    if (ht == htMD5) MD5_Final(hash, &ctx.md5);
+    else if (ht == htSHA1) SHA1_Final(hash, &ctx.sha1);
+    else if (ht == htSHA256) SHA256_Final(hash, &ctx.sha256);
+}
+
+
+Hash hashString(HashType ht, const string & s)
+{
+    Ctx ctx;
+    Hash hash(ht);
+    start(ht, ctx);
+    update(ht, ctx, (const unsigned char *) s.data(), s.length());
+    finish(ht, ctx, hash.hash);
+    return hash;
+}
+
+
+Hash hashFile(HashType ht, const Path & path)
+{
+    Ctx ctx;
+    Hash hash(ht);
+    start(ht, ctx);
+
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1) throw SysError(format("opening file `%1%'") % path);
+
+    unsigned char buf[8192];
+    ssize_t n;
+    while ((n = read(fd, buf, sizeof(buf)))) {
+        checkInterrupt();
+        if (n == -1) throw SysError(format("reading file `%1%'") % path);
+        update(ht, ctx, buf, n);
+    }
+    
+    finish(ht, ctx, hash.hash);
+    return hash;
+}
+
+
+HashSink::HashSink(HashType ht) : ht(ht)
+{
+    ctx = new Ctx;
+    bytes = 0;
+    start(ht, *ctx);
+}
+    
+HashSink::~HashSink()
+{
+    bufPos = 0;
+    delete ctx;
+}
+
+void HashSink::write(const unsigned char * data, size_t len)
+{
+    bytes += len;
+    update(ht, *ctx, data, len);
+}
+
+HashResult HashSink::finish()
+{
+    flush();
+    Hash hash(ht);
+    nix::finish(ht, *ctx, hash.hash);
+    return HashResult(hash, bytes);
+}
+
+HashResult HashSink::currentHash()
+{
+    flush();
+    Ctx ctx2 = *ctx;
+    Hash hash(ht);
+    nix::finish(ht, ctx2, hash.hash);
+    return HashResult(hash, bytes);
+}
+
+
+HashResult hashPath(
+    HashType ht, const Path & path, PathFilter & filter)
+{
+    HashSink sink(ht);
+    dumpPath(path, sink, filter);
+    return sink.finish();
+}
+
+
+Hash compressHash(const Hash & hash, unsigned int newSize)
+{
+    Hash h;
+    h.hashSize = newSize;
+    for (unsigned int i = 0; i < hash.hashSize; ++i)
+        h.hash[i % newSize] ^= hash.hash[i];
+    return h;
+}
+
+
+HashType parseHashType(const string & s)
+{
+    if (s == "md5") return htMD5;
+    else if (s == "sha1") return htSHA1;
+    else if (s == "sha256") return htSHA256;
+    else return htUnknown;
+}
+
+ 
+string printHashType(HashType ht)
+{
+    if (ht == htMD5) return "md5";
+    else if (ht == htSHA1) return "sha1";
+    else if (ht == htSHA256) return "sha256";
+    else throw Error("cannot print unknown hash type");
+}
+
+ 
+}
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
new file mode 100644
index 000000000000..2c6f176ec74c
--- /dev/null
+++ b/src/libutil/hash.hh
@@ -0,0 +1,113 @@
+#pragma once
+
+#include "types.hh"
+#include "serialise.hh"
+
+
+namespace nix {
+
+
+typedef enum { htUnknown, htMD5, htSHA1, htSHA256 } HashType;
+
+
+const int md5HashSize = 16;
+const int sha1HashSize = 20;
+const int sha256HashSize = 32;
+
+extern const string base32Chars;
+
+
+struct Hash
+{
+    static const unsigned int maxHashSize = 32;
+    unsigned int hashSize;
+    unsigned char hash[maxHashSize];
+
+    HashType type;
+
+    /* Create an unusable hash object. */
+    Hash();
+
+    /* Create a zero-filled hash object. */
+    Hash(HashType type);
+
+    /* Check whether two hash are equal. */
+    bool operator == (const Hash & h2) const;
+
+    /* Check whether two hash are not equal. */
+    bool operator != (const Hash & h2) const;
+
+    /* For sorting. */
+    bool operator < (const Hash & h) const;
+};
+
+
+/* Convert a hash to a hexadecimal representation. */
+string printHash(const Hash & hash);
+
+/* Parse a hexadecimal representation of a hash code. */
+Hash parseHash(HashType ht, const string & s);
+
+/* Returns the length of a base-32 hash representation. */
+unsigned int hashLength32(const Hash & hash);
+
+/* Convert a hash to a base-32 representation. */
+string printHash32(const Hash & hash);
+
+/* Print a hash in base-16 if it's MD5, or base-32 otherwise. */
+string printHash16or32(const Hash & hash);
+
+/* Parse a base-32 representation of a hash code. */
+Hash parseHash32(HashType ht, const string & s);
+
+/* Parse a base-16 or base-32 representation of a hash code. */
+Hash parseHash16or32(HashType ht, const string & s);
+
+/* Verify that the given string is a valid hash code. */
+bool isHash(const string & s);
+
+/* Compute the hash of the given string. */
+Hash hashString(HashType ht, const string & s);
+
+/* Compute the hash of the given file. */
+Hash hashFile(HashType ht, const Path & path);
+
+/* Compute the hash of the given path.  The hash is defined as
+   (essentially) hashString(ht, dumpPath(path)). */
+struct PathFilter;
+extern PathFilter defaultPathFilter;
+typedef std::pair<Hash, unsigned long long> HashResult;
+HashResult hashPath(HashType ht, const Path & path,
+    PathFilter & filter = defaultPathFilter);
+
+/* Compress a hash to the specified number of bytes by cyclically
+   XORing bytes together. */
+Hash compressHash(const Hash & hash, unsigned int newSize);
+
+/* Parse a string representing a hash type. */
+HashType parseHashType(const string & s);
+
+/* And the reverse. */
+string printHashType(HashType ht);
+
+
+union Ctx;
+
+class HashSink : public BufferedSink
+{
+private:
+    HashType ht;
+    Ctx * ctx;
+    unsigned long long bytes;
+
+public:
+    HashSink(HashType ht);
+    HashSink(const HashSink & h);
+    ~HashSink();
+    void write(const unsigned char * data, size_t len);
+    HashResult finish();
+    HashResult currentHash();
+};
+
+
+}
diff --git a/src/libutil/local.mk b/src/libutil/local.mk
new file mode 100644
index 000000000000..8af2e78d9ce4
--- /dev/null
+++ b/src/libutil/local.mk
@@ -0,0 +1,15 @@
+libraries += libutil
+
+libutil_NAME = libnixutil
+
+libutil_DIR := $(d)
+
+libutil_SOURCES := $(wildcard $(d)/*.cc)
+
+ifeq ($(HAVE_OPENSSL), 1)
+  libutil_LDFLAGS = $(OPENSSL_LIBS)
+else
+  libutil_SOURCES += $(d)/md5.c $(d)/sha1.c $(d)/sha256.c
+endif
+
+libutil_LIBS = libformat
diff --git a/src/libutil/md32_common.h b/src/libutil/md32_common.h
new file mode 100644
index 000000000000..0cbcfaf8a20b
--- /dev/null
+++ b/src/libutil/md32_common.h
@@ -0,0 +1,620 @@
+/* crypto/md32_common.h */
+/* ====================================================================
+ * Copyright (c) 1999-2002 The OpenSSL Project.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer. 
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * 3. All advertising materials mentioning features or use of this
+ *    software must display the following acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
+ *
+ * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
+ *    endorse or promote products derived from this software without
+ *    prior written permission. For written permission, please contact
+ *    licensing@OpenSSL.org.
+ *
+ * 5. Products derived from this software may not be called "OpenSSL"
+ *    nor may "OpenSSL" appear in their names without prior written
+ *    permission of the OpenSSL Project.
+ *
+ * 6. Redistributions of any form whatsoever must retain the following
+ *    acknowledgment:
+ *    "This product includes software developed by the OpenSSL Project
+ *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
+ * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
+ * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ * ====================================================================
+ *
+ * This product includes cryptographic software written by Eric Young
+ * (eay@cryptsoft.com).  This product includes software written by Tim
+ * Hudson (tjh@cryptsoft.com).
+ *
+ */
+
+/*
+ * This is a generic 32 bit "collector" for message digest algorithms.
+ * Whenever needed it collects input character stream into chunks of
+ * 32 bit values and invokes a block function that performs actual hash
+ * calculations.
+ *
+ * Porting guide.
+ *
+ * Obligatory macros:
+ *
+ * DATA_ORDER_IS_BIG_ENDIAN or DATA_ORDER_IS_LITTLE_ENDIAN
+ *	this macro defines byte order of input stream.
+ * HASH_CBLOCK
+ *	size of a unit chunk HASH_BLOCK operates on.
+ * HASH_LONG
+ *	has to be at lest 32 bit wide, if it's wider, then
+ *	HASH_LONG_LOG2 *has to* be defined along
+ * HASH_CTX
+ *	context structure that at least contains following
+ *	members:
+ *		typedef struct {
+ *			...
+ *			HASH_LONG	Nl,Nh;
+ *			HASH_LONG	data[HASH_LBLOCK];
+ *			unsigned int	num;
+ *			...
+ *			} HASH_CTX;
+ * HASH_UPDATE
+ *	name of "Update" function, implemented here.
+ * HASH_TRANSFORM
+ *	name of "Transform" function, implemented here.
+ * HASH_FINAL
+ *	name of "Final" function, implemented here.
+ * HASH_BLOCK_HOST_ORDER
+ *	name of "block" function treating *aligned* input message
+ *	in host byte order, implemented externally.
+ * HASH_BLOCK_DATA_ORDER
+ *	name of "block" function treating *unaligned* input message
+ *	in original (data) byte order, implemented externally (it
+ *	actually is optional if data and host are of the same
+ *	"endianess").
+ * HASH_MAKE_STRING
+ *	macro convering context variables to an ASCII hash string.
+ *
+ * Optional macros:
+ *
+ * B_ENDIAN or L_ENDIAN
+ *	defines host byte-order.
+ * HASH_LONG_LOG2
+ *	defaults to 2 if not states otherwise.
+ * HASH_LBLOCK
+ *	assumed to be HASH_CBLOCK/4 if not stated otherwise.
+ * HASH_BLOCK_DATA_ORDER_ALIGNED
+ *	alternative "block" function capable of treating
+ *	aligned input message in original (data) order,
+ *	implemented externally.
+ *
+ * MD5 example:
+ *
+ *	#define DATA_ORDER_IS_LITTLE_ENDIAN
+ *
+ *	#define HASH_LONG		MD5_LONG
+ *	#define HASH_LONG_LOG2		MD5_LONG_LOG2
+ *	#define HASH_CTX		MD5_CTX
+ *	#define HASH_CBLOCK		MD5_CBLOCK
+ *	#define HASH_LBLOCK		MD5_LBLOCK
+ *	#define HASH_UPDATE		MD5_Update
+ *	#define HASH_TRANSFORM		MD5_Transform
+ *	#define HASH_FINAL		MD5_Final
+ *	#define HASH_BLOCK_HOST_ORDER	md5_block_host_order
+ *	#define HASH_BLOCK_DATA_ORDER	md5_block_data_order
+ *
+ *					<appro@fy.chalmers.se>
+ */
+
+#if !defined(DATA_ORDER_IS_BIG_ENDIAN) && !defined(DATA_ORDER_IS_LITTLE_ENDIAN)
+#error "DATA_ORDER must be defined!"
+#endif
+
+#ifndef HASH_CBLOCK
+#error "HASH_CBLOCK must be defined!"
+#endif
+#ifndef HASH_LONG
+#error "HASH_LONG must be defined!"
+#endif
+#ifndef HASH_CTX
+#error "HASH_CTX must be defined!"
+#endif
+
+#ifndef HASH_UPDATE
+#error "HASH_UPDATE must be defined!"
+#endif
+#ifndef HASH_TRANSFORM
+#error "HASH_TRANSFORM must be defined!"
+#endif
+#ifndef HASH_FINAL
+#error "HASH_FINAL must be defined!"
+#endif
+
+#ifndef HASH_BLOCK_HOST_ORDER
+#error "HASH_BLOCK_HOST_ORDER must be defined!"
+#endif
+
+#if 0
+/*
+ * Moved below as it's required only if HASH_BLOCK_DATA_ORDER_ALIGNED
+ * isn't defined.
+ */
+#ifndef HASH_BLOCK_DATA_ORDER
+#error "HASH_BLOCK_DATA_ORDER must be defined!"
+#endif
+#endif
+
+#ifndef HASH_LBLOCK
+#define HASH_LBLOCK	(HASH_CBLOCK/4)
+#endif
+
+#ifndef HASH_LONG_LOG2
+#define HASH_LONG_LOG2	2
+#endif
+
+/*
+ * Engage compiler specific rotate intrinsic function if available.
+ */
+#undef ROTATE
+#ifndef PEDANTIC
+# if defined(_MSC_VER) || defined(__ICC)
+#  define ROTATE(a,n)	_lrotl(a,n)
+# elif defined(__MWERKS__)
+#  if defined(__POWERPC__)
+#   define ROTATE(a,n)	__rlwinm(a,n,0,31)
+#  elif defined(__MC68K__)
+    /* Motorola specific tweak. <appro@fy.chalmers.se> */
+#   define ROTATE(a,n)	( n<24 ? __rol(a,n) : __ror(a,32-n) )
+#  else
+#   define ROTATE(a,n)	__rol(a,n)
+#  endif
+# elif defined(__GNUC__) && __GNUC__>=2 && !defined(OPENSSL_NO_ASM) && !defined(OPENSSL_NO_INLINE_ASM)
+  /*
+   * Some GNU C inline assembler templates. Note that these are
+   * rotates by *constant* number of bits! But that's exactly
+   * what we need here...
+   * 					<appro@fy.chalmers.se>
+   */
+#  if defined(__i386) || defined(__i386__) || defined(__x86_64) || defined(__x86_64__)
+#   define ROTATE(a,n)	({ register unsigned int ret;	\
+				asm (			\
+				"roll %1,%0"		\
+				: "=r"(ret)		\
+				: "I"(n), "0"(a)	\
+				: "cc");		\
+			   ret;				\
+			})
+#  elif defined(__powerpc) || defined(__ppc__) || defined(__powerpc64__)
+#   define ROTATE(a,n)	({ register unsigned int ret;	\
+				asm (			\
+				"rlwinm %0,%1,%2,0,31"	\
+				: "=r"(ret)		\
+				: "r"(a), "I"(n));	\
+			   ret;				\
+			})
+#  endif
+# endif
+#endif /* PEDANTIC */
+
+#if HASH_LONG_LOG2==2	/* Engage only if sizeof(HASH_LONG)== 4 */
+/* A nice byte order reversal from Wei Dai <weidai@eskimo.com> */
+#ifdef ROTATE
+/* 5 instructions with rotate instruction, else 9 */
+#define REVERSE_FETCH32(a,l)	(					\
+		l=*(const HASH_LONG *)(a),				\
+		((ROTATE(l,8)&0x00FF00FF)|(ROTATE((l&0x00FF00FF),24)))	\
+				)
+#else
+/* 6 instructions with rotate instruction, else 8 */
+#define REVERSE_FETCH32(a,l)	(				\
+		l=*(const HASH_LONG *)(a),			\
+		l=(((l>>8)&0x00FF00FF)|((l&0x00FF00FF)<<8)),	\
+		ROTATE(l,16)					\
+				)
+/*
+ * Originally the middle line started with l=(((l&0xFF00FF00)>>8)|...
+ * It's rewritten as above for two reasons:
+ *	- RISCs aren't good at long constants and have to explicitely
+ *	  compose 'em with several (well, usually 2) instructions in a
+ *	  register before performing the actual operation and (as you
+ *	  already realized:-) having same constant should inspire the
+ *	  compiler to permanently allocate the only register for it;
+ *	- most modern CPUs have two ALUs, but usually only one has
+ *	  circuitry for shifts:-( this minor tweak inspires compiler
+ *	  to schedule shift instructions in a better way...
+ *
+ *				<appro@fy.chalmers.se>
+ */
+#endif
+#endif
+
+#ifndef ROTATE
+#define ROTATE(a,n)     (((a)<<(n))|(((a)&0xffffffff)>>(32-(n))))
+#endif
+
+/*
+ * Make some obvious choices. E.g., HASH_BLOCK_DATA_ORDER_ALIGNED
+ * and HASH_BLOCK_HOST_ORDER ought to be the same if input data
+ * and host are of the same "endianess". It's possible to mask
+ * this with blank #define HASH_BLOCK_DATA_ORDER though...
+ *
+ *				<appro@fy.chalmers.se>
+ */
+#if defined(B_ENDIAN)
+#  if defined(DATA_ORDER_IS_BIG_ENDIAN)
+#    if !defined(HASH_BLOCK_DATA_ORDER_ALIGNED) && HASH_LONG_LOG2==2
+#      define HASH_BLOCK_DATA_ORDER_ALIGNED	HASH_BLOCK_HOST_ORDER
+#    endif
+#  endif
+#elif defined(L_ENDIAN)
+#  if defined(DATA_ORDER_IS_LITTLE_ENDIAN)
+#    if !defined(HASH_BLOCK_DATA_ORDER_ALIGNED) && HASH_LONG_LOG2==2
+#      define HASH_BLOCK_DATA_ORDER_ALIGNED	HASH_BLOCK_HOST_ORDER
+#    endif
+#  endif
+#endif
+
+#if !defined(HASH_BLOCK_DATA_ORDER_ALIGNED)
+#ifndef HASH_BLOCK_DATA_ORDER
+#error "HASH_BLOCK_DATA_ORDER must be defined!"
+#endif
+#endif
+
+#if defined(DATA_ORDER_IS_BIG_ENDIAN)
+
+#ifndef PEDANTIC
+# if defined(__GNUC__) && __GNUC__>=2 && !defined(OPENSSL_NO_ASM) && !defined(OPENSSL_NO_INLINE_ASM)
+#  if defined(__i386) || defined(__i386__) || defined(__x86_64) || defined(__x86_64__)
+    /*
+     * This gives ~30-40% performance improvement in SHA-256 compiled
+     * with gcc [on P4]. Well, first macro to be frank. We can pull
+     * this trick on x86* platforms only, because these CPUs can fetch
+     * unaligned data without raising an exception.
+     */
+#   define HOST_c2l(c,l)	({ unsigned int r=*((const unsigned int *)(c));	\
+				   asm ("bswapl %0":"=r"(r):"0"(r));	\
+				   (c)+=4; (l)=r;			})
+#   define HOST_l2c(l,c)	({ unsigned int r=(l);			\
+				   asm ("bswapl %0":"=r"(r):"0"(r));	\
+				   *((unsigned int *)(c))=r; (c)+=4; r;	})
+#  endif
+# endif
+#endif
+
+#ifndef HOST_c2l
+#define HOST_c2l(c,l)	(l =(((unsigned long)(*((c)++)))<<24),		\
+			 l|=(((unsigned long)(*((c)++)))<<16),		\
+			 l|=(((unsigned long)(*((c)++)))<< 8),		\
+			 l|=(((unsigned long)(*((c)++)))    ),		\
+			 l)
+#endif
+#define HOST_p_c2l(c,l,n)	{					\
+			switch (n) {					\
+			case 0: l =((unsigned long)(*((c)++)))<<24;	\
+			case 1: l|=((unsigned long)(*((c)++)))<<16;	\
+			case 2: l|=((unsigned long)(*((c)++)))<< 8;	\
+			case 3: l|=((unsigned long)(*((c)++)));		\
+				} }
+#define HOST_p_c2l_p(c,l,sc,len) {					\
+			switch (sc) {					\
+			case 0: l =((unsigned long)(*((c)++)))<<24;	\
+				if (--len == 0) break;			\
+			case 1: l|=((unsigned long)(*((c)++)))<<16;	\
+				if (--len == 0) break;			\
+			case 2: l|=((unsigned long)(*((c)++)))<< 8;	\
+				} }
+/* NOTE the pointer is not incremented at the end of this */
+#define HOST_c2l_p(c,l,n)	{					\
+			l=0; (c)+=n;					\
+			switch (n) {					\
+			case 3: l =((unsigned long)(*(--(c))))<< 8;	\
+			case 2: l|=((unsigned long)(*(--(c))))<<16;	\
+			case 1: l|=((unsigned long)(*(--(c))))<<24;	\
+				} }
+#ifndef HOST_l2c
+#define HOST_l2c(l,c)	(*((c)++)=(unsigned char)(((l)>>24)&0xff),	\
+			 *((c)++)=(unsigned char)(((l)>>16)&0xff),	\
+			 *((c)++)=(unsigned char)(((l)>> 8)&0xff),	\
+			 *((c)++)=(unsigned char)(((l)    )&0xff),	\
+			 l)
+#endif
+
+#elif defined(DATA_ORDER_IS_LITTLE_ENDIAN)
+
+#if defined(__i386) || defined(__i386__) || defined(__x86_64) || defined(__x86_64__)
+  /* See comment in DATA_ORDER_IS_BIG_ENDIAN section. */
+# define HOST_c2l(c,l)	((l)=*((const unsigned int *)(c)), (c)+=4, l)
+# define HOST_l2c(l,c)	(*((unsigned int *)(c))=(l), (c)+=4, l)
+#endif
+
+#ifndef HOST_c2l
+#define HOST_c2l(c,l)	(l =(((unsigned long)(*((c)++)))    ),		\
+			 l|=(((unsigned long)(*((c)++)))<< 8),		\
+			 l|=(((unsigned long)(*((c)++)))<<16),		\
+			 l|=(((unsigned long)(*((c)++)))<<24),		\
+			 l)
+#endif
+#define HOST_p_c2l(c,l,n)	{					\
+			switch (n) {					\
+			case 0: l =((unsigned long)(*((c)++)));		\
+			case 1: l|=((unsigned long)(*((c)++)))<< 8;	\
+			case 2: l|=((unsigned long)(*((c)++)))<<16;	\
+			case 3: l|=((unsigned long)(*((c)++)))<<24;	\
+				} }
+#define HOST_p_c2l_p(c,l,sc,len) {					\
+			switch (sc) {					\
+			case 0: l =((unsigned long)(*((c)++)));		\
+				if (--len == 0) break;			\
+			case 1: l|=((unsigned long)(*((c)++)))<< 8;	\
+				if (--len == 0) break;			\
+			case 2: l|=((unsigned long)(*((c)++)))<<16;	\
+				} }
+/* NOTE the pointer is not incremented at the end of this */
+#define HOST_c2l_p(c,l,n)	{					\
+			l=0; (c)+=n;					\
+			switch (n) {					\
+			case 3: l =((unsigned long)(*(--(c))))<<16;	\
+			case 2: l|=((unsigned long)(*(--(c))))<< 8;	\
+			case 1: l|=((unsigned long)(*(--(c))));		\
+				} }
+#ifndef HOST_l2c
+#define HOST_l2c(l,c)	(*((c)++)=(unsigned char)(((l)    )&0xff),	\
+			 *((c)++)=(unsigned char)(((l)>> 8)&0xff),	\
+			 *((c)++)=(unsigned char)(((l)>>16)&0xff),	\
+			 *((c)++)=(unsigned char)(((l)>>24)&0xff),	\
+			 l)
+#endif
+
+#endif
+
+/*
+ * Time for some action:-)
+ */
+
+int HASH_UPDATE (HASH_CTX *c, const void *data_, size_t len)
+	{
+	const unsigned char *data=data_;
+	register HASH_LONG * p;
+	register HASH_LONG l;
+	size_t sw,sc,ew,ec;
+
+	if (len==0) return 1;
+
+	l=(c->Nl+(((HASH_LONG)len)<<3))&0xffffffffUL;
+	/* 95-05-24 eay Fixed a bug with the overflow handling, thanks to
+	 * Wei Dai <weidai@eskimo.com> for pointing it out. */
+	if (l < c->Nl) /* overflow */
+		c->Nh++;
+	c->Nh+=(len>>29);	/* might cause compiler warning on 16-bit */
+	c->Nl=l;
+
+	if (c->num != 0)
+		{
+		p=c->data;
+		sw=c->num>>2;
+		sc=c->num&0x03;
+
+		if ((c->num+len) >= HASH_CBLOCK)
+			{
+			l=p[sw]; HOST_p_c2l(data,l,sc); p[sw++]=l;
+			for (; sw<HASH_LBLOCK; sw++)
+				{
+				HOST_c2l(data,l); p[sw]=l;
+				}
+			HASH_BLOCK_HOST_ORDER (c,p,1);
+			len-=(HASH_CBLOCK-c->num);
+			c->num=0;
+			/* drop through and do the rest */
+			}
+		else
+			{
+			c->num+=(unsigned int)len;
+			if ((sc+len) < 4) /* ugly, add char's to a word */
+				{
+				l=p[sw]; HOST_p_c2l_p(data,l,sc,len); p[sw]=l;
+				}
+			else
+				{
+				ew=(c->num>>2);
+				ec=(c->num&0x03);
+				if (sc)
+					l=p[sw];
+				HOST_p_c2l(data,l,sc);
+				p[sw++]=l;
+				for (; sw < ew; sw++)
+					{
+					HOST_c2l(data,l); p[sw]=l;
+					}
+				if (ec)
+					{
+					HOST_c2l_p(data,l,ec); p[sw]=l;
+					}
+				}
+			return 1;
+			}
+		}
+
+	sw=len/HASH_CBLOCK;
+	if (sw > 0)
+		{
+#if defined(HASH_BLOCK_DATA_ORDER_ALIGNED)
+		/*
+		 * Note that HASH_BLOCK_DATA_ORDER_ALIGNED gets defined
+		 * only if sizeof(HASH_LONG)==4.
+		 */
+		if ((((size_t)data)%4) == 0)
+			{
+			/* data is properly aligned so that we can cast it: */
+			HASH_BLOCK_DATA_ORDER_ALIGNED (c,(const HASH_LONG *)data,sw);
+			sw*=HASH_CBLOCK;
+			data+=sw;
+			len-=sw;
+			}
+		else
+#if !defined(HASH_BLOCK_DATA_ORDER)
+			while (sw--)
+				{
+				memcpy (p=c->data,data,HASH_CBLOCK);
+				HASH_BLOCK_DATA_ORDER_ALIGNED(c,p,1);
+				data+=HASH_CBLOCK;
+				len-=HASH_CBLOCK;
+				}
+#endif
+#endif
+#if defined(HASH_BLOCK_DATA_ORDER)
+			{
+			HASH_BLOCK_DATA_ORDER(c,data,sw);
+			sw*=HASH_CBLOCK;
+			data+=sw;
+			len-=sw;
+			}
+#endif
+		}
+
+	if (len!=0)
+		{
+		p = c->data;
+		c->num = len;
+		ew=len>>2;	/* words to copy */
+		ec=len&0x03;
+		for (; ew; ew--,p++)
+			{
+			HOST_c2l(data,l); *p=l;
+			}
+		HOST_c2l_p(data,l,ec);
+		*p=l;
+		}
+	return 1;
+	}
+
+
+void HASH_TRANSFORM (HASH_CTX *c, const unsigned char *data)
+	{
+#if defined(HASH_BLOCK_DATA_ORDER_ALIGNED)
+	if ((((size_t)data)%4) == 0)
+		/* data is properly aligned so that we can cast it: */
+		HASH_BLOCK_DATA_ORDER_ALIGNED (c,(const HASH_LONG *)data,1);
+	else
+#if !defined(HASH_BLOCK_DATA_ORDER)
+		{
+		memcpy (c->data,data,HASH_CBLOCK);
+		HASH_BLOCK_DATA_ORDER_ALIGNED (c,c->data,1);
+		}
+#endif
+#endif
+#if defined(HASH_BLOCK_DATA_ORDER)
+	HASH_BLOCK_DATA_ORDER (c,data,1);
+#endif
+	}
+
+
+int HASH_FINAL (unsigned char *md, HASH_CTX *c)
+	{
+	register HASH_LONG *p;
+	register unsigned long l;
+	register int i,j;
+	static const unsigned char end[4]={0x80,0x00,0x00,0x00};
+	const unsigned char *cp=end;
+
+	/* c->num should definitly have room for at least one more byte. */
+	p=c->data;
+	i=c->num>>2;
+	j=c->num&0x03;
+
+#if 0
+	/* purify often complains about the following line as an
+	 * Uninitialized Memory Read.  While this can be true, the
+	 * following p_c2l macro will reset l when that case is true.
+	 * This is because j&0x03 contains the number of 'valid' bytes
+	 * already in p[i].  If and only if j&0x03 == 0, the UMR will
+	 * occur but this is also the only time p_c2l will do
+	 * l= *(cp++) instead of l|= *(cp++)
+	 * Many thanks to Alex Tang <altitude@cic.net> for pickup this
+	 * 'potential bug' */
+#ifdef PURIFY
+	if (j==0) p[i]=0; /* Yeah, but that's not the way to fix it:-) */
+#endif
+	l=p[i];
+#else
+	l = (j==0) ? 0 : p[i];
+#endif
+	HOST_p_c2l(cp,l,j); p[i++]=l; /* i is the next 'undefined word' */
+
+	if (i>(HASH_LBLOCK-2)) /* save room for Nl and Nh */
+		{
+		if (i<HASH_LBLOCK) p[i]=0;
+		HASH_BLOCK_HOST_ORDER (c,p,1);
+		i=0;
+		}
+	for (; i<(HASH_LBLOCK-2); i++)
+		p[i]=0;
+
+#if   defined(DATA_ORDER_IS_BIG_ENDIAN)
+	p[HASH_LBLOCK-2]=c->Nh;
+	p[HASH_LBLOCK-1]=c->Nl;
+#elif defined(DATA_ORDER_IS_LITTLE_ENDIAN)
+	p[HASH_LBLOCK-2]=c->Nl;
+	p[HASH_LBLOCK-1]=c->Nh;
+#endif
+	HASH_BLOCK_HOST_ORDER (c,p,1);
+
+#ifndef HASH_MAKE_STRING
+#error "HASH_MAKE_STRING must be defined!"
+#else
+	HASH_MAKE_STRING(c,md);
+#endif
+
+	c->num=0;
+	/* clear stuff, HASH_BLOCK may be leaving some stuff on the stack
+	 * but I'm not worried :-)
+	OPENSSL_cleanse((void *)c,sizeof(HASH_CTX));
+	 */
+	return 1;
+	}
+
+#ifndef MD32_REG_T
+#define MD32_REG_T long
+/*
+ * This comment was originaly written for MD5, which is why it
+ * discusses A-D. But it basically applies to all 32-bit digests,
+ * which is why it was moved to common header file.
+ *
+ * In case you wonder why A-D are declared as long and not
+ * as MD5_LONG. Doing so results in slight performance
+ * boost on LP64 architectures. The catch is we don't
+ * really care if 32 MSBs of a 64-bit register get polluted
+ * with eventual overflows as we *save* only 32 LSBs in
+ * *either* case. Now declaring 'em long excuses the compiler
+ * from keeping 32 MSBs zeroed resulting in 13% performance
+ * improvement under SPARC Solaris7/64 and 5% under AlphaLinux.
+ * Well, to be honest it should say that this *prevents* 
+ * performance degradation.
+ *				<appro@fy.chalmers.se>
+ * Apparently there're LP64 compilers that generate better
+ * code if A-D are declared int. Most notably GCC-x86_64
+ * generates better code.
+ *				<appro@fy.chalmers.se>
+ */
+#endif
diff --git a/src/libutil/md5.c b/src/libutil/md5.c
new file mode 100644
index 000000000000..b31640cdcced
--- /dev/null
+++ b/src/libutil/md5.c
@@ -0,0 +1,365 @@
+/* Functions to compute MD5 message digest of files or memory blocks.
+   according to the definition of MD5 in RFC 1321 from April 1992.
+   Copyright (C) 1995,1996,1997,1999,2000,2001 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+/* Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1995.  */
+
+#include <sys/types.h>
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "md5.h"
+
+
+static md5_uint32 SWAP(md5_uint32 n)
+{
+  static int checked = 0;
+  static int bigendian = 0;
+  static md5_uint32 test;
+
+  if (!checked) {
+    test = 1;
+    if (* (char *) &test == 0)
+      bigendian = 1;
+    checked = 1;
+  }
+
+  if (bigendian)
+    return (((n) << 24) | (((n) & 0xff00) << 8) | (((n) >> 8) & 0xff00) | ((n) >> 24));
+  else
+    return n;
+}
+
+
+/* This array contains the bytes used to pad the buffer to the next
+   64-byte boundary.  (RFC 1321, 3.1: Step 1)  */
+static const unsigned char fillbuf[64] = { 0x80, 0 /* , 0, 0, ...  */ };
+
+
+/* Initialize structure containing state of computation.
+   (RFC 1321, 3.3: Step 3)  */
+void
+MD5_Init (ctx)
+     struct MD5_CTX *ctx;
+{
+  ctx->A = 0x67452301;
+  ctx->B = 0xefcdab89;
+  ctx->C = 0x98badcfe;
+  ctx->D = 0x10325476;
+
+  ctx->total[0] = ctx->total[1] = 0;
+  ctx->buflen = 0;
+}
+
+/* Put result from CTX in first 16 bytes following RESBUF.  The result
+   must be in little endian byte order.
+
+   IMPORTANT: On some systems it is required that RESBUF is correctly
+   aligned for a 32 bits value.  */
+void *
+md5_read_ctx (ctx, resbuf)
+     const struct MD5_CTX *ctx;
+     void *resbuf;
+{
+  ((md5_uint32 *) resbuf)[0] = SWAP (ctx->A);
+  ((md5_uint32 *) resbuf)[1] = SWAP (ctx->B);
+  ((md5_uint32 *) resbuf)[2] = SWAP (ctx->C);
+  ((md5_uint32 *) resbuf)[3] = SWAP (ctx->D);
+
+  return resbuf;
+}
+
+/* Process the remaining bytes in the internal buffer and the usual
+   prolog according to the standard and write the result to RESBUF.
