#include "globals.hh" #include "misc.hh" #include "pathlocks.hh" #include "local-store.hh" #include #include #include #include #include #include #ifdef __CYGWIN__ #include #include #endif 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. */ static int 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); 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, bool careful) { /* Create directories up to `gcRoot'. */ createDirs(dirOf(link)); /* !!! shouldn't removing and creating the symlink be atomic? */ /* Remove the old symlink. */ if (pathExists(link)) { if (careful && (!isLink(link) || !isInStore(readLink(link)))) throw Error(format("cannot create symlink `%1%'; already exists") % link); unlink(link.c_str()); } /* And create the new one. */ if (symlink(target.c_str(), link.c_str()) == -1) throw SysError(format("symlinking `%1%' to `%2%'") % link % target); } 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, false); } Path addPermRoot(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) { createSymlink(gcRoot, storePath, true); 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, false); } /* Check that the root can be found by the garbage collector. */ if (queryBoolSetting("gc-check-reachability", true)) { 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. */ deletePath(fnTempRoots); fdTempRoots = openLockFile(fnTempRoots, true); fdGCLock.close(); /* Note that on Cygwin a lot of the following complexity is unnecessary, since we cannot delete open lock files. If we have the lock file open, then it's valid; if we can delete it, then it wasn't in use any more. Also note that on Cygwin we cannot "upgrade" a lock from a read lock to a write lock. */ #ifndef __CYGWIN__ 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. */ #else break; #endif } } /* 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.c_str(), s.size()); #ifndef __CYGWIN__ /* Downgrade to a read lock. */ debug(format("downgrading to read lock on `%1%'") % fnTempRoots); lockFile(fdTempRoots, ltRead, true); #else debug(format("releasing write lock on `%1%'") % fnTempRoots); lockFile(fdTempRoots, ltNone, true); #endif } void removeTempRoots() { if (fdTempRoots != -1) { fdTempRoots.close(); unlink(fnTempRoots.c_str()); } } typedef boost::shared_ptr FDPtr; typedef list 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()); for (Strings::iterator i = tempRootFiles.begin(); i != tempRootFiles.end(); ++i) { Path path = (format("%1%/%2%/%3%") % nixStateDir % tempRootsDir % *i).str(); debug(format("reading temporary root file `%1%'") % path); #ifdef __CYGWIN__ /* On Cygwin we just try to delete the lock file. */ char win32Path[MAX_PATH]; cygwin_conv_to_full_win32_path(path.c_str(), win32Path); if (DeleteFile(win32Path)) { printMsg(lvlError, format("removed stale temporary roots file `%1%'") % path); continue; } else debug(format("delete of `%1%' failed: %2%") % path % GetLastError()); #endif 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; #ifndef __CYGWIN__ /* 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; } #endif /* 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(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); for (Strings::iterator i = names.begin(); i != names.end(); ++i) findRoots(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(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(bool deleteStale) { Roots roots; Path rootsDir = canonPath((format("%1%/%2%") % nixStateDir % gcRootsDir).str()); findRoots(rootsDir, true, deleteStale, roots); return roots; } Roots LocalStore::findRoots() { return nix::findRoots(false); } static void addAdditionalRoots(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"); for (Strings::iterator i = paths.begin(); i != paths.end(); ++i) { if (isInStore(*i)) { Path path = toStorePath(*i); if (roots.find(path) == roots.end() && store->isValidPath(path)) { debug(format("found additional root `%1%'") % path); roots.insert(path); } } } } static void dfsVisit(const PathSet & paths, const Path & path, PathSet & visited, Paths & sorted) { if (visited.find(path) != visited.end()) return; visited.insert(path); PathSet references; if (store->isValidPath(path)) store->queryReferences(path, references); for (PathSet::iterator i = references.begin(); i != references.end(); ++i) /* Don't traverse into paths that don't exist. That can happen due to substitutes for non-existent paths. */ if (*i != path && paths.find(*i) != paths.end()) dfsVisit(paths, *i, visited, sorted); sorted.push_front(path); } Paths topoSortPaths(const PathSet & paths) { Paths sorted; PathSet visited; for (PathSet::const_iterator i = paths.begin(); i != paths.end(); ++i) dfsVisit(paths, *i, visited, sorted); return sorted; } void LocalStore::collectGarbage(GCAction action, const PathSet & pathsToDelete, bool ignoreLiveness, PathSet & result, unsigned long long & bytesFreed) { result.clear(); bytesFreed = 0; bool gcKeepOutputs = queryBoolSetting("gc-keep-outputs", false); bool gcKeepDerivations = queryBoolSetting("gc-keep-derivations", true); int gcKeepOutputsThreshold = queryIntSetting ("gc-keep-outputs-threshold", defaultGcLevel); /* 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. */ Roots rootMap = ignoreLiveness ? Roots() : nix::findRoots(true); PathSet roots; for (Roots::iterator i = rootMap.begin(); i != rootMap.end(); ++i) 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 (!ignoreLiveness) addAdditionalRoots(roots); if (action == gcReturnRoots) { result = roots; return; } /* Determine the live paths which is just the closure of the roots under the `references' relation. */ PathSet livePaths; for (PathSet::const_iterator i = roots.begin(); i != roots.end(); ++i) computeFSClosure(canonPath(*i), livePaths); if (gcKeepDerivations) { for (PathSet::iterator i = livePaths.begin(); i != livePaths.end(); ++i) { /* Note that the deriver need not be valid (e.g., if we previously ran the collector with `gcKeepDerivations' turned off). */ Path deriver = store->queryDeriver(*i); if (deriver != "" && store->isValidPath(deriver)) computeFSClosure(deriver, livePaths); } } if (gcKeepOutputs) { /* Hmz, identical to storePathRequisites in nix-store. */ for (PathSet::iterator i = livePaths.begin(); i != livePaths.end(); ++i) if (isDerivation(*i)) { Derivation drv = derivationFromPath(*i); string gcLevelStr = drv.env["__gcLevel"]; int gcLevel; if (!string2Int(gcLevelStr, gcLevel)) gcLevel = defaultGcLevel; if (gcLevel >= gcKeepOutputsThreshold) for (DerivationOutputs::iterator j = drv.outputs.begin(); j != drv.outputs.end(); ++j) if (store->isValidPath(j->second.path)) computeFSClosure(j->second.path, livePaths); } } if (action == gcReturnLive) { result = livePaths; return; } /* 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. */ PathSet tempRoots; FDs fds; readTempRoots(tempRoots, fds); /* Close the temporary roots. Note that we *cannot* do this in readTempRoots(), because there we may not have all locks yet, meaning that an invalid path can become valid (and thus add to the references graph) after we have added it to the closure (and computeFSClosure() assumes that the presence of a path means that it has already been closed). */ PathSet tempRootsClosed; for (PathSet::iterator i = tempRoots.begin(); i != tempRoots.end(); ++i) if (store->isValidPath(*i)) computeFSClosure(*i, tempRootsClosed); else tempRootsClosed.insert(*i); /* For testing - see tests/gc-concurrent.sh. */ if (getenv("NIX_DEBUG_GC_WAIT")) sleep(2); /* After this point the set of roots or temporary roots cannot increase, since we hold locks on everything. So everything that is not currently in in `livePaths' or `tempRootsClosed' can be deleted. */ /* Read the Nix store directory to find all currently existing paths. */ PathSet storePathSet; if (action != gcDeleteSpecific) { Paths entries = readDirectory(nixStore); for (Paths::iterator i = entries.begin(); i != entries.end(); ++i) storePathSet.insert(canonPath(nixStore + "/" + *i)); } else { for (PathSet::iterator i = pathsToDelete.begin(); i != pathsToDelete.end(); ++i) { assertStorePath(*i); storePathSet.insert(*i); } } /* Topologically sort them under the `referrers' relation. That is, a < b iff a is in referrers(b). This gives us the order in which things can be deleted safely. */ /* !!! when we have multiple output paths per derivation, this will not work anymore because we get cycles. */ Paths storePaths = topoSortPaths(storePathSet); /* Try to delete store paths in the topologically sorted order. */ for (Paths::iterator i = storePaths.begin(); i != storePaths.end(); ++i) { debug(format("considering deletion of `%1%'") % *i); if (livePaths.find(*i) != livePaths.end()) { if (action == gcDeleteSpecific) throw Error(format("cannot delete path `%1%' since it is still alive") % *i); debug(format("live path `%1%'") % *i); continue; } if (tempRootsClosed.find(*i) != tempRootsClosed.end()) { debug(format("temporary root `%1%'") % *i); continue; } debug(format("dead path `%1%'") % *i); result.insert(*i); /* If just returning the set of dead paths, we also return the space that would be freed if we deleted them. */ if (action == gcReturnDead) bytesFreed += computePathSize(*i); if (action == gcDeleteDead || action == gcDeleteSpecific) { #ifndef __CYGWIN__ AutoCloseFD fdLock; /* Only delete a lock file if we can acquire a write lock on it. That means that it's either stale, or the process that created it hasn't locked it yet. In the latter case the other process will detect that we deleted the lock, and retry (see pathlocks.cc). */ if (i->size() >= 5 && string(*i, i->size() - 5) == ".lock") { fdLock = openLockFile(*i, false); if (fdLock != -1 && !lockFile(fdLock, ltWrite, false)) { debug(format("skipping active lock `%1%'") % *i); continue; } } #endif if (!pathExists(*i)) continue; printMsg(lvlInfo, format("deleting `%1%'") % *i); /* Okay, it's safe to delete. */ try { unsigned long long freed; deleteFromStore(*i, freed); bytesFreed += freed; } catch (PathInUse & e) { printMsg(lvlError, format("warning: %1%") % e.msg()); } #ifndef __CYGWIN__ if (fdLock != -1) /* Write token to stale (deleted) lock file. */ writeFull(fdLock, (const unsigned char *) "d", 1); #endif } } } }