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-rw-r--r--third_party/nix/src/libstore/local-store.cc1453
1 files changed, 1453 insertions, 0 deletions
diff --git a/third_party/nix/src/libstore/local-store.cc b/third_party/nix/src/libstore/local-store.cc
new file mode 100644
index 000000000000..84ddd964b469
--- /dev/null
+++ b/third_party/nix/src/libstore/local-store.cc
@@ -0,0 +1,1453 @@
+#include "local-store.hh"
+#include "globals.hh"
+#include "archive.hh"
+#include "pathlocks.hh"
+#include "worker-protocol.hh"
+#include "derivations.hh"
+#include "nar-info.hh"
+
+#include <iostream>
+#include <algorithm>
+#include <cstring>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/select.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <utime.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdio.h>
+#include <time.h>
+#include <grp.h>
+
+#if __linux__
+#include <sched.h>
+#include <sys/statvfs.h>
+#include <sys/mount.h>
+#include <sys/ioctl.h>
+#include <sys/xattr.h>
+#endif
+
+#ifdef __CYGWIN__
+#include <windows.h>
+#endif
+
+#include <sqlite3.h>
+
+
+namespace nix {
+
+
+LocalStore::LocalStore(const Params & params)
+    : Store(params)
+    , LocalFSStore(params)
+    , realStoreDir_{this, false, rootDir != "" ? rootDir + "/nix/store" : storeDir, "real",
+        "physical path to the Nix store"}
+    , realStoreDir(realStoreDir_)
+    , dbDir(stateDir + "/db")
+    , linksDir(realStoreDir + "/.links")
+    , reservedPath(dbDir + "/reserved")
+    , schemaPath(dbDir + "/schema")
+    , trashDir(realStoreDir + "/trash")
+    , tempRootsDir(stateDir + "/temproots")
+    , fnTempRoots(fmt("%s/%d", tempRootsDir, getpid()))
+{
+    auto state(_state.lock());
+
+    /* Create missing state directories if they don't already exist. */
+    createDirs(realStoreDir);
+    makeStoreWritable();
+    createDirs(linksDir);
+    Path profilesDir = stateDir + "/profiles";
+    createDirs(profilesDir);
+    createDirs(tempRootsDir);
+    createDirs(dbDir);
+    Path gcRootsDir = stateDir + "/gcroots";
+    if (!pathExists(gcRootsDir)) {
+        createDirs(gcRootsDir);
+        createSymlink(profilesDir, gcRootsDir + "/profiles");
+    }
+
+    for (auto & perUserDir : {profilesDir + "/per-user", gcRootsDir + "/per-user"}) {
+        createDirs(perUserDir);
+        if (chmod(perUserDir.c_str(), 0755) == -1)
+            throw SysError("could not set permissions on '%s' to 755", perUserDir);
+    }
+
+    createUser(getUserName(), getuid());
+
+    /* Optionally, create directories and set permissions for a
+       multi-user install. */
+    if (getuid() == 0 && settings.buildUsersGroup != "") {
+        mode_t perm = 01775;
+
+        struct group * gr = getgrnam(settings.buildUsersGroup.get().c_str());
+        if (!gr)
+            printError(format("warning: the group '%1%' specified in 'build-users-group' does not exist")
+                % settings.buildUsersGroup);
+        else {
+            struct stat st;
+            if (stat(realStoreDir.c_str(), &st))
+                throw SysError(format("getting attributes of path '%1%'") % realStoreDir);
+
+            if (st.st_uid != 0 || st.st_gid != gr->gr_gid || (st.st_mode & ~S_IFMT) != perm) {
+                if (chown(realStoreDir.c_str(), 0, gr->gr_gid) == -1)
+                    throw SysError(format("changing ownership of path '%1%'") % realStoreDir);
+                if (chmod(realStoreDir.c_str(), perm) == -1)
+                    throw SysError(format("changing permissions on path '%1%'") % realStoreDir);
+            }
+        }
+    }
+
+    /* Ensure that the store and its parents are not symlinks. */
+    if (getEnv("NIX_IGNORE_SYMLINK_STORE") != "1") {
+        Path path = realStoreDir;
+        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);
+        }
+    }
+
+    /* 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 {
+        struct stat st;
+        if (stat(reservedPath.c_str(), &st) == -1 ||
+            st.st_size != settings.reservedSize)
+        {
