#include "globals.hh" #include "misc.hh" #include "local-store.hh" #include "immutable.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"; static const int defaultGcLevel = 1000; /* 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%") % 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%") % 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%") % 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 (queryBoolSetting("gc-check-reachability", false)) { 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%") % 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%") % nixStateDir % tempRootsDir).str()); foreach (Strings::iterator, i, tempRootFiles) { Path path = (format("%1%/%2%/%3%") % 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 findRoots(StoreAPI & store, const Path & path, bool recurseSymlinks, bool deleteStale, Roots & roots) { try { struct stat st; if (lstat(path.c_str(), &st) == -1) throw SysError(format("statting `%1%'") % path); printMsg(lvlVomit, format("looking at `%1%'") % path); if (S_ISDIR(st.st_mode)) { Strings names = readDirectory(path); foreach (Strings::iterator, i, names) findRoots(store, path + "/" + *i, recurseSymlinks, deleteStale, roots); } else if (S_ISLNK(st.st_mode)) { Path target = absPath(readLink(path), dirOf(path)); if (isInStore(target)) { debug(format("found root `%1%' in `%2%'") % target % path); Path storePath = toStorePath(target); if (store.isValidPath(storePath)) roots[path] = storePath; else printMsg(lvlInfo, format("skipping invalid root from `%1%' to `%2%'") % path % storePath); } else if (recurseSymlinks) { if (pathExists(target)) findRoots(store, target, false, deleteStale, roots); else if (deleteStale) { printMsg(lvlInfo, format("removing stale link from `%1%' to `%2%'") % path % target); /* Note that we only delete when recursing, i.e., when we are still in the `gcroots' tree. We never delete stuff outside that tree. */ unlink(path.c_str()); } } } } 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; } } static Roots findRoots(StoreAPI & store, bool deleteStale) { Roots roots; Path rootsDir = canonPath((format("%1%/%2%") % nixStateDir % gcRootsDir).str()); findRoots(store, rootsDir, true, deleteStale, roots); return roots; } Roots LocalStore::findRoots() { return nix::findRoots(*this, false); } static void addAdditionalRoots(StoreAPI & store, PathSet & roots) { Path rootFinder = getEnv("NIX_ROOT_FINDER", nixLibexecDir + "/nix/find-runtime-roots.pl"); if (rootFinder.empty()) return; debug(format("executing `%1%' to find additional roots") % rootFinder); string result = runProgram(rootFinder); Strings paths = tokenizeString(result, "\n"); foreach (Strings::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 deleted; PathSet live; PathSet busy; PathSet invalidated; bool gcKeepOutputs; bool gcKeepDerivations; unsigned long long bytesInvalidated; GCState(GCResults & results_) : results(results_), bytesInvalidated(0) { } }; static bool shouldDelete(GCOptions::GCAction action) { return action == GCOptions::gcDeleteDead || action == GCOptions::gcDeleteSpecific; } 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) { printMsg(lvlInfo, format("deleting `%1%'") % path); unsigned long long bytesFreed; deletePathWrapped(path, bytesFreed); state.results.bytesFreed += bytesFreed; } bool LocalStore::tryToDelete(GCState & state, const Path & path) { checkInterrupt(); if (path == linksDir) return true; struct stat st; if (lstat(path.c_str(), &st)) { if (errno == ENOENT) return true; throw SysError(format("getting status of %1%") % path); } if (state.deleted.find(path) != state.deleted.end()) return true; if (state.live.find(path) != state.live.end()) return false; startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path); if (state.roots.find(path) != state.roots.end()) { printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % path); goto isLive; } if (isValidPath(path)) { /* Recursively try to delete the referrers of this path. If any referrer can't be deleted, then this path can't be deleted either. */ PathSet referrers; queryReferrers(path, referrers); foreach (PathSet::iterator, i, referrers) if (*i != path && !tryToDelete(state, *i)) { printMsg(lvlDebug, format("cannot delete `%1%' because it has live referrers") % path); goto isLive; } /* If gc-keep-derivations is set