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-rw-r--r--src/libstore/local-store.cc1037
1 files changed, 1037 insertions, 0 deletions
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
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index 000000000000..c8bb60bce6b0
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+++ b/src/libstore/local-store.cc
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+#include "local-store.hh"
+#include "util.hh"
+#include "globals.hh"
+#include "db.hh"
+#include "archive.hh"
+#include "pathlocks.hh"
+#include "gc.hh"
+#include "aterm.hh"
+#include "derivations-ast.hh"
+    
+#include <iostream>
+#include <algorithm>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <utime.h>
+
+namespace nix {
+
+    
+/* Nix database. */
+static Database nixDB;
+
+
+/* Database tables. */
+
+/* dbValidPaths :: Path -> ()
+
+   The existence of a key $p$ indicates that path $p$ is valid (that
+   is, produced by a succesful build). */
+static TableId dbValidPaths = 0;
+
+/* dbReferences :: Path -> [Path]
+
+   This table lists the outgoing file system references for each
+   output path that has been built by a Nix derivation.  These are
+   found by scanning the path for the hash components of input
+   paths. */
+static TableId dbReferences = 0;
+
+/* dbReferrers :: Path -> Path
+
+   This table is just the reverse mapping of dbReferences.  This table
+   can have duplicate keys, each corresponding value denoting a single
+   referrer. */
+static TableId dbReferrers = 0;
+
+/* dbSubstitutes :: Path -> [[Path]]
+
+   Each pair $(p, subs)$ tells Nix that it can use any of the
+   substitutes in $subs$ to build path $p$.  Each substitute defines a
+   command-line invocation of a program (i.e., the first list element
+   is the full path to the program, the remaining elements are
+   arguments).
+
+   The main purpose of this is for distributed caching of derivates.
+   One system can compute a derivate and put it on a website (as a Nix
+   archive), for instance, and then another system can register a
+   substitute for that derivate.  The substitute in this case might be
+   a Nix derivation that fetches the Nix archive.
+*/
+static TableId dbSubstitutes = 0;
+
+/* dbDerivers :: Path -> [Path]
+
+   This table lists the derivation used to build a path.  There can
+   only be multiple such paths for fixed-output derivations (i.e.,
+   derivations specifying an expected hash). */
+static TableId dbDerivers = 0;
+
+
+bool Substitute::operator == (const Substitute & sub) const
+{
+    return program == sub.program
+        && args == sub.args;
+}
+
+
+static void upgradeStore07();
+static void upgradeStore09();
+
+
+void checkStoreNotSymlink()
+{
+    if (getEnv("NIX_IGNORE_SYMLINK_STORE") == "1") return;
+    Path path = 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)
+{
+    if (readOnlyMode) return;
+
+    checkStoreNotSymlink();
+
+    try {
+        Path reservedPath = nixDBPath + "/reserved";
+        string s = querySetting("gc-reserved-space", "");
+        int reservedSize;
+        if (!string2Int(s, reservedSize)) reservedSize = 1024 * 1024;
+        if (reserveSpace) {
+            struct stat st;
+            if (stat(reservedPath.c_str(), &st) == -1 ||
+                st.st_size != reservedSize)
+                writeFile(reservedPath, string(reservedSize, 'X'));
+        }
+        else
+            deletePath(reservedPath);
+    } catch (SysError & e) { /* don't care about errors */
+    }
+
+    try {
+        nixDB.open(nixDBPath);
+    } catch (DbNoPermission & e) {
+        printMsg(lvlTalkative, "cannot access Nix database; continuing anyway");
+        readOnlyMode = true;
+        return;
+    }
+    dbValidPaths = nixDB.openTable("validpaths");
+    dbReferences = nixDB.openTable("references");
+    dbReferrers = nixDB.openTable("referrers", true); /* must be sorted */
