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#include "util.hh"
#include "local-store.hh"
#include "immutable.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 (S_ISDIR(st.st_mode) || S_ISREG(st.st_mode)) makeMutable(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 {
/* This will make the path read-only (and restore the
immutable bit on platforms that support it). */
if (path != "") canonicalisePathMetaData(path, false);
} catch (...) {
ignoreException();
}
}
};
struct MakeImmutable
{
Path path;
MakeImmutable(const Path & path) : path(path) { }
~MakeImmutable() { makeImmutable(path); }
};
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).first;
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 ‘prevPath’ is immutable, we can't create hard links
to it, so make it mutable first (and make it immutable
again when we're done). We also have to make ‘path’
mutable, otherwise rename() will fail to delete it. */
makeMutable(prevPath.first);
MakeImmutable mk1(prevPath.first);
makeMutable(path);
MakeImmutable mk2(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 = queryAllValidPaths();
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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