+
+   IMPORTANT: On some systems it is required that RESBUF is correctly
+   aligned for a 32 bits value.  */
+void *
+MD5_Final (resbuf, ctx)
+     void *resbuf;
+     struct MD5_CTX *ctx;
+{
+  /* Take yet unprocessed bytes into account.  */
+  md5_uint32 bytes = ctx->buflen;
+  size_t pad;
+
+  /* Now count remaining bytes.  */
+  ctx->total[0] += bytes;
+  if (ctx->total[0] < bytes)
+    ++ctx->total[1];
+
+  pad = bytes >= 56 ? 64 + 56 - bytes : 56 - bytes;
+  memcpy (&ctx->buffer[bytes], fillbuf, pad);
+
+  /* Put the 64-bit file length in *bits* at the end of the buffer.  */
+  *(md5_uint32 *) &ctx->buffer[bytes + pad] = SWAP (ctx->total[0] << 3);
+  *(md5_uint32 *) &ctx->buffer[bytes + pad + 4] = SWAP ((ctx->total[1] << 3) |
+							(ctx->total[0] >> 29));
+
+  /* Process last bytes.  */
+  md5_process_block (ctx->buffer, bytes + pad + 8, ctx);
+
+  return md5_read_ctx (ctx, resbuf);
+}
+
+void
+MD5_Update (ctx, buffer, len)
+     struct MD5_CTX *ctx;
+     const void *buffer;
+     size_t len;
+{
+  /* When we already have some bits in our internal buffer concatenate
+     both inputs first.  */
+  if (ctx->buflen != 0)
+    {
+      size_t left_over = ctx->buflen;
+      size_t add = 128 - left_over > len ? len : 128 - left_over;
+
+      memcpy (&ctx->buffer[left_over], buffer, add);
+      ctx->buflen += add;
+
+      if (ctx->buflen > 64)
+	{
+	  md5_process_block (ctx->buffer, ctx->buflen & ~63, ctx);
+
+	  ctx->buflen &= 63;
+	  /* The regions in the following copy operation cannot overlap.  */
+	  memcpy (ctx->buffer, &ctx->buffer[(left_over + add) & ~63],
+		  ctx->buflen);
+	}
+
+      buffer = (const char *) buffer + add;
+      len -= add;
+    }
+
+  /* Process available complete blocks.  */
+  if (len >= 64)
+    {
+#if !_STRING_ARCH_unaligned
+/* To check alignment gcc has an appropriate operator.  Other
+   compilers don't.  */
+# if __GNUC__ >= 2
+#  define UNALIGNED_P(p) (((md5_uintptr) p) % __alignof__ (md5_uint32) != 0)
+# else
+#  define UNALIGNED_P(p) (((md5_uintptr) p) % sizeof (md5_uint32) != 0)
+# endif
+      if (UNALIGNED_P (buffer))
+	while (len > 64)
+	  {
+	    md5_process_block (memcpy (ctx->buffer, buffer, 64), 64, ctx);
+	    buffer = (const char *) buffer + 64;
+	    len -= 64;
+	  }
+      else
+#endif
+	{
+	  md5_process_block (buffer, len & ~63, ctx);
+	  buffer = (const char *) buffer + (len & ~63);
+	  len &= 63;
+	}
+    }
+
+  /* Move remaining bytes in internal buffer.  */
+  if (len > 0)
+    {
+      size_t left_over = ctx->buflen;
+
+      memcpy (&ctx->buffer[left_over], buffer, len);
+      left_over += len;
+      if (left_over >= 64)
+	{
+	  md5_process_block (ctx->buffer, 64, ctx);
+	  left_over -= 64;
+	  memcpy (ctx->buffer, &ctx->buffer[64], left_over);
+	}
+      ctx->buflen = left_over;
+    }
+}
+
+
+/* These are the four functions used in the four steps of the MD5 algorithm
+   and defined in the RFC 1321.  The first function is a little bit optimized
+   (as found in Colin Plumbs public domain implementation).  */
+/* #define FF(b, c, d) ((b & c) | (~b & d)) */
+#define FF(b, c, d) (d ^ (b & (c ^ d)))
+#define FG(b, c, d) FF (d, b, c)
+#define FH(b, c, d) (b ^ c ^ d)
+#define FI(b, c, d) (c ^ (b | ~d))
+
+/* Process LEN bytes of BUFFER, accumulating context into CTX.
+   It is assumed that LEN % 64 == 0.  */
+
+void
+md5_process_block (buffer, len, ctx)
+     const void *buffer;
+     size_t len;
+     struct MD5_CTX *ctx;
+{
+  md5_uint32 correct_words[16];
+  const md5_uint32 *words = buffer;
+  size_t nwords = len / sizeof (md5_uint32);
+  const md5_uint32 *endp = words + nwords;
+  md5_uint32 A = ctx->A;
+  md5_uint32 B = ctx->B;
+  md5_uint32 C = ctx->C;
+  md5_uint32 D = ctx->D;
+
+  /* First increment the byte count.  RFC 1321 specifies the possible
+     length of the file up to 2^64 bits.  Here we only compute the
+     number of bytes.  Do a double word increment.  */
+  ctx->total[0] += len;
+  if (ctx->total[0] < len)
+    ++ctx->total[1];
+
+  /* Process all bytes in the buffer with 64 bytes in each round of
+     the loop.  */
+  while (words < endp)
+    {
+      md5_uint32 *cwp = correct_words;
+      md5_uint32 A_save = A;
+      md5_uint32 B_save = B;
+      md5_uint32 C_save = C;
+      md5_uint32 D_save = D;
+
+      /* First round: using the given function, the context and a constant
+	 the next context is computed.  Because the algorithms processing
+	 unit is a 32-bit word and it is determined to work on words in
+	 little endian byte order we perhaps have to change the byte order
+	 before the computation.  To reduce the work for the next steps
+	 we store the swapped words in the array CORRECT_WORDS.  */
+
+#define OP(a, b, c, d, s, T)						\
+      do								\
+        {								\
+	  a += FF (b, c, d) + (*cwp++ = SWAP (*words)) + T;		\
+	  ++words;							\
+	  CYCLIC (a, s);						\
+	  a += b;							\
+        }								\
+      while (0)
+
+      /* It is unfortunate that C does not provide an operator for
+	 cyclic rotation.  Hope the C compiler is smart enough.  */
+#define CYCLIC(w, s) (w = (w << s) | (w >> (32 - s)))
+
+      /* Before we start, one word to the strange constants.
+	 They are defined in RFC 1321 as
+
+	 T[i] = (int) (4294967296.0 * fabs (sin (i))), i=1..64
+       */
+
+      /* Round 1.  */
+      OP (A, B, C, D,  7, 0xd76aa478);
+      OP (D, A, B, C, 12, 0xe8c7b756);
+      OP (C, D, A, B, 17, 0x242070db);
+      OP (B, C, D, A, 22, 0xc1bdceee);
+      OP (A, B, C, D,  7, 0xf57c0faf);
+      OP (D, A, B, C, 12, 0x4787c62a);
+      OP (C, D, A, B, 17, 0xa8304613);
+      OP (B, C, D, A, 22, 0xfd469501);
+      OP (A, B, C, D,  7, 0x698098d8);
+      OP (D, A, B, C, 12, 0x8b44f7af);
+      OP (C, D, A, B, 17, 0xffff5bb1);
+      OP (B, C, D, A, 22, 0x895cd7be);
+      OP (A, B, C, D,  7, 0x6b901122);
+      OP (D, A, B, C, 12, 0xfd987193);
+      OP (C, D, A, B, 17, 0xa679438e);
+      OP (B, C, D, A, 22, 0x49b40821);
+
+      /* For the second to fourth round we have the possibly swapped words
+	 in CORRECT_WORDS.  Redefine the macro to take an additional first
+	 argument specifying the function to use.  */
+#undef OP
+#define OP(f, a, b, c, d, k, s, T)					\
+      do 								\
+	{								\
+	  a += f (b, c, d) + correct_words[k] + T;			\
+	  CYCLIC (a, s);						\
+	  a += b;							\
+	}								\
+      while (0)
+
+      /* Round 2.  */
+      OP (FG, A, B, C, D,  1,  5, 0xf61e2562);
+      OP (FG, D, A, B, C,  6,  9, 0xc040b340);
+      OP (FG, C, D, A, B, 11, 14, 0x265e5a51);
+      OP (FG, B, C, D, A,  0, 20, 0xe9b6c7aa);
+      OP (FG, A, B, C, D,  5,  5, 0xd62f105d);
+      OP (FG, D, A, B, C, 10,  9, 0x02441453);
+      OP (FG, C, D, A, B, 15, 14, 0xd8a1e681);
+      OP (FG, B, C, D, A,  4, 20, 0xe7d3fbc8);
+      OP (FG, A, B, C, D,  9,  5, 0x21e1cde6);
+      OP (FG, D, A, B, C, 14,  9, 0xc33707d6);
+      OP (FG, C, D, A, B,  3, 14, 0xf4d50d87);
+      OP (FG, B, C, D, A,  8, 20, 0x455a14ed);
+      OP (FG, A, B, C, D, 13,  5, 0xa9e3e905);
+      OP (FG, D, A, B, C,  2,  9, 0xfcefa3f8);
+      OP (FG, C, D, A, B,  7, 14, 0x676f02d9);
+      OP (FG, B, C, D, A, 12, 20, 0x8d2a4c8a);
+
+      /* Round 3.  */
+      OP (FH, A, B, C, D,  5,  4, 0xfffa3942);
+      OP (FH, D, A, B, C,  8, 11, 0x8771f681);
+      OP (FH, C, D, A, B, 11, 16, 0x6d9d6122);
+      OP (FH, B, C, D, A, 14, 23, 0xfde5380c);
+      OP (FH, A, B, C, D,  1,  4, 0xa4beea44);
+      OP (FH, D, A, B, C,  4, 11, 0x4bdecfa9);
+      OP (FH, C, D, A, B,  7, 16, 0xf6bb4b60);
+      OP (FH, B, C, D, A, 10, 23, 0xbebfbc70);
+      OP (FH, A, B, C, D, 13,  4, 0x289b7ec6);
+      OP (FH, D, A, B, C,  0, 11, 0xeaa127fa);
+      OP (FH, C, D, A, B,  3, 16, 0xd4ef3085);
+      OP (FH, B, C, D, A,  6, 23, 0x04881d05);
+      OP (FH, A, B, C, D,  9,  4, 0xd9d4d039);
+      OP (FH, D, A, B, C, 12, 11, 0xe6db99e5);
+      OP (FH, C, D, A, B, 15, 16, 0x1fa27cf8);
+      OP (FH, B, C, D, A,  2, 23, 0xc4ac5665);
+
+      /* Round 4.  */
+      OP (FI, A, B, C, D,  0,  6, 0xf4292244);
+      OP (FI, D, A, B, C,  7, 10, 0x432aff97);
+      OP (FI, C, D, A, B, 14, 15, 0xab9423a7);
+      OP (FI, B, C, D, A,  5, 21, 0xfc93a039);
+      OP (FI, A, B, C, D, 12,  6, 0x655b59c3);
+      OP (FI, D, A, B, C,  3, 10, 0x8f0ccc92);
+      OP (FI, C, D, A, B, 10, 15, 0xffeff47d);
+      OP (FI, B, C, D, A,  1, 21, 0x85845dd1);
+      OP (FI, A, B, C, D,  8,  6, 0x6fa87e4f);
+      OP (FI, D, A, B, C, 15, 10, 0xfe2ce6e0);
+      OP (FI, C, D, A, B,  6, 15, 0xa3014314);
+      OP (FI, B, C, D, A, 13, 21, 0x4e0811a1);
+      OP (FI, A, B, C, D,  4,  6, 0xf7537e82);
+      OP (FI, D, A, B, C, 11, 10, 0xbd3af235);
+      OP (FI, C, D, A, B,  2, 15, 0x2ad7d2bb);
+      OP (FI, B, C, D, A,  9, 21, 0xeb86d391);
+
+      /* Add the starting values of the context.  */
+      A += A_save;
+      B += B_save;
+      C += C_save;
+      D += D_save;
+    }
+
+  /* Put checksum in context given as argument.  */
+  ctx->A = A;
+  ctx->B = B;
+  ctx->C = C;
+  ctx->D = D;
+}
diff --git a/src/libutil/md5.h b/src/libutil/md5.h
new file mode 100644
index 000000000000..228d4972320f
--- /dev/null
+++ b/src/libutil/md5.h
@@ -0,0 +1,82 @@
+/* Declaration of functions and data types used for MD5 sum computing
+   library functions.
+   Copyright (C) 1995,1996,1997,1999,2000,2001 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#ifndef _MD5_H
+#define _MD5_H 1
+
+#include <inttypes.h>
+typedef uint32_t md5_uint32;
+typedef uintptr_t md5_uintptr;
+
+/* Structure to save state of computation between the single steps.  */
+struct MD5_CTX
+{
+  md5_uint32 A;
+  md5_uint32 B;
+  md5_uint32 C;
+  md5_uint32 D;
+
+  md5_uint32 total[2];
+  md5_uint32 buflen;
+  char buffer[128] __attribute__ ((__aligned__ (__alignof__ (md5_uint32))));
+};
+
+/*
+ * The following three functions are build up the low level used in
+ * the functions `md5_stream' and `md5_buffer'.
+ */
+
+/* Initialize structure containing state of computation.
+   (RFC 1321, 3.3: Step 3)  */
+extern void MD5_Init (struct MD5_CTX *ctx);
+
+/* Starting with the result of former calls of this function (or the
+   initialization function update the context for the next LEN bytes
+   starting at BUFFER.
+   It is necessary that LEN is a multiple of 64!!! */
+extern void md5_process_block (const void *buffer, size_t len,
+				      struct MD5_CTX *ctx);
+
+/* Starting with the result of former calls of this function (or the
+   initialization function update the context for the next LEN bytes
+   starting at BUFFER.
+   It is NOT required that LEN is a multiple of 64.  */
+extern void MD5_Update (struct MD5_CTX *ctx, const void *buffer, size_t len);
+
+/* Process the remaining bytes in the buffer and put result from CTX
+   in first 16 bytes following RESBUF.  The result is always in little
+   endian byte order, so that a byte-wise output yields to the wanted
+   ASCII representation of the message digest.
+
+   IMPORTANT: On some systems it is required that RESBUF is correctly
+   aligned for a 32 bits value.  */
+extern void *MD5_Final (void *resbuf, struct MD5_CTX *ctx);
+
+
+/* Put result from CTX in first 16 bytes following RESBUF.  The result is
+   always in little endian byte order, so that a byte-wise output yields
+   to the wanted ASCII representation of the message digest.
+
+   IMPORTANT: On some systems it is required that RESBUF is correctly
+   aligned for a 32 bits value.  */
+extern void *md5_read_ctx (const struct MD5_CTX *ctx, void *resbuf);
+
+
+#endif /* md5.h */
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
new file mode 100644
index 000000000000..1f817a869539
--- /dev/null
+++ b/src/libutil/serialise.cc
@@ -0,0 +1,259 @@
+#include "serialise.hh"
+#include "util.hh"
+
+#include <cstring>
+#include <cerrno>
+
+
+namespace nix {
+
+
+BufferedSink::~BufferedSink()
+{
+    /* We can't call flush() here, because C++ for some insane reason
+       doesn't allow you to call virtual methods from a destructor. */
+    assert(!bufPos);
+    if (buffer) delete[] buffer;
+}
+
+    
+void BufferedSink::operator () (const unsigned char * data, size_t len)
+{
+    if (!buffer) buffer = new unsigned char[bufSize];
+    
+    while (len) {
+        /* Optimisation: bypass the buffer if the data exceeds the
+           buffer size. */
+        if (bufPos + len >= bufSize) {
+            flush();
+            write(data, len);
+            break;
+        }
+        /* Otherwise, copy the bytes to the buffer.  Flush the buffer
+           when it's full. */
+        size_t n = bufPos + len > bufSize ? bufSize - bufPos : len;
+        memcpy(buffer + bufPos, data, n);
+        data += n; bufPos += n; len -= n;
+        if (bufPos == bufSize) flush();
+    }
+}
+
+
+void BufferedSink::flush()
+{
+    if (bufPos == 0) return;
+    size_t n = bufPos;
+    bufPos = 0; // don't trigger the assert() in ~BufferedSink()
+    write(buffer, n);
+}
+
+
+FdSink::~FdSink()
+{
+    try { flush(); } catch (...) { ignoreException(); }
+}
+
+
+void FdSink::write(const unsigned char * data, size_t len)
+{
+    writeFull(fd, data, len);
+}
+
+
+void Source::operator () (unsigned char * data, size_t len)
+{
+    while (len) {
+        size_t n = read(data, len);
+        data += n; len -= n;
+    }
+}
+
+
+BufferedSource::~BufferedSource()
+{
+    if (buffer) delete[] buffer;
+}
+
+
+size_t BufferedSource::read(unsigned char * data, size_t len)
+{
+    if (!buffer) buffer = new unsigned char[bufSize];
+
+    if (!bufPosIn) bufPosIn = readUnbuffered(buffer, bufSize);
+            
+    /* Copy out the data in the buffer. */
+    size_t n = len > bufPosIn - bufPosOut ? bufPosIn - bufPosOut : len;
+    memcpy(data, buffer + bufPosOut, n);
+    bufPosOut += n;
+    if (bufPosIn == bufPosOut) bufPosIn = bufPosOut = 0;
+    return n;
+}
+
+
+bool BufferedSource::hasData()
+{
+    return bufPosOut < bufPosIn;
+}
+
+
+size_t FdSource::readUnbuffered(unsigned char * data, size_t len)
+{
+    ssize_t n;
+    do {
+        checkInterrupt();
+        n = ::read(fd, (char *) data, bufSize);
+    } while (n == -1 && errno == EINTR);
+    if (n == -1) throw SysError("reading from file");
+    if (n == 0) throw EndOfFile("unexpected end-of-file");
+    return n;
+}
+
+
+size_t StringSource::read(unsigned char * data, size_t len)
+{
+    if (pos == s.size()) throw EndOfFile("end of string reached");
+    size_t n = s.copy((char *) data, len, pos);
+    pos += n;
+    return n;
+}
+
+
+void writePadding(size_t len, Sink & sink)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        memset(zero, 0, sizeof(zero));
+        sink(zero, 8 - (len % 8));
+    }
+}
+
+
+void writeInt(unsigned int n, Sink & sink)
+{
+    unsigned char buf[8];
+    memset(buf, 0, sizeof(buf));
+    buf[0] = n & 0xff;
+    buf[1] = (n >> 8) & 0xff;
+    buf[2] = (n >> 16) & 0xff;
+    buf[3] = (n >> 24) & 0xff;
+    sink(buf, sizeof(buf));
+}
+
+
+void writeLongLong(unsigned long long n, Sink & sink)
+{
+    unsigned char buf[8];
+    buf[0] = n & 0xff;
+    buf[1] = (n >> 8) & 0xff;
+    buf[2] = (n >> 16) & 0xff;
+    buf[3] = (n >> 24) & 0xff;
+    buf[4] = (n >> 32) & 0xff;
+    buf[5] = (n >> 40) & 0xff;
+    buf[6] = (n >> 48) & 0xff;
+    buf[7] = (n >> 56) & 0xff;
+    sink(buf, sizeof(buf));
+}
+
+
+void writeString(const unsigned char * buf, size_t len, Sink & sink)
+{
+    writeInt(len, sink);
+    sink(buf, len);
+    writePadding(len, sink);
+}
+
+
+void writeString(const string & s, Sink & sink)
+{
+    writeString((const unsigned char *) s.data(), s.size(), sink);
+}
+
+
+template<class T> void writeStrings(const T & ss, Sink & sink)
+{
+    writeInt(ss.size(), sink);
+    foreach (typename T::const_iterator, i, ss)
+        writeString(*i, sink);
+}
+
+template void writeStrings(const Paths & ss, Sink & sink);
+template void writeStrings(const PathSet & ss, Sink & sink);
+
+
+void readPadding(size_t len, Source & source)
+{
+    if (len % 8) {
+        unsigned char zero[8];
+        size_t n = 8 - (len % 8);
+        source(zero, n);
+        for (unsigned int i = 0; i < n; i++)
+            if (zero[i]) throw SerialisationError("non-zero padding");
+    }
+}
+
+
+unsigned int readInt(Source & source)
+{
+    unsigned char buf[8];
+    source(buf, sizeof(buf));
+    if (buf[4] || buf[5] || buf[6] || buf[7])
+        throw SerialisationError("implementation cannot deal with > 32-bit integers");
+    return
+        buf[0] |
+        (buf[1] << 8) |
+        (buf[2] << 16) |
+        (buf[3] << 24);
+}
+
+
+unsigned long long readLongLong(Source & source)
+{
+    unsigned char buf[8];
+    source(buf, sizeof(buf));
+    return
+        ((unsigned long long) buf[0]) |
+        ((unsigned long long) buf[1] << 8) |
+        ((unsigned long long) buf[2] << 16) |
+        ((unsigned long long) buf[3] << 24) |
+        ((unsigned long long) buf[4] << 32) |
+        ((unsigned long long) buf[5] << 40) |
+        ((unsigned long long) buf[6] << 48) |
+        ((unsigned long long) buf[7] << 56);
+}
+
+
+size_t readString(unsigned char * buf, size_t max, Source & source)
+{
+    size_t len = readInt(source);
+    if (len > max) throw Error("string is too long");
+    source(buf, len);
+    readPadding(len, source);
+    return len;
+}
+
+ 
+string readString(Source & source)
+{
+    size_t len = readInt(source);
+    unsigned char * buf = new unsigned char[len];
+    AutoDeleteArray<unsigned char> d(buf);
+    source(buf, len);
+    readPadding(len, source);
+    return string((char *) buf, len);
+}
+
+ 
+template<class T> T readStrings(Source & source)
+{
+    unsigned int count = readInt(source);
+    T ss;
+    while (count--)
+        ss.insert(ss.end(), readString(source));
+    return ss;
+}
+
+template Paths readStrings(Source & source);
+template PathSet readStrings(Source & source);
+
+
+}
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
new file mode 100644
index 000000000000..e5a9df1d050a
--- /dev/null
+++ b/src/libutil/serialise.hh
@@ -0,0 +1,133 @@
+#pragma once
+
+#include "types.hh"
+
+
+namespace nix {
+
+
+/* Abstract destination of binary data. */
+struct Sink 
+{
+    virtual ~Sink() { }
+    virtual void operator () (const unsigned char * data, size_t len) = 0;
+};
+
+
+/* A buffered abstract sink. */
+struct BufferedSink : Sink
+{
+    size_t bufSize, bufPos;
+    unsigned char * buffer;
+
+    BufferedSink(size_t bufSize = 32 * 1024)
+        : bufSize(bufSize), bufPos(0), buffer(0) { }
+    ~BufferedSink();
+
+    void operator () (const unsigned char * data, size_t len);
+    
+    void flush();
+    
+    virtual void write(const unsigned char * data, size_t len) = 0;
+};
+
+
+/* Abstract source of binary data. */
+struct Source
+{
+    virtual ~Source() { }
+    
+    /* Store exactly ‘len’ bytes in the buffer pointed to by ‘data’.
+       It blocks until all the requested data is available, or throws
+       an error if it is not going to be available.   */
+    void operator () (unsigned char * data, size_t len);
+
+    /* Store up to ‘len’ in the buffer pointed to by ‘data’, and
+       return the number of bytes stored.  If blocks until at least
+       one byte is available. */
+    virtual size_t read(unsigned char * data, size_t len) = 0;
+};
+
+
+/* A buffered abstract source. */
+struct BufferedSource : Source
+{
+    size_t bufSize, bufPosIn, bufPosOut;
+    unsigned char * buffer;
+
+    BufferedSource(size_t bufSize = 32 * 1024)
+        : bufSize(bufSize), bufPosIn(0), bufPosOut(0), buffer(0) { }
+    ~BufferedSource();
+    
+    size_t read(unsigned char * data, size_t len);
+    
+    /* Underlying read call, to be overridden. */
+    virtual size_t readUnbuffered(unsigned char * data, size_t len) = 0;
+
+    bool hasData();
+};
+
+
+/* A sink that writes data to a file descriptor. */
+struct FdSink : BufferedSink
+{
+    int fd;
+
+    FdSink() : fd(-1) { }
+    FdSink(int fd) : fd(fd) { }
+    ~FdSink();
+    
+    void write(const unsigned char * data, size_t len);
+};
+
+
+/* A source that reads data from a file descriptor. */
+struct FdSource : BufferedSource
+{
+    int fd;
+    FdSource() : fd(-1) { }
+    FdSource(int fd) : fd(fd) { }
+    size_t readUnbuffered(unsigned char * data, size_t len);
+};
+
+
+/* A sink that writes data to a string. */
+struct StringSink : Sink
+{
+    string s;
+    void operator () (const unsigned char * data, size_t len)
+    {
+        s.append((const char *) data, len);
+    }
+};
+
+
+/* A source that reads data from a string. */
+struct StringSource : Source
+{
+    const string & s;
+    size_t pos;
+    StringSource(const string & _s) : s(_s), pos(0) { }
+    size_t read(unsigned char * data, size_t len);    
+};
+
+
+void writePadding(size_t len, Sink & sink);
+void writeInt(unsigned int n, Sink & sink);
+void writeLongLong(unsigned long long n, Sink & sink);
+void writeString(const unsigned char * buf, size_t len, Sink & sink);
+void writeString(const string & s, Sink & sink);
+template<class T> void writeStrings(const T & ss, Sink & sink);
+
+void readPadding(size_t len, Source & source);
+unsigned int readInt(Source & source);
+unsigned long long readLongLong(Source & source);
+size_t readString(unsigned char * buf, size_t max, Source & source);
+string readString(Source & source);
+template<class T> T readStrings(Source & source);
+
+
+MakeError(SerialisationError, Error)
+
+
+}
diff --git a/src/libutil/sha1.c b/src/libutil/sha1.c
new file mode 100644
index 000000000000..d9d294d15540
--- /dev/null
+++ b/src/libutil/sha1.c
@@ -0,0 +1,369 @@
+/* $Id$ */
+
+/* sha.c - Implementation of the Secure Hash Algorithm
+ *
+ * Copyright (C) 1995, A.M. Kuchling
+ *
+ * Distribute and use freely; there are no restrictions on further 
+ * dissemination and usage except those imposed by the laws of your 
+ * country of residence.
+ *
+ * Adapted to pike and some cleanup by Niels Möller.
+ */
+
+/* $Id$ */
+
+/* SHA: NIST's Secure Hash Algorithm */
+
+/* Based on SHA code originally posted to sci.crypt by Peter Gutmann
+   in message <30ajo5$oe8@ccu2.auckland.ac.nz>.
+   Modified to test for endianness on creation of SHA objects by AMK.
+   Also, the original specification of SHA was found to have a weakness
+   by NSA/NIST.  This code implements the fixed version of SHA.
+*/
+
+/* Here's the first paragraph of Peter Gutmann's posting:
+   
+The following is my SHA (FIPS 180) code updated to allow use of the "fixed"
+SHA, thanks to Jim Gillogly and an anonymous contributor for the information on
+what's changed in the new version.  The fix is a simple change which involves
+adding a single rotate in the initial expansion function.  It is unknown
+whether this is an optimal solution to the problem which was discovered in the
+SHA or whether it's simply a bandaid which fixes the problem with a minimum of
+effort (for example the reengineering of a great many Capstone chips).
+*/
+
+#include "sha1.h"
+
+#include <string.h>
+
+void sha_copy(struct SHA_CTX *dest, struct SHA_CTX *src)
+{
+  unsigned int i;
+
+  dest->count_l=src->count_l;
+  dest->count_h=src->count_h;
+  for(i=0; i<SHA_DIGESTLEN; i++)
+    dest->digest[i]=src->digest[i];
+  for(i=0; i < src->index; i++)
+    dest->block[i] = src->block[i];
+  dest->index = src->index;
+}
+
+
+/* The SHA f()-functions.  The f1 and f3 functions can be optimized to
+   save one boolean operation each - thanks to Rich Schroeppel,
+   rcs@cs.arizona.edu for discovering this */
+
+/*#define f1(x,y,z) ( ( x & y ) | ( ~x & z ) )          // Rounds  0-19 */
+#define f1(x,y,z)   ( z ^ ( x & ( y ^ z ) ) )           /* Rounds  0-19 */
+#define f2(x,y,z)   ( x ^ y ^ z )                       /* Rounds 20-39 */
+/*#define f3(x,y,z) ( ( x & y ) | ( x & z ) | ( y & z ) )   // Rounds 40-59 */
+#define f3(x,y,z)   ( ( x & y ) | ( z & ( x | y ) ) )   /* Rounds 40-59 */
+#define f4(x,y,z)   ( x ^ y ^ z )                       /* Rounds 60-79 */
+
+/* The SHA Mysterious Constants */
+
+#define K1  0x5A827999L                                 /* Rounds  0-19 */
+#define K2  0x6ED9EBA1L                                 /* Rounds 20-39 */
+#define K3  0x8F1BBCDCL                                 /* Rounds 40-59 */
+#define K4  0xCA62C1D6L                                 /* Rounds 60-79 */
+
+/* SHA initial values */
+
+#define h0init  0x67452301L
+#define h1init  0xEFCDAB89L
+#define h2init  0x98BADCFEL
+#define h3init  0x10325476L
+#define h4init  0xC3D2E1F0L
+
+/* 32-bit rotate left - kludged with shifts */
+
+#define ROTL(n,X)  ( ( (X) << (n) ) | ( (X) >> ( 32 - (n) ) ) )
+
+/* The initial expanding function.  The hash function is defined over an
+   80-word expanded input array W, where the first 16 are copies of the input
+   data, and the remaining 64 are defined by
+
+        W[ i ] = W[ i - 16 ] ^ W[ i - 14 ] ^ W[ i - 8 ] ^ W[ i - 3 ]
+
+   This implementation generates these values on the fly in a circular
+   buffer - thanks to Colin Plumb, colin@nyx10.cs.du.edu for this
+   optimization.
+
+   The updated SHA changes the expanding function by adding a rotate of 1
+   bit.  Thanks to Jim Gillogly, jim@rand.org, and an anonymous contributor
+   for this information */
+
+#define expand(W,i) ( W[ i & 15 ] = \
+		      ROTL( 1, ( W[ i & 15 ] ^ W[ (i - 14) & 15 ] ^ \
+				 W[ (i - 8) & 15 ] ^ W[ (i - 3) & 15 ] ) ) )
+
+
+/* The prototype SHA sub-round.  The fundamental sub-round is:
+
+        a' = e + ROTL( 5, a ) + f( b, c, d ) + k + data;
+        b' = a;
+        c' = ROTL( 30, b );
+        d' = c;
+        e' = d;
+
+   but this is implemented by unrolling the loop 5 times and renaming the
+   variables ( e, a, b, c, d ) = ( a', b', c', d', e' ) each iteration.
