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Remove setting of the immutable bit

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Using the immutable bit is problematic, especially in conjunction with
store optimisation.  For instance, if the garbage collector deletes a
file, it has to clear its immutable bit, but if the file has
additional hard links, we can't set the bit afterwards because we
don't know the remaining paths.

So now that we support having the entire Nix store as a read-only
mount, we may as well drop the immutable bit.  Unfortunately, we have
to keep the code to clear the immutable bit for backwards
compatibility.
This commit is contained in:
Eelco Dolstra 2012-09-19 16:17:54 -04:00
parent b9124a5c33
commit b9c2b4d5b4
5 changed files with 34 additions and 95 deletions
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86
src/libstore/optimise-store.cc
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@ -33,8 +33,7 @@ struct MakeReadOnly
~MakeReadOnly()
{
try {
/* This will make the path read-only (and restore the
immutable bit on platforms that support it). */
/* This will make the path read-only. */
if (path != "") canonicalisePathMetaData(path, false);
} catch (...) {
ignoreException();
@ -43,14 +42,6 @@ struct MakeReadOnly
};
struct MakeImmutable
{
Path path;
MakeImmutable(const Path & path) : path(path) { }
~MakeImmutable() { makeImmutable(path); }
};
void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path)
{
checkInterrupt();
@ -101,7 +92,6 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path)
if (!pathExists(linkPath)) {
/* Nope, create a hard link in the links directory. */
makeMutable(path);
MakeImmutable mk1(path);
if (link(path.c_str(), linkPath.c_str()) == 0) return;
if (errno != EEXIST)
throw SysError(format("cannot link `%1%' to `%2%'") % linkPath % path);
@ -134,57 +124,41 @@ void LocalStore::optimisePath_(OptimiseStats & stats, const Path & path)
MakeReadOnly makeReadOnly(mustToggle ? dirOf(path) : "");
/* If ‘linkPath’ 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. */
so make it mutable first. We also have to make ‘path’ mutable,
otherwise rename() will fail to delete it. */
makeMutable(path);
MakeImmutable mk2(path);
makeMutable(linkPath);
/* Another process might be doing the same thing (creating a new
link to ‘linkPath’) and make ‘linkPath’ immutable before we're
done. In that case, just retry. */
unsigned int retries = 1024;
while (--retries > 0) {
makeMutable(linkPath);
MakeImmutable mk1(linkPath);
Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
% settings.nixStore % getpid() % rand()).str();
Path tempLink = (format("%1%/.tmp-link-%2%-%3%")
% settings.nixStore % getpid() % rand()).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)
printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
return;
}
if (errno == EPERM) continue;
throw SysError(format("cannot link `%1%' to `%2%'") % tempLink % linkPath);
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)
printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
return;
}
/* 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)
printMsg(lvlError, format("unable to unlink `%1%'") % 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.) */
if (st.st_size)
printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
return;
}
if (errno == EPERM) continue;
throw SysError(format("cannot rename `%1%' to `%2%'") % tempLink % path);
}
break;
throw SysError(format("cannot link `%1%' to `%2%'") % tempLink % linkPath);
}
if (retries == 0) throw Error(format("cannot link `%1%' to `%2%'") % path % 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)
printMsg(lvlError, format("unable to unlink `%1%'") % 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.) */
if (st.st_size)
printMsg(lvlInfo, format("`%1%' has maximum number of links") % linkPath);
return;
}
throw SysError(format("cannot rename `%1%' to `%2%'") % tempLink % path);
}
stats.filesLinked++;
stats.bytesFreed += st.st_size;