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Re: [PATCH 3/5] xfs_repair: fix dir refcount when '.' missing and dir is

To: Brian Foster <bfoster@xxxxxxxxxx>, Eric Sandeen <sandeen@xxxxxxxxxx>
Subject: Re: [PATCH 3/5] xfs_repair: fix dir refcount when '.' missing and dir is rebuilt
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Mon, 08 Sep 2014 09:33:55 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20140908134524.GC52419@xxxxxxxxxxxxxxx>
References: <1410108065-18156-1-git-send-email-sandeen@xxxxxxxxxx> <1410108065-18156-4-git-send-email-sandeen@xxxxxxxxxx> <20140908134524.GC52419@xxxxxxxxxxxxxxx>
On 9/8/14 8:45 AM, Brian Foster wrote:
On Sun, Sep 07, 2014 at 11:41:03AM -0500, Eric Sandeen wrote:
In phase 6's longform_dir2_entry_check, if we never
find a '.' entry we never add a reference to that entry;
if we subsequently rebuild it, '.' gets added, but
no ref to it is ever made.  This leads to Phase 7 doing
i.e.:

   Phase 7 - verify and correct link counts...
   resetting inode 5184 nlinks from 2 to 1

and the next run will do:

   Phase 7 - verify and correct link counts...
   resetting inode 5184 nlinks from 1 to 2

So if '.' was never found, but the directory got
rebuilt, manually add the ref for it.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---
  repair/phase6.c |    6 ++++++
  1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/repair/phase6.c b/repair/phase6.c
index f13069f..cc36a9c 100644
--- a/repair/phase6.c
+++ b/repair/phase6.c
@@ -2288,6 +2288,12 @@ out_fix:
                        if (bplist[i])
                                libxfs_putbuf(bplist[i]);
                longform_dir2_rebuild(mp, ino, ip, irec, ino_offset, hashtab);
+               /*
+                * If we didn't find a dot, we never added a ref for it;
+                * it's there now after the rebuild, so mark it as reached.
+                */
+               if (*need_dot)
+                       add_inode_ref(irec, ino_offset);

So if I follow this correctly, we iterate through the dir, add each name
to the hashtable and handle the inode reference count in the first
longform_dir2_entry_check() loop. If something is wrong, we call
longform_dir2_rebuild() to rebuild the dir from the hashtable of
names/inodes. We may or may not have added a reference for dot at that
point, and need_dot is set appropriately.

This seems Ok, but where is the dot entry actually added? Hmm, I see
that we handle dot in the longform_dir2_rebuild() loop by just skipping
over it...

longform_dir2_rebuild calls this before the loop:

/*
 * Initialize a directory with its "." and ".." entries.
 */
int
xfs_dir_init()

But it doesn't actually create .; this creates a shortform dir,
and shortform dirs have no '.' - I guess the comment could use
an update.

In the loop we call xfs_dir_createname() for everything in the hash,
eventually things don't fit in shortform and we do xfs_dir2_sf_to_block,
which creates the dot:

        /*
         * Create entry for .
         */
        dep = xfs_dir3_data_dot_entry_p(mp, hdr);
        dep->inumber = cpu_to_be64(dp->i_ino);
        dep->namelen = 1;
        dep->name[0] = '.';

-Eric

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