+   This code is then replicated 20 times for each of the 4 functions, using
+   the next 20 values from the W[] array each time */
+
+#define subRound(a, b, c, d, e, f, k, data) \
+    ( e += ROTL( 5, a ) + f( b, c, d ) + k + data, b = ROTL( 30, b ) )
+
+/* Initialize the SHA values */
+
+void SHA1_Init(struct SHA_CTX *ctx)
+{
+  /* Set the h-vars to their initial values */
+  ctx->digest[ 0 ] = h0init;
+  ctx->digest[ 1 ] = h1init;
+  ctx->digest[ 2 ] = h2init;
+  ctx->digest[ 3 ] = h3init;
+  ctx->digest[ 4 ] = h4init;
+
+  /* Initialize bit count */
+  ctx->count_l = ctx->count_h = 0;
+  
+  /* Initialize buffer */
+  ctx->index = 0;
+}
+
+/* Perform the SHA transformation.  Note that this code, like MD5, seems to
+   break some optimizing compilers due to the complexity of the expressions
+   and the size of the basic block.  It may be necessary to split it into
+   sections, e.g. based on the four subrounds
+
+   Note that this function destroys the data area */
+
+static void sha_transform(struct SHA_CTX *ctx, uint32_t *data )
+{
+  uint32_t A, B, C, D, E;     /* Local vars */
+
+  /* Set up first buffer and local data buffer */
+  A = ctx->digest[0];
+  B = ctx->digest[1];
+  C = ctx->digest[2];
+  D = ctx->digest[3];
+  E = ctx->digest[4];
+
+  /* Heavy mangling, in 4 sub-rounds of 20 interations each. */
+  subRound( A, B, C, D, E, f1, K1, data[ 0] );
+  subRound( E, A, B, C, D, f1, K1, data[ 1] );
+  subRound( D, E, A, B, C, f1, K1, data[ 2] );
+  subRound( C, D, E, A, B, f1, K1, data[ 3] );
+  subRound( B, C, D, E, A, f1, K1, data[ 4] );
+  subRound( A, B, C, D, E, f1, K1, data[ 5] );
+  subRound( E, A, B, C, D, f1, K1, data[ 6] );
+  subRound( D, E, A, B, C, f1, K1, data[ 7] );
+  subRound( C, D, E, A, B, f1, K1, data[ 8] );
+  subRound( B, C, D, E, A, f1, K1, data[ 9] );
+  subRound( A, B, C, D, E, f1, K1, data[10] );
+  subRound( E, A, B, C, D, f1, K1, data[11] );
+  subRound( D, E, A, B, C, f1, K1, data[12] );
+  subRound( C, D, E, A, B, f1, K1, data[13] );
+  subRound( B, C, D, E, A, f1, K1, data[14] );
+  subRound( A, B, C, D, E, f1, K1, data[15] );
+  subRound( E, A, B, C, D, f1, K1, expand( data, 16 ) );
+  subRound( D, E, A, B, C, f1, K1, expand( data, 17 ) );
+  subRound( C, D, E, A, B, f1, K1, expand( data, 18 ) );
+  subRound( B, C, D, E, A, f1, K1, expand( data, 19 ) );
+
+  subRound( A, B, C, D, E, f2, K2, expand( data, 20 ) );
+  subRound( E, A, B, C, D, f2, K2, expand( data, 21 ) );
+  subRound( D, E, A, B, C, f2, K2, expand( data, 22 ) );
+  subRound( C, D, E, A, B, f2, K2, expand( data, 23 ) );
+  subRound( B, C, D, E, A, f2, K2, expand( data, 24 ) );
+  subRound( A, B, C, D, E, f2, K2, expand( data, 25 ) );
+  subRound( E, A, B, C, D, f2, K2, expand( data, 26 ) );
+  subRound( D, E, A, B, C, f2, K2, expand( data, 27 ) );
+  subRound( C, D, E, A, B, f2, K2, expand( data, 28 ) );
+  subRound( B, C, D, E, A, f2, K2, expand( data, 29 ) );
+  subRound( A, B, C, D, E, f2, K2, expand( data, 30 ) );
+  subRound( E, A, B, C, D, f2, K2, expand( data, 31 ) );
+  subRound( D, E, A, B, C, f2, K2, expand( data, 32 ) );
+  subRound( C, D, E, A, B, f2, K2, expand( data, 33 ) );
+  subRound( B, C, D, E, A, f2, K2, expand( data, 34 ) );
+  subRound( A, B, C, D, E, f2, K2, expand( data, 35 ) );
+  subRound( E, A, B, C, D, f2, K2, expand( data, 36 ) );
+  subRound( D, E, A, B, C, f2, K2, expand( data, 37 ) );
+  subRound( C, D, E, A, B, f2, K2, expand( data, 38 ) );
+  subRound( B, C, D, E, A, f2, K2, expand( data, 39 ) );
+
+  subRound( A, B, C, D, E, f3, K3, expand( data, 40 ) );
+  subRound( E, A, B, C, D, f3, K3, expand( data, 41 ) );
+  subRound( D, E, A, B, C, f3, K3, expand( data, 42 ) );
+  subRound( C, D, E, A, B, f3, K3, expand( data, 43 ) );
+  subRound( B, C, D, E, A, f3, K3, expand( data, 44 ) );
+  subRound( A, B, C, D, E, f3, K3, expand( data, 45 ) );
+  subRound( E, A, B, C, D, f3, K3, expand( data, 46 ) );
+  subRound( D, E, A, B, C, f3, K3, expand( data, 47 ) );
+  subRound( C, D, E, A, B, f3, K3, expand( data, 48 ) );
+  subRound( B, C, D, E, A, f3, K3, expand( data, 49 ) );
+  subRound( A, B, C, D, E, f3, K3, expand( data, 50 ) );
+  subRound( E, A, B, C, D, f3, K3, expand( data, 51 ) );
+  subRound( D, E, A, B, C, f3, K3, expand( data, 52 ) );
+  subRound( C, D, E, A, B, f3, K3, expand( data, 53 ) );
+  subRound( B, C, D, E, A, f3, K3, expand( data, 54 ) );
+  subRound( A, B, C, D, E, f3, K3, expand( data, 55 ) );
+  subRound( E, A, B, C, D, f3, K3, expand( data, 56 ) );
+  subRound( D, E, A, B, C, f3, K3, expand( data, 57 ) );
+  subRound( C, D, E, A, B, f3, K3, expand( data, 58 ) );
+  subRound( B, C, D, E, A, f3, K3, expand( data, 59 ) );
+
+  subRound( A, B, C, D, E, f4, K4, expand( data, 60 ) );
+  subRound( E, A, B, C, D, f4, K4, expand( data, 61 ) );
+  subRound( D, E, A, B, C, f4, K4, expand( data, 62 ) );
+  subRound( C, D, E, A, B, f4, K4, expand( data, 63 ) );
+  subRound( B, C, D, E, A, f4, K4, expand( data, 64 ) );
+  subRound( A, B, C, D, E, f4, K4, expand( data, 65 ) );
+  subRound( E, A, B, C, D, f4, K4, expand( data, 66 ) );
+  subRound( D, E, A, B, C, f4, K4, expand( data, 67 ) );
+  subRound( C, D, E, A, B, f4, K4, expand( data, 68 ) );
+  subRound( B, C, D, E, A, f4, K4, expand( data, 69 ) );
+  subRound( A, B, C, D, E, f4, K4, expand( data, 70 ) );
+  subRound( E, A, B, C, D, f4, K4, expand( data, 71 ) );
+  subRound( D, E, A, B, C, f4, K4, expand( data, 72 ) );
+  subRound( C, D, E, A, B, f4, K4, expand( data, 73 ) );
+  subRound( B, C, D, E, A, f4, K4, expand( data, 74 ) );
+  subRound( A, B, C, D, E, f4, K4, expand( data, 75 ) );
+  subRound( E, A, B, C, D, f4, K4, expand( data, 76 ) );
+  subRound( D, E, A, B, C, f4, K4, expand( data, 77 ) );
+  subRound( C, D, E, A, B, f4, K4, expand( data, 78 ) );
+  subRound( B, C, D, E, A, f4, K4, expand( data, 79 ) );
+
+  /* Build message digest */
+  ctx->digest[0] += A;
+  ctx->digest[1] += B;
+  ctx->digest[2] += C;
+  ctx->digest[3] += D;
+  ctx->digest[4] += E;
+}
+
+#if 1
+
+#ifndef EXTRACT_UCHAR
+#define EXTRACT_UCHAR(p)  (*(unsigned char *)(p))
+#endif
+
+#define STRING2INT(s) ((((((EXTRACT_UCHAR(s) << 8)    \
+			 | EXTRACT_UCHAR(s+1)) << 8)  \
+			 | EXTRACT_UCHAR(s+2)) << 8)  \
+			 | EXTRACT_UCHAR(s+3))
+#else
+uint32_t STRING2INT(unsigned char *s)
+{
+  uint32_t r;
+  unsigned int i;
+  
+  for (i = 0, r = 0; i < 4; i++, s++)
+    r = (r << 8) | *s;
+  return r;
+}
+#endif
+
+static void sha_block(struct SHA_CTX *ctx, const unsigned char *block)
+{
+  uint32_t data[SHA_DATALEN];
+  unsigned int i;
+  
+  /* Update block count */
+  if (!++ctx->count_l)
+    ++ctx->count_h;
+
+  /* Endian independent conversion */
+  for (i = 0; i<SHA_DATALEN; i++, block += 4)
+    data[i] = STRING2INT(block);
+
+  sha_transform(ctx, data);
+}
+
+void SHA1_Update(struct SHA_CTX *ctx, const unsigned char *buffer, uint32_t len)
+{
+  if (ctx->index)
+    { /* Try to fill partial block */
+      unsigned left = SHA_DATASIZE - ctx->index;
+      if (len < left)
+	{
+	  memcpy(ctx->block + ctx->index, buffer, len);
+	  ctx->index += len;
+	  return; /* Finished */
+	}
+      else
+	{
+	  memcpy(ctx->block + ctx->index, buffer, left);
+	  sha_block(ctx, ctx->block);
+	  buffer += left;
+	  len -= left;
+	}
+    }
+  while (len >= SHA_DATASIZE)
+    {
+      sha_block(ctx, buffer);
+      buffer += SHA_DATASIZE;
+      len -= SHA_DATASIZE;
+    }
+  if ((ctx->index = len))     /* This assignment is intended */
+    /* Buffer leftovers */
+    memcpy(ctx->block, buffer, len);
+}
+	  
+/* Final wrapup - pad to SHA_DATASIZE-byte boundary with the bit pattern
+   1 0* (64-bit count of bits processed, MSB-first) */
+
+void SHA1_Final(unsigned char *s, struct SHA_CTX *ctx)
+{
+  uint32_t data[SHA_DATALEN];
+  unsigned int i;
+  unsigned int words;
+  
+  i = ctx->index;
+  /* Set the first char of padding to 0x80.  This is safe since there is
+     always at least one byte free */
+  ctx->block[i++] = 0x80;
+
+  /* Fill rest of word */
+  for( ; i & 3; i++)
+    ctx->block[i] = 0;
+
+  /* i is now a multiple of the word size 4 */
+  words = i >> 2;
+  for (i = 0; i < words; i++)
+    data[i] = STRING2INT(ctx->block + 4*i);
+  
+  if (words > (SHA_DATALEN-2))
+    { /* No room for length in this block. Process it and
+       * pad with another one */
+      for (i = words ; i < SHA_DATALEN; i++)
+	data[i] = 0;
+      sha_transform(ctx, data);
+      for (i = 0; i < (SHA_DATALEN-2); i++)
+	data[i] = 0;
+    }
+  else
+    for (i = words ; i < SHA_DATALEN - 2; i++)
+      data[i] = 0;
+  /* Theres 512 = 2^9 bits in one block */
+  data[SHA_DATALEN-2] = (ctx->count_h << 9) | (ctx->count_l >> 23);
+  data[SHA_DATALEN-1] = (ctx->count_l << 9) | (ctx->index << 3);
+  sha_transform(ctx, data);
+  sha_digest(ctx, s);
+}
+
+void sha_digest(struct SHA_CTX *ctx, unsigned char *s)
+{
+  unsigned int i;
+
+  for (i = 0; i < SHA_DIGESTLEN; i++)
+    {
+      *s++ =         ctx->digest[i] >> 24;
+      *s++ = 0xff & (ctx->digest[i] >> 16);
+      *s++ = 0xff & (ctx->digest[i] >> 8);
+      *s++ = 0xff &  ctx->digest[i];
+    }
+}
diff --git a/src/libutil/sha1.h b/src/libutil/sha1.h
new file mode 100644
index 000000000000..715040dd48df
--- /dev/null
+++ b/src/libutil/sha1.h
@@ -0,0 +1,28 @@
+#ifndef _SHA_H
+#define _SHA_H
+
+#include <inttypes.h>
+
+/* The SHA block size and message digest sizes, in bytes */
+
+#define SHA_DATASIZE    64
+#define SHA_DATALEN     16
+#define SHA_DIGESTSIZE  20
+#define SHA_DIGESTLEN    5
+/* The structure for storing SHA info */
+
+struct SHA_CTX {
+  uint32_t digest[SHA_DIGESTLEN];  /* Message digest */
+  uint32_t count_l, count_h;       /* 64-bit block count */
+  uint8_t block[SHA_DATASIZE];     /* SHA data buffer */
+  unsigned int index;            /* index into buffer */
+};
+
+void SHA1_Init(struct SHA_CTX *ctx);
+void SHA1_Update(struct SHA_CTX *ctx, const unsigned char *buffer, uint32_t len);
+void SHA1_Final(unsigned char *s, struct SHA_CTX *ctx);
+void sha_digest(struct SHA_CTX *ctx, unsigned char *s);
+void sha_copy(struct SHA_CTX *dest, struct SHA_CTX *src);
+
+
+#endif /* !_SHA_H */
diff --git a/src/libutil/sha256.c b/src/libutil/sha256.c
new file mode 100644
index 000000000000..63ed0ba43011
--- /dev/null
+++ b/src/libutil/sha256.c
@@ -0,0 +1,238 @@
+/* crypto/sha/sha256.c */
+/* ====================================================================
+ * Copyright (c) 2004 The OpenSSL Project.  All rights reserved
+ * according to the OpenSSL license [found in ./md32_common.h].
+ * ====================================================================
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "sha256.h"
+
+int SHA224_Init (SHA256_CTX *c)
+	{
+	c->h[0]=0xc1059ed8UL;	c->h[1]=0x367cd507UL;
+	c->h[2]=0x3070dd17UL;	c->h[3]=0xf70e5939UL;
+	c->h[4]=0xffc00b31UL;	c->h[5]=0x68581511UL;
+	c->h[6]=0x64f98fa7UL;	c->h[7]=0xbefa4fa4UL;
+	c->Nl=0;	c->Nh=0;
+	c->num=0;	c->md_len=SHA224_DIGEST_LENGTH;
+	return 1;
+	}
+
+int SHA256_Init (SHA256_CTX *c)
+	{
+	c->h[0]=0x6a09e667UL;	c->h[1]=0xbb67ae85UL;
+	c->h[2]=0x3c6ef372UL;	c->h[3]=0xa54ff53aUL;
+	c->h[4]=0x510e527fUL;	c->h[5]=0x9b05688cUL;
+	c->h[6]=0x1f83d9abUL;	c->h[7]=0x5be0cd19UL;
+	c->Nl=0;	c->Nh=0;
+	c->num=0;	c->md_len=SHA256_DIGEST_LENGTH;
+	return 1;
+	}
+
+unsigned char *SHA224(const unsigned char *d, size_t n, unsigned char *md)
+	{
+	SHA256_CTX c;
+	static unsigned char m[SHA224_DIGEST_LENGTH];
+
+	if (md == NULL) md=m;
+	SHA224_Init(&c);
+	SHA256_Update(&c,d,n);
+	SHA256_Final(md,&c);
+	return(md);
+	}
+
+unsigned char *SHA256(const unsigned char *d, size_t n, unsigned char *md)
+	{
+	SHA256_CTX c;
+	static unsigned char m[SHA256_DIGEST_LENGTH];
+
+	if (md == NULL) md=m;
+	SHA256_Init(&c);
+	SHA256_Update(&c,d,n);
+	SHA256_Final(md,&c);
+	return(md);
+	}
+
+int SHA224_Update(SHA256_CTX *c, const void *data, size_t len)
+{   return SHA256_Update (c,data,len);   }
+int SHA224_Final (unsigned char *md, SHA256_CTX *c)
+{   return SHA256_Final (md,c);   }
+
+#define	DATA_ORDER_IS_BIG_ENDIAN
+
+#define	HASH_LONG		uint32_t
+#define	HASH_LONG_LOG2		2
+#define	HASH_CTX		SHA256_CTX
+#define	HASH_CBLOCK		SHA_CBLOCK
+#define	HASH_LBLOCK		SHA_LBLOCK
+/*
+ * Note that FIPS180-2 discusses "Truncation of the Hash Function Output."
+ * default: case below covers for it. It's not clear however if it's
+ * permitted to truncate to amount of bytes not divisible by 4. I bet not,
+ * but if it is, then default: case shall be extended. For reference.
+ * Idea behind separate cases for pre-defined lenghts is to let the
+ * compiler decide if it's appropriate to unroll small loops.
+ */
+#define	HASH_MAKE_STRING(c,s)	do {	\
+	unsigned long ll;		\
+	unsigned int  n;		\
+	switch ((c)->md_len)		\
+	{   case SHA224_DIGEST_LENGTH:	\
+		for (n=0;n<SHA224_DIGEST_LENGTH/4;n++)	\
+		{   ll=(c)->h[n]; HOST_l2c(ll,(s));   }	\
+		break;			\
+	    case SHA256_DIGEST_LENGTH:	\
+		for (n=0;n<SHA256_DIGEST_LENGTH/4;n++)	\
+		{   ll=(c)->h[n]; HOST_l2c(ll,(s));   }	\
+		break;			\
+	    default:			\
+		if ((c)->md_len > SHA256_DIGEST_LENGTH)	\
+		    return 0;				\
+		for (n=0;n<(c)->md_len/4;n++)		\
+		{   ll=(c)->h[n]; HOST_l2c(ll,(s));   }	\
+		break;			\
+	}				\
+	} while (0)
+
+#define	HASH_UPDATE		SHA256_Update
+#define	HASH_TRANSFORM		SHA256_Transform
+#define	HASH_FINAL		SHA256_Final
+#define	HASH_BLOCK_HOST_ORDER	sha256_block_host_order
+#define	HASH_BLOCK_DATA_ORDER	sha256_block_data_order
+void sha256_block_host_order (SHA256_CTX *ctx, const void *in, size_t num);
+void sha256_block_data_order (SHA256_CTX *ctx, const void *in, size_t num);
+
+#include "md32_common.h"
+
+static const uint32_t K256[64] = {
+	0x428a2f98UL,0x71374491UL,0xb5c0fbcfUL,0xe9b5dba5UL,
+	0x3956c25bUL,0x59f111f1UL,0x923f82a4UL,0xab1c5ed5UL,
+	0xd807aa98UL,0x12835b01UL,0x243185beUL,0x550c7dc3UL,
+	0x72be5d74UL,0x80deb1feUL,0x9bdc06a7UL,0xc19bf174UL,
+	0xe49b69c1UL,0xefbe4786UL,0x0fc19dc6UL,0x240ca1ccUL,
+	0x2de92c6fUL,0x4a7484aaUL,0x5cb0a9dcUL,0x76f988daUL,
+	0x983e5152UL,0xa831c66dUL,0xb00327c8UL,0xbf597fc7UL,
+	0xc6e00bf3UL,0xd5a79147UL,0x06ca6351UL,0x14292967UL,
+	0x27b70a85UL,0x2e1b2138UL,0x4d2c6dfcUL,0x53380d13UL,
+	0x650a7354UL,0x766a0abbUL,0x81c2c92eUL,0x92722c85UL,
+	0xa2bfe8a1UL,0xa81a664bUL,0xc24b8b70UL,0xc76c51a3UL,
+	0xd192e819UL,0xd6990624UL,0xf40e3585UL,0x106aa070UL,
+	0x19a4c116UL,0x1e376c08UL,0x2748774cUL,0x34b0bcb5UL,
+	0x391c0cb3UL,0x4ed8aa4aUL,0x5b9cca4fUL,0x682e6ff3UL,
+	0x748f82eeUL,0x78a5636fUL,0x84c87814UL,0x8cc70208UL,
+	0x90befffaUL,0xa4506cebUL,0xbef9a3f7UL,0xc67178f2UL };
+
+/*
+ * FIPS specification refers to right rotations, while our ROTATE macro
+ * is left one. This is why you might notice that rotation coefficients
+ * differ from those observed in FIPS document by 32-N...
+ */
+#define Sigma0(x)	(ROTATE((x),30) ^ ROTATE((x),19) ^ ROTATE((x),10))
+#define Sigma1(x)	(ROTATE((x),26) ^ ROTATE((x),21) ^ ROTATE((x),7))
+#define sigma0(x)	(ROTATE((x),25) ^ ROTATE((x),14) ^ ((x)>>3))
+#define sigma1(x)	(ROTATE((x),15) ^ ROTATE((x),13) ^ ((x)>>10))
+
+#define Ch(x,y,z)	(((x) & (y)) ^ ((~(x)) & (z)))
+#define Maj(x,y,z)	(((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
+
+#define	ROUND_00_15(i,a,b,c,d,e,f,g,h)		do {	\
+	T1 += h + Sigma1(e) + Ch(e,f,g) + K256[i];	\
+	h = Sigma0(a) + Maj(a,b,c);			\
+	d += T1;	h += T1;		} while (0)
+
+#define	ROUND_16_63(i,a,b,c,d,e,f,g,h,X)	do {	\
+	s0 = X[(i+1)&0x0f];	s0 = sigma0(s0);	\
+	s1 = X[(i+14)&0x0f];	s1 = sigma1(s1);	\
+	T1 = X[(i)&0x0f] += s0 + s1 + X[(i+9)&0x0f];	\
+	ROUND_00_15(i,a,b,c,d,e,f,g,h);		} while (0)
+
+static void sha256_block (SHA256_CTX *ctx, const void *in, size_t num, int host)
+	{
+	uint32_t a,b,c,d,e,f,g,h,s0,s1,T1;
+	uint32_t	X[16];
+	int i;
+	const unsigned char *data=in;
+
+			while (num--) {
+
+	a = ctx->h[0];	b = ctx->h[1];	c = ctx->h[2];	d = ctx->h[3];
+	e = ctx->h[4];	f = ctx->h[5];	g = ctx->h[6];	h = ctx->h[7];
+
+	if (host)
+		{
+		const uint32_t *W=(const uint32_t *)data;
+
+		T1 = X[0] = W[0];	ROUND_00_15(0,a,b,c,d,e,f,g,h);
+		T1 = X[1] = W[1];	ROUND_00_15(1,h,a,b,c,d,e,f,g);
+		T1 = X[2] = W[2];	ROUND_00_15(2,g,h,a,b,c,d,e,f);
+		T1 = X[3] = W[3];	ROUND_00_15(3,f,g,h,a,b,c,d,e);
+		T1 = X[4] = W[4];	ROUND_00_15(4,e,f,g,h,a,b,c,d);
+		T1 = X[5] = W[5];	ROUND_00_15(5,d,e,f,g,h,a,b,c);
+		T1 = X[6] = W[6];	ROUND_00_15(6,c,d,e,f,g,h,a,b);
+		T1 = X[7] = W[7];	ROUND_00_15(7,b,c,d,e,f,g,h,a);
+		T1 = X[8] = W[8];	ROUND_00_15(8,a,b,c,d,e,f,g,h);
+		T1 = X[9] = W[9];	ROUND_00_15(9,h,a,b,c,d,e,f,g);
+		T1 = X[10] = W[10];	ROUND_00_15(10,g,h,a,b,c,d,e,f);
+		T1 = X[11] = W[11];	ROUND_00_15(11,f,g,h,a,b,c,d,e);
+		T1 = X[12] = W[12];	ROUND_00_15(12,e,f,g,h,a,b,c,d);
+		T1 = X[13] = W[13];	ROUND_00_15(13,d,e,f,g,h,a,b,c);
+		T1 = X[14] = W[14];	ROUND_00_15(14,c,d,e,f,g,h,a,b);
+		T1 = X[15] = W[15];	ROUND_00_15(15,b,c,d,e,f,g,h,a);
+
+		data += SHA256_CBLOCK;
+		}
+	else
+		{
+		uint32_t l;
+
+		HOST_c2l(data,l); T1 = X[0] = l;  ROUND_00_15(0,a,b,c,d,e,f,g,h);
+		HOST_c2l(data,l); T1 = X[1] = l;  ROUND_00_15(1,h,a,b,c,d,e,f,g);
+		HOST_c2l(data,l); T1 = X[2] = l;  ROUND_00_15(2,g,h,a,b,c,d,e,f);
+		HOST_c2l(data,l); T1 = X[3] = l;  ROUND_00_15(3,f,g,h,a,b,c,d,e);
+		HOST_c2l(data,l); T1 = X[4] = l;  ROUND_00_15(4,e,f,g,h,a,b,c,d);
+		HOST_c2l(data,l); T1 = X[5] = l;  ROUND_00_15(5,d,e,f,g,h,a,b,c);
+		HOST_c2l(data,l); T1 = X[6] = l;  ROUND_00_15(6,c,d,e,f,g,h,a,b);
+		HOST_c2l(data,l); T1 = X[7] = l;  ROUND_00_15(7,b,c,d,e,f,g,h,a);
+		HOST_c2l(data,l); T1 = X[8] = l;  ROUND_00_15(8,a,b,c,d,e,f,g,h);
+		HOST_c2l(data,l); T1 = X[9] = l;  ROUND_00_15(9,h,a,b,c,d,e,f,g);
+		HOST_c2l(data,l); T1 = X[10] = l; ROUND_00_15(10,g,h,a,b,c,d,e,f);
+		HOST_c2l(data,l); T1 = X[11] = l; ROUND_00_15(11,f,g,h,a,b,c,d,e);
+		HOST_c2l(data,l); T1 = X[12] = l; ROUND_00_15(12,e,f,g,h,a,b,c,d);
+		HOST_c2l(data,l); T1 = X[13] = l; ROUND_00_15(13,d,e,f,g,h,a,b,c);
+		HOST_c2l(data,l); T1 = X[14] = l; ROUND_00_15(14,c,d,e,f,g,h,a,b);
+		HOST_c2l(data,l); T1 = X[15] = l; ROUND_00_15(15,b,c,d,e,f,g,h,a);
+		}
+
+	for (i=16;i<64;i+=8)
+		{
+		ROUND_16_63(i+0,a,b,c,d,e,f,g,h,X);
+		ROUND_16_63(i+1,h,a,b,c,d,e,f,g,X);
+		ROUND_16_63(i+2,g,h,a,b,c,d,e,f,X);
+		ROUND_16_63(i+3,f,g,h,a,b,c,d,e,X);
+		ROUND_16_63(i+4,e,f,g,h,a,b,c,d,X);
+		ROUND_16_63(i+5,d,e,f,g,h,a,b,c,X);
+		ROUND_16_63(i+6,c,d,e,f,g,h,a,b,X);
+		ROUND_16_63(i+7,b,c,d,e,f,g,h,a,X);
+		}
+
+	ctx->h[0] += a;	ctx->h[1] += b;	ctx->h[2] += c;	ctx->h[3] += d;
+	ctx->h[4] += e;	ctx->h[5] += f;	ctx->h[6] += g;	ctx->h[7] += h;
+
+			}
+	}
+
+/*
+ * Idea is to trade couple of cycles for some space. On IA-32 we save
+ * about 4K in "big footprint" case. In "small footprint" case any gain
+ * is appreciated:-)
+ */
+void HASH_BLOCK_HOST_ORDER (SHA256_CTX *ctx, const void *in, size_t num)
+{   sha256_block (ctx,in,num,1);   }
+
+void HASH_BLOCK_DATA_ORDER (SHA256_CTX *ctx, const void *in, size_t num)
+{   sha256_block (ctx,in,num,0);   }
+
+
diff --git a/src/libutil/sha256.h b/src/libutil/sha256.h
new file mode 100644
index 000000000000..0686b84f0e08
--- /dev/null
+++ b/src/libutil/sha256.h
@@ -0,0 +1,35 @@
+#ifndef _SHA256_H
+#define _SHA256_H 1
+
+#include <inttypes.h>
+
+#define SHA_LBLOCK	16
+#define SHA_CBLOCK	(SHA_LBLOCK*4)	/* SHA treats input data as a
+					 * contiguous array of 32 bit
+					 * wide big-endian values. */
+
+#define SHA256_CBLOCK	(SHA_LBLOCK*4)	/* SHA-256 treats input data as a
+					 * contiguous array of 32 bit
+					 * wide big-endian values. */
+#define SHA224_DIGEST_LENGTH	28
+#define SHA256_DIGEST_LENGTH	32
+
+typedef struct SHA256state_st
+	{
+	uint32_t h[8];
+	uint32_t Nl,Nh;
+	uint32_t data[SHA_LBLOCK];
+	unsigned int num,md_len;
+	} SHA256_CTX;
+
+int SHA224_Init(SHA256_CTX *c);
+int SHA224_Update(SHA256_CTX *c, const void *data, size_t len);
+int SHA224_Final(unsigned char *md, SHA256_CTX *c);
+unsigned char *SHA224(const unsigned char *d, size_t n,unsigned char *md);
+int SHA256_Init(SHA256_CTX *c);
+int SHA256_Update(SHA256_CTX *c, const void *data, size_t len);
+int SHA256_Final(unsigned char *md, SHA256_CTX *c);
+unsigned char *SHA256(const unsigned char *d, size_t n,unsigned char *md);
+void SHA256_Transform(SHA256_CTX *c, const unsigned char *data);
+
+#endif
diff --git a/src/libutil/types.hh b/src/libutil/types.hh
new file mode 100644
index 000000000000..a2ab1cc0ee83
--- /dev/null
+++ b/src/libutil/types.hh
@@ -0,0 +1,77 @@
+#pragma once
+
+#include "config.h"
+
+#include <string>
+#include <list>
+#include <set>
+
+#include <boost/format.hpp>
+
+
+namespace nix {
+
+
+/* Inherit some names from other namespaces for convenience. */
+using std::string;
+using std::list;
+using std::set;
+using std::vector;
+using boost::format;
+
+
+/* BaseError should generally not be caught, as it has Interrupted as
+   a subclass. Catch Error instead. */
+class BaseError : public std::exception 
+{
+protected:
+    string prefix_; // used for location traces etc.
+    string err;
+public:
+    unsigned int status; // exit status
+    BaseError(const format & f, unsigned int status = 1);
+    ~BaseError() throw () { };
+    const char * what() const throw () { return err.c_str(); }
+    const string & msg() const throw () { return err; }
+    const string & prefix() const throw () { return prefix_; }
+    BaseError & addPrefix(const format & f);
+};
+
+#define MakeError(newClass, superClass) \
+    class newClass : public superClass                  \
+    {                                                   \
+    public:                                             \
+        newClass(const format & f, unsigned int status = 1) : superClass(f, status) { }; \
+    };
+
+MakeError(Error, BaseError)
+
+class SysError : public Error
+{
+public:
+    int errNo;
+    SysError(const format & f);
+};
+
+
+typedef list<string> Strings;
+typedef set<string> StringSet;
+
+
+/* Paths are just strings. */
+typedef string Path;
+typedef list<Path> Paths;
+typedef set<Path> PathSet;
+
+ 
+typedef enum { 
+    lvlError = 0,
+    lvlInfo,
+    lvlTalkative,
+    lvlChatty,
+    lvlDebug,
+    lvlVomit
+} Verbosity;
+
+
+}
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
new file mode 100644
index 000000000000..9437a2f99a3c
--- /dev/null
+++ b/src/libutil/util.cc
@@ -0,0 +1,1145 @@
+#include "config.h"
+
+#include <iostream>
+#include <cerrno>
+#include <cstdio>
+#include <cstdlib>
+#include <sstream>
+#include <cstring>
+
+#include <sys/wait.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <limits.h>
+
+#ifdef __APPLE__
+#include <sys/syscall.h>
+#endif
+
+#include "util.hh"
+
+
+extern char * * environ;
+
+
+namespace nix {
+
+
+BaseError::BaseError(const format & f, unsigned int status)
+    : status(status)
+{
+    err = f.str();
+}
+
+
+BaseError & BaseError::addPrefix(const format & f)
+{
+    prefix_ = f.str() + prefix_;
+    return *this;
+}
+
+
+SysError::SysError(const format & f)
+    : Error(format("%1%: %2%") % f.str() % strerror(errno))
+    , errNo(errno)
+{
+}
+
+
+string getEnv(const string & key, const string & def)
+{
+    char * value = getenv(key.c_str());
+    return value ? string(value) : def;
+}
+
+
+Path absPath(Path path, Path dir)
+{
+    if (path[0] != '/') {
+        if (dir == "") {
+#ifdef __GNU__
+            /* GNU (aka. GNU/Hurd) doesn't have any limitation on path
+               lengths and doesn't define `PATH_MAX'.  */
+            char *buf = getcwd(NULL, 0);
+            if (buf == NULL)
+#else
+            char buf[PATH_MAX];
+            if (!getcwd(buf, sizeof(buf)))
+#endif
+                throw SysError("cannot get cwd");
+            dir = buf;
+#ifdef __GNU__
+            free(buf);
+#endif
+        }
+        path = dir + "/" + path;
+    }
+    return canonPath(path);
+}
+
+
+Path canonPath(const Path & path, bool resolveSymlinks)
+{
+    string s;
+
+    if (path[0] != '/')
+        throw Error(format("not an absolute path: `%1%'") % path);
+
+    string::const_iterator i = path.begin(), end = path.end();
+    string temp;
+
+    /* Count the number of times we follow a symlink and stop at some
+       arbitrary (but high) limit to prevent infinite loops. */
+    unsigned int followCount = 0, maxFollow = 1024;
+
+    while (1) {
+
+        /* Skip slashes. */
+        while (i != end && *i == '/') i++;
+        if (i == end) break;
+
+        /* Ignore `.'. */
+        if (*i == '.' && (i + 1 == end || i[1] == '/'))
+            i++;
+
+        /* If `..', delete the last component. */
+        else if (*i == '.' && i + 1 < end && i[1] == '.' &&
+            (i + 2 == end || i[2] == '/'))
+        {
+            if (!s.empty()) s.erase(s.rfind('/'));
+            i += 2;
+        }
+
+        /* Normal component; copy it. */
+        else {
+            s += '/';
+            while (i != end && *i != '/') s += *i++;
+
+            /* If s points to a symlink, resolve it and restart (since
+               the symlink target might contain new symlinks). */
+            if (resolveSymlinks && isLink(s)) {
+                if (++followCount >= maxFollow)
+                    throw Error(format("infinite symlink recursion in path `%1%'") % path);
+                temp = absPath(readLink(s), dirOf(s))
+                    + string(i, end);
+                i = temp.begin(); /* restart */
+                end = temp.end();
+                s = "";
+                /* !!! potential for infinite loop */
+            }
+        }
+    }
+
+    return s.empty() ? "/" : s;
+}
+
+
+Path dirOf(const Path & path)
+{
+    Path::size_type pos = path.rfind('/');
+    if (pos == string::npos)
+        throw Error(format("invalid file name `%1%'") % path);
+    return pos == 0 ? "/" : Path(path, 0, pos);
+}
+
+
+string baseNameOf(const Path & path)
+{
+    Path::size_type pos = path.rfind('/');
+    if (pos == string::npos)
+        throw Error(format("invalid file name `%1%'") % path);
+    return string(path, pos + 1);
+}
+
+
+bool isInDir(const Path & path, const Path & dir)
+{
+    return path[0] == '/'
+        && string(path, 0, dir.size()) == dir
+        && path.size() >= dir.size() + 2
+        && path[dir.size()] == '/';
+}
+
+
+struct stat lstat(const Path & path)
+{
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+        throw SysError(format("getting status of `%1%'") % path);
+    return st;
+}
+
+
+bool pathExists(const Path & path)
+{
+    int res;
+    struct stat st;
+    res = lstat(path.c_str(), &st);
+    if (!res) return true;
+    if (errno != ENOENT && errno != ENOTDIR)
+        throw SysError(format("getting status of %1%") % path);
+    return false;
+}
+
+
+Path readLink(const Path & path)
+{
+    checkInterrupt();
+    struct stat st = lstat(path);
+    if (!S_ISLNK(st.st_mode))
+        throw Error(format("`%1%' is not a symlink") % path);
+    char buf[st.st_size];
+    if (readlink(path.c_str(), buf, st.st_size) != st.st_size)
+        throw SysError(format("reading symbolic link `%1%'") % path);
+    return string(buf, st.st_size);
+}
+
+
+bool isLink(const Path & path)
+{
+    struct stat st = lstat(path);
+    return S_ISLNK(st.st_mode);
+}
+
+
+Strings readDirectory(const Path & path)
+{
+    Strings names;
+
+    AutoCloseDir dir = opendir(path.c_str());
+    if (!dir) throw SysError(format("opening directory `%1%'") % path);
+
+    struct dirent * dirent;
+    while (errno = 0, dirent = readdir(dir)) { /* sic */
+        checkInterrupt();
+        string name = dirent->d_name;
+        if (name == "." || name == "..") continue;
+        names.push_back(name);
+    }
+    if (errno) throw SysError(format("reading directory `%1%'") % path);
+
+    return names;
+}
+
+
+string readFile(int fd)
+{
+    struct stat st;
+    if (fstat(fd, &st) == -1)
+        throw SysError("statting file");
+
+    unsigned char * buf = new unsigned char[st.st_size];
+    AutoDeleteArray<unsigned char> d(buf);
+    readFull(fd, buf, st.st_size);
+
+    return string((char *) buf, st.st_size);
+}
+
+
+string readFile(const Path & path, bool drain)
+{
+    AutoCloseFD fd = open(path.c_str(), O_RDONLY);
+    if (fd == -1)
+        throw SysError(format("opening file `%1%'") % path);
+    return drain ? drainFD(fd) : readFile(fd);
+}
+
+
+void writeFile(const Path & path, const string & s)
+{
+    AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
+    if (fd == -1)
+        throw SysError(format("opening file `%1%'") % path);
+    writeFull(fd, (unsigned char *) s.data(), s.size());
+}
+
+
+string readLine(int fd)
+{
+    string s;
+    while (1) {
+        checkInterrupt();
+        char ch;
+        ssize_t rd = read(fd, &ch, 1);
+        if (rd == -1) {
+            if (errno != EINTR)
+                throw SysError("reading a line");
+        } else if (rd == 0)
+            throw EndOfFile("unexpected EOF reading a line");
+        else {
+            if (ch == '\n') return s;
+            s += ch;
+        }
+    }
+}
+
+
+void writeLine(int fd, string s)
+{
+    s += '\n';
+    writeFull(fd, (const unsigned char *) s.data(), s.size());
+}
+
+
+static void _computePathSize(const Path & path,
+    unsigned long long & bytes, unsigned long long & blocks)
+{
+    checkInterrupt();
+
+    struct stat st = lstat(path);
+
+    bytes += st.st_size;
+    blocks += st.st_blocks;
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+
+        for (Strings::iterator i = names.begin(); i != names.end(); ++i)
+            _computePathSize(path + "/" + *i, bytes, blocks);
+    }
+}
+
+
+void computePathSize(const Path & path,
+    unsigned long long & bytes, unsigned long long & blocks)
+{
+    bytes = 0;
+    blocks = 0;
+    _computePathSize(path, bytes, blocks);
+}
+
+
+static void _deletePath(const Path & path, unsigned long long & bytesFreed)
+{
+    checkInterrupt();
+
+    printMsg(lvlVomit, format("%1%") % path);
+
+    struct stat st = lstat(path);
+
+    if (!S_ISDIR(st.st_mode) && st.st_nlink == 1)
+        bytesFreed += st.st_blocks * 512;
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+
+        /* Make the directory writable. */
+        if (!(st.st_mode & S_IWUSR)) {
+            if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
+                throw SysError(format("making `%1%' writable") % path);
+        }
+
+        for (Strings::iterator i = names.begin(); i != names.end(); ++i)
+            _deletePath(path + "/" + *i, bytesFreed);
+    }
+
+    if (remove(path.c_str()) == -1)
+        throw SysError(format("cannot unlink `%1%'") % path);
+}
+
+
+void deletePath(const Path & path)
+{
+    unsigned long long dummy;
+    deletePath(path, dummy);
+}
+
+
+void deletePath(const Path & path, unsigned long long & bytesFreed)
+{
+    startNest(nest, lvlDebug,
+        format("recursively deleting path `%1%'") % path);
+    bytesFreed = 0;
+    _deletePath(path, bytesFreed);
+}
+
+
+void makePathReadOnly(const Path & path)
+{
+    checkInterrupt();
+
+    struct stat st = lstat(path);
+
+    if (!S_ISLNK(st.st_mode) && (st.st_mode & S_IWUSR)) {
+        if (chmod(path.c_str(), st.st_mode & ~S_IWUSR) == -1)
+            throw SysError(format("making `%1%' read-only") % path);
+    }
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+        for (Strings::iterator i = names.begin(); i != names.end(); ++i)
+            makePathReadOnly(path + "/" + *i);
+    }
+}
+
+
+static Path tempName(Path tmpRoot, const Path & prefix, bool includePid,
+    int & counter)
+{
+    tmpRoot = canonPath(tmpRoot.empty() ? getEnv("TMPDIR", "/tmp") : tmpRoot, true);
+    if (includePid)
+        return (format("%1%/%2%-%3%-%4%") % tmpRoot % prefix % getpid() % counter++).str();
+    else
+        return (format("%1%/%2%-%3%") % tmpRoot % prefix % counter++).str();
+}
+
+
+Path createTempDir(const Path & tmpRoot, const Path & prefix,
+    bool includePid, bool useGlobalCounter, mode_t mode)
+{
+    static int globalCounter = 0;
+    int localCounter = 0;
+    int & counter(useGlobalCounter ? globalCounter : localCounter);
+
+    while (1) {
+        checkInterrupt();
+        Path tmpDir = tempName(tmpRoot, prefix, includePid, counter);
+        if (mkdir(tmpDir.c_str(), mode) == 0) {
+            /* Explicitly set the group of the directory.  This is to
+               work around around problems caused by BSD's group
+               ownership semantics (directories inherit the group of
+               the parent).  For instance, the group of /tmp on
+               FreeBSD is "wheel", so all directories created in /tmp
+               will be owned by "wheel"; but if the user is not in
+               "wheel", then "tar" will fail to unpack archives that
+               have the setgid bit set on directories. */
+            if (chown(tmpDir.c_str(), (uid_t) -1, getegid()) != 0)
+                throw SysError(format("setting group of directory `%1%'") % tmpDir);
+            return tmpDir;
+        }
+        if (errno != EEXIST)
+            throw SysError(format("creating directory `%1%'") % tmpDir);
+    }
+}
+
+
+Paths createDirs(const Path & path)
+{
+    Paths created;
+    if (path == "/") return created;
+
+    struct stat st;
+    if (lstat(path.c_str(), &st) == -1) {
+        created = createDirs(dirOf(path));
+        if (mkdir(path.c_str(), 0777) == -1 && errno != EEXIST)
+            throw SysError(format("creating directory `%1%'") % path);
+        st = lstat(path);
+        created.push_back(path);
+    }
+
+    if (!S_ISDIR(st.st_mode)) throw Error(format("`%1%' is not a directory") % path);
