Re: [PATCH v2] repair: use fs rootino for dummy parent value instead of zero

[Dave Chinner <david@fromorbit.com>]

On Fri, Jul 17, 2020 at 07:59:20AM -0400, Brian Foster wrote:
> If a directory inode has an invalid parent ino on disk, repair
> replaces the invalid value with a dummy value of zero in the buffer
> and NULLFSINO in the in-core parent tracking. The zero value serves
> no functional purpose as it is still an invalid value and the parent
> must be repaired by phase 6 based on the in-core state before the
> buffer can be written out. A consequence of using an invalid dummy
> value is that phase 6 requires custom verifier infrastructure to
> detect the invalid parent inode and temporarily replace it while the
> core fork verifier runs. If we use a valid inode number as a dummy
> value earlier in repair, this workaround can be removed.
> 
> An obvious choice for a valid dummy parent inode value is the
> orphanage inode. However, the orphanage inode is not allocated until
> much later in repair when the filesystem structure is established as
> sound and placement of orphaned inodes is imminent. In this case, it
> is too early to know for sure whether the associated inodes are
> orphaned because a directory traversal later in repair can locate
> references to the inode and repair the parent value based on the
> structure of the directory tree.
> 
> Given all of this, escalate the preexisting workaround from the
> custom verifier in phase 6 and set the root inode value as a dummy
> parent for shortform directories with an invalid on-disk parent. The
> in-core parent is still tracked as NULLFSINO and so forces repair to
> either update the parent or orphan the inode before repair
> completes.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---
> 
> v2:
> - Update patch subject and commit log.

Looks good.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
-- 
Dave Chinner
david@fromorbit.com