[PATCH 0/4] More split-brain fixes for metadata uuid feature

[Nikolay Borisov <nborisov@suse.com>]

Here are 4 patches which fix a newly found split-brain scenario in the
METADATA_UUID_INCOMPAT code. They are mostly the identical with Su's
original submission but I have reworked the changelogs and some function
names. Hence, I retained his authorship of the patches.

First 2 patches factor out some code with the hopes of making find_fisd a bit
more readable and simplifying the myriad of nested 'if' in device_list_add.

Patch 3 extends find_fsid_changed to handle the case where a disk with
METADATA_UUID_INCOMPAT and FSID_CHANGING_IN_PROGRESS is scanned after a disk
which has successfully been switched to FSID == METADATA_UUID state and has
created btrfs_fs_devices.

Patch 4 handles the counterpart situation - a fully switched disk is scanned
after one which has had METADATA_UUID_INCOMPAT and FSID_CHANGING_IN_PROGRESS
set.

This series should be applied to stable branches following 5.0 when the
metadata_uuid feature got introduced.

This patchset was tested with btrfs-progs' misc 034-metadata-uuid test and a full
xfstest run with no regressions. I will also be sending an improvement to the
test case which exercises the newly added code.

  btrfs: Call find_fsid from find_fsid_inprogress
  btrfs: Factor out metadata_uuid code from find_fsid.
  btrfs: Handle another split brain scenario with metadata uuid feature
  btrfs: Fix split-brain handling when changing FSID to metadata uuid

 fs/btrfs/volumes.c | 158 ++++++++++++++++++++++++++++-----------------
 1 file changed, 100 insertions(+), 58 deletions(-)

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2.17.1