+
+    return created;
+}
+
+
+LogType logType = ltPretty;
+Verbosity verbosity = lvlInfo;
+
+static int nestingLevel = 0;
+
+
+Nest::Nest()
+{
+    nest = false;
+}
+
+
+Nest::~Nest()
+{
+    close();
+}
+
+
+static string escVerbosity(Verbosity level)
+{
+    return int2String((int) level);
+}
+
+
+void Nest::open(Verbosity level, const format & f)
+{
+    if (level <= verbosity) {
+        if (logType == ltEscapes)
+            std::cerr << "\033[" << escVerbosity(level) << "p"
+                      << f.str() << "\n";
+        else
+            printMsg_(level, f);
+        nest = true;
+        nestingLevel++;
+    }
+}
+
+
+void Nest::close()
+{
+    if (nest) {
+        nestingLevel--;
+        if (logType == ltEscapes)
+            std::cerr << "\033[q";
+        nest = false;
+    }
+}
+
+
+void printMsg_(Verbosity level, const format & f)
+{
+    checkInterrupt();
+    if (level > verbosity) return;
+    string prefix;
+    if (logType == ltPretty)
+        for (int i = 0; i < nestingLevel; i++)
+            prefix += "|   ";
+    else if (logType == ltEscapes && level != lvlInfo)
+        prefix = "\033[" + escVerbosity(level) + "s";
+    string s = (format("%1%%2%\n") % prefix % f.str()).str();
+    writeToStderr(s);
+}
+
+
+void warnOnce(bool & haveWarned, const format & f)
+{
+    if (!haveWarned) {
+        printMsg(lvlError, format("warning: %1%") % f.str());
+        haveWarned = true;
+    }
+}
+
+
+void writeToStderr(const string & s)
+{
+    try {
+        _writeToStderr((const unsigned char *) s.data(), s.size());
+    } catch (SysError & e) {
+        /* Ignore failing writes to stderr if we're in an exception
+           handler, otherwise throw an exception.  We need to ignore
+           write errors in exception handlers to ensure that cleanup
+           code runs to completion if the other side of stderr has
+           been closed unexpectedly. */
+        if (!std::uncaught_exception()) throw;
+    }
+}
+
+
+static void defaultWriteToStderr(const unsigned char * buf, size_t count)
+{
+    writeFull(STDERR_FILENO, buf, count);
+}
+
+
+void (*_writeToStderr) (const unsigned char * buf, size_t count) = defaultWriteToStderr;
+
+
+void readFull(int fd, unsigned char * buf, size_t count)
+{
+    while (count) {
+        checkInterrupt();
+        ssize_t res = read(fd, (char *) buf, count);
+        if (res == -1) {
+            if (errno == EINTR) continue;
+            throw SysError("reading from file");
+        }
+        if (res == 0) throw EndOfFile("unexpected end-of-file");
+        count -= res;
+        buf += res;
+    }
+}
+
+
+void writeFull(int fd, const unsigned char * buf, size_t count)
+{
+    while (count) {
+        checkInterrupt();
+        ssize_t res = write(fd, (char *) buf, count);
+        if (res == -1) {
+            if (errno == EINTR) continue;
+            throw SysError("writing to file");
+        }
+        count -= res;
+        buf += res;
+    }
+}
+
+
+string drainFD(int fd)
+{
+    string result;
+    unsigned char buffer[4096];
+    while (1) {
+        checkInterrupt();
+        ssize_t rd = read(fd, buffer, sizeof buffer);
+        if (rd == -1) {
+            if (errno != EINTR)
+                throw SysError("reading from file");
+        }
+        else if (rd == 0) break;
+        else result.append((char *) buffer, rd);
+    }
+    return result;
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+AutoDelete::AutoDelete(const string & p, bool recursive) : path(p)
+{
+    del = true;
+    this->recursive = recursive;
+}
+
+AutoDelete::~AutoDelete()
+{
+    try {
+        if (del) {
+            if (recursive)
+                deletePath(path);
+            else {
+                if (remove(path.c_str()) == -1)
+                    throw SysError(format("cannot unlink `%1%'") % path);
+            }
+        }
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+void AutoDelete::cancel()
+{
+    del = false;
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+AutoCloseFD::AutoCloseFD()
+{
+    fd = -1;
+}
+
+
+AutoCloseFD::AutoCloseFD(int fd)
+{
+    this->fd = fd;
+}
+
+
+AutoCloseFD::AutoCloseFD(const AutoCloseFD & fd)
+{
+    /* Copying an AutoCloseFD isn't allowed (who should get to close
+       it?).  But as an edge case, allow copying of closed
+       AutoCloseFDs.  This is necessary due to tiresome reasons
+       involving copy constructor use on default object values in STL
+       containers (like when you do `map[value]' where value isn't in
+       the map yet). */
+    this->fd = fd.fd;
+    if (this->fd != -1) abort();
+}
+
+
+AutoCloseFD::~AutoCloseFD()
+{
+    try {
+        close();
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+void AutoCloseFD::operator =(int fd)
+{
+    if (this->fd != fd) close();
+    this->fd = fd;
+}
+
+
+AutoCloseFD::operator int() const
+{
+    return fd;
+}
+
+
+void AutoCloseFD::close()
+{
+    if (fd != -1) {
+        if (::close(fd) == -1)
+            /* This should never happen. */
+            throw SysError(format("closing file descriptor %1%") % fd);
+        fd = -1;
+    }
+}
+
+
+bool AutoCloseFD::isOpen()
+{
+    return fd != -1;
+}
+
+
+/* Pass responsibility for closing this fd to the caller. */
+int AutoCloseFD::borrow()
+{
+    int oldFD = fd;
+    fd = -1;
+    return oldFD;
+}
+
+
+void Pipe::create()
+{
+    int fds[2];
+    if (pipe(fds) != 0) throw SysError("creating pipe");
+    readSide = fds[0];
+    writeSide = fds[1];
+    closeOnExec(readSide);
+    closeOnExec(writeSide);
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+AutoCloseDir::AutoCloseDir()
+{
+    dir = 0;
+}
+
+
+AutoCloseDir::AutoCloseDir(DIR * dir)
+{
+    this->dir = dir;
+}
+
+
+AutoCloseDir::~AutoCloseDir()
+{
+    close();
+}
+
+
+void AutoCloseDir::operator =(DIR * dir)
+{
+    this->dir = dir;
+}
+
+
+AutoCloseDir::operator DIR *()
+{
+    return dir;
+}
+
+
+void AutoCloseDir::close()
+{
+    if (dir) {
+        closedir(dir);
+        dir = 0;
+    }
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+Pid::Pid()
+{
+    pid = -1;
+    separatePG = false;
+    killSignal = SIGKILL;
+}
+
+
+Pid::~Pid()
+{
+    kill();
+}
+
+
+void Pid::operator =(pid_t pid)
+{
+    if (this->pid != pid) kill();
+    this->pid = pid;
+    killSignal = SIGKILL; // reset signal to default
+}
+
+
+Pid::operator pid_t()
+{
+    return pid;
+}
+
+
+void Pid::kill()
+{
+    if (pid == -1 || pid == 0) return;
+
+    printMsg(lvlError, format("killing process %1%") % pid);
+
+    /* Send the requested signal to the child.  If it has its own
+       process group, send the signal to every process in the child
+       process group (which hopefully includes *all* its children). */
+    if (::kill(separatePG ? -pid : pid, killSignal) != 0)
+        printMsg(lvlError, (SysError(format("killing process %1%") % pid).msg()));
+
+    /* Wait until the child dies, disregarding the exit status. */
+    int status;
+    while (waitpid(pid, &status, 0) == -1) {
+        checkInterrupt();
+        if (errno != EINTR) {
+            printMsg(lvlError,
+                (SysError(format("waiting for process %1%") % pid).msg()));
+            break;
+        }
+    }
+
+    pid = -1;
+}
+
+
+int Pid::wait(bool block)
+{
+    assert(pid != -1);
+    while (1) {
+        int status;
+        int res = waitpid(pid, &status, block ? 0 : WNOHANG);
+        if (res == pid) {
+            pid = -1;
+            return status;
+        }
+        if (res == 0 && !block) return -1;
+        if (errno != EINTR)
+            throw SysError("cannot get child exit status");
+        checkInterrupt();
+    }
+}
+
+
+void Pid::setSeparatePG(bool separatePG)
+{
+    this->separatePG = separatePG;
+}
+
+
+void Pid::setKillSignal(int signal)
+{
+    this->killSignal = signal;
+}
+
+
+void killUser(uid_t uid)
+{
+    debug(format("killing all processes running under uid `%1%'") % uid);
+
+    assert(uid != 0); /* just to be safe... */
+
+    /* The system call kill(-1, sig) sends the signal `sig' to all
+       users to which the current process can send signals.  So we
+       fork a process, switch to uid, and send a mass kill. */
+
+    Pid pid;
+    pid = fork();
+    switch (pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0:
+        try { /* child */
+
+            if (setuid(uid) == -1)
+                throw SysError("setting uid");
+
+            while (true) {
+#ifdef __APPLE__
+                /* OSX's kill syscall takes a third parameter that, among other
+                   things, determines if kill(-1, signo) affects the calling
+                   process. In the OSX libc, it's set to true, which means
+                   "follow POSIX", which we don't want here
+                 */
+                if (syscall(SYS_kill, -1, SIGKILL, false) == 0) break;
+#else
+                if (kill(-1, SIGKILL) == 0) break;
+#endif
+                if (errno == ESRCH) break; /* no more processes */
+                if (errno != EINTR)
+                    throw SysError(format("cannot kill processes for uid `%1%'") % uid);
+            }
+
+        } catch (std::exception & e) {
+            writeToStderr((format("killing processes belonging to uid `%1%': %2%\n") % uid % e.what()).str());
+            _exit(1);
+        }
+        _exit(0);
+    }
+
+    /* parent */
+    int status = pid.wait(true);
+    if (status != 0)
+        throw Error(format("cannot kill processes for uid `%1%': %2%") % uid % statusToString(status));
+
+    /* !!! We should really do some check to make sure that there are
+       no processes left running under `uid', but there is no portable
+       way to do so (I think).  The most reliable way may be `ps -eo
+       uid | grep -q $uid'. */
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+string runProgram(Path program, bool searchPath, const Strings & args)
+{
+    checkInterrupt();
+
+    std::vector<const char *> cargs; /* careful with c_str()! */
+    cargs.push_back(program.c_str());
+    for (Strings::const_iterator i = args.begin(); i != args.end(); ++i)
+        cargs.push_back(i->c_str());
+    cargs.push_back(0);
+
+    /* Create a pipe. */
+    Pipe pipe;
+    pipe.create();
+
+    /* Fork. */
+    Pid pid;
+    pid = maybeVfork();
+
+    switch (pid) {
+
+    case -1:
+        throw SysError("unable to fork");
+
+    case 0: /* child */
+        try {
+            if (dup2(pipe.writeSide, STDOUT_FILENO) == -1)
+                throw SysError("dupping stdout");
+
+            if (searchPath)
+                execvp(program.c_str(), (char * *) &cargs[0]);
+            else
+                execv(program.c_str(), (char * *) &cargs[0]);
+            throw SysError(format("executing `%1%'") % program);
+
+        } catch (std::exception & e) {
+            writeToStderr("error: " + string(e.what()) + "\n");
+        }
+        _exit(1);
+    }
+
+    /* Parent. */
+
+    pipe.writeSide.close();
+
+    string result = drainFD(pipe.readSide);
+
+    /* Wait for the child to finish. */
+    int status = pid.wait(true);
+    if (!statusOk(status))
+        throw Error(format("program `%1%' %2%")
+            % program % statusToString(status));
+
+    return result;
+}
+
+
+void closeMostFDs(const set<int> & exceptions)
+{
+    int maxFD = 0;
+    maxFD = sysconf(_SC_OPEN_MAX);
+    for (int fd = 0; fd < maxFD; ++fd)
+        if (fd != STDIN_FILENO && fd != STDOUT_FILENO && fd != STDERR_FILENO
+            && exceptions.find(fd) == exceptions.end())
+            close(fd); /* ignore result */
+}
+
+
+void closeOnExec(int fd)
+{
+    int prev;
+    if ((prev = fcntl(fd, F_GETFD, 0)) == -1 ||
+        fcntl(fd, F_SETFD, prev | FD_CLOEXEC) == -1)
+        throw SysError("setting close-on-exec flag");
+}
+
+
+#if HAVE_VFORK
+pid_t (*maybeVfork)() = vfork;
+#else
+pid_t (*maybeVfork)() = fork;
+#endif
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+volatile sig_atomic_t _isInterrupted = 0;
+
+void _interrupted()
+{
+    /* Block user interrupts while an exception is being handled.
+       Throwing an exception while another exception is being handled
+       kills the program! */
+    if (!std::uncaught_exception()) {
+        _isInterrupted = 0;
+        throw Interrupted("interrupted by the user");
+    }
+}
+
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+template<class C> C tokenizeString(const string & s, const string & separators)
+{
+    C result;
+    string::size_type pos = s.find_first_not_of(separators, 0);
+    while (pos != string::npos) {
+        string::size_type end = s.find_first_of(separators, pos + 1);
+        if (end == string::npos) end = s.size();
+        string token(s, pos, end - pos);
+        result.insert(result.end(), token);
+        pos = s.find_first_not_of(separators, end);
+    }
+    return result;
+}
+
+template Strings tokenizeString(const string & s, const string & separators);
+template StringSet tokenizeString(const string & s, const string & separators);
+template vector<string> tokenizeString(const string & s, const string & separators);
+
+
+string concatStringsSep(const string & sep, const Strings & ss)
+{
+    string s;
+    foreach (Strings::const_iterator, i, ss) {
+        if (s.size() != 0) s += sep;
+        s += *i;
+    }
+    return s;
+}
+
+
+string concatStringsSep(const string & sep, const StringSet & ss)
+{
+    string s;
+    foreach (StringSet::const_iterator, i, ss) {
+        if (s.size() != 0) s += sep;
+        s += *i;
+    }
+    return s;
+}
+
+
+string chomp(const string & s)
+{
+    size_t i = s.find_last_not_of(" \n\r\t");
+    return i == string::npos ? "" : string(s, 0, i + 1);
+}
+
+
+string statusToString(int status)
+{
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+        if (WIFEXITED(status))
+            return (format("failed with exit code %1%") % WEXITSTATUS(status)).str();
+        else if (WIFSIGNALED(status)) {
+            int sig = WTERMSIG(status);
+#if HAVE_STRSIGNAL
+            const char * description = strsignal(sig);
+            return (format("failed due to signal %1% (%2%)") % sig % description).str();
+#else
+            return (format("failed due to signal %1%") % sig).str();
+#endif
+        }
+        else
+            return "died abnormally";
+    } else return "succeeded";
+}
+
+
+bool statusOk(int status)
+{
+    return WIFEXITED(status) && WEXITSTATUS(status) == 0;
+}
+
+
+bool hasSuffix(const string & s, const string & suffix)
+{
+    return s.size() >= suffix.size() && string(s, s.size() - suffix.size()) == suffix;
+}
+
+
+void expect(std::istream & str, const string & s)
+{
+    char s2[s.size()];
+    str.read(s2, s.size());
+    if (string(s2, s.size()) != s)
+        throw Error(format("expected string `%1%'") % s);
+}
+
+
+string parseString(std::istream & str)
+{
+    string res;
+    expect(str, "\"");
+    int c;
+    while ((c = str.get()) != '"')
+        if (c == '\\') {
+            c = str.get();
+            if (c == 'n') res += '\n';
+            else if (c == 'r') res += '\r';
+            else if (c == 't') res += '\t';
+            else res += c;
+        }
+        else res += c;
+    return res;
+}
+
+
+bool endOfList(std::istream & str)
+{
+    if (str.peek() == ',') {
+        str.get();
+        return false;
+    }
+    if (str.peek() == ']') {
+        str.get();
+        return true;
+    }
+    return false;
+}
+
+
+string decodeOctalEscaped(const string & s)
+{
+    string r;
+    for (string::const_iterator i = s.begin(); i != s.end(); ) {
+        if (*i != '\\') { r += *i++; continue; }
+        unsigned char c = 0;
+        ++i;
+        while (i != s.end() && *i >= '0' && *i < '8')
+            c = c * 8 + (*i++ - '0');
+        r += c;
+    }
+    return r;
+}
+
+
+void ignoreException()
+{
+    try {
+        throw;
+    } catch (std::exception & e) {
+        printMsg(lvlError, format("error (ignored): %1%") % e.what());
+    }
+}
+
+
+}
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
new file mode 100644
index 000000000000..2335cbf98820
--- /dev/null
+++ b/src/libutil/util.hh
@@ -0,0 +1,353 @@
+#pragma once
+
+#include "types.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <dirent.h>
+#include <unistd.h>
+#include <signal.h>
+
+#include <cstdio>
+
+
+namespace nix {
+
+
+#define foreach(it_type, it, collection)                                \
+    for (it_type it = (collection).begin(); it != (collection).end(); ++it)
+
+#define foreach_reverse(it_type, it, collection)                                \
+    for (it_type it = (collection).rbegin(); it != (collection).rend(); ++it)
+
+
+/* Return an environment variable. */
+string getEnv(const string & key, const string & def = "");
+
+/* Return an absolutized path, resolving paths relative to the
+   specified directory, or the current directory otherwise.  The path
+   is also canonicalised. */
+Path absPath(Path path, Path dir = "");
+
+/* Canonicalise a path by removing all `.' or `..' components and
+   double or trailing slashes.  Optionally resolves all symlink
+   components such that each component of the resulting path is *not*
+   a symbolic link. */
+Path canonPath(const Path & path, bool resolveSymlinks = false);
+
+/* Return the directory part of the given canonical path, i.e.,
+   everything before the final `/'.  If the path is the root or an
+   immediate child thereof (e.g., `/foo'), this means an empty string
+   is returned. */
+Path dirOf(const Path & path);
+
+/* Return the base name of the given canonical path, i.e., everything
+   following the final `/'. */
+string baseNameOf(const Path & path);
+
+/* Check whether a given path is a descendant of the given
+   directory. */
+bool isInDir(const Path & path, const Path & dir);
+
+/* Get status of `path'. */
+struct stat lstat(const Path & path);
+
+/* Return true iff the given path exists. */
+bool pathExists(const Path & path);
+
+/* Read the contents (target) of a symbolic link.  The result is not
+   in any way canonicalised. */
+Path readLink(const Path & path);
+
+bool isLink(const Path & path);
+
+/* Read the contents of a directory.  The entries `.' and `..' are
+   removed. */
+Strings readDirectory(const Path & path);
+
+/* Read the contents of a file into a string. */
+string readFile(int fd);
+string readFile(const Path & path, bool drain = false);
+
+/* Write a string to a file. */
+void writeFile(const Path & path, const string & s);
+
+/* Read a line from a file descriptor. */
+string readLine(int fd);
+
+/* Write a line to a file descriptor. */
+void writeLine(int fd, string s);
+
+/* Compute the sum of the sizes of all files in `path'. */
+void computePathSize(const Path & path,
+    unsigned long long & bytes, unsigned long long & blocks);
+
+/* Delete a path; i.e., in the case of a directory, it is deleted
+   recursively.  Don't use this at home, kids.  The second variant
+   returns the number of bytes and blocks freed. */
+void deletePath(const Path & path);
+
+void deletePath(const Path & path, unsigned long long & bytesFreed);
+
+/* Make a path read-only recursively. */
+void makePathReadOnly(const Path & path);
+
+/* Create a temporary directory. */
+Path createTempDir(const Path & tmpRoot = "", const Path & prefix = "nix",
+    bool includePid = true, bool useGlobalCounter = true, mode_t mode = 0755);
+
+/* Create a directory and all its parents, if necessary.  Returns the
+   list of created directories, in order of creation. */
+Paths createDirs(const Path & path);
+
+
+template<class T, class A>
+T singleton(const A & a)
+{
+    T t;
+    t.insert(a);
+    return t;
+}
+
+
+/* Messages. */
+
+
+typedef enum {
+    ltPretty,   /* nice, nested output */
+    ltEscapes,  /* nesting indicated using escape codes (for log2xml) */
+    ltFlat      /* no nesting */
+} LogType;
+
+extern LogType logType;
+extern Verbosity verbosity; /* suppress msgs > this */
+
+class Nest
+{
+private:
+    bool nest;
+public:
+    Nest();
+    ~Nest();
+    void open(Verbosity level, const format & f);
+    void close();
+};
+
+void printMsg_(Verbosity level, const format & f);
+
+#define startNest(varName, level, f) \
+    Nest varName; \
+    if (level <= verbosity) { \
+      varName.open(level, (f)); \
+    }
+
+#define printMsg(level, f) \
+    do { \
+        if (level <= verbosity) { \
+            printMsg_(level, (f)); \
+        } \
+    } while (0)
+
+#define debug(f) printMsg(lvlDebug, f)
+
+void warnOnce(bool & haveWarned, const format & f);
+
+void writeToStderr(const string & s);
+
+extern void (*_writeToStderr) (const unsigned char * buf, size_t count);
+
+
+/* Wrappers arount read()/write() that read/write exactly the
+   requested number of bytes. */
+void readFull(int fd, unsigned char * buf, size_t count);
+void writeFull(int fd, const unsigned char * buf, size_t count);
+
+MakeError(EndOfFile, Error)
+
+
+/* Read a file descriptor until EOF occurs. */
+string drainFD(int fd);
+
+
+
+/* Automatic cleanup of resources. */
+
+
+template <class T>
+struct AutoDeleteArray
+{
+    T * p;
+    AutoDeleteArray(T * p) : p(p) { }
+    ~AutoDeleteArray()
+    {
+        delete [] p;
+    }
+};
+
+
+class AutoDelete
+{
+    Path path;
+    bool del;
+    bool recursive;
+public:
+    AutoDelete(const Path & p, bool recursive = true);
+    ~AutoDelete();
+    void cancel();
+};
+
+
+class AutoCloseFD
+{
+    int fd;
+public:
+    AutoCloseFD();
+    AutoCloseFD(int fd);
+    AutoCloseFD(const AutoCloseFD & fd);
+    ~AutoCloseFD();
+    void operator =(int fd);
+    operator int() const;
+    void close();
+    bool isOpen();
+    int borrow();
+};
+
+
+class Pipe
+{
+public:
+    AutoCloseFD readSide, writeSide;
+    void create();
+};
+
+
+class AutoCloseDir
+{
+    DIR * dir;
+public:
+    AutoCloseDir();
+    AutoCloseDir(DIR * dir);
+    ~AutoCloseDir();
+    void operator =(DIR * dir);
+    operator DIR *();
+    void close();
+};
+
+
+class Pid
+{
+    pid_t pid;
+    bool separatePG;
+    int killSignal;
+public:
+    Pid();
+    ~Pid();
+    void operator =(pid_t pid);
+    operator pid_t();
+    void kill();
+    int wait(bool block);
+    void setSeparatePG(bool separatePG);
+    void setKillSignal(int signal);
+};
+
+
+/* Kill all processes running under the specified uid by sending them
+   a SIGKILL. */
+void killUser(uid_t uid);
+
+
+/* Run a program and return its stdout in a string (i.e., like the
+   shell backtick operator). */
+string runProgram(Path program, bool searchPath = false,
+    const Strings & args = Strings());
+
+/* Close all file descriptors except stdin, stdout, stderr, and those
+   listed in the given set.  Good practice in child processes. */
+void closeMostFDs(const set<int> & exceptions);
+
+/* Set the close-on-exec flag for the given file descriptor. */
+void closeOnExec(int fd);
+
+/* Call vfork() if available, otherwise fork(). */
+extern pid_t (*maybeVfork)();
+
+
+/* User interruption. */
+
+extern volatile sig_atomic_t _isInterrupted;
+
+void _interrupted();
+
+void inline checkInterrupt()
+{
+    if (_isInterrupted) _interrupted();
+}
+
+MakeError(Interrupted, BaseError)
+
+
+/* String tokenizer. */
+template<class C> C tokenizeString(const string & s, const string & separators = " \t\n\r");
+
+
+/* Concatenate the given strings with a separator between the
+   elements. */
+string concatStringsSep(const string & sep, const Strings & ss);
+string concatStringsSep(const string & sep, const StringSet & ss);
+
+
+/* Remove trailing whitespace from a string. */
+string chomp(const string & s);
+
+
+/* Convert the exit status of a child as returned by wait() into an
+   error string. */
+string statusToString(int status);
+
+bool statusOk(int status);
+
+
+/* Parse a string into an integer. */
+template<class N> bool string2Int(const string & s, N & n)
+{
+    std::istringstream str(s);
+    str >> n;
+    return str && str.get() == EOF;
+}
+
+template<class N> string int2String(N n)
+{
+    std::ostringstream str;
+    str << n;
+    return str.str();
+}
+
+
+/* Return true iff `s' ends in `suffix'. */
+bool hasSuffix(const string & s, const string & suffix);
+
+
+/* Read string `s' from stream `str'. */
+void expect(std::istream & str, const string & s);
+
+
+/* Read a C-style string from stream `str'. */
+string parseString(std::istream & str);
+
+
+/* Utility function used to parse legacy ATerms. */
+bool endOfList(std::istream & str);
+
+
+/* Escape a string that contains octal-encoded escape codes such as
+   used in /etc/fstab and /proc/mounts (e.g. "foo\040bar" decodes to
+   "foo bar"). */
+string decodeOctalEscaped(const string & s);
+
+
+/* Exception handling in destructors: print an error message, then
+   ignore the exception. */
+void ignoreException();
+
+
+}
diff --git a/src/libutil/xml-writer.cc b/src/libutil/xml-writer.cc
new file mode 100644
index 000000000000..16dfb6ddc903
--- /dev/null
+++ b/src/libutil/xml-writer.cc
@@ -0,0 +1,131 @@
+#include <assert.h>
+
+#include "xml-writer.hh"
+
+
+namespace nix {
+    
+
+XMLWriter::XMLWriter(bool indent, std::ostream & output)
+    : output(output), indent(indent)
+{
+    output << "<?xml version='1.0' encoding='utf-8'?>" << std::endl;
+    closed = false;
+}
+
+
+XMLWriter::~XMLWriter()
+{
+    close();
+}
+
+
+void XMLWriter::close()
+{
+    if (closed) return;
+    while (!pendingElems.empty()) closeElement();
+    closed = true;
+}
+
+
+void XMLWriter::indent_(unsigned int depth)
+{
+    if (!indent) return;
+    output << string(depth * 2, ' ');
+}
+
+
+void XMLWriter::openElement(const string & name,
+    const XMLAttrs & attrs)
+{
+    assert(!closed);
+    indent_(pendingElems.size());
+    output << "<" << name;
+    writeAttrs(attrs);
+    output << ">";
+    if (indent) output << std::endl;
+    pendingElems.push_back(name);
+}
+
+
+void XMLWriter::closeElement()
+{
+    assert(!pendingElems.empty());
+    indent_(pendingElems.size() - 1);
+    output << "</" << pendingElems.back() << ">";
+    if (indent) output << std::endl;
+    pendingElems.pop_back();
+    if (pendingElems.empty()) closed = true;
+}
+
+
+void XMLWriter::writeEmptyElement(const string & name,
+    const XMLAttrs & attrs)
+{
+    assert(!closed);
+    indent_(pendingElems.size());
+    output << "<" << name;
+    writeAttrs(attrs);
+    output << " />";
+    if (indent) output << std::endl;
+}
+
+
+void XMLWriter::writeCharData(const string & data)
+{
+    assert(!pendingElems.empty());
+    for (unsigned int i = 0; i < data.size(); ++i) {
+        char c = data[i];
+        if (c == '<') output << "&lt;";
+        else if (c == '&') output << "&amp;";
+        else output << c;
+    }
+}
+
+
+void XMLWriter::writeAttrs(const XMLAttrs & attrs)
+{
+    for (XMLAttrs::const_iterator i = attrs.begin(); i != attrs.end(); ++i) {
+        output << " " << i->first << "=\"";
+        for (unsigned int j = 0; j < i->second.size(); ++j) {
+            char c = i->second[j];
+            if (c == '"') output << "&quot;";
+            else if (c == '<') output << "&lt;";
+            else if (c == '>') output << "&gt;";
+            else if (c == '&') output << "&amp;";
+            /* Escape newlines to prevent attribute normalisation (see
+               XML spec, section 3.3.3. */
+            else if (c == '\n') output << "&#xA;";
+            else output << c;
+        }
+        output << "\"";
+    }
+}
+
+
+#if 0
+int main(int argc, char * * argv)
+{
+    XMLWriter doc(cout);
+    
+    //    OpenElement e(doc, "foo");
+
+    doc.openElement("foo");
+
+    doc.writeCharData("dit is een test &\n");
+    doc.writeCharData("<foo>\n");
+
+    for (int i = 0; i < 5; ++i) {
+        XMLAttrs attrs;
+        attrs["a"] = "b";
+        attrs["bla"] = "<foo>'&\">";
+        XMLOpenElement e(doc, "item", attrs);
+        doc.writeCharData("x");
+    }
+
+    return 0;
+}
+#endif
+
+ 
+}
diff --git a/src/libutil/xml-writer.hh b/src/libutil/xml-writer.hh
new file mode 100644
index 000000000000..fee2eb495eaf
--- /dev/null
+++ b/src/libutil/xml-writer.hh
@@ -0,0 +1,71 @@
+#pragma once
+
+#include <iostream>
+#include <string>
+#include <list>
+#include <map>
+
+
+namespace nix {
+
+using std::string;
+using std::map;
+using std::list;
+
+
+typedef map<string, string> XMLAttrs;
+
+
+class XMLWriter
+{
+private:
+    
+    std::ostream & output;
+
+    bool indent;
+    bool closed;
+
+    list<string> pendingElems;
+
+public:
+
+    XMLWriter(bool indent, std::ostream & output);
+    ~XMLWriter();
+
+    void close();
+
+    void openElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+    void closeElement();
+
+    void writeEmptyElement(const string & name,
+        const XMLAttrs & attrs = XMLAttrs());
+    
+    void writeCharData(const string & data);
+
+private:
+    void writeAttrs(const XMLAttrs & attrs);
+
+    void indent_(unsigned int depth);
+};
+
+
+class XMLOpenElement
+{
+private:
+    XMLWriter & writer;
+public:
+    XMLOpenElement(XMLWriter & writer, const string & name,
+        const XMLAttrs & attrs = XMLAttrs())
+        : writer(writer)
+    {
+        writer.openElement(name, attrs);
+    }
+    ~XMLOpenElement()
+    {
+        writer.closeElement();
+    }
+};
+
+ 
+}
diff --git a/src/nix-daemon/local.mk b/src/nix-daemon/local.mk
new file mode 100644
index 000000000000..db071a3f7c7e
--- /dev/null
+++ b/src/nix-daemon/local.mk
@@ -0,0 +1,9 @@
+programs += nix-daemon
+
+nix-daemon_DIR := $(d)
+
+nix-daemon_SOURCES := $(d)/nix-daemon.cc
+
+nix-daemon_LIBS = libmain libstore libutil libformat
+
+$(eval $(call install-symlink, nix-daemon, $(bindir)/nix-worker))
diff --git a/src/nix-daemon/nix-daemon.cc b/src/nix-daemon/nix-daemon.cc
new file mode 100644
index 000000000000..58ef2109b313
--- /dev/null
+++ b/src/nix-daemon/nix-daemon.cc
@@ -0,0 +1,932 @@
+#include "shared.hh"
+#include "local-store.hh"
+#include "util.hh"
+#include "serialise.hh"
+#include "worker-protocol.hh"
+#include "archive.hh"
+#include "affinity.hh"
+#include "globals.hh"
+
+#include <cstring>
+#include <unistd.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <fcntl.h>
+#include <errno.h>
+
+using namespace nix;
+
+
+/* On platforms that have O_ASYNC, we can detect when a client
+   disconnects and immediately kill any ongoing builds.  On platforms
+   that lack it, we only notice the disconnection the next time we try
+   to write to the client.  So if you have a builder that never
+   generates output on stdout/stderr, the daemon will never notice
+   that the client has disconnected until the builder terminates.
+
+   GNU/Hurd does have O_ASYNC, but its Unix-domain socket translator
+   (pflocal) does not implement F_SETOWN.  See
+   <http://lists.gnu.org/archive/html/bug-guix/2013-07/msg00021.html> for
+   details.*/
+#if defined O_ASYNC && !defined __GNU__
+#define HAVE_HUP_NOTIFICATION
+#ifndef SIGPOLL
+#define SIGPOLL SIGIO
+#endif
+#endif
+
+
+static FdSource from(STDIN_FILENO);
+static FdSink to(STDOUT_FILENO);
+
+bool canSendStderr;
+pid_t myPid;
+
+
+
+/* This function is called anytime we want to write something to
+   stderr.  If we're in a state where the protocol allows it (i.e.,
+   when canSendStderr), send the message to the client over the
+   socket. */
+static void tunnelStderr(const unsigned char * buf, size_t count)
+{
+    /* Don't send the message to the client if we're a child of the
+       process handling the connection.  Otherwise we could screw up
+       the protocol.  It's up to the parent to redirect stderr and
+       send it to the client somehow (e.g., as in build.cc). */
+    if (canSendStderr && myPid == getpid()) {
+        try {
+            writeInt(STDERR_NEXT, to);
+            writeString(buf, count, to);
+            to.flush();
+        } catch (...) {
+            /* Write failed; that means that the other side is
+               gone. */
+            canSendStderr = false;
+            throw;
+        }
+    } else
+        writeFull(STDERR_FILENO, buf, count);
+}
+
+
+/* Return true if the remote side has closed its end of the
+   connection, false otherwise.  Should not be called on any socket on
+   which we expect input! */
+static bool isFarSideClosed(int socket)
+{
+    struct timeval timeout;
+    timeout.tv_sec = timeout.tv_usec = 0;
+
+    fd_set fds;
+    FD_ZERO(&fds);
+    FD_SET(socket, &fds);
+
+    while (select(socket + 1, &fds, 0, 0, &timeout) == -1)
+        if (errno != EINTR) throw SysError("select()");
+
+    if (!FD_ISSET(socket, &fds)) return false;
+
+    /* Destructive read to determine whether the select() marked the
+       socket as readable because there is actual input or because
+       we've reached EOF (i.e., a read of size 0 is available). */
+    char c;
+    int rd;
+    if ((rd = read(socket, &c, 1)) > 0)
+        throw Error("EOF expected (protocol error?)");
+    else if (rd == -1 && errno != ECONNRESET)
+        throw SysError("expected connection reset or EOF");
+
+    return true;
+}
+
+
+/* A SIGPOLL signal is received when data is available on the client
+   communication socket, or when the client has closed its side of the
+   socket.  This handler is enabled at precisely those moments in the
+   protocol when we're doing work and the client is supposed to be
+   quiet.  Thus, if we get a SIGPOLL signal, it means that the client
+   has quit.  So we should quit as well.
