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#include "util.hh"
#include "local-store.hh"
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
namespace nix {
typedef std::map<Hash, std::pair<Path, ino_t> > HashToPath;
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 {
if (path != "") canonicalisePathMetaData(path, false);
} catch (...) {
ignoreException();
}
}
};
static void hashAndLink(bool dryRun, HashToPath & hashToPath,
OptimiseStats & stats, const Path & path)
{
struct stat st;
if (lstat(path.c_str(), &st))
throw SysError(format("getting attributes of path `%1%'") % path);
/* 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. */
if (S_ISREG(st.st_mode) && (st.st_mode & S_IWUSR)) {
printMsg(lvlError, format("skipping suspicious writable file `%1%'") % path);
return;
}
/* We can hard link regular files and symlinks. */
if (S_ISREG(st.st_mode) || S_ISLNK(st.st_mode)) {
/* 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);
stats.totalFiles++;
printMsg(lvlDebug, format("`%1%' has hash `%2%'") % path % printHash(hash));
std::pair<Path, ino_t> prevPath = hashToPath[hash];
if (prevPath.first == "") {
hashToPath[hash] = std::pair<Path, ino_t>(path, st.st_ino);
return;
}
/* Yes! We've seen a file with the same contents. Replace
the current file with a hard link to that file. */
stats.sameContents++;
if (prevPath.second == st.st_ino) {
printMsg(lvlDebug, format("`%1%' is already linked to `%2%'") % path % prevPath.first);
return;
}
if (!dryRun) {
printMsg(lvlTalkative, format("linking `%1%' to `%2%'") % path % prevPath.first);
Path tempLink = (format("%1%.tmp-%2%-%3%")
% path % getpid() % rand()).str();
/* 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) : "");
if (link(prevPath.first.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 start over, creating
links to the current file. */
printMsg(lvlInfo, format("`%1%' has maximum number of links") % prevPath.first);
hashToPath[hash] = std::pair<Path, ino_t>(path, st.st_ino);
return;
}
throw SysError(format("cannot link `%1%' to `%2%'")
% tempLink % prevPath.first);
}
/* Atomically replace the old file with the new hard link. */
if (rename(tempLink.c_str(), path.c_str()) == -1) {
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.) */
printMsg(lvlInfo, format("`%1%' has maximum number of links") % prevPath.first);
hashToPath[hash] = std::pair<Path, ino_t>(path, st.st_ino);
/* Unlink the temp link. */
if (unlink(tempLink.c_str()) == -1)
printMsg(lvlError, format("unable to unlink `%1%'") % tempLink);
return;
}
throw SysError(format("cannot rename `%1%' to `%2%'")
% tempLink % path);
}
} else
printMsg(lvlTalkative, format("would link `%1%' to `%2%'") % path % prevPath.first);
stats.filesLinked++;
stats.bytesFreed += st.st_size;
stats.blocksFreed += st.st_blocks;
}
if (S_ISDIR(st.st_mode)) {
Strings names = readDirectory(path);
foreach (Strings::iterator, i, names)
hashAndLink(dryRun, hashToPath, stats, path + "/" + *i);
}
}
void LocalStore::optimiseStore(bool dryRun, OptimiseStats & stats)
{
HashToPath hashToPath;
PathSet paths = queryValidPaths();
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);
hashAndLink(dryRun, hashToPath, stats, *i);
}
}
}
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