diff options
Diffstat (limited to 'src/libstore/gc.cc')
| -rw-r--r-- | src/libstore/gc.cc | 752 |
1 files changed, 752 insertions, 0 deletions
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc new file mode 100644 index 000000000000..79bd7d56b3fe --- /dev/null +++ b/src/libstore/gc.cc @@ -0,0 +1,752 @@ +#include "globals.hh" +#include "misc.hh" +#include "local-store.hh" + +#include <boost/shared_ptr.hpp> + +#include <functional> +#include <queue> +#include <algorithm> + +#include <sys/types.h> +#include <sys/stat.h> +#include <errno.h> +#include <fcntl.h> +#include <unistd.h> + + +namespace nix { + + +static string gcLockName = "gc.lock"; +static string tempRootsDir = "temproots"; +static string gcRootsDir = "gcroots"; + + +/* Acquire the global GC lock. This is used to prevent new Nix + processes from starting after the temporary root files have been + read. To be precise: when they try to create a new temporary root + file, they will block until the garbage collector has finished / + yielded the GC lock. */ +int LocalStore::openGCLock(LockType lockType) +{ + Path fnGCLock = (format("%1%/%2%") + % settings.nixStateDir % gcLockName).str(); + + debug(format("acquiring global GC lock `%1%'") % fnGCLock); + + AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT, 0600); + if (fdGCLock == -1) + throw SysError(format("opening global GC lock `%1%'") % fnGCLock); + closeOnExec(fdGCLock); + + if (!lockFile(fdGCLock, lockType, false)) { + printMsg(lvlError, format("waiting for the big garbage collector lock...")); + lockFile(fdGCLock, lockType, true); + } + + /* !!! Restrict read permission on the GC root. Otherwise any + process that can open the file for reading can DoS the + collector. */ + + return fdGCLock.borrow(); +} + + +void createSymlink(const Path & link, const Path & target) +{ + /* Create directories up to `gcRoot'. */ + createDirs(dirOf(link)); + + /* Create the new symlink. */ + Path tempLink = (format("%1%.tmp-%2%-%3%") + % link % getpid() % rand()).str(); + if (symlink(target.c_str(), tempLink.c_str()) == -1) + throw SysError(format("symlinking `%1%' to `%2%'") + % tempLink % target); + + /* Atomically replace the old one. */ + if (rename(tempLink.c_str(), link.c_str()) == -1) + throw SysError(format("cannot rename `%1%' to `%2%'") + % tempLink % link); +} + + +void LocalStore::syncWithGC() +{ + AutoCloseFD fdGCLock = openGCLock(ltRead); +} + + +void LocalStore::addIndirectRoot(const Path & path) +{ + string hash = printHash32(hashString(htSHA1, path)); + Path realRoot = canonPath((format("%1%/%2%/auto/%3%") + % settings.nixStateDir % gcRootsDir % hash).str()); + createSymlink(realRoot, path); +} + + +Path addPermRoot(StoreAPI & store, const Path & _storePath, + const Path & _gcRoot, bool indirect, bool allowOutsideRootsDir) +{ + Path storePath(canonPath(_storePath)); + Path gcRoot(canonPath(_gcRoot)); + assertStorePath(storePath); + + if (isInStore(gcRoot)) + throw Error(format( + "creating a garbage collector root (%1%) in the Nix store is forbidden " + "(are you running nix-build inside the store?)") % gcRoot); + + if (indirect) { + /* Don't clobber the the link if it already exists and doesn't + point to the Nix store. */ + if (pathExists(gcRoot) && (!isLink(gcRoot) || !isInStore(readLink(gcRoot)))) + throw Error(format("cannot create symlink `%1%'; already exists") % gcRoot); + createSymlink(gcRoot, storePath); + store.addIndirectRoot(gcRoot); + } + + else { + if (!allowOutsideRootsDir) { + Path rootsDir = canonPath((format("%1%/%2%") % settings.nixStateDir % gcRootsDir).str()); + + if (string(gcRoot, 0, rootsDir.size() + 1) != rootsDir + "/") + throw Error(format( + "path `%1%' is not a valid garbage collector root; " + "it's not in the directory `%2%'") + % gcRoot % rootsDir); + } + + createSymlink(gcRoot, storePath); + } + + /* Check that the root can be found by the garbage collector. + !!! This can be very slow on machines that have many roots. + Instead of reading all the roots, it would be more efficient to + check if the root is in a directory in or linked from the + gcroots directory. */ + if (settings.checkRootReachability) { + Roots roots = store.findRoots(); + if (roots.find(gcRoot) == roots.end()) + printMsg(lvlError, + format( + "warning: `%1%' is not in a directory where the garbage collector looks for roots; " + "therefore, `%2%' might be removed by the garbage collector") + % gcRoot % storePath); + } + + /* Grab the global GC root, causing us to block while a GC is in + progress. This prevents the set of permanent roots from + increasing while a GC is in progress. */ + store.syncWithGC(); + + return gcRoot; +} + + +/* The file to which we write our temporary roots. */ +static Path fnTempRoots; +static AutoCloseFD fdTempRoots; + + +void LocalStore::addTempRoot(const Path & path) +{ + /* Create the temporary roots file for this process. */ + if (fdTempRoots == -1) { + + while (1) { + Path dir = (format("%1%/%2%") % settings.nixStateDir % tempRootsDir).str(); + createDirs(dir); + + fnTempRoots = (format("%1%/%2%") + % dir % getpid()).str(); + + AutoCloseFD fdGCLock = openGCLock(ltRead); + + if (pathExists(fnTempRoots)) + /* It *must* be stale, since there can be no two + processes with the same pid. */ + unlink(fnTempRoots.c_str()); + + fdTempRoots = openLockFile(fnTempRoots, true); + + fdGCLock.close(); + + debug(format("acquiring read lock on `%1%'") % fnTempRoots); + lockFile(fdTempRoots, ltRead, true); + + /* Check whether the garbage collector didn't get in our + way. */ + struct stat st; + if (fstat(fdTempRoots, &st) == -1) + throw SysError(format("statting `%1%'") % fnTempRoots); + if (st.st_size == 0) break; + + /* The garbage collector deleted this file before we could + get a lock. (It won't delete the file after we get a + lock.) Try again. */ + } + + } + + /* Upgrade the lock to a write lock. This will cause us to block + if the garbage collector is holding our lock. */ + debug(format("acquiring write lock on `%1%'") % fnTempRoots); + lockFile(fdTempRoots, ltWrite, true); + + string s = path + '\0'; + writeFull(fdTempRoots, (const unsigned char *) s.data(), s.size()); + + /* Downgrade to a read lock. */ + debug(format("downgrading to read lock on `%1%'") % fnTempRoots); + lockFile(fdTempRoots, ltRead, true); +} + + +void removeTempRoots() +{ + if (fdTempRoots != -1) { + fdTempRoots.close(); + unlink(fnTempRoots.c_str()); + } +} + + +/* Automatically clean up the temporary roots file when we exit. */ +struct RemoveTempRoots +{ + ~RemoveTempRoots() + { + removeTempRoots(); + } +}; + +static RemoveTempRoots autoRemoveTempRoots __attribute__((unused)); + + +typedef boost::shared_ptr<AutoCloseFD> FDPtr; +typedef list<FDPtr> FDs; + + +static void readTempRoots(PathSet & tempRoots, FDs & fds) +{ + /* Read the `temproots' directory for per-process temporary root + files. */ + Strings tempRootFiles = readDirectory( + (format("%1%/%2%") % settings.nixStateDir % tempRootsDir).str()); + + foreach (Strings::iterator, i, tempRootFiles) { + Path path = (format("%1%/%2%/%3%") % settings.nixStateDir % tempRootsDir % *i).str(); + + debug(format("reading temporary root file `%1%'") % path); + FDPtr fd(new AutoCloseFD(open(path.c_str(), O_RDWR, 0666))); + if (*fd == -1) { + /* It's okay if the file has disappeared. */ + if (errno == ENOENT) continue; + throw SysError(format("opening temporary roots file `%1%'") % path); + } + + /* This should work, but doesn't, for some reason. */ + //FDPtr fd(new AutoCloseFD(openLockFile(path, false))); + //if (*fd == -1) continue; + + /* Try to acquire a write lock without blocking. This can + only succeed if the owning process has died. In that case + we don't care about its temporary roots. */ + if (lockFile(*fd, ltWrite, false)) { + printMsg(lvlError, format("removing stale temporary roots file `%1%'") % path); + unlink(path.c_str()); + writeFull(*fd, (const unsigned char *) "d", 1); + continue; + } + + /* Acquire a read lock. This will prevent the owning process + from upgrading to a write lock, therefore it will block in + addTempRoot(). */ + debug(format("waiting for read lock on `%1%'") % path); + lockFile(*fd, ltRead, true); + + /* Read the entire file. */ + string contents = readFile(*fd); + + /* Extract the roots. */ + string::size_type pos = 0, end; + + while ((end = contents.find((char) 0, pos)) != string::npos) { + Path root(contents, pos, end - pos); + debug(format("got temporary root `%1%'") % root); + assertStorePath(root); + tempRoots.insert(root); + pos = end + 1; + } + + fds.push_back(fd); /* keep open */ + } +} + + +static void foundRoot(StoreAPI & store, + const Path & path, const Path & target, Roots & roots) +{ + Path storePath = toStorePath(target); + if (store.isValidPath(storePath)) + roots[path] = storePath; + else + printMsg(lvlInfo, format("skipping invalid root from `%1%' to `%2%'") % path % storePath); +} + + +static void findRoots(StoreAPI & store, const Path & path, Roots & roots) +{ + try { + + struct stat st = lstat(path); + + if (S_ISDIR(st.st_mode)) { + Strings names = readDirectory(path); + foreach (Strings::iterator, i, names) + findRoots(store, path + "/" + *i, roots); + } + + else if (S_ISLNK(st.st_mode)) { + Path target = readLink(path); + if (isInStore(target)) + foundRoot(store, path, target, roots); + + /* Handle indirect roots. */ + else { + target = absPath(target, dirOf(path)); + if (!pathExists(target)) { + if (isInDir(path, settings.nixStateDir + "/" + gcRootsDir + "/auto")) { + printMsg(lvlInfo, format("removing stale link from `%1%' to `%2%'") % path % target); + unlink(path.c_str()); + } + } else { + struct stat st2 = lstat(target); + if (!S_ISLNK(st2.st_mode)) return; + Path target2 = readLink(target); + if (isInStore(target2)) foundRoot(store, target, target2, roots); + } + } + } + + } + + catch (SysError & e) { + /* We only ignore permanent failures. */ + if (e.errNo == EACCES || e.errNo == ENOENT || e.errNo == ENOTDIR) + printMsg(lvlInfo, format("cannot read potential root `%1%'") % path); + else + throw; + } +} + + +Roots LocalStore::findRoots() +{ + Roots roots; + + /* Process direct roots in {gcroots,manifests,profiles}. */ + nix::findRoots(*this, settings.nixStateDir + "/" + gcRootsDir, roots); + nix::findRoots(*this, settings.nixStateDir + "/manifests", roots); + nix::findRoots(*this, settings.nixStateDir + "/profiles", roots); + + return roots; +} + + +static void addAdditionalRoots(StoreAPI & store, PathSet & roots) +{ + Path rootFinder = getEnv("NIX_ROOT_FINDER", + settings.nixLibexecDir + "/nix/find-runtime-roots.pl"); + + if (rootFinder.empty()) return; + + debug(format("executing `%1%' to find additional roots") % rootFinder); + + string result = runProgram(rootFinder); + + StringSet paths = tokenizeString<StringSet>(result, "\n"); + + foreach (StringSet::iterator, i, paths) { + if (isInStore(*i)) { + Path path = toStorePath(*i); + if (roots.find(path) == roots.end() && store.isValidPath(path)) { + debug(format("got additional root `%1%'") % path); + roots.insert(path); + } + } + } +} + + +struct GCLimitReached { }; + + +struct LocalStore::GCState +{ + GCOptions options; + GCResults & results; + PathSet roots; + PathSet tempRoots; + PathSet dead; + PathSet alive; + bool gcKeepOutputs; + bool