#include <cerrno>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <regex>
#include <utility>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include "globals.hh"
#include "glog/logging.h"
#include "local-store.hh"
#include "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;
}
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 __APPLE__
/* HFS/macOS has some undocumented security feature disabling hardlinking for
special files within .app dirs. *.app/Contents/PkgInfo and
*.app/Contents/Resources/\*.lproj seem to be the only paths affected. See
https://github.com/NixOS/nix/issues/1443 for more discussion. */
if (std::regex_search(path, std::regex("\\.app/Contents/.+$"))) {
debug(format("'%1%' is not allowed to be linked in macOS") % path);
return;
}
#endif
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 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