+    dbSubstitutes = nixDB.openTable("substitutes");
+    dbDerivers = nixDB.openTable("derivers");
+
+    int curSchema = 0;
+    Path schemaFN = nixDBPath + "/schema";
+    if (pathExists(schemaFN)) {
+        string s = readFile(schemaFN);
+        if (!string2Int(s, curSchema))
+            throw Error(format("`%1%' is corrupt") % schemaFN);
+    }
+
+    if (curSchema > nixSchemaVersion)
+        throw Error(format("current Nix store schema is version %1%, but I only support %2%")
+            % curSchema % nixSchemaVersion);
+
+    if (curSchema < nixSchemaVersion) {
+        if (curSchema <= 1)
+            upgradeStore07();
+        if (curSchema == 2)
+            upgradeStore09();
+        writeFile(schemaFN, (format("%1%") % nixSchemaVersion).str());
+    }
+}
+
+
+LocalStore::~LocalStore()
+{
+    /* If the database isn't open, this is a NOP. */
+    nixDB.close();
+}
+
+
+void createStoreTransaction(Transaction & txn)
+{
+    Transaction txn2(nixDB);
+    txn2.moveTo(txn);
+}
+
+
+/* Path copying. */
+
+struct CopySink : DumpSink
+{
+    string s;
+    virtual void operator () (const unsigned char * data, unsigned int len)
+    {
+        s.append((const char *) data, len);
+    }
+};
+
+
+struct CopySource : RestoreSource
+{
+    string & s;
+    unsigned int pos;
+    CopySource(string & _s) : s(_s), pos(0) { }
+    virtual void operator () (unsigned char * data, unsigned int len)
+    {
+        s.copy((char *) data, len, pos);
+        pos += len;
+        assert(pos <= s.size());
+    }
+};
+
+
+void copyPath(const Path & src, const Path & dst)
+{
+    debug(format("copying `%1%' to `%2%'") % src % dst);
+
+    /* Dump an archive of the path `src' into a string buffer, then
+       restore the archive to `dst'.  This is not a very good method
+       for very large paths, but `copyPath' is mainly used for small
+       files. */ 
+
+    CopySink sink;
+    {
+        SwitchToOriginalUser sw;
+        dumpPath(src, sink);
+    }
+
+    CopySource source(sink.s);
+    restorePath(dst, source);
+}
+
+
+void canonicalisePathMetaData(const Path & path)
+{
+    checkInterrupt();
+
+    struct stat st;
+    if (lstat(path.c_str(), &st))
+	throw SysError(format("getting attributes of path `%1%'") % path);
+
+    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_uid != getuid() || st.st_gid != getgid()) {
+            if (chown(path.c_str(), getuid(), getgid()) == -1)
+                throw SysError(format("changing owner/group of `%1%' to %2%/%3%")
+                    % path % getuid() % getgid());
+        }
+
+        if (st.st_mtime != 0) {
+            struct utimbuf utimbuf;
+            utimbuf.actime = st.st_atime;
+            utimbuf.modtime = 0;
+            if (utime(path.c_str(), &utimbuf) == -1) 
+                throw SysError(format("changing modification time of `%1%'") % path);
+        }
+
+    }
+
+    if (S_ISDIR(st.st_mode)) {
+        Strings names = readDirectory(path);
+	for (Strings::iterator i = names.begin(); i != names.end(); ++i)
+	    canonicalisePathMetaData(path + "/" + *i);
+    }
+}
+
+
+bool isValidPathTxn(const Transaction & txn, const Path & path)
+{
+    string s;
+    return nixDB.queryString(txn, dbValidPaths, path, s);
+}
+
+
+bool LocalStore::isValidPath(const Path & path)
+{
+    return isValidPathTxn(noTxn, path);
+}
+
+
+static Substitutes readSubstitutes(const Transaction & txn,
+    const Path & srcPath);
+
+
+static bool isRealisablePath(const Transaction & txn, const Path & path)
+{
+    return isValidPathTxn(txn, path)
+        || readSubstitutes(txn, path).size() > 0;
+}
+
+
+static string addPrefix(const string & prefix, const string & s)
+{
+    return prefix + string(1, (char) 0) + s;
+}
+
+
+static string stripPrefix(const string & prefix, const string & s)
+{
+    if (s.size() <= prefix.size() ||
+        string(s, 0, prefix.size()) != prefix ||
+        s[prefix.size()] != 0)
+        throw Error(format("string `%1%' is missing prefix `%2%'")