+
+   Too bad most operating systems don't support the POLL_HUP value for
+   si_code in siginfo_t.  That would make most of the SIGPOLL
+   complexity unnecessary, i.e., we could just enable SIGPOLL all the
+   time and wouldn't have to worry about races. */
+static void sigPollHandler(int sigNo)
+{
+    using namespace std;
+    try {
+        /* Check that the far side actually closed.  We're still
+           getting spurious signals every once in a while.  I.e.,
+           there is no input available, but we get a signal with
+           POLL_IN set.  Maybe it's delayed or something. */
+        if (isFarSideClosed(from.fd)) {
+            if (!blockInt) {
+                _isInterrupted = 1;
+                blockInt = 1;
+                canSendStderr = false;
+                const char * s = "SIGPOLL\n";
+                write(STDERR_FILENO, s, strlen(s));
+            }
+        } else {
+            const char * s = "spurious SIGPOLL\n";
+            write(STDERR_FILENO, s, strlen(s));
+        }
+    }
+    catch (Error & e) {
+        /* Shouldn't happen. */
+        string s = "impossible: " + e.msg() + '\n';
+        write(STDERR_FILENO, s.data(), s.size());
+        throw;
+    }
+}
+
+
+static void setSigPollAction(bool enable)
+{
+#ifdef HAVE_HUP_NOTIFICATION
+    struct sigaction act, oact;
+    act.sa_handler = enable ? sigPollHandler : SIG_IGN;
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    if (sigaction(SIGPOLL, &act, &oact))
+        throw SysError("setting handler for SIGPOLL");
+#endif
+}
+
+
+/* startWork() means that we're starting an operation for which we
+   want to send out stderr to the client. */
+static void startWork()
+{
+    canSendStderr = true;
+
+    /* Handle client death asynchronously. */
+    setSigPollAction(true);
+
+    /* Of course, there is a race condition here: the socket could
+       have closed between when we last read from / wrote to it, and
+       between the time we set the handler for SIGPOLL.  In that case
+       we won't get the signal.  So do a non-blocking select() to find
+       out if any input is available on the socket.  If there is, it
+       has to be the 0-byte read that indicates that the socket has
+       closed. */
+    if (isFarSideClosed(from.fd)) {
+        _isInterrupted = 1;
+        checkInterrupt();
+    }
+}
+
+
+/* stopWork() means that we're done; stop sending stderr to the
+   client. */
+static void stopWork(bool success = true, const string & msg = "", unsigned int status = 0)
+{
+    /* Stop handling async client death; we're going to a state where
+       we're either sending or receiving from the client, so we'll be
+       notified of client death anyway. */
+    setSigPollAction(false);
+
+    canSendStderr = false;
+
+    if (success)
+        writeInt(STDERR_LAST, to);
+    else {
+        writeInt(STDERR_ERROR, to);
+        writeString(msg, to);
+        if (status != 0) writeInt(status, to);
+    }
+}
+
+
+struct TunnelSink : Sink
+{
+    Sink & to;
+    TunnelSink(Sink & to) : to(to) { }
+    virtual void operator () (const unsigned char * data, size_t len)
+    {
+        writeInt(STDERR_WRITE, to);
+        writeString(data, len, to);
+    }
+};
+
+
+struct TunnelSource : BufferedSource
+{
+    Source & from;
+    TunnelSource(Source & from) : from(from) { }
+    size_t readUnbuffered(unsigned char * data, size_t len)
+    {
+        /* Careful: we're going to receive data from the client now,
+           so we have to disable the SIGPOLL handler. */
+        setSigPollAction(false);
+        canSendStderr = false;
+
+        writeInt(STDERR_READ, to);
+        writeInt(len, to);
+        to.flush();
+        size_t n = readString(data, len, from);
+
+        startWork();
+        if (n == 0) throw EndOfFile("unexpected end-of-file");
+        return n;
+    }
+};
+
+
+/* If the NAR archive contains a single file at top-level, then save
+   the contents of the file to `s'.  Otherwise barf. */
+struct RetrieveRegularNARSink : ParseSink
+{
+    bool regular;
+    string s;
+
+    RetrieveRegularNARSink() : regular(true) { }
+
+    void createDirectory(const Path & path)
+    {
+        regular = false;
+    }
+
+    void receiveContents(unsigned char * data, unsigned int len)
+    {
+        s.append((const char *) data, len);
+    }
+
+    void createSymlink(const Path & path, const string & target)
+    {
+        regular = false;
+    }
+};
+
+
+/* Adapter class of a Source that saves all data read to `s'. */
+struct SavingSourceAdapter : Source
+{
+    Source & orig;
+    string s;
+    SavingSourceAdapter(Source & orig) : orig(orig) { }
+    size_t read(unsigned char * data, size_t len)
+    {
+        size_t n = orig.read(data, len);
+        s.append((const char *) data, n);
+        return n;
+    }
+};
+
+
+static void performOp(bool trusted, unsigned int clientVersion,
+    Source & from, Sink & to, unsigned int op)
+{
+    switch (op) {
+
+#if 0
+    case wopQuit: {
+        /* Close the database. */
+        store.reset((StoreAPI *) 0);
+        writeInt(1, to);
+        break;
+    }
+#endif
+
+    case wopIsValidPath: {
+        Path path = readStorePath(from);
+        startWork();
+        bool result = store->isValidPath(path);
+        stopWork();
+        writeInt(result, to);
+        break;
+    }
+
+    case wopQueryValidPaths: {
+        PathSet paths = readStorePaths<PathSet>(from);
+        startWork();
+        PathSet res = store->queryValidPaths(paths);
+        stopWork();
+        writeStrings(res, to);
+        break;
+    }
+
+    case wopHasSubstitutes: {
+        Path path = readStorePath(from);
+        startWork();
+        PathSet res = store->querySubstitutablePaths(singleton<PathSet>(path));
+        stopWork();
+        writeInt(res.find(path) != res.end(), to);
+        break;
+    }
+
+    case wopQuerySubstitutablePaths: {
+        PathSet paths = readStorePaths<PathSet>(from);
+        startWork();
+        PathSet res = store->querySubstitutablePaths(paths);
+        stopWork();
+        writeStrings(res, to);
+        break;
+    }
+
+    case wopQueryPathHash: {
+        Path path = readStorePath(from);
+        startWork();
+        Hash hash = store->queryPathHash(path);
+        stopWork();
+        writeString(printHash(hash), to);
+        break;
+    }
+
+    case wopQueryReferences:
+    case wopQueryReferrers:
+    case wopQueryValidDerivers:
+    case wopQueryDerivationOutputs: {
+        Path path = readStorePath(from);
+        startWork();
+        PathSet paths;
+        if (op == wopQueryReferences)
+            store->queryReferences(path, paths);
+        else if (op == wopQueryReferrers)
+            store->queryReferrers(path, paths);
+        else if (op == wopQueryValidDerivers)
+            paths = store->queryValidDerivers(path);
+        else paths = store->queryDerivationOutputs(path);
+        stopWork();
+        writeStrings(paths, to);
+        break;
+    }
+
+    case wopQueryDerivationOutputNames: {
+        Path path = readStorePath(from);
+        startWork();
+        StringSet names;
+        names = store->queryDerivationOutputNames(path);
+        stopWork();
+        writeStrings(names, to);
+        break;
+    }
+
+    case wopQueryDeriver: {
+        Path path = readStorePath(from);
+        startWork();
+        Path deriver = store->queryDeriver(path);
+        stopWork();
+        writeString(deriver, to);
+        break;
+    }
+
+    case wopQueryPathFromHashPart: {
+        string hashPart = readString(from);
+        startWork();
+        Path path = store->queryPathFromHashPart(hashPart);
+        stopWork();
+        writeString(path, to);
+        break;
+    }
+
+    case wopAddToStore: {
+        string baseName = readString(from);
+        bool fixed = readInt(from) == 1; /* obsolete */
+        bool recursive = readInt(from) == 1;
+        string s = readString(from);
+        /* Compatibility hack. */
+        if (!fixed) {
+            s = "sha256";
+            recursive = true;
+        }
+        HashType hashAlgo = parseHashType(s);
+
+        SavingSourceAdapter savedNAR(from);
+        RetrieveRegularNARSink savedRegular;
+
+        if (recursive) {
+            /* Get the entire NAR dump from the client and save it to
+               a string so that we can pass it to
+               addToStoreFromDump(). */
+            ParseSink sink; /* null sink; just parse the NAR */
+            parseDump(sink, savedNAR);
+        } else
+            parseDump(savedRegular, from);
+
+        startWork();
+        if (!savedRegular.regular) throw Error("regular file expected");
+        Path path = dynamic_cast<LocalStore *>(store.get())
+            ->addToStoreFromDump(recursive ? savedNAR.s : savedRegular.s, baseName, recursive, hashAlgo);
+        stopWork();
+
+        writeString(path, to);
+        break;
+    }
+
+    case wopAddTextToStore: {
+        string suffix = readString(from);
+        string s = readString(from);
+        PathSet refs = readStorePaths<PathSet>(from);
+        startWork();
+        Path path = store->addTextToStore(suffix, s, refs);
+        stopWork();
+        writeString(path, to);
+        break;
+    }
+
+    case wopExportPath: {
+        Path path = readStorePath(from);
+        bool sign = readInt(from) == 1;
+        startWork();
+        TunnelSink sink(to);
+        store->exportPath(path, sign, sink);
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopImportPaths: {
+        startWork();
+        TunnelSource source(from);
+        Paths paths = store->importPaths(true, source);
+        stopWork();
+        writeStrings(paths, to);
+        break;
+    }
+
+    case wopBuildPaths: {
+        PathSet drvs = readStorePaths<PathSet>(from);
+        startWork();
+        store->buildPaths(drvs);
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopEnsurePath: {
+        Path path = readStorePath(from);
+        startWork();
+        store->ensurePath(path);
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopAddTempRoot: {
+        Path path = readStorePath(from);
+        startWork();
+        store->addTempRoot(path);
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopAddIndirectRoot: {
+        Path path = absPath(readString(from));
+        startWork();
+        store->addIndirectRoot(path);
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopSyncWithGC: {
+        startWork();
+        store->syncWithGC();
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopFindRoots: {
+        startWork();
+        Roots roots = store->findRoots();
+        stopWork();
+        writeInt(roots.size(), to);
+        for (Roots::iterator i = roots.begin(); i != roots.end(); ++i) {
+            writeString(i->first, to);
+            writeString(i->second, to);
+        }
+        break;
+    }
+
+    case wopCollectGarbage: {
+        GCOptions options;
+        options.action = (GCOptions::GCAction) readInt(from);
+        options.pathsToDelete = readStorePaths<PathSet>(from);
+        options.ignoreLiveness = readInt(from);
+        options.maxFreed = readLongLong(from);
+        readInt(from); // obsolete field
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 5) {
+            /* removed options */
+            readInt(from);
+            readInt(from);
+        }
+
+        GCResults results;
+
+        startWork();
+        if (options.ignoreLiveness)
+            throw Error("you are not allowed to ignore liveness");
+        store->collectGarbage(options, results);
+        stopWork();
+
+        writeStrings(results.paths, to);
+        writeLongLong(results.bytesFreed, to);
+        writeLongLong(0, to); // obsolete
+
+        break;
+    }
+
+    case wopSetOptions: {
+        settings.keepFailed = readInt(from) != 0;
+        settings.keepGoing = readInt(from) != 0;
+        settings.tryFallback = readInt(from) != 0;
+        verbosity = (Verbosity) readInt(from);
+        settings.maxBuildJobs = readInt(from);
+        settings.maxSilentTime = readInt(from);
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 2)
+            settings.useBuildHook = readInt(from) != 0;
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 4) {
+            settings.buildVerbosity = (Verbosity) readInt(from);
+            logType = (LogType) readInt(from);
+            settings.printBuildTrace = readInt(from) != 0;
+        }
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 6)
+            settings.buildCores = readInt(from);
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 10)
+            settings.useSubstitutes = readInt(from) != 0;
+        if (GET_PROTOCOL_MINOR(clientVersion) >= 12) {
+            unsigned int n = readInt(from);
+            for (unsigned int i = 0; i < n; i++) {
+                string name = readString(from);
+                string value = readString(from);
+                if (name == "build-timeout")
+                    string2Int(value, settings.buildTimeout);
+                else
+                    settings.set(trusted ? name : "untrusted-" + name, value);
+            }
+        }
+        startWork();
+        stopWork();
+        break;
+    }
+
+    case wopQuerySubstitutablePathInfo: {
+        Path path = absPath(readString(from));
+        startWork();
+        SubstitutablePathInfos infos;
+        store->querySubstitutablePathInfos(singleton<PathSet>(path), infos);
+        stopWork();
+        SubstitutablePathInfos::iterator i = infos.find(path);
+        if (i == infos.end())
+            writeInt(0, to);
+        else {
+            writeInt(1, to);
+            writeString(i->second.deriver, to);
+            writeStrings(i->second.references, to);
+            writeLongLong(i->second.downloadSize, to);
+            if (GET_PROTOCOL_MINOR(clientVersion) >= 7)
+                writeLongLong(i->second.narSize, to);
+        }
+        break;
+    }
+
+    case wopQuerySubstitutablePathInfos: {
+        PathSet paths = readStorePaths<PathSet>(from);
+        startWork();
+        SubstitutablePathInfos infos;
+        store->querySubstitutablePathInfos(paths, infos);
+        stopWork();
+        writeInt(infos.size(), to);
+        foreach (SubstitutablePathInfos::iterator, i, infos) {
+            writeString(i->first, to);
+            writeString(i->second.deriver, to);
+            writeStrings(i->second.references, to);
+            writeLongLong(i->second.downloadSize, to);
+            writeLongLong(i->second.narSize, to);
+        }
+        break;
+    }
+
+    case wopQueryAllValidPaths: {
+        startWork();
+        PathSet paths = store->queryAllValidPaths();
+        stopWork();
+        writeStrings(paths, to);
+        break;
+    }
+
+    case wopQueryFailedPaths: {
+        startWork();
+        PathSet paths = store->queryFailedPaths();
+        stopWork();
+        writeStrings(paths, to);
+        break;
+    }
+
+    case wopClearFailedPaths: {
+        PathSet paths = readStrings<PathSet>(from);
+        startWork();
+        store->clearFailedPaths(paths);
+        stopWork();
+        writeInt(1, to);
+        break;
+    }
+
+    case wopQueryPathInfo: {
+        Path path = readStorePath(from);
+        startWork();
+        ValidPathInfo info = store->queryPathInfo(path);
+        stopWork();
+        writeString(info.deriver, to);
+        writeString(printHash(info.hash), to);
+        writeStrings(info.references, to);
+        writeInt(info.registrationTime, to);
+        writeLongLong(info.narSize, to);
+        break;
+    }
+
+    default:
+        throw Error(format("invalid operation %1%") % op);
+    }
+}
+
+
+static void processConnection(bool trusted)
+{
+    canSendStderr = false;
+    myPid = getpid();
+    _writeToStderr = tunnelStderr;
+
+#ifdef HAVE_HUP_NOTIFICATION
+    /* Allow us to receive SIGPOLL for events on the client socket. */
+    setSigPollAction(false);
+    if (fcntl(from.fd, F_SETOWN, getpid()) == -1)
+        throw SysError("F_SETOWN");
+    if (fcntl(from.fd, F_SETFL, fcntl(from.fd, F_GETFL, 0) | O_ASYNC) == -1)
+        throw SysError("F_SETFL");
+#endif
+
+    /* Exchange the greeting. */
+    unsigned int magic = readInt(from);
+    if (magic != WORKER_MAGIC_1) throw Error("protocol mismatch");
+    writeInt(WORKER_MAGIC_2, to);
+    writeInt(PROTOCOL_VERSION, to);
+    to.flush();
+    unsigned int clientVersion = readInt(from);
+
+    if (GET_PROTOCOL_MINOR(clientVersion) >= 14 && readInt(from))
+        setAffinityTo(readInt(from));
+
+    bool reserveSpace = true;
+    if (GET_PROTOCOL_MINOR(clientVersion) >= 11)
+        reserveSpace = readInt(from) != 0;
+
+    /* Send startup error messages to the client. */
+    startWork();
+
+    try {
+
+        /* If we can't accept clientVersion, then throw an error
+           *here* (not above). */
+
+#if 0
+        /* Prevent users from doing something very dangerous. */
+        if (geteuid() == 0 &&
+            querySetting("build-users-group", "") == "")
+            throw Error("if you run `nix-daemon' as root, then you MUST set `build-users-group'!");
+#endif
+
+        /* Open the store. */
+        store = boost::shared_ptr<StoreAPI>(new LocalStore(reserveSpace));
+
+        stopWork();
+        to.flush();
+
+    } catch (Error & e) {
+        stopWork(false, e.msg());
+        to.flush();
+        return;
+    }
+
+    /* Process client requests. */
+    unsigned int opCount = 0;
+
+    while (true) {
+        WorkerOp op;
+        try {
+            op = (WorkerOp) readInt(from);
+        } catch (EndOfFile & e) {
+            break;
+        }
+
+        opCount++;
+
+        try {
+            performOp(trusted, clientVersion, from, to, op);
+        } catch (Error & e) {
+            /* If we're not in a state where we can send replies, then
+               something went wrong processing the input of the
+               client.  This can happen especially if I/O errors occur
+               during addTextToStore() / importPath().  If that
+               happens, just send the error message and exit. */
+            bool errorAllowed = canSendStderr;
+            if (!errorAllowed) printMsg(lvlError, format("error processing client input: %1%") % e.msg());
+            stopWork(false, e.msg(), GET_PROTOCOL_MINOR(clientVersion) >= 8 ? e.status : 0);
+            if (!errorAllowed) break;
+        } catch (std::bad_alloc & e) {
+            if (canSendStderr)
+                stopWork(false, "Nix daemon out of memory", GET_PROTOCOL_MINOR(clientVersion) >= 8 ? 1 : 0);
+            throw;
+        }
+
+        to.flush();
+
+        assert(!canSendStderr);
+    };
+
+    printMsg(lvlError, format("%1% operations") % opCount);
+}
+
+
+static void sigChldHandler(int sigNo)
+{
+    /* Reap all dead children. */
+    while (waitpid(-1, 0, WNOHANG) > 0) ;
+}
+
+
+static void setSigChldAction(bool autoReap)
+{
+    struct sigaction act, oact;
+    act.sa_handler = autoReap ? sigChldHandler : SIG_DFL;
+    sigfillset(&act.sa_mask);
+    act.sa_flags = 0;
+    if (sigaction(SIGCHLD, &act, &oact))
+        throw SysError("setting SIGCHLD handler");
+}
+
+
+#define SD_LISTEN_FDS_START 3
+
+
+static void daemonLoop()
+{
+    /* Get rid of children automatically; don't let them become
+       zombies. */
+    setSigChldAction(true);
+
+    AutoCloseFD fdSocket;
+
+    /* Handle socket-based activation by systemd. */
+    if (getEnv("LISTEN_FDS") != "") {
+        if (getEnv("LISTEN_PID") != int2String(getpid()) || getEnv("LISTEN_FDS") != "1")
+            throw Error("unexpected systemd environment variables");
+        fdSocket = SD_LISTEN_FDS_START;
+    }
+
+    /* Otherwise, create and bind to a Unix domain socket. */
+    else {
+
+        /* Create and bind to a Unix domain socket. */
+        fdSocket = socket(PF_UNIX, SOCK_STREAM, 0);
+        if (fdSocket == -1)
+            throw SysError("cannot create Unix domain socket");
+
+        string socketPath = settings.nixDaemonSocketFile;
+
+        createDirs(dirOf(socketPath));
+
+        /* Urgh, sockaddr_un allows path names of only 108 characters.
+           So chdir to the socket directory so that we can pass a
+           relative path name. */
+        chdir(dirOf(socketPath).c_str());
+        Path socketPathRel = "./" + baseNameOf(socketPath);
+
+        struct sockaddr_un addr;
+        addr.sun_family = AF_UNIX;
+        if (socketPathRel.size() >= sizeof(addr.sun_path))
+            throw Error(format("socket path `%1%' is too long") % socketPathRel);
+        strcpy(addr.sun_path, socketPathRel.c_str());
+
+        unlink(socketPath.c_str());
+
+        /* Make sure that the socket is created with 0666 permission
+           (everybody can connect --- provided they have access to the
+           directory containing the socket). */
+        mode_t oldMode = umask(0111);
+        int res = bind(fdSocket, (struct sockaddr *) &addr, sizeof(addr));
+        umask(oldMode);
+        if (res == -1)
+            throw SysError(format("cannot bind to socket `%1%'") % socketPath);
+
+        chdir("/"); /* back to the root */
+
+        if (listen(fdSocket, 5) == -1)
+            throw SysError(format("cannot listen on socket `%1%'") % socketPath);
+    }
+
+    closeOnExec(fdSocket);
+
+    /* Loop accepting connections. */
+    while (1) {
+
+        try {
+            /* Important: the server process *cannot* open the SQLite
+               database, because it doesn't like forks very much. */
+            assert(!store);
+
+            /* Accept a connection. */
+            struct sockaddr_un remoteAddr;
+            socklen_t remoteAddrLen = sizeof(remoteAddr);
+
+            AutoCloseFD remote = accept(fdSocket,
+                (struct sockaddr *) &remoteAddr, &remoteAddrLen);
+            checkInterrupt();
+            if (remote == -1) {
+                if (errno == EINTR)
+                    continue;
+                else
+                    throw SysError("accepting connection");
+            }
+
+            closeOnExec(remote);
+
+            /* Get the identity of the caller, if possible. */
+            uid_t clientUid = -1;
+            pid_t clientPid = -1;
+            bool trusted = false;
+
+#if defined(SO_PEERCRED)
+            ucred cred;
+            socklen_t credLen = sizeof(cred);
+            if (getsockopt(remote, SOL_SOCKET, SO_PEERCRED, &cred, &credLen) != -1) {
+                clientPid = cred.pid;
+                clientUid = cred.uid;
+                if (clientUid == 0) trusted = true;
+            }
+#endif
+
+            printMsg(lvlInfo, format("accepted connection from pid %1%, uid %2%") % clientPid % clientUid);
+
+            /* Fork a child to handle the connection. */
+            pid_t child;
+            child = fork();
+
+            switch (child) {
+
+            case -1:
+                throw SysError("unable to fork");
+
+            case 0:
+                try { /* child */
+
+                    /* Background the daemon. */
+                    if (setsid() == -1)
+                        throw SysError(format("creating a new session"));
+
+                    /* Restore normal handling of SIGCHLD. */
+                    setSigChldAction(false);
+
+                    /* For debugging, stuff the pid into argv[1]. */
+                    if (clientPid != -1 && argvSaved[1]) {
+                        string processName = int2String(clientPid);
+                        strncpy(argvSaved[1], processName.c_str(), strlen(argvSaved[1]));
+                    }
+
+                    /* Handle the connection. */
+                    from.fd = remote;
+                    to.fd = remote;
+                    processConnection(trusted);
+
+                } catch (std::exception & e) {
+                    writeToStderr("unexpected Nix daemon error: " + string(e.what()) + "\n");
+                }
+                exit(0);
+            }
+
+        } catch (Interrupted & e) {
+            throw;
+        } catch (Error & e) {
+            printMsg(lvlError, format("error processing connection: %1%") % e.msg());
+        }
+    }
+}
+
+
+void run(Strings args)
+{
+    for (Strings::iterator i = args.begin(); i != args.end(); ) {
+        string arg = *i++;
+        if (arg == "--daemon") /* ignored for backwards compatibility */;
+    }
+
+    chdir("/");
+    daemonLoop();
+}
+
+
+void printHelp()
+{
+    showManPage("nix-daemon");
+}
+
+
+string programId = "nix-daemon";
diff --git a/src/nix-env/local.mk b/src/nix-env/local.mk
new file mode 100644
index 000000000000..e80719cd76f7
--- /dev/null
+++ b/src/nix-env/local.mk
@@ -0,0 +1,7 @@
+programs += nix-env
+
+nix-env_DIR := $(d)
+
+nix-env_SOURCES := $(wildcard $(d)/*.cc)
+
+nix-env_LIBS = libexpr libmain libstore libutil libformat
diff --git a/src/nix-env/nix-env.cc b/src/nix-env/nix-env.cc
new file mode 100644
index 000000000000..e2781e540bf2
--- /dev/null
+++ b/src/nix-env/nix-env.cc
@@ -0,0 +1,1426 @@
+#include "profiles.hh"
+#include "names.hh"
+#include "globals.hh"
+#include "misc.hh"
+#include "shared.hh"
+#include "eval.hh"
+#include "get-drvs.hh"
+#include "attr-path.hh"
+#include "common-opts.hh"
+#include "xml-writer.hh"
+#include "store-api.hh"
+#include "user-env.hh"
+#include "util.hh"
+#include "value-to-json.hh"
+
+#include <cerrno>
+#include <ctime>
+#include <algorithm>
+#include <iostream>
+#include <sstream>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+
+using namespace nix;
+using std::cout;
+
+
+typedef enum {
+    srcNixExprDrvs,
+    srcNixExprs,
+    srcStorePaths,
+    srcProfile,
+    srcAttrPath,
+    srcUnknown
+} InstallSourceType;
+
+
+struct InstallSourceInfo
+{
+    InstallSourceType type;
+    Path nixExprPath; /* for srcNixExprDrvs, srcNixExprs */
+    Path profile; /* for srcProfile */
+    string systemFilter; /* for srcNixExprDrvs */
+    Bindings autoArgs;
+};
+
+
+struct Globals
+{
+    InstallSourceInfo instSource;
+    Path profile;
+    EvalState state;
+    bool dryRun;
+    bool preserveInstalled;
+    bool removeAll;
+    string forceName;
+    bool prebuiltOnly;
+};
+
+
+typedef void (* Operation) (Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs);
+
+
+void printHelp()
+{
+    showManPage("nix-env");
+}
+
+
+static string needArg(Strings::iterator & i,
+    Strings & args, const string & arg)
+{
+    if (i == args.end()) throw UsageError(
+        format("`%1%' requires an argument") % arg);
+    return *i++;
+}
+
+
+static bool parseInstallSourceOptions(Globals & globals,
+    Strings::iterator & i, Strings & args, const string & arg)
+{
+    if (arg == "--from-expression" || arg == "-E")
+        globals.instSource.type = srcNixExprs;
+    else if (arg == "--from-profile") {
+        globals.instSource.type = srcProfile;
+        globals.instSource.profile = needArg(i, args, arg);
+    }
+    else if (arg == "--attr" || arg == "-A")
+        globals.instSource.type = srcAttrPath;
+    else return false;
+    return true;
+}
+
+
+static bool isNixExpr(const Path & path, struct stat & st)
+{
+    return S_ISREG(st.st_mode) || (S_ISDIR(st.st_mode) && pathExists(path + "/default.nix"));
+}
+
+
+static void getAllExprs(EvalState & state,
+    const Path & path, StringSet & attrs, Value & v)
+{
+    Strings names = readDirectory(path);
+    StringSet namesSorted(names.begin(), names.end());
+
+    foreach (StringSet::iterator, i, namesSorted) {
+        /* Ignore the manifest.nix used by profiles.  This is
+           necessary to prevent it from showing up in channels (which
+           are implemented using profiles). */
+        if (*i == "manifest.nix") continue;
+
+        Path path2 = path + "/" + *i;
+
+        struct stat st;
+        if (stat(path2.c_str(), &st) == -1)
+            continue; // ignore dangling symlinks in ~/.nix-defexpr
+
+        if (isNixExpr(path2, st) && (!S_ISREG(st.st_mode) || hasSuffix(path2, ".nix"))) {
+            /* Strip off the `.nix' filename suffix (if applicable),
+               otherwise the attribute cannot be selected with the
+               `-A' option.  Useful if you want to stick a Nix
+               expression directly in ~/.nix-defexpr. */
+            string attrName = *i;
+            if (hasSuffix(attrName, ".nix"))
+                attrName = string(attrName, 0, attrName.size() - 4);
+            if (attrs.find(attrName) != attrs.end()) {
+                printMsg(lvlError, format("warning: name collision in input Nix expressions, skipping `%1%'") % path2);
+                continue;
+            }
+            attrs.insert(attrName);
+            /* Load the expression on demand. */
+            Value & vFun(*state.allocValue());
+            Value & vArg(*state.allocValue());
+            state.getBuiltin("import", vFun);
+            mkString(vArg, path2);
+            mkApp(*state.allocAttr(v, state.symbols.create(attrName)), vFun, vArg);
+        }
+        else if (S_ISDIR(st.st_mode))
+            /* `path2' is a directory (with no default.nix in it);
+               recurse into it. */
+            getAllExprs(state, path2, attrs, v);
+    }
+}
+
+
+static void loadSourceExpr(EvalState & state, const Path & path, Value & v)
+{
+    struct stat st;
+    if (stat(path.c_str(), &st) == -1)
+        throw SysError(format("getting information about `%1%'") % path);
+
+    if (isNixExpr(path, st)) {
+        state.evalFile(path, v);
+        return;
+    }
+
+    /* The path is a directory.  Put the Nix expressions in the
+       directory in a set, with the file name of each expression as
+       the attribute name.  Recurse into subdirectories (but keep the
+       set flat, not nested, to make it easier for a user to have a
+       ~/.nix-defexpr directory that includes some system-wide
+       directory). */
+    if (S_ISDIR(st.st_mode)) {
+        state.mkAttrs(v, 16);
+        state.mkList(*state.allocAttr(v, state.symbols.create("_combineChannels")), 0);
+        StringSet attrs;
+        getAllExprs(state, path, attrs, v);
+        v.attrs->sort();
+    }
+}
+
+
+static void loadDerivations(EvalState & state, Path nixExprPath,
+    string systemFilter, Bindings & autoArgs,
+    const string & pathPrefix, DrvInfos & elems)
+{
+    Value vRoot;
+    loadSourceExpr(state, nixExprPath, vRoot);
+
+    Value & v(*findAlongAttrPath(state, pathPrefix, autoArgs, vRoot));
+
+    getDerivations(state, v, pathPrefix, autoArgs, elems, true);
+
+    /* Filter out all derivations not applicable to the current
+       system. */
+    for (DrvInfos::iterator i = elems.begin(), j; i != elems.end(); i = j) {
+        j = i; j++;
+        if (systemFilter != "*" && i->system != systemFilter)
+            elems.erase(i);
+    }
+}
+
+
+static Path getHomeDir()
+{
+    Path homeDir(getEnv("HOME", ""));
+    if (homeDir == "") throw Error("HOME environment variable not set");
+    return homeDir;
+}
+
+
+static Path getDefNixExprPath()
+{
+    return getHomeDir() + "/.nix-defexpr";
+}
+
+
+static int getPriority(EvalState & state, DrvInfo & drv)
+{
+    return drv.queryMetaInt("priority", 0);
+}
+
+
+static int comparePriorities(EvalState & state, DrvInfo & drv1, DrvInfo & drv2)
+{
+    return getPriority(state, drv2) - getPriority(state, drv1);
+}
+
+
+// FIXME: this function is rather slow since it checks a single path
+// at a time.
+static bool isPrebuilt(EvalState & state, DrvInfo & elem)
+{
+    Path path = elem.queryOutPath();
+    if (store->isValidPath(path)) return true;
+    PathSet ps = store->querySubstitutablePaths(singleton<PathSet>(path));
+    return ps.find(path) != ps.end();
+}
+
+
+static void checkSelectorUse(DrvNames & selectors)
+{
+    /* Check that all selectors have been used. */
+    foreach (DrvNames::iterator, i, selectors)
+        if (i->hits == 0 && i->fullName != "*")
+            throw Error(format("selector `%1%' matches no derivations") % i->fullName);
+}
+
+
+static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
+    const Strings & args, bool newestOnly)
+{
+    DrvNames selectors = drvNamesFromArgs(args);
+    if (selectors.empty())
+        selectors.push_back(DrvName("*"));
+
+    DrvInfos elems;
+    set<unsigned int> done;
+
+    foreach (DrvNames::iterator, i, selectors) {
+        typedef list<std::pair<DrvInfo, unsigned int> > Matches;
+        Matches matches;
+        unsigned int n = 0;
+        for (DrvInfos::const_iterator j = allElems.begin();
+             j != allElems.end(); ++j, ++n)
+        {
+            DrvName drvName(j->name);
+            if (i->matches(drvName)) {
+                i->hits++;
+                matches.push_back(std::pair<DrvInfo, unsigned int>(*j, n));
+            }
+        }
+
+        /* If `newestOnly', if a selector matches multiple derivations
+           with the same name, pick the one matching the current
+           system.  If there are still multiple derivations, pick the
+           one with the highest priority.  If there are still multiple
+           derivations, pick the one with the highest version.
