1 files changed, 296 insertions, 0 deletions
diff --git a/third_party/nix/src/libstore/optimise-store.cc b/third_party/nix/src/libstore/optimise-store.cc
new file mode 100644
index 0000000000..eb24633c18
--- /dev/null
+++ b/third_party/nix/src/libstore/optimise-store.cc
@@ -0,0 +1,296 @@
+#include <cerrno>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <regex>
+#include <utility>
+
+#include <glog/logging.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "libstore/globals.hh"
+#include "libstore/local-store.hh"
+#include "libutil/util.hh"
+
+namespace nix {
+
+static void makeWritable(const Path& path) {
+  struct stat st;
+  if (lstat(path.c_str(), &st) != 0) {
+    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;
+  explicit MakeReadOnly(Path path) : path(std::move(path)) {}
+  ~MakeReadOnly() {
+    try {
+      /* This will make the path read-only. */
+      if (!path.empty()) {
+        canonicaliseTimestampAndPermissions(path);
+      }
+    } catch (...) {
+      ignoreException();
+    }
+  }
+};
+
+LocalStore::InodeHash LocalStore::loadInodeHash() {
+  DLOG(INFO) << "loading hash inodes in memory";
+  InodeHash inodeHash;
+
+  AutoCloseDir dir(opendir(linksDir.c_str()));
+  if (!dir) {
+    throw SysError(format("opening directory '%1%'") % linksDir);
+  }
+
+  struct dirent* dirent;
+  while (errno = 0, dirent = readdir(dir.get())) { /* sic */
+    checkInterrupt();
+    // We don't care if we hit non-hash files, anything goes
+    inodeHash.insert(dirent->d_ino);
+  }
+  if (errno) {
+    throw SysError(format("reading directory '%1%'") % linksDir);
+  }
+
+  DLOG(INFO) << "loaded " << inodeHash.size() << " hash inodes";
+
+  return inodeHash;
+}
+
+Strings LocalStore::readDirectoryIgnoringInodes(const Path& path,
+                                                const InodeHash& inodeHash) {
+  Strings names;
+
+  AutoCloseDir dir(opendir(path.c_str()));
+  if (!dir) {
+    throw SysError(format("opening directory '%1%'") % path);
+  }
+
+  struct dirent* dirent;
+  while (errno = 0, dirent = readdir(dir.get())) { /* sic */
+    checkInterrupt();
+
+    if (inodeHash.count(dirent->d_ino) != 0u) {
+      DLOG(WARNING) << dirent->d_name << " is already linked";
+      continue;
+    }
+
+    std::string name = dirent->d_name;
+    if (name == "." || name == "..") {
+      continue;
+    }
+    names.push_back(name);
+  }
+  if (errno) {
+    throw SysError(format("reading directory '%1%'") % path);
+  }
+
+  return names;
+}
+
+void LocalStore::optimisePath_(OptimiseStats& stats, const Path& path,
+                               InodeHash& inodeHash) {
+  checkInterrupt();
+
+  struct stat st;
+  if (lstat(path.c_str(), &st) != 0) {
+    throw SysError(format("getting attributes of path '%1%'") % path);
+  }
+
+  if (S_ISDIR(st.st_mode)) {
+    Strings names = readDirectoryIgnoringInodes(path, inodeHash);
+    for (auto& i : names) {
+      optimisePath_(stats, path + "/" + i, inodeHash);
+    }
+    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) != 0u)) {
+    LOG(WARNING) << "skipping suspicious writable file '" << path << "'";
+    return;
+  }
+
+  /* This can still happen on top-level files. */
+  if (st.st_nlink > 1 && (inodeHash.count(st.st_ino) != 0u)) {
+    DLOG(INFO) << path << " is already linked, with " << (st.st_nlink - 2)
+               << " other file(s)";
+    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;
+  LOG(INFO) << path << " has hash " << hash.to_string();
+
+  /* Check if this is a known hash. */
+  Path linkPath = linksDir + "/" + hash.to_string(Base32, false);
+
+retry:
+  if (!pathExists(linkPath)) {
+    /* Nope, create a hard link in the links directory. */
+    if (link(path.c_str(), linkPath.c_str()) == 0) {
+      inodeHash.insert(st.st_ino);
+      return;
+    }
+
+    switch (errno) {
+      case EEXIST:
+        /* Fall through if another process created ‘linkPath’ before
+           we did. */
+        break;
+
+      case ENOSPC:
+        /* On ext4, that probably means the directory index is
+           full.  When that happens, it's fine to ignore it: we
+           just effectively disable deduplication of this
+           file.  */
+        LOG(WARNING) << "cannot link '" << linkPath << " to " << path << ": "
+                     << strerror(errno);
+
+        return;
+
+      default:
+        throw SysError("cannot link '%1%' to '%2%'", linkPath, path);
+    }
+  }
+
+  /* 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) != 0) {
+    throw SysError(format("getting attributes of path '%1%'") % linkPath);
+  }
+
+  if (st.st_ino == stLink.st_ino) {
+    DLOG(INFO) << path << " is already linked to " << linkPath;
+    return;
+  }
+
+  if (st.st_size != stLink.st_size) {
+    LOG(WARNING) << "removing corrupted link '" << linkPath << "'";
+    unlink(linkPath.c_str());
+    goto retry;
+  }
+
+  DLOG(INFO) << "linking '" << path << "' to '" << 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 = dirOf(path) != realStoreDir;
+  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%") % realStoreDir % getpid() % random())
+          .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 != 0) {
+        LOG(WARNING) << linkPath << " has maximum number of links";
+      }
+      return;
+    }
+    throw SysError("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) {
+      LOG(ERROR) << "unable to unlink '" << 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.) */
+      DLOG(WARNING) << "'" << linkPath
+                    << "' has reached maximum number of links";
+      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();
+  InodeHash inodeHash = loadInodeHash();
+
+  uint64_t done = 0;
+
+  for (auto& i : paths) {
+    addTempRoot(i);
+    if (!isValidPath(i)) {
+      continue;
+    } /* path was GC'ed, probably */
+    {
+      LOG(INFO) << "optimising path '" << i << "'";
+      optimisePath_(stats, realStoreDir + "/" + baseNameOf(i), inodeHash);
+    }
+    done++;
+  }
+}
+
+static std::string showBytes(unsigned long long bytes) {
+  return (format("%.2f MiB") % (bytes / (1024.0 * 1024.0))).str();
+}
+
+void LocalStore::optimiseStore() {
+  OptimiseStats stats;
+
+  optimiseStore(stats);
+
+  LOG(INFO) << showBytes(stats.bytesFreed) << " freed by hard-linking "
+            << stats.filesLinked << " files";
+}
+
+void LocalStore::optimisePath(const Path& path) {
+  OptimiseStats stats;
+  InodeHash inodeHash;
+
+  if (settings.autoOptimiseStore) {
+    optimisePath_(stats, path, inodeHash);
+  }
+}
+
+}  // namespace nix