+            % s % prefix);
+    return string(s, prefix.size() + 1);
+}
+
+
+static PathSet getReferrers(const Transaction & txn, const Path & storePath)
+{
+    PathSet referrers;
+    Strings keys;
+    nixDB.enumTable(txn, dbReferrers, keys, storePath + string(1, (char) 0));
+    for (Strings::iterator i = keys.begin(); i != keys.end(); ++i)
+        referrers.insert(stripPrefix(storePath, *i));
+    return referrers;
+}
+
+
+void setReferences(const Transaction & txn, const Path & storePath,
+    const PathSet & references)
+{
+    /* For unrealisable paths, we can only clear the references. */
+    if (references.size() > 0 && !isRealisablePath(txn, storePath))
+        throw Error(
+            format("cannot set references for path `%1%' which is invalid and has no substitutes")
+            % storePath);
+
+    Paths oldReferences;
+    nixDB.queryStrings(txn, dbReferences, storePath, oldReferences);
+
+    PathSet oldReferences2(oldReferences.begin(), oldReferences.end());
+    if (oldReferences2 == references) return;
+    
+    nixDB.setStrings(txn, dbReferences, storePath,
+        Paths(references.begin(), references.end()));
+
+    /* Update the referrers mappings of all new referenced paths. */
+    for (PathSet::const_iterator i = references.begin();
+         i != references.end(); ++i)
+        if (oldReferences2.find(*i) == oldReferences2.end())
+            nixDB.setString(txn, dbReferrers, addPrefix(*i, storePath), "");
+
+    /* Remove referrer mappings from paths that are no longer
+       references. */
+    for (Paths::iterator i = oldReferences.begin();
+         i != oldReferences.end(); ++i)
+        if (references.find(*i) == references.end())
+            nixDB.delPair(txn, dbReferrers, addPrefix(*i, storePath));
+}
+
+
+void queryReferences(const Transaction & txn,
+    const Path & storePath, PathSet & references)
+{
+    Paths references2;
+    if (!isRealisablePath(txn, storePath))
+        throw Error(format("path `%1%' is not valid") % storePath);
+    nixDB.queryStrings(txn, dbReferences, storePath, references2);
+    references.insert(references2.begin(), references2.end());
+}
+
+
+void LocalStore::queryReferences(const Path & storePath,
+    PathSet & references)
+{
+    nix::queryReferences(noTxn, storePath, references);
+}
+
+
+void queryReferrers(const Transaction & txn,
+    const Path & storePath, PathSet & referrers)
+{
+    if (!isRealisablePath(txn, storePath))
+        throw Error(format("path `%1%' is not valid") % storePath);
+    PathSet referrers2 = getReferrers(txn, storePath);
+    referrers.insert(referrers2.begin(), referrers2.end());
+}
+
+
+void LocalStore::queryReferrers(const Path & storePath,
+    PathSet & referrers)
+{
+    nix::queryReferrers(noTxn, storePath, referrers);
+}
+
+
+void setDeriver(const Transaction & txn, const Path & storePath,
+    const Path & deriver)
+{
+    assertStorePath(storePath);
+    if (deriver == "") return;
+    assertStorePath(deriver);
+    if (!isRealisablePath(txn, storePath))
+        throw Error(format("path `%1%' is not valid") % storePath);
+    nixDB.setString(txn, dbDerivers, storePath, deriver);
+}
+
+
+Path queryDeriver(const Transaction & txn, const Path & storePath)
+{
+    if (!isRealisablePath(txn, storePath))
+        throw Error(format("path `%1%' is not valid") % storePath);
+    Path deriver;
+    if (nixDB.queryString(txn, dbDerivers, storePath, deriver))
+        return deriver;
+    else
+        return "";
+}
+
+
+const int substituteVersion = 2;
+
+
+static Substitutes readSubstitutes(const Transaction & txn,
+    const Path & srcPath)
+{
+    Strings ss;
+    nixDB.queryStrings(txn, dbSubstitutes, srcPath, ss);
+
+    Substitutes subs;
+    
+    for (Strings::iterator i = ss.begin(); i != ss.end(); ++i) {
+        if (i->size() < 4 || (*i)[3] != 0) {
+            /* Old-style substitute.  !!! remove this code
