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

["Darrick J. Wong" <darrick.wong@oracle.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>

Finally this stupid dragon dies!

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> 
> v2:
> - Update patch subject and commit log.
> 
>  repair/dir2.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/repair/dir2.c b/repair/dir2.c
> index caf6963d..9c789b4a 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -165,7 +165,6 @@ process_sf_dir2(
>  	int			tmp_elen;
>  	int			tmp_len;
>  	xfs_dir2_sf_entry_t	*tmp_sfep;
> -	xfs_ino_t		zero = 0;
>  
>  	sfp = (struct xfs_dir2_sf_hdr *)XFS_DFORK_DPTR(dip);
>  	max_size = XFS_DFORK_DSIZE(dip, mp);
> @@ -497,7 +496,7 @@ _("bogus .. inode number (%" PRIu64 ") in directory inode %" PRIu64 ", "),
>  		if (!no_modify)  {
>  			do_warn(_("clearing inode number\n"));
>  
> -			libxfs_dir2_sf_put_parent_ino(sfp, zero);
> +			libxfs_dir2_sf_put_parent_ino(sfp, mp->m_sb.sb_rootino);
>  			*dino_dirty = 1;
>  			*repair = 1;
>  		} else  {
> @@ -532,7 +531,7 @@ _("bad .. entry in directory inode %" PRIu64 ", points to self, "),
>  		if (!no_modify)  {
>  			do_warn(_("clearing inode number\n"));
>  
> -			libxfs_dir2_sf_put_parent_ino(sfp, zero);
> +			libxfs_dir2_sf_put_parent_ino(sfp, mp->m_sb.sb_rootino);
>  			*dino_dirty = 1;
>  			*repair = 1;
>  		} else  {
> -- 
> 2.21.3
>