Re: [PATCH] btrfs-progs: rescue: introduce clear-uuid-tree

[David Sterba <dsterba@suse.cz>]

On Thu, Nov 11, 2021 at 08:37:24AM +0200, Nikolay Borisov wrote:
> On 11.11.21 г. 4:41, Qu Wenruo wrote:
> > [BUG]
> > There is a bug report that a corrupted key type (expected
> > UUID_KEY_SUBVOL, has EXTENT_ITEM) causing newer kernel to reject a
> > mount.
> > 
> > Although the root cause is not determined yet, with roll out of v5.11
> > kernel to various distros, such problem should be prevented by
> > tree-checker, no matter if it's hardware problem or not.
> > 
> > And older kernel with "-o uuid_rescan" mount option won't help, as
> > uuid_rescan will only delete items with
> > UUID_KEY_SUBVOL/UUID_KEY_RECEIVED_SUBVOL key types, not deleting such
> > corrupted key.
> > 
> > [FIX]
> > To fix such problem we have to rely on offline tool, thus there we
> > introduce a new rescue tool, clear-uuid-tree, to empty and then remove
> > uuid tree.
> > 
> > Kernel will re-generate the correct uuid tree at next mount.
> 
> SHouldn't this be made part of btrfs repair, why do we need specific
> rescue subcom ?

This is a one-shot fix for that we have the rescue subcommand, check
could do a normal pass and verify the tree but that's a bit different
what this patch does and requiring --repair goes opposite to what we
recommend to do.