+            AutoCloseFD fd = open(reservedPath.c_str(), O_WRONLY | O_CREAT | O_CLOEXEC, 0600);
+            int res = -1;
+#if HAVE_POSIX_FALLOCATE
+            res = posix_fallocate(fd.get(), 0, settings.reservedSize);
+#endif
+            if (res == -1) {
+                writeFull(fd.get(), string(settings.reservedSize, 'X'));
+                [[gnu::unused]] auto res2 = ftruncate(fd.get(), settings.reservedSize);
+            }
+        }
+    } 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. */
+    Path globalLockPath = dbDir + "/big-lock";
+    globalLock = openLockFile(globalLockPath.c_str(), true);
+
+    if (!lockFile(globalLock.get(), ltRead, false)) {
+        printError("waiting for the big Nix store lock...");
+        lockFile(globalLock.get(), 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(*state, 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 (curSchema < 6)
+            throw Error(
+                "Your Nix store has a database in flat file format,\n"
+                "which is no longer supported. To convert to the new format,\n"
+                "please upgrade Nix to version 1.11 first.");
+
+        if (!lockFile(globalLock.get(), ltWrite, false)) {
+            printError("waiting for exclusive access to the Nix store...");
+            lockFile(globalLock.get(), ltWrite, true);
+        }
+
+        /* Get the schema version again, because another process may
+           have performed the upgrade already. */
+        curSchema = getSchema();
+
+        if (curSchema < 7) { upgradeStore7(); }
+
+        openDB(*state, false);
+
+        if (curSchema < 8) {
+            SQLiteTxn txn(state->db);
+            state->db.exec("alter table ValidPaths add column ultimate integer");
+            state->db.exec("alter table ValidPaths add column sigs text");
+            txn.commit();
+        }
+
+        if (curSchema < 9) {
+            SQLiteTxn txn(state->db);
+            state->db.exec("drop table FailedPaths");
+            txn.commit();
+        }
+
+        if (curSchema < 10) {
+            SQLiteTxn txn(state->db);
+            state->db.exec("alter table ValidPaths add column ca text");
+            txn.commit();
+        }
+
+        writeFile(schemaPath, (format("%1%") % nixSchemaVersion).str());
+
+        lockFile(globalLock.get(), ltRead, true);
+    }
+
+    else openDB(*state, false);
+
+    /* Prepare SQL statements. */
+    state->stmtRegisterValidPath.create(state->db,
+        "insert into ValidPaths (path, hash, registrationTime, deriver, narSize, ultimate, sigs, ca) values (?, ?, ?, ?, ?, ?, ?, ?);");
+    state->stmtUpdatePathInfo.create(state->db,
+        "update ValidPaths set narSize = ?, hash = ?, ultimate = ?, sigs = ?, ca = ? where path = ?;");
+    state->stmtAddReference.create(state->db,
+        "insert or replace into Refs (referrer, reference) values (?, ?);");
+    state->stmtQueryPathInfo.create(state->db,
+        "select id, hash, registrationTime, deriver, narSize, ultimate, sigs, ca from ValidPaths where path = ?;");
+    state->stmtQueryReferences.create(state->db,
+        "select path from Refs join ValidPaths on reference = id where referrer = ?;");
+    state->stmtQueryReferrers.create(state->db,
+        "select path from Refs join ValidPaths on referrer = id where reference = (select id from ValidPaths where path = ?);");
+    state->stmtInvalidatePath.create(state->db,
+        "delete from ValidPaths where path = ?;");
+    state->stmtAddDerivationOutput.create(state->db,
+        "insert or replace into DerivationOutputs (drv, id, path) values (?, ?, ?);");
+    state->stmtQueryValidDerivers.create(state->db,
+        "select v.id, v.path from DerivationOutputs d join ValidPaths v on d.drv = v.id where d.path = ?;");
+    state->stmtQueryDerivationOutputs.create(state->db,
+        "select id, path from DerivationOutputs where drv = ?;");
+    // Use "path >= ?" with limit 1 rather than "path like '?%'" to
+    // ensure efficient lookup.
