forked from lix-project/lix
e974f20c98
By preloading all inodes in the /nix/store/.links directory, we can quickly determine of a hardlinked file was already linked to the hashed links. This is tolerant of removing the .links directory, it will simply recalculate all hashes in the store.
209 lines
6.7 KiB
C++
209 lines
6.7 KiB
C++
#include "config.h"
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#include "util.hh"
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#include "local-store.hh"
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#include "globals.hh"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <errno.h>
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#include <stdio.h>
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namespace nix {
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static void makeWritable(const Path & path)
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{
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struct stat st;
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if (lstat(path.c_str(), &st))
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throw SysError(format("getting attributes of path `%1%'") % path);
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if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
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throw SysError(format("changing writability of `%1%'") % path);
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}
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struct MakeReadOnly
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{
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Path path;
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MakeReadOnly(const Path & path) : path(path) { }
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~MakeReadOnly()
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{
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try {
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/* This will make the path read-only. */
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if (path != "") canonicaliseTimestampAndPermissions(path);
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} catch (...) {
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ignoreException();
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}
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}
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};
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// TODO Make this a map and keep count and size stats, for giggles
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void LocalStore::loadHashes(Hashes & hashes)
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{
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printMsg(lvlDebug, "loading hash inodes in memory");
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Strings names = readDirectory(linksDir);
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foreach (Strings::iterator, i, names) {
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struct stat st;
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string path = linksDir + "/" + *i;
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if (lstat(path.c_str(), &st))
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throw SysError(format("getting attributes of path `%1%'") % path);
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hashes.insert(st.st_ino);
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}
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printMsg(lvlDebug, format("loaded %1% hashes") % hashes.size());
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}
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void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path, Hashes & hashes)
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{
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checkInterrupt();
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struct stat st;
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if (lstat(path.c_str(), &st))
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throw SysError(format("getting attributes of path `%1%'") % path);
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if (S_ISDIR(st.st_mode)) {
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Strings names = readDirectory(path);
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foreach (Strings::iterator, i, names)
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optimisePath_(stats, path + "/" + *i, hashes);
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return;
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}
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/* We can hard link regular files and maybe symlinks. */
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if (!S_ISREG(st.st_mode)
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#if CAN_LINK_SYMLINK
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&& !S_ISLNK(st.st_mode)
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#endif
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) return;
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/* Sometimes SNAFUs can cause files in the Nix store to be
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modified, in particular when running programs as root under
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NixOS (example: $fontconfig/var/cache being modified). Skip
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those files. FIXME: check the modification time. */
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if (S_ISREG(st.st_mode) && (st.st_mode & S_IWUSR)) {
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printMsg(lvlError, format("skipping suspicious writable file `%1%'") % path);
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return;
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}
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stats.totalFiles++;
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if (st.st_nlink > 1 && hashes.count(st.st_ino)) {
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printMsg(lvlDebug, format("`%1%' is already linked, with %2% other file(s).") % path % (st.st_nlink - 2));
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return;
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}
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/* Hash the file. Note that hashPath() returns the hash over the
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NAR serialisation, which includes the execute bit on the file.
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Thus, executable and non-executable files with the same
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contents *won't* be linked (which is good because otherwise the
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permissions would be screwed up).
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Also note that if `path' is a symlink, then we're hashing the
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contents of the symlink (i.e. the result of readlink()), not
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the contents of the target (which may not even exist). */
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Hash hash = hashPath(htSHA256, path).first;
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printMsg(lvlDebug, format("`%1%' has hash `%2%'") % path % printHash(hash));
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/* Check if this is a known hash. */
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Path linkPath = linksDir + "/" + printHash32(hash);
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if (!pathExists(linkPath)) {
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/* Nope, create a hard link in the links directory. */
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if (link(path.c_str(), linkPath.c_str()) == 0) {
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hashes.insert(st.st_ino);
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return;
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}
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if (errno != EEXIST)
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throw SysError(format("cannot link `%1%' to `%2%'") % linkPath % path);
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/* Fall through if another process created ‘linkPath’ before
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we did. */
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}
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/* Yes! We've seen a file with the same contents. Replace the
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current file with a hard link to that file. */
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struct stat stLink;
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if (lstat(linkPath.c_str(), &stLink))
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throw SysError(format("getting attributes of path `%1%'") % linkPath);
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stats.sameContents++;
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if (st.st_ino == stLink.st_ino) {
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printMsg(lvlDebug, format("`%1%' is already linked to `%2%'") % path % linkPath);
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return;
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}
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printMsg(lvlTalkative, format("linking `%1%' to `%2%'") % path % linkPath);
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/* Make the containing directory writable, but only if it's not
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the store itself (we don't want or need to mess with its
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permissions). */
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bool mustToggle = !isStorePath(path);
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if (mustToggle) makeWritable(dirOf(path));
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/* When we're done, make the directory read-only again and reset
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its timestamp back to 0. */
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MakeReadOnly makeReadOnly(mustToggle ? dirOf(path) : "");
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Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
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% settings.nixStore % getpid() % rand()).str();
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if (link(linkPath.c_str(), tempLink.c_str()) == -1) {
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if (errno == EMLINK) {
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/* Too many links to the same file (>= 32000 on most file
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systems). This is likely to happen with empty files.
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Just shrug and ignore. */
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if (st.st_size)
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printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
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return;
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}
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throw SysError(format("cannot link `%1%' to `%2%'") % tempLink % linkPath);
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}
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/* Atomically replace the old file with the new hard link. */
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if (rename(tempLink.c_str(), path.c_str()) == -1) {
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if (unlink(tempLink.c_str()) == -1)
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printMsg(lvlError, format("unable to unlink `%1%'") % tempLink);
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if (errno == EMLINK) {
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/* Some filesystems generate too many links on the rename,
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rather than on the original link. (Probably it
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temporarily increases the st_nlink field before
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decreasing it again.) */
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if (st.st_size)
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printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
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return;
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}
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throw SysError(format("cannot rename `%1%' to `%2%'") % tempLink % path);
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}
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stats.filesLinked++;
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stats.bytesFreed += st.st_size;
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stats.blocksFreed += st.st_blocks;
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}
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void LocalStore::optimiseStore(OptimiseStats & stats)
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{
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PathSet paths = queryAllValidPaths();
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Hashes hashes;
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loadHashes(hashes);
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foreach (PathSet::iterator, i, paths) {
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addTempRoot(*i);
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if (!isValidPath(*i)) continue; /* path was GC'ed, probably */
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startNest(nest, lvlChatty, format("hashing files in `%1%'") % *i);
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optimisePath_(stats, *i, hashes);
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}
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}
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void LocalStore::optimisePath(const Path & path)
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{
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OptimiseStats stats;
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Hashes hashes;
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if (settings.autoOptimiseStore) optimisePath_(stats, path, hashes);
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}
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}
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