forked from lix-project/lix
b6c989b801
This is a problem because one process may set the immutable bit before the second process has created its link. Addressed random Hydra failures such as: error: cannot rename `/nix/store/.tmp-link-17397-1804289383' to `/nix/store/rsvzm574rlfip3830ac7kmaa028bzl6h-nixos-0.1pre-git/upstart-interface-version': Operation not permitted
216 lines
7 KiB
C++
216 lines
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 "immutable.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 (S_ISDIR(st.st_mode) || S_ISREG(st.st_mode)) makeMutable(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 (and restore the
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immutable bit on platforms that support it). */
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if (path != "") canonicalisePathMetaData(path, false);
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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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struct MakeImmutable
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{
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Path path;
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MakeImmutable(const Path & path) : path(path) { }
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~MakeImmutable() { makeImmutable(path); }
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};
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void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path)
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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);
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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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/* 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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stats.totalFiles++;
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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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makeMutable(path);
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MakeImmutable mk1(path);
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if (link(path.c_str(), linkPath.c_str()) == 0) return;
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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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/* If ‘linkPath’ is immutable, we can't create hard links to it,
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so make it mutable first (and make it immutable again when
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we're done). We also have to make ‘path’ mutable, otherwise
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rename() will fail to delete it. */
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makeMutable(path);
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MakeImmutable mk2(path);
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/* Another process might be doing the same thing (creating a new
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link to ‘linkPath’) and make ‘linkPath’ immutable before we're
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done. In that case, just retry. */
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unsigned int retries = 1024;
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while (--retries > 0) {
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makeMutable(linkPath);
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MakeImmutable mk1(linkPath);
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Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
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% 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
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file systems). This is likely to happen with empty
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files. Just shrug and ignore. */
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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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if (errno == EPERM) continue;
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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
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rename, rather than on the original link.
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(Probably it temporarily increases the st_nlink
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field before decreasing it again.) */
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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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if (errno == EPERM) continue;
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throw SysError(format("cannot rename `%1%' to `%2%'") % tempLink % path);
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}
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break;
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}
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if (retries == 0) throw Error(format("cannot link `%1%' to `%2%'") % path % linkPath);
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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 = queryValidPaths();
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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);
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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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if (queryBoolSetting("auto-optimise-store", true)) {
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OptimiseStats stats;
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optimisePath_(stats, path);
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}
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}
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}
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