+    state->stmtQueryPathFromHashPart.create(state->db,
+        "select path from ValidPaths where path >= ? limit 1;");
+    state->stmtQueryValidPaths.create(state->db, "select path from ValidPaths");
+}
+
+
+LocalStore::~LocalStore()
+{
+    std::shared_future<void> future;
+
+    {
+        auto state(_state.lock());
+        if (state->gcRunning)
+            future = state->gcFuture;
+    }
+
+    if (future.valid()) {
+        printError("waiting for auto-GC to finish on exit...");
+        future.get();
+    }
+
+    try {
+        auto state(_state.lock());
+        if (state->fdTempRoots) {
+            state->fdTempRoots = -1;
+            unlink(fnTempRoots.c_str());
+        }
+    } catch (...) {
+        ignoreException();
+    }
+}
+
+
+std::string LocalStore::getUri()
+{
+    return "local";
+}
+
+
+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(State & state, bool create)
+{
+    if (access(dbDir.c_str(), R_OK | W_OK))
+        throw SysError(format("Nix database directory '%1%' is not writable") % dbDir);
+
+    /* Open the Nix database. */
+    string dbPath = dbDir + "/db.sqlite";
+    auto & db(state.db);
+    if (sqlite3_open_v2(dbPath.c_str(), &db.db,
+            SQLITE_OPEN_READWRITE | (create ? SQLITE_OPEN_CREATE : 0), 0) != SQLITE_OK)
+        throw Error(format("cannot open Nix database '%1%'") % dbPath);
+
+#ifdef __CYGWIN__
+    /* The cygwin version of sqlite3 has a patch which calls
+       SetDllDirectory("/usr/bin") on init. It was intended to fix extension
+       loading, which we don't use, and the effect of SetDllDirectory is
+       inherited by child processes, and causes libraries to be loaded from
+       /usr/bin instead of $PATH. This breaks quite a few things (e.g.
+       checkPhase on openssh), so we set it back to default behaviour. */
+    SetDllDirectoryW(L"");
+#endif
+
+    if (sqlite3_busy_timeout(db, 60 * 60 * 1000) != SQLITE_OK)
+        throwSQLiteError(db, "setting timeout");
+
+    db.exec("pragma foreign_keys = 1");
+
+    /* !!! 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";
+    db.exec("pragma synchronous = " + syncMode);
+
+    /* 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.gen.hh"
+            ;
+        db.exec(schema);
+    }
+}
+
+
+/* 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 __linux__
+    if (getuid() != 0) return;
+    /* Check if /nix/store is on a read-only mount. */
+    struct statvfs stat;
+    if (statvfs(realStoreDir.c_str(), &stat) != 0)
+        throw SysError("getting info about the Nix store mount point");
+
+    if (stat.f_flag & ST_RDONLY) {
+        if (unshare(CLONE_NEWNS) == -1)
+            throw SysError("setting up a private mount namespace");
+
+        if (mount(0, realStoreDir.c_str(), "none", MS_REMOUNT | MS_BIND, 0) == -1)
+            throw SysError(format("remounting %1% writable") % realStoreDir);
+    }
+#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();
+
+#if __APPLE__
+    /* Remove flags, in particular UF_IMMUTABLE which would prevent
+       the file from being garbage-collected. FIXME: Use
+       setattrlist() to remove other attributes as well. */
+    if (lchflags(path.c_str(), 0)) {
+        if (errno != ENOTSUP)
+            throw SysError(format("clearing flags of path '%1%'") % path);
+    }
+#endif
+
+    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. */
+    if (!(S_ISREG(st.st_mode) || S_ISDIR(st.st_mode) || S_ISLNK(st.st_mode)))
+        throw Error(format("file '%1%' has an unsupported type") % path);
+
+#if __linux__
+    /* Remove extended attributes / ACLs. */
+    ssize_t eaSize = llistxattr(path.c_str(), nullptr, 0);
+
+    if (eaSize < 0) {
+        if (errno != ENOTSUP && errno != ENODATA)
+            throw SysError("querying extended attributes of '%s'", path);
+    } else if (eaSize > 0) {
+        std::vector<char> eaBuf(eaSize);
+
+        if ((eaSize = llistxattr(path.c_str(), eaBuf.data(), eaBuf.size())) < 0)
+            throw SysError("querying extended attributes of '%s'", path);
+
+        for (auto & eaName: tokenizeString<Strings>(std::string(eaBuf.data(), eaSize), std::string("\000", 1))) {
+            /* Ignore SELinux security labels since these cannot be
+               removed even by root. */
+            if (eaName == "security.selinux") continue;
+            if (lremovexattr(path.c_str(), eaName.c_str()) == -1)
+                throw SysError("removing extended attribute '%s' from '%s'", eaName, path);
+        }
+     }
+#endif
+
+    /* 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(), getegid()) == -1)
+#else
+        if (!S_ISLNK(st.st_mode) &&
+            chown(path.c_str(), geteuid(), getegid()) == -1)
+#endif
+            throw SysError(format("changing owner of '%1%' to %2%")
