Re: [PATCH v2 2/2] btrfs: introduce more accurate usebackuproot options

[Boris Burkov <boris@bur.io>]

On Sun, Sep 06, 2026 at 04:33:38PM +0930, Qu Wenruo wrote:
> 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

What do you think about mirroring the compression levels and having the
option parse as rescue=usebackuproot[:N] rather than 4 options?

> 
> 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.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>