Bug#691568: btrfs: can't have many hardlinks to a given inode in a given directory

[Jonathan Nieder <jrnieder@gmail.com>]

Source: linux
Version: 3.2.32-1
Severity: wishlist
Justification: difficult
Tags: upstream patch moreinfo

Hi,

As described at [1], btrfs limits (to less than 200 or so) on the
number of hard links to a single inode in a given directory.  This is
due to a flaw in the on-disk format.

This hurts busybox-style programs like git that want to keep many
links to a single binary and backup programs like backuppc.

3.7-rc1 is said to fix this[2], provided users set an appropriate
on-disk flag to accept the format bump.  Ideally I'd like to see these
patches in wheezy so that wheezy could read such filesystems once they
become more widespread.

  b916a59adfdc Btrfs: add missing read locks in backref.c
  5a1d7843ca4b btrfs: improved readablity for add_inode_ref
  f186373fef00 btrfs: extended inode refs
  d24bec3ae528 btrfs: extended inode ref iteration

Untested.  Patches attached for reference.  Any heroes to try these
with xfstests and then in everyday use?  Until they get more testing,
perhaps they can provide some amusement.

Thanks,
Jonathan

[1] http://bugs.debian.org/642603
http://thread.gmane.org/gmane.comp.file-systems.btrfs/6285/focus=6354
[2] http://thread.gmane.org/gmane.comp.file-systems.btrfs/19287