+                % path % geteuid());
+    }
+
+    if (S_ISDIR(st.st_mode)) {
+        DirEntries entries = readDirectory(path);
+        for (auto & i : entries)
+            canonicalisePathMetaData_(path + "/" + i.name, 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 (drv.isFixedOutput()) {
+        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; Hash h;
+        out->second.parseHashInfo(recursive, h);
+        Path outPath = makeFixedOutputPath(recursive, 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);
+        for (auto & i : drvCopy.outputs) {
+            i.second.path = "";
+            drvCopy.env[i.first] = "";
+        }
+
+        Hash h = hashDerivationModulo(*this, drvCopy);
+
+        for (auto & 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);
+        }
+    }
+}
+
+
+uint64_t LocalStore::addValidPath(State & state,
+    const ValidPathInfo & info, bool checkOutputs)
+{
+    if (info.ca != "" && !info.isContentAddressed(*this))
+        throw Error("cannot add path '%s' to the Nix store because it claims to be content-addressed but isn't", info.path);
+
+    state.stmtRegisterValidPath.use()
+        (info.path)
+        (info.narHash.to_string(Base16))
+        (info.registrationTime == 0 ? time(0) : info.registrationTime)
+        (info.deriver, info.deriver != "")
+        (info.narSize, info.narSize != 0)
+        (info.ultimate ? 1 : 0, info.ultimate)
+        (concatStringsSep(" ", info.sigs), !info.sigs.empty())
+        (info.ca, !info.ca.empty())
+        .exec();
+    uint64_t id = sqlite3_last_insert_rowid(state.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 = readDerivation(realStoreDir + "/" + baseNameOf(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);
+
+        for (auto & i : drv.outputs) {
+            state.stmtAddDerivationOutput.use()
+                (id)
+                (i.first)
+                (i.second.path)
+                .exec();
+        }
+    }
+
+    {
+        auto state_(Store::state.lock());
+        state_->pathInfoCache.upsert(storePathToHash(info.path), std::make_shared<ValidPathInfo>(info));
+    }
+
+    return id;
+}
+
+
+void LocalStore::queryPathInfoUncached(const Path & path,
+    Callback<std::shared_ptr<ValidPathInfo>> callback) noexcept
+{
+    try {
+        auto info = std::make_shared<ValidPathInfo>();
+        info->path = path;
+
+        assertStorePath(path);
+
+        callback(retrySQLite<std::shared_ptr<ValidPathInfo>>([&]() {
+            auto state(_state.lock());
+
+            /* Get the path info. */
+            auto useQueryPathInfo(state->stmtQueryPathInfo.use()(path));
+
+            if (!useQueryPathInfo.next())
+                return std::shared_ptr<ValidPathInfo>();
+
+            info->id = useQueryPathInfo.getInt(0);
+
+            try {
+                info->narHash = Hash(useQueryPathInfo.getStr(1));
+            } catch (BadHash & e) {
+                throw Error("in valid-path entry for '%s': %s", path, e.what());
+            }
+
+            info->registrationTime = useQueryPathInfo.getInt(2);
+
+            auto s = (const char *) sqlite3_column_text(state->stmtQueryPathInfo, 3);
+            if (s) info->deriver = s;
+
+            /* Note that narSize = NULL yields 0. */
+            info->narSize = useQueryPathInfo.getInt(4);
+
+            info->ultimate = useQueryPathInfo.getInt(5) == 1;
+
+            s = (const char *) sqlite3_column_text(state->stmtQueryPathInfo, 6);
+            if (s) info->sigs = tokenizeString<StringSet>(s, " ");
+
+            s = (const char *) sqlite3_column_text(state->stmtQueryPathInfo, 7);
+            if (s) info->ca = s;
+
+            /* Get the references. */
+            auto useQueryReferences(state->stmtQueryReferences.use()(info->id));
+
+            while (useQueryReferences.next())
+                info->references.insert(useQueryReferences.getStr(0));
+
+            return info;
+        }));
+
+    } catch (...) { callback.rethrow(); }
+}
+
+
+/* Update path info in the database. */
+void LocalStore::updatePathInfo(State & state, const ValidPathInfo & info)
+{
+    state.stmtUpdatePathInfo.use()
+        (info.narSize, info.narSize != 0)
+        (info.narHash.to_string(Base16))
+        (info.ultimate ? 1 : 0, info.ultimate)
+        (concatStringsSep(" ", info.sigs), !info.sigs.empty())
+        (info.ca, !info.ca.empty())
+        (info.path)
+        .exec();
+}
+
+
+uint64_t LocalStore::queryValidPathId(State & state, const Path & path)
+{
+    auto use(state.stmtQueryPathInfo.use()(path));
+    if (!use.next())
+        throw Error(format("path '%1%' is not valid") % path);
+    return use.getInt(0);
+}
+
+
+bool LocalStore::isValidPath_(State & state, const Path & path)