gcKeepDerivations; + unsigned long long bytesInvalidated; + Path trashDir; + bool shouldDelete; + GCState(GCResults & results_) : results(results_), bytesInvalidated(0) { } +}; + + +bool LocalStore::isActiveTempFile(const GCState & state, + const Path & path, const string & suffix) +{ + return hasSuffix(path, suffix) + && state.tempRoots.find(string(path, 0, path.size() - suffix.size())) != state.tempRoots.end(); +} + + +void LocalStore::deleteGarbage(GCState & state, const Path & path) +{ + unsigned long long bytesFreed; + deletePath(path, bytesFreed); + state.results.bytesFreed += bytesFreed; +} + + +void LocalStore::deletePathRecursive(GCState & state, const Path & path) +{ + checkInterrupt(); + + unsigned long long size = 0; + + if (isValidPath(path)) { + PathSet referrers; + queryReferrers(path, referrers); + foreach (PathSet::iterator, i, referrers) + if (*i != path) deletePathRecursive(state, *i); + size = queryPathInfo(path).narSize; + invalidatePathChecked(path); + } + + struct stat st; + if (lstat(path.c_str(), &st)) { + if (errno == ENOENT) return; + throw SysError(format("getting status of %1%") % path); + } + + printMsg(lvlInfo, format("deleting `%1%'") % path); + + state.results.paths.insert(path); + + /* If the path is not a regular file or symlink, move it to the + trash directory. The move is to ensure that later (when we're + not holding the global GC lock) we can delete the path without + being afraid that the path has become alive again. Otherwise + delete it right away. */ + if (S_ISDIR(st.st_mode)) { + // Estimate the amount freed using the narSize field. FIXME: + // if the path was not valid, need to determine the actual + // size. + state.bytesInvalidated += size; + // Mac OS X cannot rename directories if they are read-only. + if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1) + throw SysError(format("making `%1%' writable") % path); + Path tmp = state.trashDir + "/" + baseNameOf(path); + if (rename(path.c_str(), tmp.c_str())) + throw SysError(format("unable to rename `%1%' to `%2%'") % path % tmp); + } else + deleteGarbage(state, path); + + if (state.results.bytesFreed + state.bytesInvalidated > state.options.maxFreed) { + printMsg(lvlInfo, format("deleted or invalidated more than %1% bytes; stopping") % state.options.maxFreed); + throw GCLimitReached(); + } +} + + +bool LocalStore::canReachRoot(GCState & state, PathSet & visited, const Path & path) +{ + if (visited.find(path) != visited.end()) return false; + + if (state.alive.find(path) != state.alive.end()) { + return true; + } + + if (state.dead.find(path) != state.dead.end()) { + return false; + } + + if (state.roots.find(path) != state.roots.end()) { + printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % path); + state.alive.insert(path); + return true; + } + + visited.insert(path); + + if (!isValidPath(path)) return false; + + PathSet incoming; + + /* Don't delete this path if any of its referrers are alive. */ + queryReferrers(path, incoming); + + /* If gc-keep-derivations is set and this is a derivation, then + don't delete the derivation if any of the outputs are alive. */ + if (state.gcKeepDerivations && isDerivation(path)) { + PathSet outputs = queryDerivationOutputs(path); + foreach (PathSet::iterator, i, outputs) + if (isValidPath(*i) && queryDeriver(*i) == path) + incoming.insert(*i); + } + + /* If gc-keep-outputs is set, then don't delete this path if there + are derivers of this path that are not garbage. */ + if (state.gcKeepOutputs) { + PathSet derivers = queryValidDerivers(path); + foreach (PathSet::iterator, i, derivers) + incoming.insert(*i); + } + + foreach (PathSet::iterator, i, incoming) + if (*i != path) + if (canReachRoot(state, visited, *i)) { + state.alive.insert(path); + return