+           Finally, if there are still multiple derivations,
+           arbitrarily pick the first one. */
+        if (newestOnly) {
+
+            /* Map from package names to derivations. */
+            typedef map<string, std::pair<DrvInfo, unsigned int> > Newest;
+            Newest newest;
+            StringSet multiple;
+
+            for (Matches::iterator j = matches.begin(); j != matches.end(); ++j) {
+                DrvName drvName(j->first.name);
+                int d = 1;
+
+                Newest::iterator k = newest.find(drvName.name);
+
+                if (k != newest.end()) {
+                    d = j->first.system == k->second.first.system ? 0 :
+                        j->first.system == settings.thisSystem ? 1 :
+                        k->second.first.system == settings.thisSystem ? -1 : 0;
+                    if (d == 0)
+                        d = comparePriorities(state, j->first, k->second.first);
+                    if (d == 0)
+                        d = compareVersions(drvName.version, DrvName(k->second.first.name).version);
+                }
+
+                if (d > 0) {
+                    newest.erase(drvName.name);
+                    newest.insert(Newest::value_type(drvName.name, *j));
+                    multiple.erase(j->first.name);
+                } else if (d == 0) {
+                    multiple.insert(j->first.name);
+                }
+            }
+
+            matches.clear();
+            for (Newest::iterator j = newest.begin(); j != newest.end(); ++j) {
+                if (multiple.find(j->second.first.name) != multiple.end())
+                    printMsg(lvlInfo,
+                        format("warning: there are multiple derivations named `%1%'; using the first one")
+                        % j->second.first.name);
+                matches.push_back(j->second);
+            }
+        }
+
+        /* Insert only those elements in the final list that we
+           haven't inserted before. */
+        for (Matches::iterator j = matches.begin(); j != matches.end(); ++j)
+            if (done.find(j->second) == done.end()) {
+                done.insert(j->second);
+                elems.push_back(j->first);
+            }
+    }
+
+    checkSelectorUse(selectors);
+
+    return elems;
+}
+
+
+static bool isPath(const string & s)
+{
+    return s.find('/') != string::npos;
+}
+
+
+static void queryInstSources(EvalState & state,
+    InstallSourceInfo & instSource, const Strings & args,
+    DrvInfos & elems, bool newestOnly)
+{
+    InstallSourceType type = instSource.type;
+    if (type == srcUnknown && args.size() > 0 && isPath(args.front()))
+        type = srcStorePaths;
+
+    switch (type) {
+
+        /* Get the available user environment elements from the
+           derivations specified in a Nix expression, including only
+           those with names matching any of the names in `args'. */
+        case srcUnknown:
+        case srcNixExprDrvs: {
+
+            /* Load the derivations from the (default or specified)
+               Nix expression. */
+            DrvInfos allElems;
+            loadDerivations(state, instSource.nixExprPath,
+                instSource.systemFilter, instSource.autoArgs, "", allElems);
+
+            elems = filterBySelector(state, allElems, args, newestOnly);
+
+            break;
+        }
+
+        /* Get the available user environment elements from the Nix
+           expressions specified on the command line; these should be
+           functions that take the default Nix expression file as
+           argument, e.g., if the file is `./foo.nix', then the
+           argument `x: x.bar' is equivalent to `(x: x.bar)
+           (import ./foo.nix)' = `(import ./foo.nix).bar'. */
+        case srcNixExprs: {
+
+            Value vArg;
+            loadSourceExpr(state, instSource.nixExprPath, vArg);
+
+            foreach (Strings::const_iterator, i, args) {
+                Expr * eFun = state.parseExprFromString(*i, absPath("."));
+                Value vFun, vTmp;
+                state.eval(eFun, vFun);
+                mkApp(vTmp, vFun, vArg);
+                getDerivations(state, vTmp, "", instSource.autoArgs, elems, true);
+            }
+
+            break;
+        }
+
+        /* The available user environment elements are specified as a
+           list of store paths (which may or may not be
+           derivations). */
+        case srcStorePaths: {
+
+            foreach (Strings::const_iterator, i, args) {
+                Path path = followLinksToStorePath(*i);
+
+                string name = baseNameOf(path);
+                string::size_type dash = name.find('-');
+                if (dash != string::npos)
+                    name = string(name, dash + 1);
+
+                DrvInfo elem(state, name, "", "", 0);
+
+                if (isDerivation(path)) {
+                    elem.setDrvPath(path);
+                    elem.setOutPath(findOutput(derivationFromPath(*store, path), "out"));
+                    if (name.size() >= drvExtension.size() &&
+                        string(name, name.size() - drvExtension.size()) == drvExtension)
+                        name = string(name, 0, name.size() - drvExtension.size());
+                }
+                else elem.setOutPath(path);
+
+                elems.push_back(elem);
+            }
+
+            break;
+        }
+
+        /* Get the available user environment elements from another
+           user environment.  These are then filtered as in the
+           `srcNixExprDrvs' case. */
+        case srcProfile: {
+            elems = filterBySelector(state,
+                queryInstalled(state, instSource.profile),
+                args, newestOnly);
+            break;
+        }
+
+        case srcAttrPath: {
+            Value vRoot;
+            loadSourceExpr(state, instSource.nixExprPath, vRoot);
+            foreach (Strings::const_iterator, i, args) {
+                Value & v(*findAlongAttrPath(state, *i, instSource.autoArgs, vRoot));
+                getDerivations(state, v, "", instSource.autoArgs, elems, true);
+            }
+            break;
+        }
+    }
+}
+
+
+static void printMissing(EvalState & state, DrvInfos & elems)
+{
+    PathSet targets;
+    foreach (DrvInfos::iterator, i, elems) {
+        Path drvPath = i->queryDrvPath();
+        if (drvPath != "")
+            targets.insert(drvPath);
+        else
+            targets.insert(i->queryOutPath());
+    }
+
+    printMissing(*store, targets);
+}
+
+
+static bool keep(DrvInfo & drv)
+{
+    return drv.queryMetaBool("keep", false);
+}
+
+
+static void installDerivations(Globals & globals,
+    const Strings & args, const Path & profile)
+{
+    debug(format("installing derivations"));
+
+    /* Get the set of user environment elements to be installed. */
+    DrvInfos newElems, newElemsTmp;
+    queryInstSources(globals.state, globals.instSource, args, newElemsTmp, true);
+
+    /* If --prebuilt-only is given, filter out source-only packages. */
+    foreach (DrvInfos::iterator, i, newElemsTmp)
+        if (!globals.prebuiltOnly || isPrebuilt(globals.state, *i))
+            newElems.push_back(*i);
+
+    StringSet newNames;
+    for (DrvInfos::iterator i = newElems.begin(); i != newElems.end(); ++i) {
+        /* `forceName' is a hack to get package names right in some
+           one-click installs, namely those where the name used in the
+           path is not the one we want (e.g., `java-front' versus
+           `java-front-0.9pre15899'). */
+        if (globals.forceName != "")
+            i->name = globals.forceName;
+        newNames.insert(DrvName(i->name).name);
+    }
+
+
+    while (true) {
+        string lockToken = optimisticLockProfile(profile);
+
+        DrvInfos allElems(newElems);
+
+        /* Add in the already installed derivations, unless they have
+           the same name as a to-be-installed element. */
+        if (!globals.removeAll) {
+            DrvInfos installedElems = queryInstalled(globals.state, profile);
+
+            foreach (DrvInfos::iterator, i, installedElems) {
+                DrvName drvName(i->name);
+                if (!globals.preserveInstalled &&
+                    newNames.find(drvName.name) != newNames.end() &&
+                    !keep(*i))
+                    printMsg(lvlInfo, format("replacing old `%1%'") % i->name);
+                else
+                    allElems.push_back(*i);
+            }
+
+            foreach (DrvInfos::iterator, i, newElems)
+                printMsg(lvlInfo, format("installing `%1%'") % i->name);
+        }
+
+        printMissing(globals.state, newElems);
+
+        if (globals.dryRun) return;
+
+        if (createUserEnv(globals.state, allElems,
+                profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opInstall(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        string arg = *i++;
+        if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
+        else if (arg == "--preserve-installed" || arg == "-P")
+            globals.preserveInstalled = true;
+        else if (arg == "--remove-all" || arg == "-r")
+            globals.removeAll = true;
+        else throw UsageError(format("unknown flag `%1%'") % arg);
+    }
+
+    installDerivations(globals, opArgs, globals.profile);
+}
+
+
+typedef enum { utLt, utLeq, utEq, utAlways } UpgradeType;
+
+
+static void upgradeDerivations(Globals & globals,
+    const Strings & args, UpgradeType upgradeType)
+{
+    debug(format("upgrading derivations"));
+
+    /* Upgrade works as follows: we take all currently installed
+       derivations, and for any derivation matching any selector, look
+       for a derivation in the input Nix expression that has the same
+       name and a higher version number. */
+
+    while (true) {
+        string lockToken = optimisticLockProfile(globals.profile);
+
+        DrvInfos installedElems = queryInstalled(globals.state, globals.profile);
+
+        /* Fetch all derivations from the input file. */
+        DrvInfos availElems;
+        queryInstSources(globals.state, globals.instSource, args, availElems, false);
+
+        /* Go through all installed derivations. */
+        DrvInfos newElems;
+        foreach (DrvInfos::iterator, i, installedElems) {
+            DrvName drvName(i->name);
+
+            try {
+
+                if (keep(*i)) {
+                    newElems.push_back(*i);
+                    continue;
+                }
+
+                /* Find the derivation in the input Nix expression
+                   with the same name that satisfies the version
+                   constraints specified by upgradeType.  If there are
+                   multiple matches, take the one with the highest
+                   priority.  If there are still multiple matches,
+                   take the one with the highest version. */
+                DrvInfos::iterator bestElem = availElems.end();
+                DrvName bestName;
+                foreach (DrvInfos::iterator, j, availElems) {
+                    DrvName newName(j->name);
+                    if (newName.name == drvName.name) {
+                        int d = comparePriorities(globals.state, *i, *j);
+                        if (d == 0) d = compareVersions(drvName.version, newName.version);
+                        if ((upgradeType == utLt && d < 0) ||
+                            (upgradeType == utLeq && d <= 0) ||
+                            (upgradeType == utEq && d == 0) ||
+                            upgradeType == utAlways)
+                        {
+                            int d2 = -1;
+                            if (bestElem != availElems.end()) {
+                                d2 = comparePriorities(globals.state, *bestElem, *j);
+                                if (d2 == 0) d2 = compareVersions(bestName.version, newName.version);
+                            }
+                            if (d2 < 0 && (!globals.prebuiltOnly || isPrebuilt(globals.state, *j))) {
+                                bestElem = j;
+                                bestName = newName;
+                            }
+                        }
+                    }
+                }
+
+                if (bestElem != availElems.end() &&
+                    i->queryOutPath() !=
+                    bestElem->queryOutPath())
+                {
+                    printMsg(lvlInfo,
+                        format("upgrading `%1%' to `%2%'")
+                        % i->name % bestElem->name);
+                    newElems.push_back(*bestElem);
+                } else newElems.push_back(*i);
+
+            } catch (Error & e) {
+                e.addPrefix(format("while trying to find an upgrade for `%1%':\n") % i->name);
+                throw;
+            }
+        }
+
+        printMissing(globals.state, newElems);
+
+        if (globals.dryRun) return;
+
+        if (createUserEnv(globals.state, newElems,
+                globals.profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opUpgrade(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    UpgradeType upgradeType = utLt;
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        string arg = *i++;
+        if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
+        else if (arg == "--lt") upgradeType = utLt;
+        else if (arg == "--leq") upgradeType = utLeq;
+        else if (arg == "--eq") upgradeType = utEq;
+        else if (arg == "--always") upgradeType = utAlways;
+        else throw UsageError(format("unknown flag `%1%'") % arg);
+    }
+
+    upgradeDerivations(globals, opArgs, upgradeType);
+}
+
+
+static void setMetaFlag(EvalState & state, DrvInfo & drv,
+    const string & name, const string & value)
+{
+    Value * v = state.allocValue();
+    mkString(*v, value.c_str());
+    drv.setMeta(name, v);
+}
+
+
+static void opSetFlag(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+    if (opArgs.size() < 2)
+        throw UsageError("not enough arguments to `--set-flag'");
+
+    Strings::iterator arg = opArgs.begin();
+    string flagName = *arg++;
+    string flagValue = *arg++;
+    DrvNames selectors = drvNamesFromArgs(Strings(arg, opArgs.end()));
+
+    while (true) {
+        string lockToken = optimisticLockProfile(globals.profile);
+
+        DrvInfos installedElems = queryInstalled(globals.state, globals.profile);
+
+        /* Update all matching derivations. */
+        foreach (DrvInfos::iterator, i, installedElems) {
+            DrvName drvName(i->name);
+            foreach (DrvNames::iterator, j, selectors)
+                if (j->matches(drvName)) {
+                    printMsg(lvlInfo, format("setting flag on `%1%'") % i->name);
+                    j->hits++;
+                    setMetaFlag(globals.state, *i, flagName, flagValue);
+                    break;
+                }
+        }
+
+        checkSelectorUse(selectors);
+
+        /* Write the new user environment. */
+        if (createUserEnv(globals.state, installedElems,
+                globals.profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opSet(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    for (Strings::iterator i = opFlags.begin(); i != opFlags.end(); ) {
+        string arg = *i++;
+        if (parseInstallSourceOptions(globals, i, opFlags, arg)) ;
+        else throw UsageError(format("unknown flag `%1%'") % arg);
+    }
+
+    DrvInfos elems;
+    queryInstSources(globals.state, globals.instSource, opArgs, elems, true);
+
+    if (elems.size() != 1)
+        throw Error("--set requires exactly one derivation");
+
+    DrvInfo & drv(elems.front());
+
+    if (drv.queryDrvPath() != "") {
+        PathSet paths = singleton<PathSet>(drv.queryDrvPath());
+        printMissing(*store, paths);
+        if (globals.dryRun) return;
+        store->buildPaths(paths, globals.state.repair);
+    }
+    else {
+        printMissing(*store, singleton<PathSet>(drv.queryOutPath()));
+        if (globals.dryRun) return;
+        store->ensurePath(drv.queryOutPath());
+    }
+
+    debug(format("switching to new user environment"));
+    Path generation = createGeneration(globals.profile, drv.queryOutPath());
+    switchLink(globals.profile, generation);
+}
+
+
+static void uninstallDerivations(Globals & globals, Strings & selectors,
+    Path & profile)
+{
+    while (true) {
+        string lockToken = optimisticLockProfile(profile);
+
+        DrvInfos installedElems = queryInstalled(globals.state, profile);
+        DrvInfos newElems;
+
+        foreach (DrvInfos::iterator, i, installedElems) {
+            DrvName drvName(i->name);
+            bool found = false;
+            foreach (Strings::iterator, j, selectors)
+                /* !!! the repeated calls to followLinksToStorePath()
+                   are expensive, should pre-compute them. */
+                if ((isPath(*j) && i->queryOutPath() == followLinksToStorePath(*j))
+                    || DrvName(*j).matches(drvName))
+                {
+                    printMsg(lvlInfo, format("uninstalling `%1%'") % i->name);
+                    found = true;
+                    break;
+                }
+            if (!found) newElems.push_back(*i);
+        }
+
+        if (globals.dryRun) return;
+
+        if (createUserEnv(globals.state, newElems,
+                profile, settings.envKeepDerivations, lockToken)) break;
+    }
+}
+
+
+static void opUninstall(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+    uninstallDerivations(globals, opArgs, globals.profile);
+}
+
+
+static bool cmpChars(char a, char b)
+{
+    return toupper(a) < toupper(b);
+}
+
+
+static bool cmpElemByName(const DrvInfo & a, const DrvInfo & b)
+{
+    return lexicographical_compare(
+        a.name.begin(), a.name.end(),
+        b.name.begin(), b.name.end(), cmpChars);
+}
+
+
+typedef list<Strings> Table;
+
+
+void printTable(Table & table)
+{
+    unsigned int nrColumns = table.size() > 0 ? table.front().size() : 0;
+
+    vector<unsigned int> widths;
+    widths.resize(nrColumns);
+
+    foreach (Table::iterator, i, table) {
+        assert(i->size() == nrColumns);
+        Strings::iterator j;
+        unsigned int column;
+        for (j = i->begin(), column = 0; j != i->end(); ++j, ++column)
+            if (j->size() > widths[column]) widths[column] = j->size();
+    }
+
+    foreach (Table::iterator, i, table) {
+        Strings::iterator j;
+        unsigned int column;
+        for (j = i->begin(), column = 0; j != i->end(); ++j, ++column) {
+            string s = *j;
+            replace(s.begin(), s.end(), '\n', ' ');
+            cout << s;
+            if (column < nrColumns - 1)
+                cout << string(widths[column] - s.size() + 2, ' ');
+        }
+        cout << std::endl;
+    }
+}
+
+
+/* This function compares the version of an element against the
+   versions in the given set of elements.  `cvLess' means that only
+   lower versions are in the set, `cvEqual' means that at most an
+   equal version is in the set, and `cvGreater' means that there is at
+   least one element with a higher version in the set.  `cvUnavail'
+   means that there are no elements with the same name in the set. */
+
+typedef enum { cvLess, cvEqual, cvGreater, cvUnavail } VersionDiff;
+
+static VersionDiff compareVersionAgainstSet(
+    const DrvInfo & elem, const DrvInfos & elems, string & version)
+{
+    DrvName name(elem.name);
+
+    VersionDiff diff = cvUnavail;
+    version = "?";
+
+    for (DrvInfos::const_iterator i = elems.begin(); i != elems.end(); ++i) {
+        DrvName name2(i->name);
+        if (name.name == name2.name) {
+            int d = compareVersions(name.version, name2.version);
+            if (d < 0) {
+                diff = cvGreater;
+                version = name2.version;
+            }
+            else if (diff != cvGreater && d == 0) {
+                diff = cvEqual;
+                version = name2.version;
+            }
+            else if (diff != cvGreater && diff != cvEqual && d > 0) {
+                diff = cvLess;
+                if (version == "" || compareVersions(version, name2.version) < 0)
+                    version = name2.version;
+            }
+        }
+    }
+
+    return diff;
+}
+
+
+static string colorString(const string & s)
+{
+    if (!isatty(STDOUT_FILENO)) return s;
+    return "\e[1;31m" + s + "\e[0m";
+}
+
+
+static void queryJSON(Globals & globals, vector<DrvInfo> & elems)
+{
+    JSONObject topObj(cout);
+    foreach (vector<DrvInfo>::iterator, i, elems) {
+        topObj.attr(i->attrPath);
+        JSONObject pkgObj(cout);
+
+        pkgObj.attr("name", i->name);
+        pkgObj.attr("system", i->system);
+
+        pkgObj.attr("meta");
+        JSONObject metaObj(cout);
+        StringSet metaNames = i->queryMetaNames();
+        foreach (StringSet::iterator, j, metaNames) {
+            metaObj.attr(*j);
+            Value * v = i->queryMeta(*j);
+            if (!v)
+                printMsg(lvlError, format("derivation `%1%' has invalid meta attribute `%2%'") % i->name % *j);
+            else {
+                PathSet context;
+                printValueAsJSON(globals.state, true, *v, cout, context);
+            }
+        }
+    }
+}
+
+
+static void opQuery(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    Strings remaining;
+    string attrPath;
+
+    bool printStatus = false;
+    bool printName = true;
+    bool printAttrPath = false;
+    bool printSystem = false;
+    bool printDrvPath = false;
+    bool printOutPath = false;
+    bool printDescription = false;
+    bool printMeta = false;
+    bool compareVersions = false;
+    bool xmlOutput = false;
+    bool jsonOutput = false;
+
+    enum { sInstalled, sAvailable } source = sInstalled;
+
+    settings.readOnlyMode = true; /* makes evaluation a bit faster */
+
+    for (Strings::iterator i = args.begin(); i != args.end(); ) {
+        string arg = *i++;
+        if (arg == "--status" || arg == "-s") printStatus = true;
+        else if (arg == "--no-name") printName = false;
+        else if (arg == "--system") printSystem = true;
+        else if (arg == "--description") printDescription = true;
+        else if (arg == "--compare-versions" || arg == "-c") compareVersions = true;
+        else if (arg == "--drv-path") printDrvPath = true;
+        else if (arg == "--out-path") printOutPath = true;
+        else if (arg == "--meta") printMeta = true;
+        else if (arg == "--installed") source = sInstalled;
+        else if (arg == "--available" || arg == "-a") source = sAvailable;
+        else if (arg == "--xml") xmlOutput = true;
+        else if (arg == "--json") jsonOutput = true;
+        else if (arg == "--attr-path" || arg == "-P") printAttrPath = true;
+        else if (arg == "--attr" || arg == "-A")
+            attrPath = needArg(i, args, arg);
+        else if (arg[0] == '-')
+            throw UsageError(format("unknown flag `%1%'") % arg);
+        else remaining.push_back(arg);
+    }
+
+
+    /* Obtain derivation information from the specified source. */
+    DrvInfos availElems, installedElems;
+
+    if (source == sInstalled || compareVersions || printStatus)
+        installedElems = queryInstalled(globals.state, globals.profile);
+
+    if (source == sAvailable || compareVersions)
+        loadDerivations(globals.state, globals.instSource.nixExprPath,
+            globals.instSource.systemFilter, globals.instSource.autoArgs,
+            attrPath, availElems);
+
+    DrvInfos elems_ = filterBySelector(globals.state,
+        source == sInstalled ? installedElems : availElems,
+        remaining, false);
+
+    DrvInfos & otherElems(source == sInstalled ? availElems : installedElems);
+
+
+    /* Sort them by name. */
+    /* !!! */
+    vector<DrvInfo> elems;
+    for (DrvInfos::iterator i = elems_.begin(); i != elems_.end(); ++i)
+        elems.push_back(*i);
+    sort(elems.begin(), elems.end(), cmpElemByName);
+
+
+    /* We only need to know the installed paths when we are querying
+       the status of the derivation. */
+    PathSet installed; /* installed paths */
+
+    if (printStatus) {
+        for (DrvInfos::iterator i = installedElems.begin();
+             i != installedElems.end(); ++i)
+            installed.insert(i->queryOutPath());
+    }
+
+
+    /* Query which paths have substitutes. */
+    PathSet validPaths, substitutablePaths;
+    if (printStatus || globals.prebuiltOnly) {
+        PathSet paths;
+        foreach (vector<DrvInfo>::iterator, i, elems)
+            try {
+                paths.insert(i->queryOutPath());
+            } catch (AssertionError & e) {
+                printMsg(lvlTalkative, format("skipping derivation named `%1%' which gives an assertion failure") % i->name);
+                i->setFailed();
+            }
+        validPaths = store->queryValidPaths(paths);
+        substitutablePaths = store->querySubstitutablePaths(paths);
+    }
+
+
+    /* Print the desired columns, or XML output. */
+    if (jsonOutput) {
+        queryJSON(globals, elems);
+        return;
+    }
+
+    Table table;
+    std::ostringstream dummy;
+    XMLWriter xml(true, *(xmlOutput ? &cout : &dummy));
+    XMLOpenElement xmlRoot(xml, "items");
+
+    foreach (vector<DrvInfo>::iterator, i, elems) {
+        try {
+            if (i->hasFailed()) continue;
+
+            startNest(nest, lvlDebug, format("outputting query result `%1%'") % i->attrPath);
+
+            if (globals.prebuiltOnly &&
+                validPaths.find(i->queryOutPath()) == validPaths.end() &&
+                substitutablePaths.find(i->queryOutPath()) == substitutablePaths.end())
+                continue;
+
+            /* For table output. */
+            Strings columns;
+
+            /* For XML output. */
+            XMLAttrs attrs;
+
+            if (printStatus) {
+                Path outPath = i->queryOutPath();
+                bool hasSubs = substitutablePaths.find(outPath) != substitutablePaths.end();
+                bool isInstalled = installed.find(outPath) != installed.end();
+                bool isValid = validPaths.find(outPath) != validPaths.end();
+                if (xmlOutput) {
+                    attrs["installed"] = isInstalled ? "1" : "0";
+                    attrs["valid"] = isValid ? "1" : "0";
+                    attrs["substitutable"] = hasSubs ? "1" : "0";
+                } else
+                    columns.push_back(
+                        (string) (isInstalled ? "I" : "-")
+                        + (isValid ? "P" : "-")
+                        + (hasSubs ? "S" : "-"));
+            }
+
+            if (xmlOutput)
+                attrs["attrPath"] = i->attrPath;
+            else if (printAttrPath)
+                columns.push_back(i->attrPath);
+
+            if (xmlOutput)
+                attrs["name"] = i->name;
+            else if (printName)
+                columns.push_back(i->name);
+
+            if (compareVersions) {
+                /* Compare this element against the versions of the
+                   same named packages in either the set of available
+                   elements, or the set of installed elements.  !!!
+                   This is O(N * M), should be O(N * lg M). */
+                string version;
+                VersionDiff diff = compareVersionAgainstSet(*i, otherElems, version);
+
+                char ch;
+                switch (diff) {
+                    case cvLess: ch = '>'; break;
+                    case cvEqual: ch = '='; break;
+                    case cvGreater: ch = '<'; break;
+                    case cvUnavail: ch = '-'; break;
+                    default: abort();
+                }
+
+                if (xmlOutput) {
+                    if (diff != cvUnavail) {
+                        attrs["versionDiff"] = ch;
+                        attrs["maxComparedVersion"] = version;
+                    }
+                } else {
+                    string column = (string) "" + ch + " " + version;
+                    if (diff == cvGreater) column = colorString(column);
+                    columns.push_back(column);
+                }
+            }
+
+            if (xmlOutput) {
+                if (i->system != "") attrs["system"] = i->system;
+            }
+            else if (printSystem)
+                columns.push_back(i->system);
+
+            if (printDrvPath) {
+                string drvPath = i->queryDrvPath();
+                if (xmlOutput) {
+                    if (drvPath != "") attrs["drvPath"] = drvPath;
+                } else
+                    columns.push_back(drvPath == "" ? "-" : drvPath);
+            }
+
+            if (printOutPath && !xmlOutput) {
+                DrvInfo::Outputs outputs = i->queryOutputs();
+                string s;
+                foreach (DrvInfo::Outputs::iterator, j, outputs) {
+                    if (!s.empty()) s += ';';
+                    if (j->first != "out") { s += j->first; s += "="; }
+                    s += j->second;
+                }
+                columns.push_back(s);
+            }
+
+            if (printDescription) {
+                string descr = i->queryMetaString("description");
+                if (xmlOutput) {
+                    if (descr != "") attrs["description"] = descr;
+                } else
+                    columns.push_back(descr);
+            }
+
+            if (xmlOutput) {
+                if (printOutPath || printMeta) {
+                    XMLOpenElement item(xml, "item", attrs);
+                    if (printOutPath) {
+                        DrvInfo::Outputs outputs = i->queryOutputs();
+                        foreach (DrvInfo::Outputs::iterator, j, outputs) {
+                            XMLAttrs attrs2;
+                            attrs2["name"] = j->first;
+                            attrs2["path"] = j->second;
+                            xml.writeEmptyElement("output", attrs2);
+                        }
+                    }
+                    if (printMeta) {
+                        StringSet metaNames = i->queryMetaNames();
+                        foreach (StringSet::iterator, j, metaNames) {
+                            XMLAttrs attrs2;
+                            attrs2["name"] = *j;
+                            Value * v = i->queryMeta(*j);
+                            if (!v)
+                                printMsg(lvlError, format("derivation `%1%' has invalid meta attribute `%2%'") % i->name % *j);
+                            else {
+                                if (v->type == tString) {
+                                    attrs2["type"] = "string";
+                                    attrs2["value"] = v->string.s;
+                                    xml.writeEmptyElement("meta", attrs2);
+                                } else if (v->type == tInt) {
+                                    attrs2["type"] = "int";
+                                    attrs2["value"] = (format("%1%") % v->integer).str();
+                                    xml.writeEmptyElement("meta", attrs2);
+                                } else if (v->type == tBool) {
+                                    attrs2["type"] = "bool";
+                                    attrs2["value"] = v->boolean ? "true" : "false";
+                                    xml.writeEmptyElement("meta", attrs2);
+                                } else if (v->type == tList) {
+                                    attrs2["type"] = "strings";
+                                    XMLOpenElement m(xml, "meta", attrs2);
+                                    for (unsigned int j = 0; j < v->list.length; ++j) {
+                                        if (v->list.elems[j]->type != tString) continue;
+                                        XMLAttrs attrs3;
+                                        attrs3["value"] = v->list.elems[j]->string.s;
+                                        xml.writeEmptyElement("string", attrs3);
+                                    }
+                                }
+                            }
+                        }
+                    }
+                } else
+                    xml.writeEmptyElement("item", attrs);
+            } else
+                table.push_back(columns);
+
+            cout.flush();
+
+        } catch (AssertionError & e) {
+            printMsg(lvlTalkative, format("skipping derivation named `%1%' which gives an assertion failure") % i->name);
+        } catch (Error & e) {
+            e.addPrefix(format("while querying the derivation named `%1%':\n") % i->name);
+            throw;
+        }
+    }
+
+    if (!xmlOutput) printTable(table);
+}
+
+
+static void opSwitchProfile(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+    if (opArgs.size() != 1)
+        throw UsageError(format("exactly one argument expected"));
+
+    Path profile = absPath(opArgs.front());
+    Path profileLink = getHomeDir() + "/.nix-profile";
+
+    switchLink(profileLink, profile);
+}
+
+
+static const int prevGen = -2;
+
+
+static void switchGeneration(Globals & globals, int dstGen)
+{
+    PathLocks lock;
+    lockProfile(lock, globals.profile);
+
+    int curGen;
+    Generations gens = findGenerations(globals.profile, curGen);
+
+    Generation dst;
+    for (Generations::iterator i = gens.begin(); i != gens.end(); ++i)
+        if ((dstGen == prevGen && i->number < curGen) ||
+            (dstGen >= 0 && i->number == dstGen))
+            dst = *i;
+
+    if (!dst) {
+        if (dstGen == prevGen)
+            throw Error(format("no generation older than the current (%1%) exists")
+                % curGen);
+        else
+            throw Error(format("generation %1% does not exist") % dstGen);
+    }
+
+    printMsg(lvlInfo, format("switching from generation %1% to %2%")
+        % curGen % dst.number);
+
+    if (globals.dryRun) return;
+
+    switchLink(globals.profile, dst.path);
+}
+
+
+static void opSwitchGeneration(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+    if (opArgs.size() != 1)
+        throw UsageError(format("exactly one argument expected"));
+
+    int dstGen;
+    if (!string2Int(opArgs.front(), dstGen))
+        throw UsageError(format("expected a generation number"));
+
+    switchGeneration(globals, dstGen);
+}
+
+
+static void opRollback(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+    if (opArgs.size() != 0)
+        throw UsageError(format("no arguments expected"));
+
+    switchGeneration(globals, prevGen);
+}
+
+
+static void opListGenerations(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+    if (opArgs.size() != 0)
+        throw UsageError(format("no arguments expected"));
+
+    PathLocks lock;
+    lockProfile(lock, globals.profile);
+
+    int curGen;
+    Generations gens = findGenerations(globals.profile, curGen);
+
+    for (Generations::iterator i = gens.begin(); i != gens.end(); ++i) {
+        tm t;
+        if (!localtime_r(&i->creationTime, &t)) throw Error("cannot convert time");
+        cout << format("%|4|   %|4|-%|02|-%|02| %|02|:%|02|:%|02|   %||\n")
+            % i->number
+            % (t.tm_year + 1900) % (t.tm_mon + 1) % t.tm_mday
+            % t.tm_hour % t.tm_min % t.tm_sec
+            % (i->number == curGen ? "(current)" : "");
+    }
+}
+
+
+static void deleteGeneration2(Globals & globals, unsigned int gen)
+{
+    if (globals.dryRun)
+        printMsg(lvlInfo, format("would remove generation %1%") % gen);
+    else {
+        printMsg(lvlInfo, format("removing generation %1%") % gen);
+        deleteGeneration(globals.profile, gen);
+    }
+
+}
+
+
+static void opDeleteGenerations(Globals & globals,
+    Strings args, Strings opFlags, Strings opArgs)
+{
+    if (opFlags.size() > 0)
+        throw UsageError(format("unknown flag `%1%'") % opFlags.front());
+
+    PathLocks lock;
+    lockProfile(lock, globals.profile);
+
+    int curGen;
+    Generations gens = findGenerations(globals.profile, curGen);
+
+    for (Strings::iterator i = opArgs.begin(); i != opArgs.end(); ++i) {
+
+        if (*i == "old") {
+            for (Generations::iterator j = gens.begin(); j != gens.end(); ++j)
+                if (j->number != curGen)
+                    deleteGeneration2(globals, j->number);
+        }
+
+        else {
+            int n;
+            if (!string2Int(*i, n) || n < 0)
+                throw UsageError(format("invalid generation specifier `%1%'")  % *i);
+            bool found = false;
+            for (Generations::iterator j = gens.begin(); j != gens.end(); ++j) {
+                if (j->number == n) {
+                    deleteGeneration2(globals, j->number);
+                    found = true;
+                    break;
+                }
+            }
+            if (!found)
+                printMsg(lvlError, format("generation %1% does not exist") % n);
+        }
+    }
+}
+
+
+void run(Strings args)
+{
+    Strings opFlags, opArgs, remaining;
+    Operation op = 0;
+
+    Globals globals;
+
+    globals.instSource.type = srcUnknown;
+    globals.instSource.nixExprPath = getDefNixExprPath();
+    globals.instSource.systemFilter = "*";
+
+    globals.dryRun = false;
+    globals.preserveInstalled = false;
+    globals.removeAll = false;
+    globals.prebuiltOnly = false;
+
+    for (Strings::iterator i = args.begin(); i != args.end(); ) {
+        string arg = *i++;
+
+        Operation oldOp = op;
+
+        if (arg == "--install" || arg == "-i")
+            op = opInstall;
+        else if (parseOptionArg(arg, i, args.end(),
+                     globals.state, globals.instSource.autoArgs))
+            ;
+        else if (parseSearchPathArg(arg, i, args.end(), globals.state))
+            ;
+        else if (arg == "--force-name") // undocumented flag for nix-install-package
+            globals.forceName = needArg(i, args, arg);
+        else if (arg == "--uninstall" || arg == "-e")
+            op = opUninstall;
+        else if (arg == "--upgrade" || arg == "-u")
+            op = opUpgrade;
+        else if (arg == "--set-flag")
+            op = opSetFlag;
+        else if (arg == "--set")
+            op = opSet;
+        else if (arg == "--query" || arg == "-q")
+            op = opQuery;
+        else if (arg == "--profile" || arg == "-p")
+            globals.profile = absPath(needArg(i, args, arg));
+        else if (arg == "--file" || arg == "-f")
+            globals.instSource.nixExprPath = lookupFileArg(globals.state, needArg(i, args, arg));
+        else if (arg == "--switch-profile" || arg == "-S")
+            op = opSwitchProfile;
+        else if (arg == "--switch-generation" || arg == "-G")
+            op = opSwitchGeneration;
+        else if (arg == "--rollback")
+            op = opRollback;
+        else if (arg == "--list-generations")
+            op = opListGenerations;
+        else if (arg == "--delete-generations")
+            op = opDeleteGenerations;
+        else if (arg == "--dry-run") {
+            printMsg(lvlInfo, "(dry run; not doing anything)");
+            globals.dryRun = true;
+        }
+        else if (arg == "--system-filter")
+            globals.instSource.systemFilter = needArg(i, args, arg);
+        else if (arg == "--prebuilt-only" || arg == "-b")
+            globals.prebuiltOnly = true;
+        else if (arg == "--repair")
+            globals.state.repair = true;
+        else {
+            remaining.push_back(arg);
+            if (arg[0] == '-') {
+                opFlags.push_back(arg);
+                if (arg == "--from-profile") { /* !!! hack */
+                    if (i != args.end()) opFlags.push_back(*i++);
+                }
+            } else opArgs.push_back(arg);
+        }
+
+        if (oldOp && oldOp != op)
+            throw UsageError("only one operation may be specified");
+    }
+
+    if (!op) throw UsageError("no operation specified");
+
+    if (globals.profile == "")
+        globals.profile = getEnv("NIX_PROFILE", "");
+
+    if (globals.profile == "") {
+        Path profileLink = getHomeDir() + "/.nix-profile";
+        globals.profile = pathExists(profileLink)
+            ? absPath(readLink(profileLink), dirOf(profileLink))
+            : canonPath(settings.nixStateDir + "/profiles/default");
+    }
+
+    store = openStore();
+
+    op(globals, remaining, opFlags, opArgs);
+
+    globals.state.printStats();
+}
+
+
+string programId = "nix-env";
diff --git a/src/nix-env/profiles.cc b/src/nix-env/profiles.cc
new file mode 100644
index 000000000000..c327993594e8
--- /dev/null
+++ b/src/nix-env/profiles.cc
@@ -0,0 +1,148 @@
+#include "profiles.hh"
+#include "store-api.hh"
+#include "util.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+
+
+namespace nix {
+
+
+static bool cmpGensByNumber(const Generation & a, const Generation & b)
+{
+    return a.number < b.number;
+}
+
+
+/* Parse a generation name of the format
+   `<profilename>-<number>-link'. */
+static int parseName(const string & profileName, const string & name)
+{
+    if (string(name, 0, profileName.size() + 1) != profileName + "-") return -1;
+    string s = string(name, profileName.size() + 1);
+    string::size_type p = s.find("-link");
+    if (p == string::npos) return -1;
+    int n;
+    if (string2Int(string(s, 0, p), n) && n >= 0)
+        return n;
+    else
+        return -1;
+}
+
+
+
+Generations findGenerations(Path profile, int & curGen)
+{
+    Generations gens;
+
+    Path profileDir = dirOf(profile);
+    string profileName = baseNameOf(profile);
+
+    Strings names = readDirectory(profileDir);
+    for (Strings::iterator i = names.begin(); i != names.end(); ++i) {
+        int n;
+        if ((n = parseName(profileName, *i)) != -1) {
+            Generation gen;
+            gen.path = profileDir + "/" + *i;
+            gen.number = n;
+            struct stat st;
+            if (lstat(gen.path.c_str(), &st) != 0)
+                throw SysError(format("statting `%1%'") % gen.path);
+            gen.creationTime = st.st_mtime;
+            gens.push_back(gen);
+        }
+    }
+
+    gens.sort(cmpGensByNumber);
+
+    curGen = pathExists(profile)
+        ? parseName(profileName, readLink(profile))
+        : -1;
+
+    return gens;
+}
+
+
+static void makeName(const Path & profile, unsigned int num,
+    Path & outLink)
+{
+    Path prefix = (format("%1%-%2%") % profile % num).str();
+    outLink = prefix + "-link";
+}
+
+
+Path createGeneration(Path profile, Path outPath)
+{
+    /* The new generation number should be higher than old the
+       previous ones. */
+    int dummy;
+    Generations gens = findGenerations(profile, dummy);
+    unsigned int num = gens.size() > 0 ? gens.back().number : 0;
+
+    /* Create the new generation.  Note that addPermRoot() blocks if
+       the garbage collector is running to prevent the stuff we've
+       built from moving from the temporary roots (which the GC knows)
+       to the permanent roots (of which the GC would have a stale
+       view).  If we didn't do it this way, the GC might remove the
+       user environment etc. we've just built. */
+    Path generation;
+    makeName(profile, num + 1, generation);
+    addPermRoot(*store, outPath, generation, false, true);
+
+    return generation;
+}
+
+
+static void removeFile(const Path & path)
+{
+    if (remove(path.c_str()) == -1)
+        throw SysError(format("cannot unlink `%1%'") % path);
+}
+
+
+void deleteGeneration(const Path & profile, unsigned int gen)
+{
+    Path generation;
+    makeName(profile, gen, generation);
+    removeFile(generation);
+}
+
+
+void switchLink(Path link, Path target)
+{
+    /* Hacky. */
+    if (dirOf(target) == dirOf(link)) target = baseNameOf(target);
+
+    Path tmp = canonPath(dirOf(link) + "/.new_" + baseNameOf(link));
+    if (symlink(target.c_str(), tmp.c_str()) != 0)
+        throw SysError(format("creating symlink `%1%'") % tmp);
+    /* The rename() system call is supposed to be essentially atomic
+       on Unix.  That is, if we have links `current -> X' and
+       `new_current -> Y', and we rename new_current to current, a
+       process accessing current will see X or Y, but never a
+       file-not-found or other error condition.  This is sufficient to
+       atomically switch user environments. */
+    if (rename(tmp.c_str(), link.c_str()) != 0)
+        throw SysError(format("renaming `%1%' to `%2%'") % tmp % link);
+}
+
+
+void lockProfile(PathLocks & lock, const Path & profile)
+{
+    lock.lockPaths(singleton<PathSet>(profile),
+        (format("waiting for lock on profile `%1%'") % profile).str());
+    lock.setDeletion(true);
+}
+
+
+string optimisticLockProfile(const Path & profile)
+{
+    return pathExists(profile) ? readLink(profile) : "";
+}
+
+
+}
diff --git a/src/nix-env/profiles.hh b/src/nix-env/profiles.hh
new file mode 100644
index 000000000000..30d2376d998c
--- /dev/null
+++ b/src/nix-env/profiles.hh
@@ -0,0 +1,55 @@
+#pragma once
+
+#include "types.hh"
+#include "pathlocks.hh"
+
+#include <time.h>
+
+
+namespace nix {
+
+
+struct Generation
+{
+    int number;
+    Path path;
+    time_t creationTime;
+    Generation()
+    {
+        number = -1;
+    }
+    operator bool() const
+    {
+        return number != -1;
+    }
+};
+
+typedef list<Generation> Generations;
+
+
+/* Returns the list of currently present generations for the specified
+   profile, sorted by generation number. */
+Generations findGenerations(Path profile, int & curGen);
+    
+Path createGeneration(Path profile, Path outPath);
+
+void deleteGeneration(const Path & profile, unsigned int gen);
+
+void switchLink(Path link, Path target);
+
+/* Ensure exclusive access to a profile.  Any command that modifies
+   the profile first acquires this lock. */
+void lockProfile(PathLocks & lock, const Path & profile);
+
+/* Optimistic locking is used by long-running operations like `nix-env
+   -i'.  Instead of acquiring the exclusive lock for the entire
+   duration of the operation, we just perform the operation
+   optimistically (without an exclusive lock), and check at the end
+   whether the profile changed while we were busy (i.e., the symlink
+   target changed).  If so, the operation is restarted.  Restarting is
+   generally cheap, since the build results are still in the Nix
+   store.  Most of the time, only the user environment has to be
+   rebuilt. */
+string optimisticLockProfile(const Path & profile);
+
+}
diff --git a/src/nix-env/user-env.cc b/src/nix-env/user-env.cc
new file mode 100644
index 000000000000..3a73f2647a6b
--- /dev/null
+++ b/src/nix-env/user-env.cc
@@ -0,0 +1,148 @@
+#include "user-env.hh"
+#include "util.hh"
+#include "derivations.hh"
+#include "store-api.hh"
+#include "globals.hh"
+#include "shared.hh"
+#include "eval.hh"
+#include "eval-inline.hh"
+#include "profiles.hh"
+
+
+namespace nix {
+
+
+DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
+{
+    DrvInfos elems;
+    Path manifestFile = userEnv + "/manifest.nix";
+    if (pathExists(manifestFile)) {
+        Value v;
+        state.evalFile(manifestFile, v);
+        Bindings bindings;
+        getDerivations(state, v, "", bindings, elems, false);
+    }
+    return elems;
+}
+
+
+bool createUserEnv(EvalState & state, DrvInfos & elems,
+    const Path & profile, bool keepDerivations,
+    const string & lockToken)
+{
+    /* Build the components in the user environment, if they don't
+       exist already. */
+    PathSet drvsToBuild;
+    foreach (DrvInfos::iterator, i, elems)
+        if (i->queryDrvPath() != "")
+            drvsToBuild.insert(i->queryDrvPath());
+
+    debug(format("building user environment dependencies"));
+    store->buildPaths(drvsToBuild, state.repair);
+
+    /* Construct the whole top level derivation. */
+    PathSet references;
+    Value manifest;
+    state.mkList(manifest, elems.size());
+    unsigned int n = 0;
+    foreach (DrvInfos::iterator, i, elems) {
+        /* Create a pseudo-derivation containing the name, system,
+           output paths, and optionally the derivation path, as well
+           as the meta attributes. */
+        Path drvPath = keepDerivations ? i->queryDrvPath() : "";
+
+        Value & v(*state.allocValue());
+        manifest.list.elems[n++] = &v;
+        state.mkAttrs(v, 16);
+
+        mkString(*state.allocAttr(v, state.sType), "derivation");
+        mkString(*state.allocAttr(v, state.sName), i->name);
+        if (!i->system.empty())
+            mkString(*state.allocAttr(v, state.sSystem), i->system);
+        mkString(*state.allocAttr(v, state.sOutPath), i->queryOutPath());
+        if (drvPath != "")
+            mkString(*state.allocAttr(v, state.sDrvPath), i->queryDrvPath());
+
+        // Copy each output.