+{
+    return state.stmtQueryPathInfo.use()(path).next();
+}
+
+
+bool LocalStore::isValidPathUncached(const Path & path)
+{
+    return retrySQLite<bool>([&]() {
+        auto state(_state.lock());
+        return isValidPath_(*state, path);
+    });
+}
+
+
+PathSet LocalStore::queryValidPaths(const PathSet & paths, SubstituteFlag maybeSubstitute)
+{
+    PathSet res;
+    for (auto & i : paths)
+        if (isValidPath(i)) res.insert(i);
+    return res;
+}
+
+
+PathSet LocalStore::queryAllValidPaths()
+{
+    return retrySQLite<PathSet>([&]() {
+        auto state(_state.lock());
+        auto use(state->stmtQueryValidPaths.use());
+        PathSet res;
+        while (use.next()) res.insert(use.getStr(0));
+        return res;
+    });
+}
+
+
+void LocalStore::queryReferrers(State & state, const Path & path, PathSet & referrers)
+{
+    auto useQueryReferrers(state.stmtQueryReferrers.use()(path));
+
+    while (useQueryReferrers.next())
+        referrers.insert(useQueryReferrers.getStr(0));
+}
+
+
+void LocalStore::queryReferrers(const Path & path, PathSet & referrers)
+{
+    assertStorePath(path);
+    return retrySQLite<void>([&]() {
+        auto state(_state.lock());
+        queryReferrers(*state, path, referrers);
+    });
+}
+
+
+PathSet LocalStore::queryValidDerivers(const Path & path)
+{
+    assertStorePath(path);
+
+    return retrySQLite<PathSet>([&]() {
+        auto state(_state.lock());
+
+        auto useQueryValidDerivers(state->stmtQueryValidDerivers.use()(path));
+
+        PathSet derivers;
+        while (useQueryValidDerivers.next())
+            derivers.insert(useQueryValidDerivers.getStr(1));
+
+        return derivers;
+    });
+}
+
+
+PathSet LocalStore::queryDerivationOutputs(const Path & path)
+{
+    return retrySQLite<PathSet>([&]() {
+        auto state(_state.lock());
+
+        auto useQueryDerivationOutputs(state->stmtQueryDerivationOutputs.use()
+            (queryValidPathId(*state, path)));
+
+        PathSet outputs;
+        while (useQueryDerivationOutputs.next())
+            outputs.insert(useQueryDerivationOutputs.getStr(1));
+
+        return outputs;
+    });
+}
+
+
+StringSet LocalStore::queryDerivationOutputNames(const Path & path)
+{
+    return retrySQLite<StringSet>([&]() {
+        auto state(_state.lock());
+
+        auto useQueryDerivationOutputs(state->stmtQueryDerivationOutputs.use()
+            (queryValidPathId(*state, path)));
+
+        StringSet outputNames;
+        while (useQueryDerivationOutputs.next())
+            outputNames.insert(useQueryDerivationOutputs.getStr(0));
+
+        return outputNames;
+    });
+}
+
+
+Path LocalStore::queryPathFromHashPart(const string & hashPart)
+{
+    if (hashPart.size() != storePathHashLen) throw Error("invalid hash part");
+
+    Path prefix = storeDir + "/" + hashPart;
+
+    return retrySQLite<Path>([&]() -> std::string {
+        auto state(_state.lock());
+
+        auto useQueryPathFromHashPart(state->stmtQueryPathFromHashPart.use()(prefix));
+
+        if (!useQueryPathFromHashPart.next()) return "";
+
+        const char * s = (const char *) sqlite3_column_text(state->stmtQueryPathFromHashPart, 0);
+        return s && prefix.compare(0, prefix.size(), s, prefix.size()) == 0 ? s : "";
+    });
+}
+
+
+PathSet LocalStore::querySubstitutablePaths(const PathSet & paths)
+{
+    if (!settings.useSubstitutes) return PathSet();
+
+    auto remaining = paths;
+    PathSet res;
+
+    for (auto & sub : getDefaultSubstituters()) {
+        if (remaining.empty()) break;
+        if (sub->storeDir != storeDir) continue;
+        if (!sub->wantMassQuery()) continue;
+
+        auto valid = sub->queryValidPaths(remaining);
+
+        PathSet remaining2;
+        for (auto & path : remaining)
+            if (valid.count(path))
+                res.insert(path);
+            else
+                remaining2.insert(path);
+
+        std::swap(remaining, remaining2);
+    }
+
+    return res;
+}
+
+
+void LocalStore::querySubstitutablePathInfos(const PathSet & paths,
+    SubstitutablePathInfos & infos)
+{
+    if (!settings.useSubstitutes) return;
+    for (auto & sub : getDefaultSubstituters()) {
+        if (sub->storeDir != storeDir) continue;
+        for (auto & path : paths) {
+            if (infos.count(path)) continue;
+            debug(format("checking substituter '%s' for path '%s'")
+                % sub->getUri() % path);
+            try {
+                auto info = sub->queryPathInfo(path);
+                auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
+                    std::shared_ptr<const ValidPathInfo>(info));
+                infos[path] = SubstitutablePathInfo{
+                    info->deriver,
+                    info->references,