+               eventually? */
+            break;
+        }
+        Strings ss2 = unpackStrings(*i);
+        if (ss2.size() == 0) continue;
+        int version;
+        if (!string2Int(ss2.front(), version)) continue;
+        if (version != substituteVersion) continue;
+        if (ss2.size() != 4) throw Error("malformed substitute");
+        Strings::iterator j = ss2.begin();
+        j++;
+        Substitute sub;
+        sub.deriver = *j++;
+        sub.program = *j++;
+        sub.args = unpackStrings(*j++);
+        subs.push_back(sub);
+    }
+
+    return subs;
+}
+
+
+static void writeSubstitutes(const Transaction & txn,
+    const Path & srcPath, const Substitutes & subs)
+{
+    Strings ss;
+
+    for (Substitutes::const_iterator i = subs.begin();
+         i != subs.end(); ++i)
+    {
+        Strings ss2;
+        ss2.push_back((format("%1%") % substituteVersion).str());
+        ss2.push_back(i->deriver);
+        ss2.push_back(i->program);
+        ss2.push_back(packStrings(i->args));
+        ss.push_back(packStrings(ss2));
+    }
+
+    nixDB.setStrings(txn, dbSubstitutes, srcPath, ss);
+}
+
+
+void registerSubstitute(const Transaction & txn,
+    const Path & srcPath, const Substitute & sub)
+{
+    assertStorePath(srcPath);
+    
+    Substitutes subs = readSubstitutes(txn, srcPath);
+
+    if (find(subs.begin(), subs.end(), sub) != subs.end())
+        return;
+
+    /* New substitutes take precedence over old ones.  If the
+       substitute is already present, it's moved to the front. */
+    remove(subs.begin(), subs.end(), sub);
+    subs.push_front(sub);
+        
+    writeSubstitutes(txn, srcPath, subs);
+}
+
+
+Substitutes querySubstitutes(const Transaction & txn, const Path & srcPath)
+{
+    return readSubstitutes(txn, srcPath);
+}
+
+
+Substitutes LocalStore::querySubstitutes(const Path & srcPath)
+{
+    return nix::querySubstitutes(noTxn, srcPath);
+}
+
+
+static void invalidatePath(Transaction & txn, const Path & path);
+
+
+void clearSubstitutes()
+{
+    Transaction txn(nixDB);
+    
+    /* Iterate over all paths for which there are substitutes. */
+    Paths subKeys;
+    nixDB.enumTable(txn, dbSubstitutes, subKeys);
+    for (Paths::iterator i = subKeys.begin(); i != subKeys.end(); ++i) {
+        
+        /* Delete all substitutes for path *i. */
+        nixDB.delPair(txn, dbSubstitutes, *i);
+        
+        /* Maintain the cleanup invariant. */
+        if (!isValidPathTxn(txn, *i))
+            invalidatePath(txn, *i);
+    }
+
+    /* !!! there should be no referrers to any of the invalid
+       substitutable paths.  This should be the case by construction
+       (the only referrers can be other invalid substitutable paths,
+       which have all been removed now). */
+    
+    txn.commit();
+}
+
+
+static void setHash(const Transaction & txn, const Path & storePath,
+    const Hash & hash)
+{
+    assert(hash.type == htSHA256);
+    nixDB.setString(txn, dbValidPaths, storePath, "sha256:" + printHash(hash));
+}
+
+
+static Hash queryHash(const Transaction & txn, const Path & storePath)
+{
+    string s;
+    nixDB.queryString(txn, dbValidPaths, storePath, s);
+    string::size_type colon = s.find(':');
+    if (colon == string::npos)
+        throw Error(format("corrupt hash `%1%' in valid-path entry for `%2%'")
+            % s % storePath);
+    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) % storePath);
+    return parseHash(ht, string(s, colon + 1));
+}
+
+
+Hash LocalStore::queryPathHash(const Path & path)
+{
+    if (!isValidPath(path))
+        throw Error(format("path `%1%' is not valid") % path);
+    return queryHash(noTxn, path);
+}
+
+
+void registerValidPath(const Transaction & txn,
+    const Path & path, const Hash & hash, const PathSet & references,
+    const Path & deriver)
+{
+    ValidPathInfo info;
+    info.path = path;
+    info.hash = hash;
+    info.references = references;
