[PATCH 0/2] btrfs: qgroup fixes for btrfs_drop_snapshot

[Mark Fasheh <mfasheh@suse.de>]

Hi, the following patches try to fix a long outstanding issue with qgroups
and snapshot deletion. The core problem is that btrfs_drop_snapshot will
skip shared extents during it's tree walk. This results in an inconsistent
qgroup state once the drop is processed.

The first patch adds some tracing which I found very useful in debugging
qgroup operations. The second patch is an actual fix to the problem.

Even with this patch series, we still have some inconsistency in qgroups
when a snapshot is deleted.  As far as I can tell this is because shared
subtree roots are not completely skipped and may get passed to the qgroup
subsystem via a number of ref operations that happen during drop snapshot. 
I am working on a fix for that issue, but feel that what I have here gets us
90% of the way to a full fix.

Please review, thanks. Diffstat follows,
	--Mark

 fs/btrfs/extent-tree.c       |  234 +++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/qgroup.c            |  169 +++++++++++++++++++++++++++++--
 fs/btrfs/qgroup.h            |    1 
 fs/btrfs/super.c             |    1 
 include/trace/events/btrfs.h |   57 ++++++++++
 5 files changed, 456 insertions(+), 6 deletions(-)