btrfs: introduce more accurate usebackuproot options

Previously we had no way to tell btrfs to use which backup slot, but
always use the newest backup, and retry until all backup roots are
exhausted.

This doesn't give any control to the end user, even if the end user
wants to use a specific backup slot.

To address this problem, allow more fine-control on usebackuproot rescue
option by introducing the following 4 rescue mount options:

- rescue=usebackuproot_0
- rescue=usebackuproot_1
- rescue=usebackuproot_2
- rescue=usebackuproot_3

The number 0 means the newest slot, which should be the same as the one
recorded in the super block and no need to load any backup root.

1/2/3 means the second/third/fourth(oldest) backup slot to use.

The existing "rescue=usebackuproot" is just an alias of
"rescue=usebackuproot_1".

This will allow users to choose which backup root to use, thus can have
a better control than blindly choose any slot that can pass the very
basic root node checks.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

0 files changed, 0 insertions, 0 deletions