Merge branch 'master' into core-updates

1 files changed, 2010 insertions, 0 deletions

diff --git a/nix/libstore/local-store.cc b/nix/libstore/local-store.cc
new file mode 100644
index 0000000000..1293a6e8f2
--- /dev/null
+++ b/nix/libstore/local-store.cc
@@ -0,0 +1,2010 @@
+#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);
+        createSymlink(profilesDir, gcRootsDir + "/profiles");
+    }
+
+    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)
+{
+    if (access(settings.nixDBPath.c_str(), R_OK | W_OK))
+        throw SysError(format("Nix database directory `%1%' is not writable") % settings.nixDBPath);
+
+    /* Open the Nix database. */
+    string dbPath = settings.nixDBPath + "/db.sqlite";
+    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);
+
+    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 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, 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, false);
+            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));
+        }
+
+        /* Check that the derivation outputs are correct.  We can't do
+           this in addValidPath() above, because the references might
+           not be valid yet. */
+        foreach (ValidPathInfos::const_iterator, i, infos)
+            if (isDerivation(i->path)) {
+                // FIXME: inefficient; we already loaded the
+                // derivation in addValidPath().
+                Derivation drv = parseDerivation(readFile(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(*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");
+}
+
+
+}