+        DrvInfo::Outputs outputs = i->queryOutputs();
+        Value & vOutputs = *state.allocAttr(v, state.sOutputs);
+        state.mkList(vOutputs, outputs.size());
+        unsigned int m = 0;
+        foreach (DrvInfo::Outputs::iterator, j, outputs) {
+            mkString(*(vOutputs.list.elems[m++] = state.allocValue()), j->first);
+            Value & vOutputs = *state.allocAttr(v, state.symbols.create(j->first));
+            state.mkAttrs(vOutputs, 2);
+            mkString(*state.allocAttr(vOutputs, state.sOutPath), j->second);
+
+            /* This is only necessary when installing store paths, e.g.,
+               `nix-env -i /nix/store/abcd...-foo'. */
+            store->addTempRoot(j->second);
+            store->ensurePath(j->second);
+
+            references.insert(j->second);
+        }
+
+        // Copy the meta attributes.
+        Value & vMeta = *state.allocAttr(v, state.sMeta);
+        state.mkAttrs(vMeta, 16);
+        StringSet metaNames = i->queryMetaNames();
+        foreach (StringSet::iterator, j, metaNames) {
+            Value * v = i->queryMeta(*j);
+            if (!v) continue;
+            vMeta.attrs->push_back(Attr(state.symbols.create(*j), v));
+        }
+        v.attrs->sort();
+
+        if (drvPath != "") references.insert(drvPath);
+    }
+
+    /* Also write a copy of the list of user environment elements to
+       the store; we need it for future modifications of the
+       environment. */
+    Path manifestFile = store->addTextToStore("env-manifest.nix",
+        (format("%1%") % manifest).str(), references);
+
+    /* Get the environment builder expression. */
+    Value envBuilder;
+    state.evalFile(state.findFile("nix/buildenv.nix"), envBuilder);
+
+    /* Construct a Nix expression that calls the user environment
+       builder with the manifest as argument. */
+    Value args, topLevel;
+    state.mkAttrs(args, 3);
+    mkString(*state.allocAttr(args, state.symbols.create("manifest")),
+        manifestFile, singleton<PathSet>(manifestFile));
+    args.attrs->push_back(Attr(state.symbols.create("derivations"), &manifest));
+    args.attrs->sort();
+    mkApp(topLevel, envBuilder, args);
+
+    /* Evaluate it. */
+    debug("evaluating user environment builder");
+    state.forceValue(topLevel);
+    PathSet context;
+    Path topLevelDrv = state.coerceToPath(*topLevel.attrs->find(state.sDrvPath)->value, context);
+    Path topLevelOut = state.coerceToPath(*topLevel.attrs->find(state.sOutPath)->value, context);
+
+    /* Realise the resulting store expression. */
+    debug("building user environment");
+    store->buildPaths(singleton<PathSet>(topLevelDrv), state.repair);
+
+    /* Switch the current user environment to the output path. */
+    PathLocks lock;
+    lockProfile(lock, profile);
+
+    Path lockTokenCur = optimisticLockProfile(profile);
+    if (lockToken != lockTokenCur) {
+        printMsg(lvlError, format("profile `%1%' changed while we were busy; restarting") % profile);
+        return false;
+    }
+
+    debug(format("switching to new user environment"));
+    Path generation = createGeneration(profile, topLevelOut);
+    switchLink(profile, generation);
+
+    return true;
+}
+
+
+}
diff --git a/src/nix-env/user-env.hh b/src/nix-env/user-env.hh
new file mode 100644
index 000000000000..f188efe9b4a9
--- /dev/null
+++ b/src/nix-env/user-env.hh
@@ -0,0 +1,13 @@
+#pragma once
+
+#include "get-drvs.hh"
+
+namespace nix {
+
+DrvInfos queryInstalled(EvalState & state, const Path & userEnv);
+
+bool createUserEnv(EvalState & state, DrvInfos & elems,
+    const Path & profile, bool keepDerivations,
+    const string & lockToken);
+
+}
diff --git a/src/nix-hash/local.mk b/src/nix-hash/local.mk
new file mode 100644
index 000000000000..7c290ca8466e
--- /dev/null
+++ b/src/nix-hash/local.mk
@@ -0,0 +1,7 @@
+programs += nix-hash
+
+nix-hash_DIR := $(d)
+
+nix-hash_SOURCES := $(d)/nix-hash.cc
+
+nix-hash_LIBS = libmain libstore libutil libformat
diff --git a/src/nix-hash/nix-hash.cc b/src/nix-hash/nix-hash.cc
new file mode 100644
index 000000000000..af3dda4ad7b8
--- /dev/null
+++ b/src/nix-hash/nix-hash.cc
@@ -0,0 +1,64 @@
+#include "hash.hh"
+#include "shared.hh"
+
+#include <iostream>
+
+
+using namespace nix;
+
+
+void printHelp()
+{
+    showManPage("nix-hash");
+}
+
+
+void run(Strings args)
+{
+    HashType ht = htMD5;
+    bool flat = false;
+    bool base32 = false;
+    bool truncate = false;
+    enum { opHash, opTo32, opTo16 } op = opHash;
+
+    Strings ss;
+
+    for (Strings::iterator i = args.begin();
+         i != args.end(); i++)
+    {
+        if (*i == "--flat") flat = true;
+        else if (*i == "--base32") base32 = true;
+        else if (*i == "--truncate") truncate = true;
+        else if (*i == "--type") {
+            ++i;
+            if (i == args.end()) throw UsageError("`--type' requires an argument");
+            ht = parseHashType(*i);
+            if (ht == htUnknown)
+                throw UsageError(format("unknown hash type `%1%'") % *i);
+        }
+        else if (*i == "--to-base16") op = opTo16;
+        else if (*i == "--to-base32") op = opTo32;
+        else ss.push_back(*i);
+    }
+
+    if (op == opHash) {
+        foreach (Strings::iterator, i, ss) {
+            Hash h = flat ? hashFile(ht, *i) : hashPath(ht, *i).first;
+            if (truncate && h.hashSize > 20) h = compressHash(h, 20);
+            std::cout << format("%1%\n") %
+                (base32 ? printHash32(h) : printHash(h));
+        }
+    }
+
+    else {
+        foreach (Strings::iterator, i, ss) {
+            Hash h = parseHash16or32(ht, *i);
+            std::cout << format("%1%\n") %
+                (op == opTo16 ? printHash(h) : printHash32(h));
+        }
+    }
+}
+
+
+string programId = "nix-hash";
+
diff --git a/src/nix-instantiate/local.mk b/src/nix-instantiate/local.mk
new file mode 100644
index 000000000000..7d1bc5ec9dfb
--- /dev/null
+++ b/src/nix-instantiate/local.mk
@@ -0,0 +1,7 @@
+programs += nix-instantiate
+
+nix-instantiate_DIR := $(d)
+
+nix-instantiate_SOURCES := $(d)/nix-instantiate.cc
+
+nix-instantiate_LIBS = libexpr libmain libstore libutil libformat
diff --git a/src/nix-instantiate/nix-instantiate.cc b/src/nix-instantiate/nix-instantiate.cc
new file mode 100644
index 000000000000..b7f944062cec
--- /dev/null
+++ b/src/nix-instantiate/nix-instantiate.cc
@@ -0,0 +1,176 @@
+#include "globals.hh"
+#include "shared.hh"
+#include "eval.hh"
+#include "eval-inline.hh"
+#include "get-drvs.hh"
+#include "attr-path.hh"
+#include "value-to-xml.hh"
+#include "util.hh"
+#include "store-api.hh"
+#include "common-opts.hh"
+#include "misc.hh"
+
+#include <map>
+#include <iostream>
+
+
+using namespace nix;
+
+
+void printHelp()
+{
+    showManPage("nix-instantiate");
+}
+
+
+static Expr * parseStdin(EvalState & state)
+{
+    startNest(nest, lvlTalkative, format("parsing standard input"));
+    return state.parseExprFromString(drainFD(0), absPath("."));
+}
+
+
+static Path gcRoot;
+static int rootNr = 0;
+static bool indirectRoot = false;
+
+
+void processExpr(EvalState & state, const Strings & attrPaths,
+    bool parseOnly, bool strict, Bindings & autoArgs,
+    bool evalOnly, bool xmlOutput, bool location, Expr * e)
+{
+    if (parseOnly) {
+        std::cout << format("%1%\n") % *e;
+        return;
+    }
+
+    Value vRoot;
+    state.eval(e, vRoot);
+
+    foreach (Strings::const_iterator, i, attrPaths) {
+        Value & v(*findAlongAttrPath(state, *i, autoArgs, vRoot));
+        state.forceValue(v);
+
+        PathSet context;
+        if (evalOnly)
+            if (xmlOutput)
+                printValueAsXML(state, strict, location, v, std::cout, context);
+            else {
+                if (strict) state.strictForceValue(v);
+                std::cout << v << std::endl;
+            }
+        else {
+            DrvInfos drvs;
+            getDerivations(state, v, "", autoArgs, drvs, false);
+            foreach (DrvInfos::iterator, i, drvs) {
+                Path drvPath = i->queryDrvPath();
+
+                /* What output do we want? */
+                string outputName = i->queryOutputName();
+                if (outputName == "")
+                    throw Error(format("derivation `%1%' lacks an `outputName' attribute ") % drvPath);
+
+                if (gcRoot == "")
+                    printGCWarning();
+                else {
+                    Path rootName = gcRoot;
+                    if (++rootNr > 1) rootName += "-" + int2String(rootNr);
+                    drvPath = addPermRoot(*store, drvPath, rootName, indirectRoot);
+                }
+                std::cout << format("%1%%2%\n") % drvPath % (outputName != "out" ? "!" + outputName : "");
+            }
+        }
+    }
+}
+
+
+void run(Strings args)
+{
+    EvalState state;
+    Strings files;
+    bool readStdin = false;
+    bool findFile = false;
+    bool evalOnly = false;
+    bool parseOnly = false;
+    bool xmlOutput = false;
+    bool xmlOutputSourceLocation = true;
+    bool strict = false;
+    Strings attrPaths;
+    Bindings autoArgs;
+
+    for (Strings::iterator i = args.begin(); i != args.end(); ) {
+        string arg = *i++;
+
+        if (arg == "-")
+            readStdin = true;
+        else if (arg == "--eval-only") {
+            settings.readOnlyMode = true;
+            evalOnly = true;
+        }
+        else if (arg == "--parse-only") {
+            settings.readOnlyMode = true;
+            parseOnly = evalOnly = true;
+        }
+        else if (arg == "--find-file")
+            findFile = true;
+        else if (arg == "--attr" || arg == "-A") {
+            if (i == args.end())
+                throw UsageError("`--attr' requires an argument");
+            attrPaths.push_back(*i++);
+        }
+        else if (parseOptionArg(arg, i, args.end(), state, autoArgs))
+            ;
+        else if (parseSearchPathArg(arg, i, args.end(), state))
+            ;
+        else if (arg == "--add-root") {
+            if (i == args.end())
+                throw UsageError("`--add-root' requires an argument");
+            gcRoot = absPath(*i++);
+        }
+        else if (arg == "--indirect")
+            indirectRoot = true;
+        else if (arg == "--xml")
+            xmlOutput = true;
+        else if (arg == "--no-location")
+            xmlOutputSourceLocation = false;
+        else if (arg == "--strict")
+            strict = true;
+        else if (arg == "--repair")
+            state.repair = true;
+        else if (arg[0] == '-')
+            throw UsageError(format("unknown flag `%1%'") % arg);
+        else
+            files.push_back(arg);
+    }
+
+    if (attrPaths.empty()) attrPaths.push_back("");
+
+    if (findFile) {
+        foreach (Strings::iterator, i, files) {
+            Path p = state.findFile(*i);
+            if (p == "") throw Error(format("unable to find `%1%'") % *i);
+            std::cout << p << std::endl;
+        }
+        return;
+    }
+
+    store = openStore();
+
+    if (readStdin) {
+        Expr * e = parseStdin(state);
+        processExpr(state, attrPaths, parseOnly, strict, autoArgs,
+            evalOnly, xmlOutput, xmlOutputSourceLocation, e);
+    } else if (files.empty())
+        files.push_back("./default.nix");
+
+    foreach (Strings::iterator, i, files) {
+        Expr * e = state.parseExprFromFile(resolveExprPath(lookupFileArg(state, *i)));
+        processExpr(state, attrPaths, parseOnly, strict, autoArgs,
+            evalOnly, xmlOutput, xmlOutputSourceLocation, e);
+    }
+
+    state.printStats();
+}
+
+
+string programId = "nix-instantiate";
diff --git a/src/nix-log2xml/local.mk b/src/nix-log2xml/local.mk
new file mode 100644
index 000000000000..46eb2e02ca64
--- /dev/null
+++ b/src/nix-log2xml/local.mk
@@ -0,0 +1,8 @@
+programs += nix-log2xml
+
+nix-log2xml_DIR := $(d)
+
+nix-log2xml_SOURCES := $(d)/log2xml.cc
+
+$(foreach file, mark-errors.xsl log2html.xsl treebits.js, \
+  $(eval $(call install-data-in, $(d)/$(file), $(datadir)/nix/log2html)))
diff --git a/src/nix-log2xml/log2html.xsl b/src/nix-log2xml/log2html.xsl
new file mode 100644
index 000000000000..209399470640
--- /dev/null
+++ b/src/nix-log2xml/log2html.xsl
@@ -0,0 +1,83 @@
+<?xml version="1.0"?>
+
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+
+  <xsl:output method='html' encoding="UTF-8"
+              doctype-public="-//W3C//DTD HTML 4.01//EN"
+              doctype-system="http://www.w3.org/TR/html4/strict.dtd" />
+
+  <xsl:template match="logfile">
+    <html>
+      <head>
+        <script type="text/javascript" src="treebits.js" />
+        <link rel="stylesheet" href="logfile.css" type="text/css" />
+        <title>Log File</title>
+      </head>
+      <body>
+        <ul class='toplevel'>
+          <xsl:for-each select='line|nest'>
+            <li>
+              <xsl:apply-templates select='.'/>
+            </li>
+          </xsl:for-each>
+        </ul>
+      </body>
+    </html>
+  </xsl:template>
+
+  
+  <xsl:template match="nest">
+
+    <!-- The tree should be collapsed by default if all children are
+         unimportant or if the header is unimportant. -->
+<!--    <xsl:variable name="collapsed"
+                  select="count(.//line[not(@priority = 3)]) = 0 or ./head[@priority = 3]" /> -->
+    <xsl:variable name="collapsed" select="count(.//*[@error]) = 0"/>
+                  
+    <xsl:variable name="style"><xsl:if test="$collapsed">display: none;</xsl:if></xsl:variable>
+    <xsl:variable name="arg"><xsl:choose><xsl:when test="$collapsed">true</xsl:when><xsl:otherwise>false</xsl:otherwise></xsl:choose></xsl:variable>
+    
+    <script type='text/javascript'>showTreeToggle(<xsl:value-of select="$collapsed"/>)</script>
+    <xsl:apply-templates select='head'/>
+
+    <!-- Be careful to only generate <ul>s if there are <li>s, otherwise it’s malformed. -->
+    <xsl:if test="line|nest">
+      
+      <ul class='nesting' style="{$style}">
+        <xsl:for-each select='line|nest'>
+
+          <!-- Is this the last line?  If so, mark it as such so that it
+               can be rendered differently. -->
+          <xsl:variable  name="class"><xsl:choose><xsl:when test="position() != last()">line</xsl:when><xsl:otherwise>lastline</xsl:otherwise></xsl:choose></xsl:variable>
+        
+          <li class='{$class}'>
+            <span class='lineconn' />
+            <span class='linebody'>
+              <xsl:apply-templates select='.'/>
+            </span>
+          </li>
+        </xsl:for-each>
+      </ul>
+    </xsl:if>
+    
+  </xsl:template>
+
+  
+  <xsl:template match="head|line">
+    <code>
+      <xsl:if test="@error">
+        <xsl:attribute name="class">error</xsl:attribute>
+      </xsl:if>
+      <xsl:apply-templates/>
+    </code>
+  </xsl:template>
+
+  
+  <xsl:template match="storeref">
+    <em class='storeref'>
+      <span class='popup'><xsl:apply-templates/></span>
+      <span class='elided'>/...</span><xsl:apply-templates select='name'/><xsl:apply-templates select='path'/>
+    </em>
+  </xsl:template>
+  
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/src/nix-log2xml/log2xml.cc b/src/nix-log2xml/log2xml.cc
new file mode 100644
index 000000000000..6645dc500fed
--- /dev/null
+++ b/src/nix-log2xml/log2xml.cc
@@ -0,0 +1,200 @@
+#include <vector>
+#include <iostream>
+#include <cstdio>
+#include <string>
+#include <cstring>
+
+using namespace std;
+
+
+struct Decoder
+{
+    enum { stTop, stEscape, stCSI } state;
+    string line;
+    bool inHeader;
+    int level;
+    vector<int> args;
+    bool newNumber;
+    int priority;
+    bool ignoreLF;
+    int lineNo, charNo;
+    bool warning;
+    bool error;
+
+    Decoder()
+    {
+        state = stTop;
+        line = "";
+        inHeader = false;
+        level = 0;
+        priority = 1;
+        ignoreLF = false;
+        lineNo = 1;
+        charNo = 0;
+        warning = false;
+        error = false;
+    }
+
+    void pushChar(char c);
+
+    void finishLine();
+
+    void decodeFile(istream & st);
+};
+
+
+void Decoder::pushChar(char c)
+{
+    if (c == '\n') {
+        lineNo++;
+        charNo = 0;
+    } else charNo++;
+    
+    switch (state) {
+        
+        case stTop:
+            if (c == '\e') {
+                state = stEscape;
+            } else if (c == '\n' && !ignoreLF) {
+                finishLine();
+            } else line += c;
+            break;
+
+        case stEscape:
+            if (c == '[') {
+                state = stCSI;
+                args.clear();
+                newNumber = true;
+            } else
+                state = stTop; /* !!! wrong */
+            break;
+
+        case stCSI:
+            if (c >= 0x40 && c != 0x7e) {
+                state = stTop;
+                switch (c) {
+                    case 'p':
+                        if (line.size()) finishLine();
+                        level++;
+                        inHeader = true;
+                        cout << "<nest>" << endl;
+                        priority = args.size() >= 1 ? args[0] : 1;
+                        break;
+                    case 'q':
+                        if (line.size()) finishLine();
+                        if (level > 0) {
+                            level--;
+                            cout << "</nest>" << endl;
+                        } else
+                            cerr << "not enough nesting levels at line "
+                                 << lineNo << ", character " << charNo  << endl;
+                        break;
+                    case 's':
+                        if (line.size()) finishLine();
+                        priority = args.size() >= 1 ? args[0] : 1;
+                        break;
+                    case 'a':
+                        ignoreLF = true;
+                        break;
+                    case 'b':
+                        ignoreLF = false;
+                        break;
+                    case 'e':
+                        error = true;
+                        break;
+                    case 'w':
+                        warning = true;
+                        break;
+                }
+            } else if (c >= '0' && c <= '9') {
+                int n = 0;
+                if (!newNumber) {
+                    n = args.back() * 10;
+                    args.pop_back();
+                }
+                n += c - '0';
+                args.push_back(n);
+            }
+            break;
+            
+    }
+}
+
+
+void Decoder::finishLine()
+{
+    string storeDir = "/nix/store/";
+    int sz = storeDir.size();
+    string tag = inHeader ? "head" : "line";
+    cout << "<" << tag;
+    if (priority != 1) cout << " priority='" << priority << "'";
+    if (warning) cout << " warning='1'";
+    if (error) cout << " error='1'";
+    cout << ">";
+
+    for (unsigned int i = 0; i < line.size(); i++) {
+
+        if (line[i] == '<') cout << "&lt;";
+        else if (line[i] == '&') cout << "&amp;";
+        else if (line[i] == '\r') ; /* ignore carriage return */
+        else if (line[i] < 32 && line[i] != 9) cout << "&#xfffd;";
+        else if (i + sz + 33 < line.size() &&
+            string(line, i, sz) == storeDir &&
+            line[i + sz + 32] == '-')
+        {
+            int j = i + sz + 32;
+            /* skip name */
+            while (!strchr("/\n\r\t ()[]:;?<>", line[j])) j++;
+            int k = j;
+            while (!strchr("\n\r\t ()[]:;?<>", line[k])) k++;
+            // !!! escaping
+            cout << "<storeref>"
+                 << "<storedir>"
+                 << string(line, i, sz)
+                 << "</storedir>"
+                 << "<hash>"
+                 << string(line, i + sz, 32)
+                 << "</hash>"
+                 << "<name>"
+                 << string(line, i + sz + 32, j - (i + sz + 32))
+                 << "</name>"
+                 << "<path>"
+                 << string(line, j, k - j)
+                 << "</path>"
+                 << "</storeref>";
+            i = k - 1;
+        } else cout << line[i];
+    }
+    
+    cout << "</" << tag << ">" << endl;
+    line = "";
+    inHeader = false;
+    priority = 1;
+    warning = false;
+    error = false;
+}
+
+
+void Decoder::decodeFile(istream & st)
+{
+    int c;
+    
+    cout << "<logfile>" << endl;
+    
+    while ((c = st.get()) != EOF) {
+        pushChar(c);
+    }
+
+    if (line.size()) finishLine();
+
+    while (level--) cout << "</nest>" << endl;
+    
+    cout << "</logfile>" << endl;
+}
+
+
+int main(int argc, char * * argv)
+{
+    Decoder dec;
+    dec.decodeFile(cin);
+}
diff --git a/src/nix-log2xml/logfile.css b/src/nix-log2xml/logfile.css
new file mode 100644
index 000000000000..ed390d64a9ef
--- /dev/null
+++ b/src/nix-log2xml/logfile.css
@@ -0,0 +1,86 @@
+body {
+    font-family: sans-serif;
+    background: white;
+}
+
+
+ul.nesting, ul.toplevel {
+    padding: 0;
+    margin: 0;
+}
+
+ul.toplevel {
+    list-style-type: none;
+}
+
+ul.nesting li.line, ul.nesting li.lastline {
+    position: relative;
+    list-style-type: none;
+}
+
+ul.nesting li.line {
+    padding-left: 1.1em;
+}
+
+ul.nesting li.lastline {
+    padding-left: 1.2em; // for the 0.1em border-left in .lastline > .lineconn
+}
+
+li.line {
+    border-left: 0.1em solid #6185a0;
+}
+
+li.line > span.lineconn, li.lastline > span.lineconn {
+    position: absolute;
+    height: 0.65em;
+    left: 0em;
+    width: 1em;
+    border-bottom: 0.1em solid #6185a0;
+}
+
+li.lastline > span.lineconn {
+    border-left: 0.1em solid #6185a0;
+}
+
+
+em.storeref {
+    color: #500000;
+    position: relative; 
+    width: 100%;
+}
+
+em.storeref:hover {
+    background-color: #eeeeee;
+}
+
+*.popup {
+    display: none;
+/*    background: url('http://losser.st-lab.cs.uu.nl/~mbravenb/menuback.png') repeat; */
+    background: #ffffcd;
+    border: solid #555555 1px;
+    position: absolute;
+    top: 0em;
+    left: 0em;
+    margin: 0;
+    padding: 0;
+    z-index: 100;
+}
+
+em.storeref:hover span.popup {
+    display: inline;
+}
+
+
+.toggle {
+    text-decoration: none;
+}
+
+.showTree, .hideTree {
+    font-family: monospace;
+    font-size: larger;
+}
+
+.error {
+    color: #ff0000;
+    font-weight: bold;
+}
\ No newline at end of file
diff --git a/src/nix-log2xml/mark-errors.xsl b/src/nix-log2xml/mark-errors.xsl
new file mode 100644
index 000000000000..4e91913e570a
--- /dev/null
+++ b/src/nix-log2xml/mark-errors.xsl
@@ -0,0 +1,24 @@
+<?xml version="1.0"?>
+
+<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
+
+  <xsl:template match="@*|node()">
+    <xsl:copy>
+      <xsl:apply-templates select="@*|node()"/>
+    </xsl:copy>
+  </xsl:template>
+
+  <xsl:template match="line">
+    <line>
+      <xsl:if test="contains(text(), ' *** ') or
+                    contains(text(), 'LaTeX Error') or
+                    contains(text(), 'FAIL:') or
+                    contains(text(), ' error: ') or
+                    true">
+         <xsl:attribute name="error"></xsl:attribute>
+      </xsl:if>
+      <xsl:apply-templates select="@*|node()"/>
+    </line>
+  </xsl:template>
+  
+</xsl:stylesheet>
\ No newline at end of file
diff --git a/src/nix-log2xml/treebits.js b/src/nix-log2xml/treebits.js
new file mode 100644
index 000000000000..3011b391d88b
--- /dev/null
+++ b/src/nix-log2xml/treebits.js
@@ -0,0 +1,50 @@
+/* Acknowledgement: this is based on the Wikipedia table-of-contents
+ * toggle. */
+
+
+var idCounter = 0;
+
+
+function showTreeToggle(isHidden) {
+    if (document.getElementById) {
+        var id = "toggle_" + idCounter;
+        document.writeln(
+            '<a href="javascript:toggleTree(\'' + id + '\')" class="toggle" id="' + id + '">' +
+            '<span class="showTree" ' + (isHidden ? '' : 'style="display: none;"') + '>+</span>' +
+            '<span class="hideTree" ' + (isHidden ? 'style="display: none;"' : '') + '>-</span>' +
+            '</a>');
+        idCounter = idCounter + 1;
+    }
+}
+
+
+function toggleTree(id) {
+
+    var href = document.getElementById(id);
+
+    var node = href;
+    var tree = null;
+    while (node != null) {
+        if (node.className == "nesting") tree = node;
+        node = node.nextSibling;
+    }
+
+    node = href.firstChild;
+    var hideTree = null;
+    var showTree = null;
+    while (node != null) {
+        if (node.className == "showTree") showTree = node;
+        else if (node.className == "hideTree") hideTree = node;
+        node = node.nextSibling;
+    }
+    
+    if (tree.style.display == 'none') {
+        tree.style.display = '';
+        hideTree.style.display = '';
+        showTree.style.display = 'none';
+    } else {
+        tree.style.display = 'none';
+        hideTree.style.display = 'none';
+        showTree.style.display = '';
+    }
+}
diff --git a/src/nix-store/dotgraph.cc b/src/nix-store/dotgraph.cc
new file mode 100644
index 000000000000..72146eb68efc
--- /dev/null
+++ b/src/nix-store/dotgraph.cc
@@ -0,0 +1,162 @@
+#include "dotgraph.hh"
+#include "util.hh"
+#include "store-api.hh"
+
+#include <iostream>
+
+
+using std::cout;
+
+namespace nix {
+
+
+static string dotQuote(const string & s)
+{
+    return "\"" + s + "\"";
+}
+
+
+static string nextColour()
+{
+    static int n = 0;
+    static string colours[] =
+	{ "black", "red", "green", "blue"
+	, "magenta", "burlywood" };
+    return colours[n++ % (sizeof(colours) / sizeof(string))];
+}
+
+
+static string makeEdge(const string & src, const string & dst)
+{
+    format f = format("%1% -> %2% [color = %3%];\n")
+	% dotQuote(src) % dotQuote(dst) % dotQuote(nextColour());
+    return f.str();
+}
+
+
+static string makeNode(const string & id, const string & label,
+    const string & colour)
+{
+    format f = format("%1% [label = %2%, shape = box, "
+	"style = filled, fillcolor = %3%];\n")
+	% dotQuote(id) % dotQuote(label) % dotQuote(colour);
+    return f.str();
+}
+
+
+static string symbolicName(const string & path)
+{
+    string p = baseNameOf(path);
+    int dash = p.find('-');
+    return string(p, dash + 1);
+}
+
+
+#if 0
+string pathLabel(const Path & nePath, const string & elemPath)
+{
+    return (string) nePath + "-" + elemPath;
+}
+
+
+void printClosure(const Path & nePath, const StoreExpr & fs)
+{
+    PathSet workList(fs.closure.roots);
+    PathSet doneSet;
+
+    for (PathSet::iterator i = workList.begin(); i != workList.end(); ++i) {
+	cout << makeEdge(pathLabel(nePath, *i), nePath);
+    }
+
+    while (!workList.empty()) {
+	Path path = *(workList.begin());
+	workList.erase(path);
+
+	if (doneSet.find(path) == doneSet.end()) {
+	    doneSet.insert(path);
+
+	    ClosureElems::const_iterator elem = fs.closure.elems.find(path);
+	    if (elem == fs.closure.elems.end())
+		throw Error(format("bad closure, missing path `%1%'") % path);
+
+	    for (StringSet::const_iterator i = elem->second.refs.begin();
+		 i != elem->second.refs.end(); ++i)
+	    {
+		workList.insert(*i);
+		cout << makeEdge(pathLabel(nePath, *i), pathLabel(nePath, path));
+	    }
+
+	    cout << makeNode(pathLabel(nePath, path), 
+		symbolicName(path), "#ff0000");
+	}
+    }
+}
+#endif
+
+
+void printDotGraph(const PathSet & roots)
+{
+    PathSet workList(roots);
+    PathSet doneSet;
+            
+    cout << "digraph G {\n";
+
+    while (!workList.empty()) {
+	Path path = *(workList.begin());
+	workList.erase(path);
+
+	if (doneSet.find(path) != doneSet.end()) continue;
+        doneSet.insert(path);
+
+        cout << makeNode(path, symbolicName(path), "#ff0000");
+        
+        PathSet references;
+        store->queryReferences(path, references);
+
+        for (PathSet::iterator i = references.begin();
+             i != references.end(); ++i)
+        {
+            if (*i != path) {
+                workList.insert(*i);
+                cout << makeEdge(*i, path);
+            }
+        }
+            
+
+#if 0        
+	    StoreExpr ne = storeExprFromPath(path);
+
+	    string label, colour;
+                    
+	    if (ne.type == StoreExpr::neDerivation) {
+		for (PathSet::iterator i = ne.derivation.inputs.begin();
+		     i != ne.derivation.inputs.end(); ++i)
+		{
+		    workList.insert(*i);
+		    cout << makeEdge(*i, path);
+		}
+
+		label = "derivation";
+		colour = "#00ff00";
+		for (StringPairs::iterator i = ne.derivation.env.begin();
+		     i != ne.derivation.env.end(); ++i)
+		    if (i->first == "name") label = i->second;
+	    }
+
+	    else if (ne.type == StoreExpr::neClosure) {
+		label = "<closure>";
+		colour = "#00ffff";
+		printClosure(path, ne);
+	    }
+
+	    else abort();
+
+	    cout << makeNode(path, label, colour);
+#endif
+    }
+
+    cout << "}\n";
+}
+
+ 
+}
diff --git a/src/nix-store/dotgraph.hh b/src/nix-store/dotgraph.hh
new file mode 100644
index 000000000000..68410d84156d
--- /dev/null
+++ b/src/nix-store/dotgraph.hh
@@ -0,0 +1,9 @@
+#pragma once
+
+#include "types.hh"
+
+namespace nix {
+
+void printDotGraph(const PathSet & roots);
+
+}
diff --git a/src/nix-store/local.mk b/src/nix-store/local.mk
new file mode 100644
index 000000000000..7f93e4c19196
--- /dev/null
+++ b/src/nix-store/local.mk
@@ -0,0 +1,9 @@
+programs += nix-store
+
+nix-store_DIR := $(d)
+
+nix-store_SOURCES := $(wildcard $(d)/*.cc)
+
+nix-store_LIBS = libmain libstore libutil libformat
+
+nix-store_LDFLAGS = -lbz2
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
new file mode 100644
index 000000000000..69a98fe4726d
--- /dev/null
+++ b/src/nix-store/nix-store.cc
@@ -0,0 +1,929 @@
+#include "globals.hh"
+#include "misc.hh"
+#include "archive.hh"
+#include "shared.hh"
+#include "dotgraph.hh"
+#include "xmlgraph.hh"
+#include "local-store.hh"
+#include "util.hh"
+
+#include <iostream>
+#include <algorithm>
+#include <cstdio>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include <bzlib.h>
+
+
+using namespace nix;
+using std::cin;
+using std::cout;
+
+
+typedef void (* Operation) (Strings opFlags, Strings opArgs);
+
+
+void printHelp()
+{
+    showManPage("nix-store");
+}
+
+
+static Path gcRoot;
+static int rootNr = 0;
+static bool indirectRoot = false;
+static bool noOutput = false;
+
+
+LocalStore & ensureLocalStore()
+{
+    LocalStore * store2(dynamic_cast<LocalStore *>(store.get()));
+    if (!store2) throw Error("you don't have sufficient rights to use this command");
+    return *store2;
+}
+
+
+static Path useDeriver(Path path)
+{
+    if (!isDerivation(path)) {
+        path = store->queryDeriver(path);
+        if (path == "")
+            throw Error(format("deriver of path `%1%' is not known") % path);
+    }
+    return path;
+}
+
+
+/* Realise the given path.  For a derivation that means build it; for
+   other paths it means ensure their validity. */
+static PathSet realisePath(const Path & path, bool build = true)
+{
+    DrvPathWithOutputs p = parseDrvPathWithOutputs(path);
+
+    if (isDerivation(p.first)) {
+        if (build) store->buildPaths(singleton<PathSet>(path));
+        Derivation drv = derivationFromPath(*store, p.first);
