Re: [PATCH v3 1/3] btrfs: enhance unsupported compat RO flags handling

[David Sterba <dsterba@suse.cz>]

On Tue, Aug 09, 2022 at 01:02:16PM +0800, Qu Wenruo wrote:
> Currently there are two corner cases not handling compat RO flags
> correctly:
> 
> - Remount
>   We can still mount the fs RO with compat RO flags, then remount it RW.
>   We should not allow any write into a fs with unsupported RO flags.
> 
> - Still try to search block group items
>   In fact, behavior/on-disk format change to extent tree should not
>   need a full incompat flag.
> 
>   And since we can ensure fs with unsupported RO flags never got any
>   writes (with above case fixed), then we can even skip block group
>   items search at mount time.
> 
> This patch will enhance the unsupported RO compat flags by:
> 
> - Reject RW remount if there is unsupported RO compat flags
> 
> - Go dummy block group items directly for unsupported RO compat flags
>   In fact, only changes to chunk/subvolume/root/csum trees should go
>   incompat flags.
> 
> The latter part should allow future change to extent tree to be compat
> RO flags.
> 
> Thus this patch also needs to be backported to all stable trees.
> 
> Cc: stable@vger.kernel.org

This applies cleanly only to 5.19, anything else would need a separate
backport. I'm planning to send this patch among 6.0 fixes so this
should give us time to get it to older stable kernels before the block
group tree is released.