and this is a derivation, then don't delete the derivation if any of the outputs are live. */ if (state.gcKeepDerivations && isDerivation(path)) { PathSet outputs = queryDerivationOutputs(path); foreach (PathSet::iterator, i, outputs) if (!tryToDelete(state, *i)) { printMsg(lvlDebug, format("cannot delete derivation `%1%' because its output `%2%' is alive") % path % *i); goto isLive; } } /* If gc-keep-derivations and gc-keep-outputs are both set, it's possible that the path has already been deleted (due to the recursion below), so bail out. */ if (!pathExists(path)) return true; /* 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, deriver, derivers) { /* Break an infinite recursion if gc-keep-derivations and gc-keep-outputs are both set by tentatively assuming that this path is garbage. This is a safe assumption because at this point, the only thing that can prevent it from being garbage is the deriver. Since tryToDelete() works "upwards" through the dependency graph, it won't encouter this path except in the call to tryToDelete() in the gc-keep-derivation branch. */ state.deleted.insert(path); if (!tryToDelete(state, *deriver)) { state.deleted.erase(path); printMsg(lvlDebug, format("cannot delete `%1%' because its deriver `%2%' is alive") % path % *deriver); goto isLive; } } } } else { /* A lock file belonging to a path that we're building right now isn't garbage. */ if (isActiveTempFile(state, path, ".lock")) return false; /* Don't delete .chroot directories for derivations that are currently being built. */ if (isActiveTempFile(state, path, ".chroot")) return false; } /* The path is garbage, so delete it. */ if (shouldDelete(state.options.action)) { /* If it's a valid path that's not a regular file or symlink, invalidate it, rename it, and schedule it for deletion. The renaming 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 (isValidPath(path)) { if (S_ISDIR(st.st_mode)) { printMsg(lvlInfo, format("invalidating `%1%'") % path); // Estimate the amount freed using the narSize field. state.bytesInvalidated += queryPathInfo(path).narSize; invalidatePathChecked(path); makeMutable(path.c_str()); // 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 = (format("%1%-gc-%2%") % path % getpid()).str(); if (rename(path.c_str(), tmp.c_str())) throw SysError(format("unable to rename `%1%' to `%2%'") % path % tmp); state.invalidated.insert(tmp); } else { invalidatePathChecked(path); deleteGarbage(state, path); } } 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(); } } else printMsg(lvlTalkative, format("would delete `%1%'") % path); state.deleted.insert(path); if (state.options.action != GCOptions::gcReturnLive) state.results.paths.insert(path); return true; isLive: state.live.insert(path); if (state.options.action == GCOptions::gcReturnLive) state.results.paths.insert(path); return false; } /* 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); unsigned 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); unsigned 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.gcKeepOutputs = queryBoolSetting("gc-keep-outputs", false); state.gcKeepDerivations = queryBoolSetting("gc-keep-derivations", true); /* 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; } /* 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() : nix::findRoots(*this, true); 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'. */ /* 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); if (!tryToDelete(state, *i)) throw Error(format("cannot delete path `%1%' since it is still alive") % *i); } } else if (options.maxFreed > 0) { if (shouldDelete(state.options.action)) printMsg(lvlError, format("deleting garbage...")); else printMsg(lvlError, format("determining live/dead paths...")); try { AutoCloseDir dir = opendir(nixStore.c_str()); if (!dir) throw SysError(format("opening directory `%1%'") % 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 = 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) { } } /* Allow other processes to add to the store from here on. */ fdGCLock.close(); /* Delete the invalidated paths now that the lock has been released. */ foreach (PathSet::iterator, i, state.invalidated) deleteGarbage(state, *i); /* Clean up the links directory. */ printMsg(lvlError, format("deleting unused links...")); removeUnusedLinks(state); } }