[PATCHv3 0/4] hfsplus: stop using write_supers and s_dirt

[Artem Bityutskiy <dedekind1@gmail.com>]

Hi Andrew, here is v3 of the patches, could you please pick them instead of the
ones you have in your tree? The differences to v2 are:

1. checkpatch.pl warnings fixed
2. removed 'cancel_delayed_work()' from 'hfsplus_sync_fs()' because it is not
   enough to just cancel the job, we need to set the work_queued flag to zero
   as well. I could do this, but it is simpler to just remove this tiny
   optimization - we do not gain much with it. I caught this bug while doing
   some more testing.

This patch-set makes hfsplus file-system stop using the VFS '->write_supers()'
call-back and the '->s_dirt' superblock field because I plan to remove them
once all users are gone.

Like some other similar patch-sets (affs, hfs, ufs, reiserfs), we switch to
a delayed job for writing out the superblock instead of using the 's_dirt'
flag. Additionally, this patch-set includes several clean-ups.

Tested using the fsstress test from the LTP project.

 fs/hfsplus/bitmap.c     |    4 ++--
 fs/hfsplus/dir.c        |    2 +-
 fs/hfsplus/hfsplus_fs.h |    7 +++++--
 fs/hfsplus/inode.c      |    6 +++---
 fs/hfsplus/super.c      |   46 +++++++++++++++++++++++++++++++++-------------
 5 files changed, 44 insertions(+), 21 deletions(-)

Reminder
========

The goal is to get rid of the 'sync_supers()' kernel thread. This kernel thread
wakes up every 5 seconds (by default) and calls '->write_super()' for all
mounted file-systems. And the bad thing is that this is done even if all the
superblocks are clean. Moreover, many file-systems do not even need this and
they do not even register the '->write_super()' method at all (e.g., btrfs).

So 'sync_supers()' mostly just generates useless wake-ups and wastes power.
I am trying to make all file-systems independent of '->write_super()' and plan
to remove 'sync_supers()' and '->write_super()' completely once there are no
more users.

Overall status
==============

1.  ext4: patches submitted (v7)
    http://thread.gmane.org/gmane.linux.kernel/1326181/focus=33332
2.  ufs: patches submitted,
    https://lkml.org/lkml/2012/7/12/248
3.  exofs: patch submitted,
    https://lkml.org/lkml/2012/6/4/211
4.  sysv: patches submitted,
    http://lkml.org/lkml/2012/7/3/250
5.  udf: patch sits in Jan Kara's tree:
    https://lkml.org/lkml/2012/6/4/233
    git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs for_testing
6.  affs: patches sit in Al Viro's tree:
    https://lkml.org/lkml/2012/6/6/400
    git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs for-next
7.  hfs: patches sit in Andrew Morton's tree (-mm, visible in linux-next)
8.  hfsplus: patches sit in Andrew Morton's tree (-mm, visible in linux-next)
9.  ext2:     done, see commit f72cf5e223a28d3b3ea7dc9e40464fd534e359e8
10. vfat:     done, see commit 78491189ddb6d84d4a4abae992ed891a236d0263
11. jffs2:    done, see commit 208b14e507c00ff7f108e1a388dd3d8cc805a443
12. reiserfs: done, see commit 033369d1af1264abc23bea2e174aa47cdd212f6f

Thanks,
Artem.