+    info.deriver = deriver;
+    ValidPathInfos infos;
+    infos.push_back(info);
+    registerValidPaths(txn, infos);
+}
+
+
+void registerValidPaths(const Transaction & txn,
+    const ValidPathInfos & infos)
+{
+    PathSet newPaths;
+    for (ValidPathInfos::const_iterator i = infos.begin();
+         i != infos.end(); ++i)
+        newPaths.insert(i->path);
+        
+    for (ValidPathInfos::const_iterator i = infos.begin();
+         i != infos.end(); ++i)
+    {
+        assertStorePath(i->path);
+
+        debug(format("registering path `%1%'") % i->path);
+        setHash(txn, i->path, i->hash);
+
+        setReferences(txn, i->path, i->references);
+    
+        /* Check that all referenced paths are also valid (or about to
+           become valid). */
+        for (PathSet::iterator j = i->references.begin();
+             j != i->references.end(); ++j)
+            if (!isValidPathTxn(txn, *j) && newPaths.find(*j) == newPaths.end())
+                throw Error(format("cannot register path `%1%' as valid, since its reference `%2%' is invalid")
+                    % i->path % *j);
+
+        setDeriver(txn, i->path, i->deriver);
+    }
+}
+
+
+/* Invalidate a path.  The caller is responsible for checking that
+   there are no referrers. */
+static void invalidatePath(Transaction & txn, const Path & path)
+{
+    debug(format("unregistering path `%1%'") % path);
+
+    /* Clear the `references' entry for this path, as well as the
+       inverse `referrers' entries, and the `derivers' entry; but only
+       if there are no substitutes for this path.  This maintains the
+       cleanup invariant. */
+    if (querySubstitutes(txn, path).size() == 0) {
+        setReferences(txn, path, PathSet());
+        nixDB.delPair(txn, dbDerivers, path);
+    }
+    
+    nixDB.delPair(txn, dbValidPaths, path);
+}
+
+
+Path LocalStore::_addToStore(bool fixed, bool recursive,
+    string hashAlgo, const Path & _srcPath)
+{
+    Path srcPath(absPath(_srcPath));
+    debug(format("adding `%1%' to the store") % srcPath);
+
+    Hash h(htSHA256);
+    {
+        SwitchToOriginalUser sw;
+        h = hashPath(htSHA256, srcPath);
+    }
+
+    string baseName = baseNameOf(srcPath);
+
+    Path dstPath;
+    
+    if (fixed) {
+
+        HashType ht(parseHashType(hashAlgo));
+        Hash h2(ht);
+        {
+            SwitchToOriginalUser sw;
+            h2 = recursive ? hashPath(ht, srcPath) : hashFile(ht, srcPath);
+        }
+        
+        dstPath = makeFixedOutputPath(recursive, hashAlgo, h2, baseName);
+    }
+        
+    else dstPath = makeStorePath("source", h, baseName);
+
+    if (!readOnlyMode) addTempRoot(dstPath);
+
+    if (!readOnlyMode && !isValidPath(dstPath)) {
+
+        /* The first check above is an optimisation to prevent
+           unnecessary lock acquisition. */
+
+        PathLocks outputLock(singleton<PathSet, Path>(dstPath));
+
+        if (!isValidPath(dstPath)) {
+
+            if (pathExists(dstPath)) deletePath(dstPath);
+
+            copyPath(srcPath, dstPath);
+
+            Hash h2 = hashPath(htSHA256, dstPath);
+            if (h != h2)
+                throw Error(format("contents of `%1%' changed while copying it to `%2%' (%3% -> %4%)")
+                    % srcPath % dstPath % printHash(h) % printHash(h2));
+
+            canonicalisePathMetaData(dstPath);
+            
+            Transaction txn(nixDB);
+            registerValidPath(txn, dstPath, h, PathSet(), "");
+            txn.commit();
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+Path LocalStore::addToStore(const Path & srcPath)
+{
+    return _addToStore(false, false, "", srcPath);
+}
+
+
+Path LocalStore::addToStoreFixed(bool recursive, string hashAlgo, const Path & srcPath)
+{
+    return _addToStore(true, recursive, hashAlgo, srcPath);
+}
+
+
+Path LocalStore::addTextToStore(const string & suffix, const string & s,
