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authorLudovic Courtès <ludo@gnu.org>2014-12-17 23:00:42 +0100
committerLudovic Courtès <ludo@gnu.org>2014-12-19 22:47:37 +0100
commit36457566f9917dc7c0c348d012816a2ca333ef1b (patch)
tree6f1d22a195ea2483b9ce539227d65e8e2a9c137d /nix/libstore/optimise-store.cc
parent2c7ee1672029aa43afb509af5b5f7261244fa2d1 (diff)
Merge branch 'nix' into 'master'.
Diffstat (limited to 'nix/libstore/optimise-store.cc')
-rw-r--r--nix/libstore/optimise-store.cc180
1 files changed, 180 insertions, 0 deletions
diff --git a/nix/libstore/optimise-store.cc b/nix/libstore/optimise-store.cc
new file mode 100644
index 0000000000..d833f3aa05
--- /dev/null
+++ b/nix/libstore/optimise-store.cc
@@ -0,0 +1,180 @@
+#include "config.h"
+
+#include "util.hh"
+#include "local-store.hh"
+#include "globals.hh"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+
+
+namespace nix {
+
+
+static void makeWritable(const Path & path)
+{
+ struct stat st;
+ if (lstat(path.c_str(), &st))
+ throw SysError(format("getting attributes of path `%1%'") % path);
+ if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
+ throw SysError(format("changing writability of `%1%'") % path);
+}
+
+
+struct MakeReadOnly
+{
+ Path path;
+ MakeReadOnly(const Path & path) : path(path) { }
+ ~MakeReadOnly()
+ {
+ try {
+ /* This will make the path read-only. */
+ if (path != "") canonicaliseTimestampAndPermissions(path);
+ } catch (...) {
+ ignoreException();
+ }
+ }
+};
+
+
+void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path)
+{
+ checkInterrupt();
+
+ struct stat st;
+ if (lstat(path.c_str(), &st))
+ throw SysError(format("getting attributes of path `%1%'") % path);
+
+ if (S_ISDIR(st.st_mode)) {
+ Strings names = readDirectory(path);
+ foreach (Strings::iterator, i, names)
+ optimisePath_(stats, path + "/" + *i);
+ return;
+ }
+
+ /* We can hard link regular files and maybe symlinks. */
+ if (!S_ISREG(st.st_mode)
+#if CAN_LINK_SYMLINK
+ && !S_ISLNK(st.st_mode)
+#endif
+ ) return;
+
+ /* Sometimes SNAFUs can cause files in the Nix store to be
+ modified, in particular when running programs as root under
+ NixOS (example: $fontconfig/var/cache being modified). Skip
+ those files. FIXME: check the modification time. */
+ if (S_ISREG(st.st_mode) && (st.st_mode & S_IWUSR)) {
+ printMsg(lvlError, format("skipping suspicious writable file `%1%'") % path);
+ return;
+ }
+
+ /* Hash the file. Note that hashPath() returns the hash over the
+ NAR serialisation, which includes the execute bit on the file.
+ Thus, executable and non-executable files with the same
+ contents *won't* be linked (which is good because otherwise the
+ permissions would be screwed up).
+
+ Also note that if `path' is a symlink, then we're hashing the
+ contents of the symlink (i.e. the result of readlink()), not
+ the contents of the target (which may not even exist). */
+ Hash hash = hashPath(htSHA256, path).first;
+ stats.totalFiles++;
+ printMsg(lvlDebug, format("`%1%' has hash `%2%'") % path % printHash(hash));
+
+ /* Check if this is a known hash. */
+ Path linkPath = linksDir + "/" + printHash32(hash);
+
+ if (!pathExists(linkPath)) {
+ /* Nope, create a hard link in the links directory. */
+ if (link(path.c_str(), linkPath.c_str()) == 0) return;
+ if (errno != EEXIST)
+ throw SysError(format("cannot link `%1%' to `%2%'") % linkPath % path);
+ /* Fall through if another process created ‘linkPath’ before
+ we did. */
+ }
+
+ /* Yes! We've seen a file with the same contents. Replace the
+ current file with a hard link to that file. */
+ struct stat stLink;
+ if (lstat(linkPath.c_str(), &stLink))
+ throw SysError(format("getting attributes of path `%1%'") % linkPath);
+
+ stats.sameContents++;
+ if (st.st_ino == stLink.st_ino) {
+ printMsg(lvlDebug, format("`%1%' is already linked to `%2%'") % path % linkPath);
+ return;
+ }
+
+ printMsg(lvlTalkative, format("linking `%1%' to `%2%'") % path % linkPath);
+
+ /* Make the containing directory writable, but only if it's not
+ the store itself (we don't want or need to mess with its
+ permissions). */
+ bool mustToggle = !isStorePath(path);
+ if (mustToggle) makeWritable(dirOf(path));
+
+ /* When we're done, make the directory read-only again and reset
+ its timestamp back to 0. */
+ MakeReadOnly makeReadOnly(mustToggle ? dirOf(path) : "");
+
+ Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
+ % settings.nixStore % getpid() % rand()).str();
+
+ if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
+ if (errno == EMLINK) {
+ /* Too many links to the same file (>= 32000 on most file
+ systems). This is likely to happen with empty files.
+ Just shrug and ignore. */
+ if (st.st_size)
+ printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
+ return;
+ }
+ throw SysError(format("cannot link `%1%' to `%2%'") % tempLink % linkPath);
+ }
+
+ /* Atomically replace the old file with the new hard link. */
+ if (rename(tempLink.c_str(), path.c_str()) == -1) {
+ if (unlink(tempLink.c_str()) == -1)
+ printMsg(lvlError, format("unable to unlink `%1%'") % tempLink);
+ if (errno == EMLINK) {
+ /* Some filesystems generate too many links on the rename,
+ rather than on the original link. (Probably it
+ temporarily increases the st_nlink field before
+ decreasing it again.) */
+ if (st.st_size)
+ printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
+ return;
+ }
+ throw SysError(format("cannot rename `%1%' to `%2%'") % tempLink % path);
+ }
+
+ stats.filesLinked++;
+ stats.bytesFreed += st.st_size;
+ stats.blocksFreed += st.st_blocks;
+}
+
+
+void LocalStore::optimiseStore(OptimiseStats & stats)
+{
+ PathSet paths = queryAllValidPaths();
+
+ foreach (PathSet::iterator, i, paths) {
+ addTempRoot(*i);
+ if (!isValidPath(*i)) continue; /* path was GC'ed, probably */
+ startNest(nest, lvlChatty, format("hashing files in `%1%'") % *i);
+ optimisePath_(stats, *i);
+ }
+}
+
+
+void LocalStore::optimisePath(const Path & path)
+{
+ OptimiseStats stats;
+ if (settings.autoOptimiseStore) optimisePath_(stats, path);
+}
+
+
+}