true; + } + + return false; +} + + +void LocalStore::tryToDelete(GCState & state, const Path & path) +{ + checkInterrupt(); + + if (path == linksDir || path == state.trashDir) return; + + startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path); + + if (!isValidPath(path)) { + /* A lock file belonging to a path that we're building right + now isn't garbage. */ + if (isActiveTempFile(state, path, ".lock")) return; + + /* Don't delete .chroot directories for derivations that are + currently being built. */ + if (isActiveTempFile(state, path, ".chroot")) return; + } + + PathSet visited; + + if (canReachRoot(state, visited, path)) { + printMsg(lvlDebug, format("cannot delete `%1%' because it's still reachable") % path); + } else { + /* No path we visited was a root, so everything is garbage. + But we only delete ‘path’ and its referrers here so that + ‘nix-store --delete’ doesn't have the unexpected effect of + recursing into derivations and outputs. */ + state.dead.insert(visited.begin(), visited.end()); + if (state.shouldDelete) + deletePathRecursive(state, path); + } +} + + +/* Unlink all files in /nix/store/.links that have a link count of 1, + which indicates that there are no other links and so they can be + safely deleted. FIXME: race condition with optimisePath(): we + might see a link count of 1 just before optimisePath() increases + the link count. */ +void LocalStore::removeUnusedLinks(const GCState & state) +{ + AutoCloseDir dir = opendir(linksDir.c_str()); + if (!dir) throw SysError(format("opening directory `%1%'") % linksDir); + + long long actualSize = 0, unsharedSize = 0; + + struct dirent * dirent; + while (errno = 0, dirent = readdir(dir)) { + checkInterrupt(); + string name = dirent->d_name; + if (name == "." || name == "..") continue; + Path path = linksDir + "/" + name; + + struct stat st; + if (lstat(path.c_str(), &st) == -1) + throw SysError(format("statting `%1%'") % path); + + if (st.st_nlink != 1) { + unsigned long long size = st.st_blocks * 512ULL; + actualSize += size; + unsharedSize += (st.st_nlink - 1) * size; + continue; + } + + printMsg(lvlTalkative, format("deleting unused link `%1%'") % path); + + if (unlink(path.c_str()) == -1) + throw SysError(format("deleting `%1%'") % path); + + state.results.bytesFreed += st.st_blocks * 512; + } + + struct stat st; + if (stat(linksDir.c_str(), &st) == -1) + throw SysError(format("statting `%1%'") % linksDir); + long long overhead = st.st_blocks * 512ULL; + + printMsg(lvlInfo, format("note: currently hard linking saves %.2f MiB") + % ((unsharedSize - actualSize - overhead) / (1024.0 * 1024.0))); +} + + +void LocalStore::collectGarbage(const GCOptions & options, GCResults & results) +{ + GCState state(results); + state.options = options; + state.trashDir = settings.nixStore + "/trash"; + state.gcKeepOutputs = settings.gcKeepOutputs; + state.gcKeepDerivations = settings.gcKeepDerivations; + + /* Using `--ignore-liveness' with `--delete' can have unintended + consequences if `gc-keep-outputs' or `gc-keep-derivations' are + true (the garbage collector will recurse into deleting the + outputs or derivers, respectively). So disable them. */ + if (options.action == GCOptions::gcDeleteSpecific && options.ignoreLiveness) { + state.gcKeepOutputs = false; + state.gcKeepDerivations = false; + } + + state.shouldDelete = options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific; + + /* Acquire the global GC root. This prevents + a) New roots from being added. + b) Processes from creating new temporary root files. */ + AutoCloseFD fdGCLock = openGCLock(ltWrite); + + /* Find the roots. Since we've grabbed the GC lock, the set of + permanent roots cannot increase now. */ + printMsg(lvlError, format("finding