+                    narInfo ? narInfo->fileSize : 0,
+                    info->narSize};
+            } catch (InvalidPath &) {
+            } catch (SubstituterDisabled &) {
+            } catch (Error & e) {
+                if (settings.tryFallback)
+                    printError(e.what());
+                else
+                    throw;
+            }
+        }
+    }
+}
+
+
+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();
+
+    return retrySQLite<void>([&]() {
+        auto state(_state.lock());
+
+        SQLiteTxn txn(state->db);
+        PathSet paths;
+
+        for (auto & i : infos) {
+            assert(i.narHash.type == htSHA256);
+            if (isValidPath_(*state, i.path))
+                updatePathInfo(*state, i);
+            else
+                addValidPath(*state, i, false);
+            paths.insert(i.path);
+        }
+
+        for (auto & i : infos) {
+            auto referrer = queryValidPathId(*state, i.path);
+            for (auto & j : i.references)
+                state->stmtAddReference.use()(referrer)(queryValidPathId(*state, j)).exec();
+        }
+
+        /* Check that the derivation outputs are correct.  We can't do
+           this in addValidPath() above, because the references might
+           not be valid yet. */
+        for (auto & i : infos)
+            if (isDerivation(i.path)) {
+                // FIXME: inefficient; we already loaded the
+                // derivation in addValidPath().
+                Derivation drv = readDerivation(realStoreDir + "/" + baseNameOf(i.path));
+                checkDerivationOutputs(i.path, drv);
+            }
+
+        /* 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(paths);
+
+        txn.commit();
+    });
+}
+
+
+/* Invalidate a path.  The caller is responsible for checking that
+   there are no referrers. */
+void LocalStore::invalidatePath(State & state, const Path & path)
+{
+    debug(format("invalidating path '%1%'") % path);
+
+    state.stmtInvalidatePath.use()(path).exec();
+
+    /* Note that the foreign key constraints on the Refs table take
+       care of deleting the references entries for `path'. */
+
+    {
+        auto state_(Store::state.lock());
+        state_->pathInfoCache.erase(storePathToHash(path));
+    }
+}
+
+
+const PublicKeys & LocalStore::getPublicKeys()
+{
+    auto state(_state.lock());
+    if (!state->publicKeys)
+        state->publicKeys = std::make_unique<PublicKeys>(getDefaultPublicKeys());
+    return *state->publicKeys;
+}
+
+
+void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
+    RepairFlag repair, CheckSigsFlag checkSigs, std::shared_ptr<FSAccessor> accessor)
+{
+    if (!info.narHash)
+        throw Error("cannot add path '%s' because it lacks a hash", info.path);
+
+    if (requireSigs && checkSigs && !info.checkSignatures(*this, getPublicKeys()))
+        throw Error("cannot add path '%s' because it lacks a valid signature", info.path);
+
+    addTempRoot(info.path);
+
+    if (repair || !isValidPath(info.path)) {
+
+        PathLocks outputLock;
+
+        Path realPath = realStoreDir + "/" + baseNameOf(info.path);
+
+        /* 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). */
+        if (!locksHeld.count(info.path))
+            outputLock.lockPaths({realPath});
+
+        if (repair || !isValidPath(info.path)) {
+
+            deletePath(realPath);
+
+            /* While restoring the path from the NAR, compute the hash
+               of the NAR. */
+            HashSink hashSink(htSHA256);
+
+            LambdaSource wrapperSource([&](unsigned char * data, size_t len) -> size_t {
+                size_t n = source.read(data, len);
+                hashSink(data, n);
+                return n;
+            });
+
+            restorePath(realPath, wrapperSource);
+
+            auto hashResult = hashSink.finish();
+
+            if (hashResult.first != info.narHash)
+                throw Error("hash mismatch importing path '%s';\n  wanted: %s\n  got:    %s",
+                    info.path, info.narHash.to_string(), hashResult.first.to_string());
+
+            if (hashResult.second != info.narSize)
+                throw Error("size mismatch importing path '%s';\n  wanted: %s\n  got:   %s",
+                    info.path, info.narSize, hashResult.second);
+
+            autoGC();
+
+            canonicalisePathMetaData(realPath, -1);
+
+            optimisePath(realPath); // FIXME: combine with hashPath()
+
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+}
+
+
+Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
+    bool recursive, HashType hashAlgo, RepairFlag repair)
+{
+    Hash h = hashString(hashAlgo, dump);
+
+    Path dstPath = makeFixedOutputPath(recursive, h, name);
+
