[Rdiff-backup-bugs] [bug #13476] hardlink problem when devloc changes but inode doesn't

[dean gaudet]

URL:
  <http://savannah.nongnu.org/bugs/?func=detailitem&item_id=13476>

                 Summary: hardlink problem when devloc changes but inode
doesn't
                 Project: rdiff-backup
            Submitted by: dgaudet
            Submitted on: Mon 06/20/2005 at 01:25
                Category: None
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open

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Details:

this problem occurs when you have a pair of hardlinked files, which have been
backed up at least once.  then you modify the file and change the devloc
without changing the inode.

this sort of thing can happen when you move the disk to another controller --
in my case it was happenning regularly because i was using LVM snapshot
volumes and the snapshot device number is not fixed from one backup to the
next.

here is a script which demonstrates the problem on linux using an ext2 image
file, sudo, and two different loopback devices.

mkdir src || exit 1
dd if=/dev/zero of=src.img bs=1M count=2 || exit 1
mke2fs -qF -m 0 src.img || exit 1
sudo mount -o loop=/dev/loop3 src.img src || exit 1
echo hi >src/a || exit 1
ln src/a src/b || exit 1
rdiff-backup src dst || exit 1
sudo umount src
sudo mount -o loop=/dev/loop4 src.img src || exit 1
mv src/b src/c || exit 1
sleep 1; rdiff-backup src dst || exit 1
sleep 1; rdiff-backup src dst || exit 1
sudo umount src || exit 1

the second invocation of rdiff-backup produces a broken metadata file with two
different DeviceLoc for the hardlinked files.  the third (and any subsequent
invocations) produce a bogus warning, but the problem is never resolved:

Warning: Attempt to rename over same inode: dst/rdiff-backup.tmp.1 to dst/c

i believe the fix is to treat devloc similar to inode in RORPath.__eq__ ...
we're ignoring devloc currently, and that is broken... you can't compare
inodes without comparing devices.  the attached patch implements this idea.

-dean





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File Attachments:


-------------------------------------------------------
Date: Mon 06/20/2005 at 01:25  Name: hardlink2.patch  Size: 1.03KB   By:
dgaudet
proposed fix
<http://savannah.nongnu.org/bugs/download.php?item_id=13476&item_file_id=2616>

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