[PATCH 0/17 v3] quota: Unify VFS and XFS quota interfaces

[Jan Kara <jack@suse.cz>]

  Hello,

  this is another iteration of patches to unify VFS and XFS quota interfaces so
that XFS quotactls work for filesystems with VFS quotas and vice versa.  This
is useful so that userspace doesn't have to care that much about which
filesystem it is using at least when using basic quota functionality. In
particular we should be able to reuse project quota tests in xfstests for ext4.

The patches are based on quota cleanup series [1] and XFS cleanup series [2]
I've sent previously and based on 3.19-rc4 + for-next branch of XFS tree.  I
could further split this series into per-quotactl series but frankly I don't
think it will help reviewers in any way (the patches in the current series are
already ordered by quotactl).

I would like to get some review especially of the fs-specific parts of the
series - mostly for XFS where things aren't always trivial.

Some more details about the series below:

In this patch set I unify quotaon / quotaoff handling (Q_QUOTAON, Q_QUOTAOFF,
Q_XQUOTAON, Q_XQUOTAOFF calls), fix some bugs in the Q_XGETQUOTA, Q_XSETQLIM,
Q_GETQUOTA, Q_SETQUOTA calls done by Christoph some time ago, unify
Q_GETXSTATE, Q_GETXSTATV with Q_GETINFO, and also wire up Q_SETINFO to work
with XFS (and Q_XSETQLIM for id 0 to modify time limits for VFS quotas).
So after these patches xfs_quota can manipulate quotas for ext4 filesystem and
similarly quota-tools can be used to manipulate quotas for xfs filesystem.

I have also verified that xfstests pass fine both for xfs and ext4 so
hopefully I didn't introduce any regression in the current functionality (I
also did a couple of manual checks for timer setting etc).

All the comments to the first version of the series are hopefully addressed,
except for Dave's request to reduce number of copying of dquot information -
I have benchmarked that reducing number of copies from 3 to 2 brings just 2%
improvement in speed in my test setup and getting quota information isn't IMHO
so performance critical that it would be worth the complications of the code.

								Honza

[1] http://www.spinics.net/lists/linux-fsdevel/msg81903.html
[2] http://www.spinics.net/lists/xfs/msg31389.html