[PATCH v3 0/6] btrfs: use the super_block as bdev holder

[Qu Wenruo <wqu@suse.com>]

[CHANGELOG]
v3:
- Drop the btrfs_fs_devices::opened split
  It turns out to cause problems during tests.

- Extra cleanup related to the btrfs_get_tree_*()
  Now the re-entry through vfs_get_tree() is completely dropped.

- Extra comments explaining the sget_fc() behavior

- Call bdev_fput() instead of fput()
  This alignes us to all the other fses.

- Updated patch to delay btrfs_open_devices() until sget_fc()
  Instead of relying on the previous solution (split
  btrfs_open_devices::opened), just expand the uuid_mutex critical
  section.

This is the refreshed series based on the one submitted by Johannes,
which is further based on the original series from Christoph.

This series is to make btrfs use its super block as blk_holder, this
allows future usage of fs_holder_ops to support block device operations.

This is done by:

- Get rid of the re-entry of btrfs_get_tree()
  Now it's a simple call chain:

   btrfs_get_tree() -> btrfs_get_tree_subvol() -> btrfs_get_tree_super()

- Make it more clear on the sget_fc() behavior
  And what should be cleaned up.

- Call btrfs_close_devices() from kill_sb() callback

- Call bdev_fput() instead of deferred fput()
  This ensures we won't get some block devices with invalid holder,
  while the fs is already closed.

- Delay btrfs_open_devices(0 until super block is created
  This is done in a simpler way, just expand the uuid_mutex critical
  section to cover sget_fc().

- Use super block as blk_holder


Christoph Hellwig (2):
  btrfs: call btrfs_close_devices from ->kill_sb
  btrfs: use the super_block as holder when mounting file systems

Qu Wenruo (4):
  btrfs: get rid of the re-entry of btrfs_get_tree()
  btrfs: add comments to make super block creation more clear
  btrfs: call bdev_fput() to reclaim the blk_holder immediately
  btrfs: delay btrfs_open_devices() until super block is created

 fs/btrfs/dev-replace.c |  4 +-
 fs/btrfs/disk-io.c     |  4 +-
 fs/btrfs/fs.h          |  2 -
 fs/btrfs/ioctl.c       |  4 +-
 fs/btrfs/super.c       | 96 ++++++++++++++++++------------------------
 fs/btrfs/volumes.c     | 22 +++++-----
 6 files changed, 59 insertions(+), 73 deletions(-)

-- 
2.49.0