+    const PathSet & references)
+{
+    Hash hash = hashString(htSHA256, s);
+
+    Path dstPath = makeStorePath("text", hash, suffix);
+    
+    if (!readOnlyMode) addTempRoot(dstPath);
+
+    if (!readOnlyMode && !isValidPath(dstPath)) {
+
+        PathLocks outputLock(singleton<PathSet, Path>(dstPath));
+
+        if (!isValidPath(dstPath)) {
+
+            if (pathExists(dstPath)) deletePath(dstPath);
+
+            writeStringToFile(dstPath, s);
+
+            canonicalisePathMetaData(dstPath);
+            
+            Transaction txn(nixDB);
+            registerValidPath(txn, dstPath,
+                hashPath(htSHA256, dstPath), references, "");
+            txn.commit();
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+void deleteFromStore(const Path & _path, unsigned long long & bytesFreed)
+{
+    bytesFreed = 0;
+    Path path(canonPath(_path));
+
+    assertStorePath(path);
+
+    Transaction txn(nixDB);
+    if (isValidPathTxn(txn, path)) {
+        PathSet referrers = getReferrers(txn, path);
+        for (PathSet::iterator i = referrers.begin();
+             i != referrers.end(); ++i)
+            if (*i != path && isValidPathTxn(txn, *i))
+                throw Error(format("cannot delete path `%1%' because it is in use by path `%2%'") % path % *i);
+        invalidatePath(txn, path);
+    }
+    txn.commit();
+
+    deletePath(path, bytesFreed);
+}
+
+
+void verifyStore(bool checkContents)
+{
+    Transaction txn(nixDB);
+
+    Paths paths;
+    PathSet validPaths;
+    nixDB.enumTable(txn, dbValidPaths, paths);
+
+    for (Paths::iterator i = paths.begin(); i != paths.end(); ++i) {
+        if (!pathExists(*i)) {
+            printMsg(lvlError, format("path `%1%' disappeared") % *i);
+            invalidatePath(txn, *i);
+        } else if (!isStorePath(*i)) {
+            printMsg(lvlError, format("path `%1%' is not in the Nix store") % *i);
+            invalidatePath(txn, *i);
+        } else {
+            if (checkContents) {
+                debug(format("checking contents of `%1%'") % *i);
+                Hash expected = queryHash(txn, *i);
+                Hash current = hashPath(expected.type, *i);
+                if (current != expected) {
+                    printMsg(lvlError, format("path `%1%' was modified! "
+                                 "expected hash `%2%', got `%3%'")
+                        % *i % printHash(expected) % printHash(current));
+                }
+            }
+            validPaths.insert(*i);
+        }
+    }
+
+    /* "Usable" paths are those that are valid or have a
+       substitute. */
+    PathSet usablePaths(validPaths);
+
+    /* Check that the values of the substitute mappings are valid
+       paths. */ 
+    Paths subKeys;
+    nixDB.enumTable(txn, dbSubstitutes, subKeys);
+    for (Paths::iterator i = subKeys.begin(); i != subKeys.end(); ++i) {
+        Substitutes subs = readSubstitutes(txn, *i);
+        if (!isStorePath(*i)) {
+            printMsg(lvlError, format("found substitutes for non-store path `%1%'") % *i);
+            nixDB.delPair(txn, dbSubstitutes, *i);
+        }
+        else if (subs.size() == 0)
+            nixDB.delPair(txn, dbSubstitutes, *i);
+        else
+	    usablePaths.insert(*i);
+    }
+
+    /* Check the cleanup invariant: only usable paths can have
+       `references', `referrers', or `derivers' entries. */
+
+    /* Check the `derivers' table. */
+    Paths deriversKeys;
+    nixDB.enumTable(txn, dbDerivers, deriversKeys);
+    for (Paths::iterator i = deriversKeys.begin();
+         i != deriversKeys.end(); ++i)
+    {
+        if (usablePaths.find(*i) == usablePaths.end()) {
+            printMsg(lvlError, format("found deriver entry for unusable path `%1%'")
+                % *i);
+            nixDB.delPair(txn, dbDerivers, *i);
+        }
+        else {
+            Path deriver = queryDeriver(txn, *i);
+            if (!isStorePath(deriver)) {
