more blkdev_get and holder work

[Christoph Hellwig <hch@lst.de>]

Hi all,

this series sits on top of the vfs.super branch in the VFS tree and does a
few closely related things:

  1) it also converts nilfs2 and btrfs to the new scheme where the file system
     only opens the block devices after we know that a new super_block was
     allocated.
  2) it then makes sure that for all file system openers the super_block is
     stored in bd_holder, and makes use of that fact in the mark_dead method
     so that it doesn't have to fall get_super and thus can also work on
     block devices that sb->s_bdev doesn't point to
  3) it then drops the fs-specific holder ops in ext4 and xfs and uses the
     generic fs_holder_ops there

A git tree is available here:

    git://git.infradead.org/users/hch/misc.git fs-holder-rework

Gitweb:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/fs-holder-rework

Diffstat:
 fs/btrfs/super.c           |   67 ++++++++++++++++---------------------
 fs/btrfs/volumes.c         |    8 ++--
 fs/btrfs/volumes.h         |    2 -
 fs/ext4/super.c            |   18 +++-------
 fs/f2fs/super.c            |    7 +--
 fs/nilfs2/super.c          |   81 ++++++++++++++++-----------------------------
 fs/super.c                 |   44 ++++++++++++++++++------
 fs/xfs/xfs_super.c         |   32 +++++++----------
 include/linux/blkdev.h     |    2 +
 include/linux/fs_context.h |    2 +
 10 files changed, 126 insertions(+), 137 deletions(-)