Re: [PATCH] btrfs: do not reject a valid running dev-replace

[David Sterba <dsterba@suse.cz>]

On Wed, Apr 01, 2026 at 09:32:57AM +1030, Qu Wenruo wrote:
> [BUG]
> There is a bug report that a btrfs with running dev-replace got rejected
> with the following messages:
> 
>  BTRFS error (device sdk1): devid 0 path /dev/sdk1 is registered but not found in chunk tree
>  BTRFS error (device sdk1): remove the above devices or use 'btrfs device scan --forget <dev>' to unregister them before mount
>  BTRFS error (device sdk1): open_ctree failed: -117
> 
> [CAUSE]
> The tree and super block dumps show the fs is completely sane, except
> one thing, there is no dev item for devid 0 in chunk tree.
> 
> However this is not a bug, as we do not insert dev item for devid 0 in
> the first place.
> Since the devid 0 is only there temporarily we do not really need to
> insert a dev item for it and then later remove it again.
> 
> It is the commit 34308187395f ("btrfs: add extra device item checks at
> mount") adding a overly strict check that triggers a false alert and
> rejected the valid filesystem.
> 
> [FIX]
> Add a special handling for devid 0, and doesn't require devid 0 to
> have a device item in chunk tree.
> 
> Reported-by: Jaron Viëtor <jaron@vietors.com>
> Link: https://lore.kernel.org/linux-btrfs/CAF1bhLVYLZvD=j2XyuxXDKD-NWNJAwDnpVN+UYeQW-HbzNRn1A@mail.gmail.com/
> Fixes: 34308187395f ("btrfs: add extra device item checks at mount")
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: David Sterba <dsterba@suse.com>