Re: [PATCH v2 2/6] xfs_repair: don't error out on dirs with a single leafn block

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

On Tue, Dec 04, 2018 at 10:11:50PM -0600, Eric Sandeen wrote:
> 
> 
> On 12/4/18 9:48 PM, Eric Sandeen wrote:
> > On 11/22/18 12:13 PM, Darrick J. Wong wrote:
> >> From: Darrick J. Wong <darrick.wong@oracle.com>
> >>
> >> In process_node_dir2, we need to distinguish between a directory with a
> >> single leafn block (yes, they exist) having no interior da nodes, and a
> >> directory with a da tree that incorrectly points to dablk 0.  If we
> >> happened to fill out any part of the da cursor then we have a da btree
> >> with garbage in it; otherwise, we have a single leafn block.
> >>
> >> This was found by repair repeatedly rebuilding a directory containing a
> >> single leafn block (xfs/495).
> >>
> >> Fixes: 67a79e2cc932 ("xfs_repair: treat zero da btree pointers as corruption")
> >> Reported-by: Dave Chinner <david@fromorbit.com>
> >> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > I'm finding the commit log hard to parse/understand.
> > 
> > Let's reference
> > 
> > 71a6af8 Revert "xfs_repair: treat zero da btree pointers as corruption"
> > 
> > for starters, but can we do something like this....?
> > 
> > ===
> > 
> > As explained in
> > 
> > 71a6af8 Revert "xfs_repair: treat zero da btree pointers as corruption"
> > 
> > a single root LEAFN block can exist in a directory until it grows further.
> > 
> > This is why, normally, we skip directories with a root marked
> > XFS_DIR2_LEAFN_MAGIC, as detected by the left-most leaf block being 
> > found at file block 0.
> > 
> > However, if we traversed any level of a btree to get here (as
> > indicated by da_cursor.active > 0), then a leaf block claiming block
> > 0 indicates corruption, and we should handle it as such, and rebuild
> > the directory.
> > 
> > This was found by repair repeatedly rebuilding a directory containing a
> > single leafn block (xfs/495).
> > 
> > Fixes: 67a79e2cc932 ("xfs_repair: treat zero da btree pointers as corruption")
> > Reported-by: Dave Chinner <david@fromorbit.com>
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > ===
> > 
> > I'm not hung up on rewriting the commit log, but if you like it give me
> > thumbs up.  I needed to think it through that way to grok the change.
> > Anyway, for the change now that I do grok it,
> > 
> > Reviewed-by: Eric Sandeen <sandeen@redhat.com>
> 
> Uh, the summary is wrong too,  o?  We /already/ "don't error out"
> on dirs with a single leafn block.  Maybe:
> 
> xfs_repair: rebuild directory when non-root leafn blocks claim block 0
> 
> ?

Works for me.  Want a resend or are you fixing it up on the way in?

--D