+        rootNr++;
+
+        if (p.second.empty())
+            foreach (DerivationOutputs::iterator, i, drv.outputs) p.second.insert(i->first);
+
+        PathSet outputs;
+        foreach (StringSet::iterator, j, p.second) {
+            DerivationOutputs::iterator i = drv.outputs.find(*j);
+            if (i == drv.outputs.end())
+                throw Error(format("derivation `%1%' does not have an output named `%2%'") % p.first % *j);
+            Path outPath = i->second.path;
+            if (gcRoot == "")
+                printGCWarning();
+            else {
+                Path rootName = gcRoot;
+                if (rootNr > 1) rootName += "-" + int2String(rootNr);
+                if (i->first != "out") rootName += "-" + i->first;
+                outPath = addPermRoot(*store, outPath, rootName, indirectRoot);
+            }
+            outputs.insert(outPath);
+        }
+        return outputs;
+    }
+
+    else {
+        if (build) store->ensurePath(path);
+        else if (!store->isValidPath(path)) throw Error(format("path `%1%' does not exist and cannot be created") % path);
+        return singleton<PathSet>(path);
+    }
+}
+
+
+/* Realise the given paths. */
+static void opRealise(Strings opFlags, Strings opArgs)
+{
+    bool dryRun = false;
+    bool repair = false;
+    bool ignoreUnknown = false;
+
+    foreach (Strings::iterator, i, opFlags)
+        if (*i == "--dry-run") dryRun = true;
+        else if (*i == "--repair") repair = true;
+        else if (*i == "--ignore-unknown") ignoreUnknown = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    Paths paths;
+    foreach (Strings::iterator, i, opArgs) {
+        DrvPathWithOutputs p = parseDrvPathWithOutputs(*i);
+        paths.push_back(makeDrvPathWithOutputs(followLinksToStorePath(p.first), p.second));
+    }
+
+    unsigned long long downloadSize, narSize;
+    PathSet willBuild, willSubstitute, unknown;
+    queryMissing(*store, PathSet(paths.begin(), paths.end()),
+        willBuild, willSubstitute, unknown, downloadSize, narSize);
+
+    if (ignoreUnknown) {
+        Paths paths2;
+        foreach (Paths::iterator, i, paths)
+            if (unknown.find(*i) == unknown.end()) paths2.push_back(*i);
+        paths = paths2;
+        unknown = PathSet();
+    }
+
+    printMissing(willBuild, willSubstitute, unknown, downloadSize, narSize);
+
+    if (dryRun) return;
+
+    /* Build all paths at the same time to exploit parallelism. */
+    store->buildPaths(PathSet(paths.begin(), paths.end()), repair);
+
+    if (!ignoreUnknown)
+        foreach (Paths::iterator, i, paths) {
+            PathSet paths = realisePath(*i, false);
+            if (!noOutput)
+                foreach (PathSet::iterator, j, paths)
+                    cout << format("%1%\n") % *j;
+        }
+}
+
+
+/* Add files to the Nix store and print the resulting paths. */
+static void opAdd(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+
+    for (Strings::iterator i = opArgs.begin(); i != opArgs.end(); ++i)
+        cout << format("%1%\n") % store->addToStore(*i);
+}
+
+
+/* Preload the output of a fixed-output derivation into the Nix
+   store. */
+static void opAddFixed(Strings opFlags, Strings opArgs)
+{
+    bool recursive = false;
+
+    for (Strings::iterator i = opFlags.begin();
+         i != opFlags.end(); ++i)
+        if (*i == "--recursive") recursive = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    if (opArgs.empty())
+        throw UsageError("first argument must be hash algorithm");
+
+    HashType hashAlgo = parseHashType(opArgs.front());
+    opArgs.pop_front();
+
+    for (Strings::iterator i = opArgs.begin(); i != opArgs.end(); ++i)
+        cout << format("%1%\n") % store->addToStore(*i, recursive, hashAlgo);
+}
+
+
+/* Hack to support caching in `nix-prefetch-url'. */
+static void opPrintFixedPath(Strings opFlags, Strings opArgs)
+{
+    bool recursive = false;
+
+    for (Strings::iterator i = opFlags.begin();
+         i != opFlags.end(); ++i)
+        if (*i == "--recursive") recursive = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    if (opArgs.size() != 3)
+        throw UsageError(format("`--print-fixed-path' requires three arguments"));
+
+    Strings::iterator i = opArgs.begin();
+    HashType hashAlgo = parseHashType(*i++);
+    string hash = *i++;
+    string name = *i++;
+
+    cout << format("%1%\n") %
+        makeFixedOutputPath(recursive, hashAlgo,
+            parseHash16or32(hashAlgo, hash), name);
+}
+
+
+static PathSet maybeUseOutputs(const Path & storePath, bool useOutput, bool forceRealise)
+{
+    if (forceRealise) realisePath(storePath);
+    if (useOutput && isDerivation(storePath)) {
+        Derivation drv = derivationFromPath(*store, storePath);
+        PathSet outputs;
+        foreach (DerivationOutputs::iterator, i, drv.outputs)
+            outputs.insert(i->second.path);
+        return outputs;
+    }
+    else return singleton<PathSet>(storePath);
+}
+
+
+/* Some code to print a tree representation of a derivation dependency
+   graph.  Topological sorting is used to keep the tree relatively
+   flat. */
+
+const string treeConn = "+---";
+const string treeLine = "|   ";
+const string treeNull = "    ";
+
+
+static void printTree(const Path & path,
+    const string & firstPad, const string & tailPad, PathSet & done)
+{
+    if (done.find(path) != done.end()) {
+        cout << format("%1%%2% [...]\n") % firstPad % path;
+        return;
+    }
+    done.insert(path);
+
+    cout << format("%1%%2%\n") % firstPad % path;
+
+    PathSet references;
+    store->queryReferences(path, references);
+
+    /* Topologically sort under the relation A < B iff A \in
+       closure(B).  That is, if derivation A is an (possibly indirect)
+       input of B, then A is printed first.  This has the effect of
+       flattening the tree, preventing deeply nested structures.  */
+    Paths sorted = topoSortPaths(*store, references);
+    reverse(sorted.begin(), sorted.end());
+
+    foreach (Paths::iterator, i, sorted) {
+        Paths::iterator j = i; ++j;
+        printTree(*i, tailPad + treeConn,
+            j == sorted.end() ? tailPad + treeNull : tailPad + treeLine,
+            done);
+    }
+}
+
+
+/* Perform various sorts of queries. */
+static void opQuery(Strings opFlags, Strings opArgs)
+{
+    enum { qOutputs, qRequisites, qReferences, qReferrers
+         , qReferrersClosure, qDeriver, qBinding, qHash, qSize
+         , qTree, qGraph, qXml, qResolve, qRoots } query = qOutputs;
+    bool useOutput = false;
+    bool includeOutputs = false;
+    bool forceRealise = false;
+    string bindingName;
+
+    foreach (Strings::iterator, i, opFlags)
+        if (*i == "--outputs") query = qOutputs;
+        else if (*i == "--requisites" || *i == "-R") query = qRequisites;
+        else if (*i == "--references") query = qReferences;
+        else if (*i == "--referrers" || *i == "--referers") query = qReferrers;
+        else if (*i == "--referrers-closure" || *i == "--referers-closure") query = qReferrersClosure;
+        else if (*i == "--deriver" || *i == "-d") query = qDeriver;
+        else if (*i == "--binding" || *i == "-b") {
+            if (opArgs.size() == 0)
+                throw UsageError("expected binding name");
+            bindingName = opArgs.front();
+            opArgs.pop_front();
+            query = qBinding;
+        }
+        else if (*i == "--hash") query = qHash;
+        else if (*i == "--size") query = qSize;
+        else if (*i == "--tree") query = qTree;
+        else if (*i == "--graph") query = qGraph;
+        else if (*i == "--xml") query = qXml;
+        else if (*i == "--resolve") query = qResolve;
+        else if (*i == "--roots") query = qRoots;
+        else if (*i == "--use-output" || *i == "-u") useOutput = true;
+        else if (*i == "--force-realise" || *i == "--force-realize" || *i == "-f") forceRealise = true;
+        else if (*i == "--include-outputs") includeOutputs = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    switch (query) {
+
+        case qOutputs: {
+            foreach (Strings::iterator, i, opArgs) {
+                *i = followLinksToStorePath(*i);
+                if (forceRealise) realisePath(*i);
+                Derivation drv = derivationFromPath(*store, *i);
+                foreach (DerivationOutputs::iterator, j, drv.outputs)
+                    cout << format("%1%\n") % j->second.path;
+            }
+            break;
+        }
+
+        case qRequisites:
+        case qReferences:
+        case qReferrers:
+        case qReferrersClosure: {
+            PathSet paths;
+            foreach (Strings::iterator, i, opArgs) {
+                PathSet ps = maybeUseOutputs(followLinksToStorePath(*i), useOutput, forceRealise);
+                foreach (PathSet::iterator, j, ps) {
+                    if (query == qRequisites) computeFSClosure(*store, *j, paths, false, includeOutputs);
+                    else if (query == qReferences) store->queryReferences(*j, paths);
+                    else if (query == qReferrers) store->queryReferrers(*j, paths);
+                    else if (query == qReferrersClosure) computeFSClosure(*store, *j, paths, true);
+                }
+            }
+            Paths sorted = topoSortPaths(*store, paths);
+            for (Paths::reverse_iterator i = sorted.rbegin();
+                 i != sorted.rend(); ++i)
+                cout << format("%s\n") % *i;
+            break;
+        }
+
+        case qDeriver:
+            foreach (Strings::iterator, i, opArgs) {
+                Path deriver = store->queryDeriver(followLinksToStorePath(*i));
+                cout << format("%1%\n") %
+                    (deriver == "" ? "unknown-deriver" : deriver);
+            }
+            break;
+
+        case qBinding:
+            foreach (Strings::iterator, i, opArgs) {
+                Path path = useDeriver(followLinksToStorePath(*i));
+                Derivation drv = derivationFromPath(*store, path);
+                StringPairs::iterator j = drv.env.find(bindingName);
+                if (j == drv.env.end())
+                    throw Error(format("derivation `%1%' has no environment binding named `%2%'")
+                        % path % bindingName);
+                cout << format("%1%\n") % j->second;
+            }
+            break;
+
+        case qHash:
+        case qSize:
+            foreach (Strings::iterator, i, opArgs) {
+                PathSet paths = maybeUseOutputs(followLinksToStorePath(*i), useOutput, forceRealise);
+                foreach (PathSet::iterator, j, paths) {
+                    ValidPathInfo info = store->queryPathInfo(*j);
+                    if (query == qHash) {
+                        assert(info.hash.type == htSHA256);
+                        cout << format("sha256:%1%\n") % printHash32(info.hash);
+                    } else if (query == qSize)
+                        cout << format("%1%\n") % info.narSize;
+                }
+            }
+            break;
+
+        case qTree: {
+            PathSet done;
+            foreach (Strings::iterator, i, opArgs)
+                printTree(followLinksToStorePath(*i), "", "", done);
+            break;
+        }
+
+        case qGraph: {
+            PathSet roots;
+            foreach (Strings::iterator, i, opArgs) {
+                PathSet paths = maybeUseOutputs(followLinksToStorePath(*i), useOutput, forceRealise);
+                roots.insert(paths.begin(), paths.end());
+            }
+            printDotGraph(roots);
+            break;
+        }
+
+        case qXml: {
+            PathSet roots;
+            foreach (Strings::iterator, i, opArgs) {
+                PathSet paths = maybeUseOutputs(followLinksToStorePath(*i), useOutput, forceRealise);
+                roots.insert(paths.begin(), paths.end());
+            }
+            printXmlGraph(roots);
+            break;
+        }
+
+        case qResolve: {
+            foreach (Strings::iterator, i, opArgs)
+                cout << format("%1%\n") % followLinksToStorePath(*i);
+            break;
+        }
+
+        case qRoots: {
+            PathSet referrers;
+            foreach (Strings::iterator, i, opArgs) {
+                PathSet paths = maybeUseOutputs(followLinksToStorePath(*i), useOutput, forceRealise);
+                foreach (PathSet::iterator, j, paths)
+                    computeFSClosure(*store, *j, referrers, true,
+                        settings.gcKeepOutputs, settings.gcKeepDerivations);
+            }
+            Roots roots = store->findRoots();
+            foreach (Roots::iterator, i, roots)
+                if (referrers.find(i->second) != referrers.end())
+                    cout << format("%1%\n") % i->first;
+            break;
+        }
+
+        default:
+            abort();
+    }
+}
+
+
+static string shellEscape(const string & s)
+{
+    string r;
+    foreach (string::const_iterator, i, s)
+        if (*i == '\'') r += "'\\''"; else r += *i;
+    return r;
+}
+
+
+static void opPrintEnv(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    if (opArgs.size() != 1) throw UsageError("`--print-env' requires one derivation store path");
+
+    Path drvPath = opArgs.front();
+    Derivation drv = derivationFromPath(*store, drvPath);
+
+    /* Print each environment variable in the derivation in a format
+       that can be sourced by the shell. */
+    foreach (StringPairs::iterator, i, drv.env)
+        cout << format("export %1%; %1%='%2%'\n") % i->first % shellEscape(i->second);
+
+    /* Also output the arguments.  This doesn't preserve whitespace in
+       arguments. */
+    cout << "export _args; _args='";
+    foreach (Strings::iterator, i, drv.args) {
+        if (i != drv.args.begin()) cout << ' ';
+        cout << shellEscape(*i);
+    }
+    cout << "'\n";
+}
+
+
+static void opReadLog(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+
+    foreach (Strings::iterator, i, opArgs) {
+        Path path = useDeriver(followLinksToStorePath(*i));
+
+        for (int j = 0; j <= 2; j++) {
+            if (j == 2) throw Error(format("build log of derivation `%1%' is not available") % path);
+
+            string baseName = baseNameOf(path);
+            Path logPath =
+                j == 0
+                ? (format("%1%/%2%/%3%/%4%") % settings.nixLogDir % drvsLogDir % string(baseName, 0, 2) % string(baseName, 2)).str()
+                : (format("%1%/%2%/%3%") % settings.nixLogDir % drvsLogDir % baseName).str();
+            Path logBz2Path = logPath + ".bz2";
+
+            if (pathExists(logPath)) {
+                /* !!! Make this run in O(1) memory. */
+                string log = readFile(logPath);
+                writeFull(STDOUT_FILENO, (const unsigned char *) log.data(), log.size());
+                break;
+            }
+
+            else if (pathExists(logBz2Path)) {
+                AutoCloseFD fd = open(logBz2Path.c_str(), O_RDONLY);
+                FILE * f = 0;
+                if (fd == -1 || (f = fdopen(fd.borrow(), "r")) == 0)
+                    throw SysError(format("opening file `%1%'") % logBz2Path);
+                int err;
+                BZFILE * bz = BZ2_bzReadOpen(&err, f, 0, 0, 0, 0);
+                if (!bz) throw Error(format("cannot open bzip2 file `%1%'") % logBz2Path);
+                unsigned char buf[128 * 1024];
+                do {
+                    int n = BZ2_bzRead(&err, bz, buf, sizeof(buf));
+                    if (err != BZ_OK && err != BZ_STREAM_END)
+                        throw Error(format("error reading bzip2 file `%1%'") % logBz2Path);
+                    writeFull(STDOUT_FILENO, buf, n);
+                } while (err != BZ_STREAM_END);
+                BZ2_bzReadClose(&err, bz);
+                break;
+            }
+        }
+    }
+}
+
+
+static void opDumpDB(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    if (!opArgs.empty())
+        throw UsageError("no arguments expected");
+    PathSet validPaths = store->queryAllValidPaths();
+    foreach (PathSet::iterator, i, validPaths)
+        cout << store->makeValidityRegistration(singleton<PathSet>(*i), true, true);
+}
+
+
+static void registerValidity(bool reregister, bool hashGiven, bool canonicalise)
+{
+    ValidPathInfos infos;
+
+    while (1) {
+        ValidPathInfo info = decodeValidPathInfo(cin, hashGiven);
+        if (info.path == "") break;
+        if (!store->isValidPath(info.path) || reregister) {
+            /* !!! races */
+            if (canonicalise)
+                canonicalisePathMetaData(info.path, -1);
+            if (!hashGiven) {
+                HashResult hash = hashPath(htSHA256, info.path);
+                info.hash = hash.first;
+                info.narSize = hash.second;
+            }
+            infos.push_back(info);
+        }
+    }
+
+    ensureLocalStore().registerValidPaths(infos);
+}
+
+
+static void opLoadDB(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    if (!opArgs.empty())
+        throw UsageError("no arguments expected");
+    registerValidity(true, true, false);
+}
+
+
+static void opRegisterValidity(Strings opFlags, Strings opArgs)
+{
+    bool reregister = false; // !!! maybe this should be the default
+    bool hashGiven = false;
+
+    for (Strings::iterator i = opFlags.begin();
+         i != opFlags.end(); ++i)
+        if (*i == "--reregister") reregister = true;
+        else if (*i == "--hash-given") hashGiven = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    if (!opArgs.empty()) throw UsageError("no arguments expected");
+
+    registerValidity(reregister, hashGiven, true);
+}
+
+
+static void opCheckValidity(Strings opFlags, Strings opArgs)
+{
+    bool printInvalid = false;
+
+    for (Strings::iterator i = opFlags.begin();
+         i != opFlags.end(); ++i)
+        if (*i == "--print-invalid") printInvalid = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    for (Strings::iterator i = opArgs.begin();
+         i != opArgs.end(); ++i)
+    {
+        Path path = followLinksToStorePath(*i);
+        if (!store->isValidPath(path)) {
+            if (printInvalid)
+                cout << format("%1%\n") % path;
+            else
+                throw Error(format("path `%1%' is not valid") % path);
+        }
+    }
+}
+
+
+static string showBytes(unsigned long long bytes)
+{
+    return (format("%.2f MiB") % (bytes / (1024.0 * 1024.0))).str();
+}
+
+
+struct PrintFreed
+{
+    bool show;
+    const GCResults & results;
+    PrintFreed(bool show, const GCResults & results)
+        : show(show), results(results) { }
+    ~PrintFreed()
+    {
+        if (show)
+            cout << format("%1% store paths deleted, %2% freed\n")
+                % results.paths.size()
+                % showBytes(results.bytesFreed);
+    }
+};
+
+
+static void opGC(Strings opFlags, Strings opArgs)
+{
+    bool printRoots = false;
+    GCOptions options;
+    options.action = GCOptions::gcDeleteDead;
+
+    GCResults results;
+
+    /* Do what? */
+    foreach (Strings::iterator, i, opFlags)
+        if (*i == "--print-roots") printRoots = true;
+        else if (*i == "--print-live") options.action = GCOptions::gcReturnLive;
+        else if (*i == "--print-dead") options.action = GCOptions::gcReturnDead;
+        else if (*i == "--delete") options.action = GCOptions::gcDeleteDead;
+        else if (*i == "--max-freed") {
+            long long maxFreed = getIntArg<long long>(*i, i, opFlags.end());
+            options.maxFreed = maxFreed >= 0 ? maxFreed : 0;
+        }
+        else throw UsageError(format("bad sub-operation `%1%' in GC") % *i);
+
+    if (!opArgs.empty()) throw UsageError("no arguments expected");
+
+    if (printRoots) {
+        Roots roots = store->findRoots();
+        foreach (Roots::iterator, i, roots)
+            cout << i->first << " -> " << i->second << std::endl;
+    }
+
+    else {
+        PrintFreed freed(options.action == GCOptions::gcDeleteDead, results);
+        store->collectGarbage(options, results);
+
+        if (options.action != GCOptions::gcDeleteDead)
+            foreach (PathSet::iterator, i, results.paths)
+                cout << *i << std::endl;
+    }
+}
+
+
+/* Remove paths from the Nix store if possible (i.e., if they do not
+   have any remaining referrers and are not reachable from any GC
+   roots). */
+static void opDelete(Strings opFlags, Strings opArgs)
+{
+    GCOptions options;
+    options.action = GCOptions::gcDeleteSpecific;
+
+    foreach (Strings::iterator, i, opFlags)
+        if (*i == "--ignore-liveness") options.ignoreLiveness = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    foreach (Strings::iterator, i, opArgs)
+        options.pathsToDelete.insert(followLinksToStorePath(*i));
+
+    GCResults results;
+    PrintFreed freed(true, results);
+    store->collectGarbage(options, results);
+}
+
+
+/* Dump a path as a Nix archive.  The archive is written to standard
+   output. */
+static void opDump(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    if (opArgs.size() != 1) throw UsageError("only one argument allowed");
+
+    FdSink sink(STDOUT_FILENO);
+    string path = *opArgs.begin();
+    dumpPath(path, sink);
+}
+
+
+/* Restore a value from a Nix archive.  The archive is read from
+   standard input. */
+static void opRestore(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    if (opArgs.size() != 1) throw UsageError("only one argument allowed");
+
+    FdSource source(STDIN_FILENO);
+    restorePath(*opArgs.begin(), source);
+}
+
+
+static void opExport(Strings opFlags, Strings opArgs)
+{
+    bool sign = false;
+    for (Strings::iterator i = opFlags.begin();
+         i != opFlags.end(); ++i)
+        if (*i == "--sign") sign = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    FdSink sink(STDOUT_FILENO);
+    Paths sorted = topoSortPaths(*store, PathSet(opArgs.begin(), opArgs.end()));
+    reverse(sorted.begin(), sorted.end());
+    exportPaths(*store, sorted, sign, sink);
+}
+
+
+static void opImport(Strings opFlags, Strings opArgs)
+{
+    bool requireSignature = false;
+    foreach (Strings::iterator, i, opFlags)
+        if (*i == "--require-signature") requireSignature = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    if (!opArgs.empty()) throw UsageError("no arguments expected");
+
+    FdSource source(STDIN_FILENO);
+    Paths paths = store->importPaths(requireSignature, source);
+
+    foreach (Paths::iterator, i, paths)
+        cout << format("%1%\n") % *i << std::flush;
+}
+
+
+/* Initialise the Nix databases. */
+static void opInit(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty()) throw UsageError("unknown flag");
+    if (!opArgs.empty())
+        throw UsageError("no arguments expected");
+    /* Doesn't do anything right now; database tables are initialised
+       automatically. */
+}
+
+
+/* Verify the consistency of the Nix environment. */
+static void opVerify(Strings opFlags, Strings opArgs)
+{
+    if (!opArgs.empty())
+        throw UsageError("no arguments expected");
+
+    bool checkContents = false;
+    bool repair = false;
+
+    for (Strings::iterator i = opFlags.begin();
+         i != opFlags.end(); ++i)
+        if (*i == "--check-contents") checkContents = true;
+        else if (*i == "--repair") repair = true;
+        else throw UsageError(format("unknown flag `%1%'") % *i);
+
+    if (ensureLocalStore().verifyStore(checkContents, repair)) {
+        printMsg(lvlError, "warning: not all errors were fixed");
+        exitCode = 1;
+    }
+}
+
+
+/* Verify whether the contents of the given store path have not changed. */
+static void opVerifyPath(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty())
+        throw UsageError("no flags expected");
+
+    foreach (Strings::iterator, i, opArgs) {
+        Path path = followLinksToStorePath(*i);
+        printMsg(lvlTalkative, format("checking path `%1%'...") % path);
+        ValidPathInfo info = store->queryPathInfo(path);
+        HashResult current = hashPath(info.hash.type, path);
+        if (current.first != info.hash) {
+            printMsg(lvlError,
+                format("path `%1%' was modified! expected hash `%2%', got `%3%'")
+                % path % printHash(info.hash) % printHash(current.first));
+            exitCode = 1;
+        }
+    }
+}
+
+
+/* Repair the contents of the given path by redownloading it using a
+   substituter (if available). */
+static void opRepairPath(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty())
+        throw UsageError("no flags expected");
+
+    foreach (Strings::iterator, i, opArgs) {
+        Path path = followLinksToStorePath(*i);
+        ensureLocalStore().repairPath(path);
+    }
+}
+
+
+static void showOptimiseStats(OptimiseStats & stats)
+{
+    printMsg(lvlError,
+        format("%1% freed by hard-linking %2% files; there are %3% files with equal contents out of %4% files in total")
+        % showBytes(stats.bytesFreed)
+        % stats.filesLinked
+        % stats.sameContents
+        % stats.totalFiles);
+}
+
+
+/* Optimise the disk space usage of the Nix store by hard-linking
+   files with the same contents. */
+static void opOptimise(Strings opFlags, Strings opArgs)
+{
+    if (!opArgs.empty() || !opFlags.empty())
+        throw UsageError("no arguments expected");
+
+    OptimiseStats stats;
+    try {
+        ensureLocalStore().optimiseStore(stats);
+    } catch (...) {
+        showOptimiseStats(stats);
+        throw;
+    }
+    showOptimiseStats(stats);
+}
+
+
+static void opQueryFailedPaths(Strings opFlags, Strings opArgs)
+{
+    if (!opArgs.empty() || !opFlags.empty())
+        throw UsageError("no arguments expected");
+    PathSet failed = store->queryFailedPaths();
+    foreach (PathSet::iterator, i, failed)
+        cout << format("%1%\n") % *i;
+}
+
+
+static void opClearFailedPaths(Strings opFlags, Strings opArgs)
+{
+    if (!opFlags.empty())
+        throw UsageError("no flags expected");
+    store->clearFailedPaths(PathSet(opArgs.begin(), opArgs.end()));
+}
+
+
+/* Scan the arguments; find the operation, set global flags, put all
+   other flags in a list, and put all other arguments in another
+   list. */
+void run(Strings args)
+{
+    Strings opFlags, opArgs;
+    Operation op = 0;
+
+    for (Strings::iterator i = args.begin(); i != args.end(); ) {
+        string arg = *i++;
+
+        Operation oldOp = op;
+
+        if (arg == "--realise" || arg == "--realize" || arg == "-r")
+            op = opRealise;
+        else if (arg == "--add" || arg == "-A")
+            op = opAdd;
+        else if (arg == "--add-fixed")
+            op = opAddFixed;
+        else if (arg == "--print-fixed-path")
+            op = opPrintFixedPath;
+        else if (arg == "--delete")
+            op = opDelete;
+        else if (arg == "--query" || arg == "-q")
+            op = opQuery;
+        else if (arg == "--print-env")
+            op = opPrintEnv;
+        else if (arg == "--read-log" || arg == "-l")
+            op = opReadLog;
+        else if (arg == "--dump-db")
+            op = opDumpDB;
+        else if (arg == "--load-db")
+            op = opLoadDB;
+        else if (arg == "--register-validity")
+            op = opRegisterValidity;
+        else if (arg == "--check-validity")
+            op = opCheckValidity;
+        else if (arg == "--gc")
+            op = opGC;
+        else if (arg == "--dump")
+            op = opDump;
+        else if (arg == "--restore")
+            op = opRestore;
+        else if (arg == "--export")
+            op = opExport;
+        else if (arg == "--import")
+            op = opImport;
+        else if (arg == "--init")
+            op = opInit;
+        else if (arg == "--verify")
+            op = opVerify;
+        else if (arg == "--verify-path")
+            op = opVerifyPath;
+        else if (arg == "--repair-path")
+            op = opRepairPath;
+        else if (arg == "--optimise" || arg == "--optimize")
+            op = opOptimise;
+        else if (arg == "--query-failed-paths")
+            op = opQueryFailedPaths;
+        else if (arg == "--clear-failed-paths")
+            op = opClearFailedPaths;
+        else if (arg == "--add-root") {
+            if (i == args.end())
+                throw UsageError("`--add-root requires an argument");
+            gcRoot = absPath(*i++);
+        }
+        else if (arg == "--indirect")
+            indirectRoot = true;
+        else if (arg == "--no-output")
+            noOutput = true;
+        else if (arg[0] == '-') {
+            opFlags.push_back(arg);
+            if (arg == "--max-freed" || arg == "--max-links" || arg == "--max-atime") { /* !!! hack */
+                if (i != args.end()) opFlags.push_back(*i++);
+            }
+        }
+        else
+            opArgs.push_back(arg);
+
+        if (oldOp && oldOp != op)
+            throw UsageError("only one operation may be specified");
+    }
+
+    if (!op) throw UsageError("no operation specified");
+
+    if (op != opDump && op != opRestore) /* !!! hack */
+        store = openStore(op != opGC);
+
+    op(opFlags, opArgs);
+}
+
+
+string programId = "nix-store";
diff --git a/src/nix-store/xmlgraph.cc b/src/nix-store/xmlgraph.cc
new file mode 100644
index 000000000000..1b3ad3d28ad4
--- /dev/null
+++ b/src/nix-store/xmlgraph.cc
@@ -0,0 +1,71 @@
+#include "xmlgraph.hh"
+#include "util.hh"
+#include "store-api.hh"
+
+#include <iostream>
+
+
+using std::cout;
+
+namespace nix {
+
+
+static inline const string & xmlQuote(const string & s)
+{
+    // Luckily, store paths shouldn't contain any character that needs to be
+    // quoted.
+    return s;
+}
+
+
+static string makeEdge(const string & src, const string & dst)
+{
+    format f = format("  <edge src=\"%1%\" dst=\"%2%\"/>\n")
+      % xmlQuote(src) % xmlQuote(dst);
+    return f.str();
+}
+
+
+static string makeNode(const string & id)
+{
+    format f = format("  <node name=\"%1%\"/>\n") % xmlQuote(id);
+    return f.str();
+}
+
+
+void printXmlGraph(const PathSet & roots)
+{
+    PathSet workList(roots);
+    PathSet doneSet;
+
+    cout << "<?xml version='1.0' encoding='utf-8'?>\n"
+	 << "<nix>\n";
+
+    while (!workList.empty()) {
+	Path path = *(workList.begin());
+	workList.erase(path);
+
+	if (doneSet.find(path) != doneSet.end()) continue;
+	doneSet.insert(path);
+
+	cout << makeNode(path);
+
+	PathSet references;
+	store->queryReferences(path, references);
+
+	for (PathSet::iterator i = references.begin();
+	     i != references.end(); ++i)
+	{
+	    if (*i != path) {
+		workList.insert(*i);
+		cout << makeEdge(*i, path);
+	    }
+	}
+
+    }
+
+    cout << "</nix>\n";
+}
+
+
+}
diff --git a/src/nix-store/xmlgraph.hh b/src/nix-store/xmlgraph.hh
new file mode 100644
index 000000000000..c2216c5a4627
--- /dev/null
+++ b/src/nix-store/xmlgraph.hh
@@ -0,0 +1,9 @@
+#pragma once
+
+#include "types.hh"
+
+namespace nix {
+
+void printXmlGraph(const PathSet & roots);
+
+}