garbage collector roots...")); + Roots rootMap = options.ignoreLiveness ? Roots() : findRoots(); + + foreach (Roots::iterator, i, rootMap) state.roots.insert(i->second); + + /* Add additional roots returned by the program specified by the + NIX_ROOT_FINDER environment variable. This is typically used + to add running programs to the set of roots (to prevent them + from being garbage collected). */ + if (!options.ignoreLiveness) + addAdditionalRoots(*this, state.roots); + + /* Read the temporary roots. This acquires read locks on all + per-process temporary root files. So after this point no paths + can be added to the set of temporary roots. */ + FDs fds; + readTempRoots(state.tempRoots, fds); + state.roots.insert(state.tempRoots.begin(), state.tempRoots.end()); + + /* After this point the set of roots or temporary roots cannot + increase, since we hold locks on everything. So everything + that is not reachable from `roots'. */ + + if (state.shouldDelete) { + if (pathExists(state.trashDir)) deleteGarbage(state, state.trashDir); + createDirs(state.trashDir); + } + + /* Now either delete all garbage paths, or just the specified + paths (for gcDeleteSpecific). */ + + if (options.action == GCOptions::gcDeleteSpecific) { + + foreach (PathSet::iterator, i, options.pathsToDelete) { + assertStorePath(*i); + tryToDelete(state, *i); + if (state.dead.find(*i) == state.dead.end()) + throw Error(format("cannot delete path `%1%' since it is still alive") % *i); + } + + } else if (options.maxFreed > 0) { + + if (state.shouldDelete) + printMsg(lvlError, format("deleting garbage...")); + else + printMsg(lvlError, format("determining live/dead paths...")); + + try { + + AutoCloseDir dir = opendir(settings.nixStore.c_str()); + if (!dir) throw SysError(format("opening directory `%1%'") % settings.nixStore); + + /* Read the store and immediately delete all paths that + aren't valid. When using --max-freed etc., deleting + invalid paths is preferred over deleting unreachable + paths, since unreachable paths could become reachable + again. We don't use readDirectory() here so that GCing + can start faster. */ + Paths entries; + struct dirent * dirent; + while (errno = 0, dirent = readdir(dir)) { + checkInterrupt(); + string name = dirent->d_name; + if (name == "." || name == "..") continue; + Path path = settings.nixStore + "/" + name; + if (isValidPath(path)) + entries.push_back(path); + else + tryToDelete(state, path); + } + + dir.close(); + + /* Now delete the unreachable valid paths. Randomise the + order in which we delete entries to make the collector + less biased towards deleting paths that come + alphabetically first (e.g. /nix/store/000...). This + matters when using --max-freed etc. */ + vector<Path> entries_(entries.begin(), entries.end()); + random_shuffle(entries_.begin(), entries_.end()); + + foreach (vector<Path>::iterator, i, entries_) + tryToDelete(state, *i); + + } catch (GCLimitReached & e) { + } + } + + if (state.options.action == GCOptions::gcReturnLive) { + state.results.paths = state.alive; + return; + } + + if (state.options.action == GCOptions::gcReturnDead) { + state.results.paths = state.dead; + return; + } + + /* Allow other processes to add to the store from here on. */ + fdGCLock.close(); + fds.clear(); + + /* Delete the trash directory. */ + printMsg(lvlInfo, format("deleting `%1%'") % state.trashDir); + deleteGarbage(state, state.trashDir); + + /* Clean up the links directory. */ + if (options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific) { + printMsg(lvlError, format("deleting unused links...")); + removeUnusedLinks(state); + } + + /* While we're at it, vacuum the database. */ + if (options.action == GCOptions::gcDeleteDead) vacuumDB(); +} + + +} |