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Re: [PATCH 4/4] xfs_repair: remove last-entry hack in process_sf_dir2

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [PATCH 4/4] xfs_repair: remove last-entry hack in process_sf_dir2
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Fri, 13 Mar 2015 10:41:27 -0400
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <54FF5E0A.5040800@xxxxxxxxxxx>
References: <54FF59DA.60700@xxxxxxxxxxx> <54FF5E0A.5040800@xxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Tue, Mar 10, 2015 at 05:11:38PM -0400, Eric Sandeen wrote:
> process_sf_dir2() tries to special-case the last entry in
> a short form dir, and salvage it if the name length is wrong
> by using the dir size as a clue to what the length should be.
> 
> However, this doesn't actually work; there is either a 32-bit
> or 64-bit inode after the name, and with dirv3 there's a file
> type in there as well.  Extending the name length to the dir
> size means it overlaps these fields, which often have a 0 in
> the top bits, and then namecheck() fails the result and junks
> it anyway:
> 
> > entry #1 is zero length in shortform dir 67, resetting to 29
> > entry contains illegal character in shortform dir 67
> > junking entry "bbbbbbbbbbbbbbbbbbbbbbbb" in directory inode 67
> 
> And depending on the corruption, the current code will set
> a new negative namelen if it turns out that the name itself
> starts beyond dir size; it can't be shortened enough.
> 
> So, we could fix this up, and choose a new namelen such that
> the xfs_dir2_ino8_t and/or xfs_dir2_ino8_t and/or file type
> still fits at the end, but we really seem to be reaching the
> point of diminishing returns.  The chances that nothing but
> the name length is wrong, and that the remaining few
> bytes at the end of the dir size are actually correct, seems
> awfully small.
> 
> Therefore just remove this special case, which I think is
> of questionable value.
> 

Yeah... Unless I'm missing something, this doesn't seem to be worth the
lines of code. The entry is going to be junked anyways on recent
filesystems. With the optimization being for the last entry in the dir,
removing it shouldn't cause any kind of increase in junked entries in
the event that this occurs. Looks good to me:

Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>

> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
> 
> diff --git a/repair/dir2.c b/repair/dir2.c
> index 5512e41..b1816f4 100644
> --- a/repair/dir2.c
> +++ b/repair/dir2.c
> @@ -874,43 +874,20 @@ _("entry \"%*.*s\" in shortform directory %" PRIu64 " 
> references %s inode %" PRI
>               }
>  
>               if (bad_sfnamelen) {
> +                     do_warn(
> +_("entry #%d %s in shortform dir %" PRIu64),
> +                             i, junkreason, ino);
> +                     if (!no_modify)
> +                             do_warn(_(", junking %d entries\n"),
> +                                     num_entries - i);
> +                     else
> +                             do_warn(_(", would junk %d entries\n"),
> +                                     num_entries - i);
>                       /*
> -                      * if we're really lucky, this is the last entry in
> -                      * case we can use the dir size to set the namelen
> -                      * value.  otherwise, forget it because we're not going
> -                      * to be able to find the next entry.
> +                      * don't process the rest of the directory,
> +                      * break out of processing loop
>                        */
> -                     if (i == num_entries - 1)  {
> -                             namelen = ino_dir_size -
> -                                     ((__psint_t) &sfep->name[0] -
> -                                      (__psint_t) sfp);
> -                             if (!no_modify)  {
> -                                     do_warn(
> -_("entry #%d %s in shortform dir %" PRIu64 ", resetting to %d\n"),
> -                                             i, junkreason, ino, namelen);
> -                                     sfep->namelen = namelen;
> -                                     *dino_dirty = 1;
> -                             } else  {
> -                                     do_warn(
> -_("entry #%d %s in shortform dir %" PRIu64 ", would set to %d\n"),
> -                                             i, junkreason, ino, namelen);
> -                             }
> -                     } else  {
> -                             do_warn(
> -_("entry #%d %s in shortform dir %" PRIu64),
> -                                     i, junkreason, ino);
> -                             if (!no_modify)
> -                                     do_warn(_(", junking %d entries\n"),
> -                                             num_entries - i);
> -                             else
> -                                     do_warn(_(", would junk %d entries\n"),
> -                                             num_entries - i);
> -                             /*
> -                              * don't process the rest of the directory,
> -                              * break out of processing looop
> -                              */
> -                             break;
> -                     }
> +                     break;
>               }
>  
>               /*
> 
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