Re: [PATCH v7 2/2] btrfs: Introduce new mount option to skip block group items scan

[Josef Bacik <josef@toxicpanda.com>]

On 6/4/20 3:18 AM, Qu Wenruo wrote:
> [PROBLEM]
> There are some reports of corrupted fs which can't be mounted due to
> corrupted extent tree.
> 
> However under such situation, it's more likely the fs/subvolume trees
> are still fine.
> 
> For such case we normally go btrfs-restore and salvage as much as we
> can. However btrfs-restore can't list subvolumes as "btrfs subv list",
> making it harder to restore a fs.
> 
> [ENHANCEMENT]
> This patch will introduce a new mount option "rescue=skipbg" to skip
> the mount time block group scan, and use chunk info solely to populate
> fake block group cache.
> 
> The mount option has the following dependency:
> - RO mount
>    Obviously.
> 
> - No dirty log.
>    Either there is no log, or use rescue=nologreplay mount option.
> 
> - No way to remoutn RW
>    Similar to rescue=nologreplay option.
> 
> This allow kernel to accept all extent tree corruption, even when the
> whole extent tree is corrupted, and allow user to salvage data and
> subvolume info.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef