Messages in this thread | | | Date | Tue, 2 Jan 2007 01:04:06 +0100 (CET) | From | Mikulas Patocka <> | Subject | Re: Finding hardlinks |
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On Mon, 1 Jan 2007, Jan Harkes wrote:
> On Mon, Jan 01, 2007 at 11:47:06PM +0100, Mikulas Patocka wrote: >>> Anyway, cp -a is not the only application that wants to do hardlink >>> detection. >> >> I tested programs for ino_t collision (I intentionally injected it) and >> found that CP from coreutils 6.7 fails to copy directories but displays >> error messages (coreutils 5 work fine). MC and ARJ skip directories with >> colliding ino_t and pretend that operation completed successfuly. FTS >> library fails to walk directories returning FTS_DC error. Diffutils, find, >> grep fail to search directories with coliding inode numbers. Tar seems >> tolerant except incremental backup (which I didn't try). All programs >> except diff were tolerant to coliding ino_t on files. > > Thanks for testing so many programs, but... did the files/symlinks with > colliding inode number have i_nlink > 1? Or did you also have directories > with colliding inode numbers. It looks like you've introduced hardlinked > directories in your test which are definitely not supported, in fact it > will probably cause not only issues for userspace programs, but also > locking and garbage collection issues in the kernel's dcache.
I tested it only on files without hardlink (with i_nlink == 1) --- most programs (except diff) are tolerant to collision, they won't store st_ino in memory unless i_nlink > 1.
I didn't hardlink directories, I just patched stat, lstat and fstat to always return st_ino == 0 --- and I've seen those failures. These failures are going to happen on non-POSIX filesystems in real world too, very rarely.
BTW. POSIX supports (optionally) hardlinked directories but doesn't supoprt colliding st_ino --- so programs act according to POSIX --- but the problem is that this POSIX requirement no longer represents real world situation.
> I'm surprised you're seeing so many problems. The only find problem that > I am aware of is the one where it assumes that there will be only > i_nlink-2 subdirectories in a given directory, this optimization can be > disabled with -noleaf.
This is not a bug but a feature. If filesystem doesn't count subdirectories, it should set directory's n_link to 1 and find will be ok.
> The only problems I've encountered with ino_t collisions are archivers > and other programs that recursively try to copy a tree while preserving > hardlinks. And in all cases these seem to have no problem with such > collisions as long as i_nlink == 1.
Yes, but they have big problems with directory ino_t collisions. They think that directories are hardlinked and skip processing them.
Mikulas
> Jan > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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