+                printMsg(lvlError, format("found corrupt deriver `%1%' for `%2%'")
+                    % deriver % *i);
+                nixDB.delPair(txn, dbDerivers, *i);
+            }
+        }
+    }
+
+    /* Check the `references' table. */
+    Paths referencesKeys;
+    nixDB.enumTable(txn, dbReferences, referencesKeys);
+    for (Paths::iterator i = referencesKeys.begin();
+         i != referencesKeys.end(); ++i)
+    {
+        if (usablePaths.find(*i) == usablePaths.end()) {
+            printMsg(lvlError, format("found references entry for unusable path `%1%'")
+                % *i);
+            setReferences(txn, *i, PathSet());
+        }
+        else {
+            bool isValid = validPaths.find(*i) != validPaths.end();
+            PathSet references;
+            queryReferences(txn, *i, references);
+            for (PathSet::iterator j = references.begin();
+                 j != references.end(); ++j)
+            {
+                string dummy;
+                if (!nixDB.queryString(txn, dbReferrers, addPrefix(*j, *i), dummy)) {
+                    printMsg(lvlError, format("missing referrer mapping from `%1%' to `%2%'")
+                        % *j % *i);
+                    nixDB.setString(txn, dbReferrers, addPrefix(*j, *i), "");
+                }
+                if (isValid && validPaths.find(*j) == validPaths.end()) {
+                    printMsg(lvlError, format("incomplete closure: `%1%' needs missing `%2%'")
+                        % *i % *j);
+                }
+            }
+        }
+    }
+
+#if 0 // !!!
+    /* Check the `referrers' table. */
+    Paths referrersKeys;
+    nixDB.enumTable(txn, dbReferrers, referrersKeys);
+    for (Paths::iterator i = referrersKeys.begin();
+         i != referrersKeys.end(); ++i)
+    {
+        if (usablePaths.find(*i) == usablePaths.end()) {
+            printMsg(lvlError, format("found referrers entry for unusable path `%1%'")
+                % *i);
+            nixDB.delPair(txn, dbReferrers, *i);
+        }
+        else {
+            PathSet referrers, newReferrers;
+            queryReferrers(txn, *i, referrers);
+            for (PathSet::iterator j = referrers.begin();
+                 j != referrers.end(); ++j)
+            {
+                Paths references;
+                if (usablePaths.find(*j) == usablePaths.end()) {
+                    printMsg(lvlError, format("referrer mapping from `%1%' to unusable `%2%'")
+                        % *i % *j);
+                } else {
+                    nixDB.queryStrings(txn, dbReferences, *j, references);
+                    if (find(references.begin(), references.end(), *i) == references.end()) {
+                        printMsg(lvlError, format("missing reference mapping from `%1%' to `%2%'")
+                            % *j % *i);
+                        /* !!! repair by inserting *i into references */
+                    }
+                    else newReferrers.insert(*j);
+                }
+            }
+            if (referrers != newReferrers)
+                nixDB.setStrings(txn, dbReferrers, *i,
+                    Paths(newReferrers.begin(), newReferrers.end()));
+        }
+    }
+#endif    
+
+    txn.commit();
+}
+
+
+/* Upgrade from schema 1 (Nix <= 0.7) to schema 2 (Nix >= 0.8). */
+static void upgradeStore07()
+{
+    printMsg(lvlError, "upgrading Nix store to new schema (this may take a while)...");
+
+    Transaction txn(nixDB);
+
+    Paths validPaths2;
+    nixDB.enumTable(txn, dbValidPaths, validPaths2);
+    PathSet validPaths(validPaths2.begin(), validPaths2.end());
+
+    std::cerr << "hashing paths...";
+    int n = 0;
+    for (PathSet::iterator i = validPaths.begin(); i != validPaths.end(); ++i) {
+        checkInterrupt();
+        string s;
+        nixDB.queryString(txn, dbValidPaths, *i, s);
+        if (s == "") {
+            Hash hash = hashPath(htSHA256, *i);