+    addTempRoot(dstPath);
+
+    if (repair || !isValidPath(dstPath)) {
+
+        /* The first check above is an optimisation to prevent
+           unnecessary lock acquisition. */
+
+        Path realPath = realStoreDir + "/" + baseNameOf(dstPath);
+
+        PathLocks outputLock({realPath});
+
+        if (repair || !isValidPath(dstPath)) {
+
+            deletePath(realPath);
+
+            autoGC();
+
+            if (recursive) {
+                StringSource source(dump);
+                restorePath(realPath, source);
+            } else
+                writeFile(realPath, dump);
+
+            canonicalisePathMetaData(realPath, -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, realPath);
+
+            optimisePath(realPath); // FIXME: combine with hashPath()
+
+            ValidPathInfo info;
+            info.path = dstPath;
+            info.narHash = hash.first;
+            info.narSize = hash.second;
+            info.ca = makeFixedOutputCA(recursive, h);
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+Path LocalStore::addToStore(const string & name, const Path & _srcPath,
+    bool recursive, HashType hashAlgo, PathFilter & filter, RepairFlag repair)
+{
+    Path srcPath(absPath(_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 = make_ref<std::string>(readFile(srcPath));
+
+    return addToStoreFromDump(*sink.s, name, recursive, hashAlgo, repair);
+}
+
+
+Path LocalStore::addTextToStore(const string & name, const string & s,
+    const PathSet & references, RepairFlag repair)
+{
+    auto hash = hashString(htSHA256, s);
+    auto dstPath = makeTextPath(name, hash, references);
+
+    addTempRoot(dstPath);
+
+    if (repair || !isValidPath(dstPath)) {
+
+        Path realPath = realStoreDir + "/" + baseNameOf(dstPath);
+
+        PathLocks outputLock({realPath});
+
+        if (repair || !isValidPath(dstPath)) {
+
+            deletePath(realPath);
+
+            autoGC();
+
+            writeFile(realPath, s);
+
+            canonicalisePathMetaData(realPath, -1);
+
+            StringSink sink;
+            dumpString(s, sink);
+            auto narHash = hashString(htSHA256, *sink.s);
+
+            optimisePath(realPath);
+
+            ValidPathInfo info;
+            info.path = dstPath;
+            info.narHash = narHash;
+            info.narSize = sink.s->size();
+            info.references = references;
+            info.ca = "text:" + hash.to_string();
+            registerValidPath(info);
+        }
+
+        outputLock.setDeletion(true);
+    }
+
+    return dstPath;
+}
+
+
+/* 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(realStoreDir);
+        addTempRoot(tmpDir);
+    } while (!pathExists(tmpDir));
+    return tmpDir;
+}
+
+
+void LocalStore::invalidatePathChecked(const Path & path)
+{
+    assertStorePath(path);
+
+    retrySQLite<void>([&]() {
+        auto state(_state.lock());
+
+        SQLiteTxn txn(state->db);
+
+        if (isValidPath_(*state, path)) {
+            PathSet referrers; queryReferrers(*state, 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(*state, path);
+        }
+
+        txn.commit();
+    });
+}
+
+
+bool LocalStore::verifyStore(bool checkContents, RepairFlag repair)
+{
+    printError(format("reading the Nix store..."));
+
+    bool errors = false;
+
+    /* Acquire the global GC lock to get a consistent snapshot of
+       existing and valid paths. */
+    AutoCloseFD fdGCLock = openGCLock(ltWrite);
+
+    PathSet store;
+    for (auto & i : readDirectory(realStoreDir)) store.insert(i.name);
+
+    /* Check whether all valid paths actually exist. */
+    printInfo("checking path existence...");
+
+    PathSet validPaths2 = queryAllValidPaths(), validPaths, done;
+
+    fdGCLock = -1;
+
+    for (auto & i : validPaths2)
+        verifyPath(i, store, done, validPaths, repair, errors);
+
+    /* Optionally, check the content hashes (slow). */
+    if (checkContents) {
+        printInfo("checking hashes...");
+
+        Hash nullHash(htSHA256);
+
+        for (auto & i : validPaths) {
+            try {
+                auto info = std::const_pointer_cast<ValidPathInfo>(std::shared_ptr<const ValidPathInfo>(queryPathInfo(i)));
+
+                /* Check the content hash (optionally - slow). */
+                printMsg(lvlTalkative, format("checking contents of '%1%'") % i);
+                HashResult current = hashPath(info->narHash.type, toRealPath(i));
+
+                if (info->narHash != nullHash && info->narHash != current.first) {
+                    printError(format("path '%1%' was modified! "
+                            "expected hash '%2%', got '%3%'")
+                        % i % info->narHash.to_string() % current.first.to_string());
+                    if (repair) repairPath(i); else errors = true;
