The kernel reunites split-brained devices after a failed `btrfstune -m|M`
operation. We can achieve the same in btrfs-progs. So port it here.
Ref the discussion here:

   https://lore.kernel.org/all/1fa6802b-5812-14a8-3fc8-5da54bb5f79d@oracle.com/ (local)

Patch 1/16 wasn't integrated as part of the set
	[PATCH 00/10 v2] fixes and preparatory related to metadata_uuid
it's now merged with this patchset.

Patches [2-6,11,12] are cleanup patches.

Patches [7,8,10] are preparatory.

Patch [9] addresses a bug.

Patches [13, 14, 15] provide recovery from previously failed
`btrfstune -m|M` operations.

Patch [16] enhances the misc-test `034-metadata-uuid` to also validate this
new recovery feature.

This set has been successfully tested with the btrfs-progs testsuite.

This patchset is on top the latest devel last commit:
 8aba9b0052b6 btrfs-progs: btrfstune: consolidate error handling in main()


Anand Jain (16):
  btrfs-progs: track num_devices per fs_devices
  btrfs-progs: tune can use local fs_info variable
  btrfs-progs: rename set_metadata_uuid arg to new_fsid_str
  btrfs-progs: rename set_metadata_uuid new_fsid to fsid
  btrfs-progs: rename set_metadata_uuid new_uuid to new_fsid
  btrfs-progs: rename set_metadata_uuid uuid_changed to fsid_changed
  btrfs-progs: pass fsid in check_unfinished_fsid_change arg2
  btrfs-progs: pass metadata_uuid in check_unfinished_fsid_change arg3
  btrfs-progs: fix return without flag reset commit in tune
  btrfs-progs: preparing the latest device's superblock for commit
  btrfs-progs: rename fs_devices::list to match the kernel
  btrfs-progs: rename fs_devices::latest_trans to match the kernel
  btrfs-progs: tune use the latest bdev in fs_devices for super_copy
  btrfs-progs: add support to fix superblock with CHANGING_FSID_V2 flag
  btrfs-progs: recover from the failed btrfstune -m|M
  btrfs-progs: test btrfstune -m|M ability to fix previous failures

 cmds/filesystem.c                          |  14 +-
 common/device-scan.c                       |   2 +-
 kernel-shared/disk-io.c                    |   3 +
 kernel-shared/disk-io.h                    |   5 +
 kernel-shared/volumes.c                    | 203 +++++++++++++++++++--
 kernel-shared/volumes.h                    |   5 +-
 tests/misc-tests/034-metadata-uuid/test.sh |  70 +++++--
 tune/change-metadata-uuid.c                |  56 +++---
 tune/main.c                                |  35 ++--
 9 files changed, 312 insertions(+), 81 deletions(-)

-- 
2.39.3