+            setHash(txn, *i, hash);
+            std::cerr << ".";
+            if (++n % 1000 == 0) {
+                txn.commit();
+                txn.begin(nixDB);
+            }
+        }
+    }
+    std::cerr << std::endl;
+
+    txn.commit();
+
+    txn.begin(nixDB);
+    
+    std::cerr << "processing closures...";
+    for (PathSet::iterator i = validPaths.begin(); i != validPaths.end(); ++i) {
+        checkInterrupt();
+        if (i->size() > 6 && string(*i, i->size() - 6) == ".store") {
+            ATerm t = ATreadFromNamedFile(i->c_str());
+            if (!t) throw Error(format("cannot read aterm from `%1%'") % *i);
+
+            ATermList roots, elems;
+            if (!matchOldClosure(t, roots, elems)) continue;
+
+            for (ATermIterator j(elems); j; ++j) {
+
+                ATerm path2;
+                ATermList references2;
+                if (!matchOldClosureElem(*j, path2, references2)) continue;
+
+                Path path = aterm2String(path2);
+                if (validPaths.find(path) == validPaths.end())
+                    /* Skip this path; it's invalid.  This is a normal
+                       condition (Nix <= 0.7 did not enforce closure
+                       on closure store expressions). */
+                    continue;
+
+                PathSet references;
+                for (ATermIterator k(references2); k; ++k) {
+                    Path reference = aterm2String(*k);
+                    if (validPaths.find(reference) == validPaths.end())
+                        /* Bad reference.  Set it anyway and let the
+                           user fix it. */
+                        printMsg(lvlError, format("closure `%1%' contains reference from `%2%' "
+                                     "to invalid path `%3%' (run `nix-store --verify')")
+                            % *i % path % reference);
+                    references.insert(reference);
+                }
+
+                PathSet prevReferences;
+                queryReferences(txn, path, prevReferences);
+                if (prevReferences.size() > 0 && references != prevReferences)
+                    printMsg(lvlError, format("warning: conflicting references for `%1%'") % path);
+
+                if (references != prevReferences)
+                    setReferences(txn, path, references);
+            }
+            
+            std::cerr << ".";
+        }
+    }
+    std::cerr << std::endl;
+
+    /* !!! maybe this transaction is way too big */
+    txn.commit();
+}
+
+
+/* Upgrade from schema 2 (0.8 <= Nix <= 0.9) to schema 3 (Nix >=
+   0.10).  The only thing to do here is to upgrade the old `referer'
+   table (which causes quadratic complexity in some cases) to the new
+   (and properly spelled) `referrer' table. */
+static void upgradeStore09() 
+{
+    /* !!! we should disallow concurrent upgrades */
+    
+    printMsg(lvlError, "upgrading Nix store to new schema (this may take a while)...");
+
+    if (!pathExists(nixDBPath + "/referers")) return;
+
+    Transaction txn(nixDB);
+
+    std::cerr << "converting referers to referrers...";
+
+    TableId dbReferers = nixDB.openTable("referers"); /* sic! */
+
+    Paths referersKeys;
+    nixDB.enumTable(txn, dbReferers, referersKeys);
+
+    int n = 0;
+    for (Paths::iterator i = referersKeys.begin();
+         i != referersKeys.end(); ++i)
+    {
+        Paths referers;
+        nixDB.queryStrings(txn, dbReferers, *i, referers);
+        for (Paths::iterator j = referers.begin();
+             j != referers.end(); ++j)
+            nixDB.setString(txn, dbReferrers, addPrefix(*i, *j), "");
+        if (++n % 1000 == 0) {
+            txn.commit();
+            txn.begin(nixDB);
+            std::cerr << "|";
+        }
+        std::cerr << ".";
+    }
+
+    txn.commit();
+    
+    std::cerr << std::endl;
+
+    nixDB.closeTable(dbReferers);
+
+    nixDB.deleteTable("referers");
+}
+
+ 
+}