+                } else {
+
+                    bool update = false;
+
+                    /* Fill in missing hashes. */
+                    if (info->narHash == nullHash) {
+                        printError(format("fixing missing hash on '%1%'") % i);
+                        info->narHash = current.first;
+                        update = true;
+                    }
+
+                    /* Fill in missing narSize fields (from old stores). */
+                    if (info->narSize == 0) {
+                        printError(format("updating size field on '%1%' to %2%") % i % current.second);
+                        info->narSize = current.second;
+                        update = true;
+                    }
+
+                    if (update) {
+                        auto state(_state.lock());
+                        updatePathInfo(*state, *info);
+                    }
+
+                }
+
+            } catch (Error & e) {
+                /* It's possible that the path got GC'ed, so ignore
+                   errors on invalid paths. */
+                if (isValidPath(i))
+                    printError(format("error: %1%") % e.msg());
+                else
+                    printError(format("warning: %1%") % e.msg());
+                errors = true;
+            }
+        }
+    }
+
+    return errors;
+}
+
+
+void LocalStore::verifyPath(const Path & path, const PathSet & store,
+    PathSet & done, PathSet & validPaths, RepairFlag repair, bool & errors)
+{
+    checkInterrupt();
+
+    if (done.find(path) != done.end()) return;
+    done.insert(path);
+
+    if (!isStorePath(path)) {
+        printError(format("path '%1%' is not in the Nix store") % path);
+        auto state(_state.lock());
+        invalidatePath(*state, 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);
+        for (auto & i : referrers)
+            if (i != path) {
+                verifyPath(i, store, done, validPaths, repair, errors);
+                if (validPaths.find(i) != validPaths.end())
+                    canInvalidate = false;
+            }
+
+        if (canInvalidate) {
+            printError(format("path '%1%' disappeared, removing from database...") % path);
+            auto state(_state.lock());
+            invalidatePath(*state, path);
+        } else {
+            printError(format("path '%1%' disappeared, but it still has valid referrers!") % path);
+            if (repair)
+                try {
+                    repairPath(path);
+                } catch (Error & e) {
+                    printError(format("warning: %1%") % e.msg());
+                    errors = true;
+                }
+            else errors = true;
+        }
+
+        return;
+    }
+
+    validPaths.insert(path);
+}
+
+
+unsigned int LocalStore::getProtocol()
+{
+    return PROTOCOL_VERSION;
+}
+
+
+#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)) {
+        for (auto & i : readDirectory(path))
+            makeMutable(path + "/" + i.name);
+    }
+
+    /* 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 | O_CLOEXEC);
+    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;
+    printError("removing immutable bits from the Nix store (this may take a while)...");
+    makeMutable(realStoreDir);
+}
+
+#else
+
+void LocalStore::upgradeStore7()
+{
+}
+
+#endif
+
+
+void LocalStore::vacuumDB()
+{
+    auto state(_state.lock());
+    state->db.exec("vacuum");
+}
+
+
+void LocalStore::addSignatures(const Path & storePath, const StringSet & sigs)
+{
+    retrySQLite<void>([&]() {
+        auto state(_state.lock());
+
+        SQLiteTxn txn(state->db);
+
+        auto info = std::const_pointer_cast<ValidPathInfo>(std::shared_ptr<const ValidPathInfo>(queryPathInfo(storePath)));
+
+        info->sigs.insert(sigs.begin(), sigs.end());
+
+        updatePathInfo(*state, *info);
+
+        txn.commit();
+    });
+}
+
+
+void LocalStore::signPathInfo(ValidPathInfo & info)
+{
+    // FIXME: keep secret keys in memory.
+
+    auto secretKeyFiles = settings.secretKeyFiles;
+
+    for (auto & secretKeyFile : secretKeyFiles.get()) {
+        SecretKey secretKey(readFile(secretKeyFile));
+        info.sign(secretKey);
+    }
+}
+
+
+void LocalStore::createUser(const std::string & userName, uid_t userId)
+{
+    for (auto & dir : {
+        fmt("%s/profiles/per-user/%s", stateDir, userName),
+        fmt("%s/gcroots/per-user/%s", stateDir, userName)
+    }) {
+        createDirs(dir);
+        if (chmod(dir.c_str(), 0755) == -1)
+            throw SysError("changing permissions of directory '%s'", dir);
+        if (chown(dir.c_str(), userId, getgid()) == -1)
+            throw SysError("changing owner of directory '%s'", dir);
+    }
+}
+
+
+}