linux-ext4 - Re: [PATCH] dir_index: error out instead of BUG on corrupt hash dir limit

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Message-ID: <20070810181901.GT6689@schatzie.adilger.int>
Date:	Fri, 10 Aug 2007 12:19:02 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] dir_index: error out instead of BUG on corrupt hash dir limit

On Aug 10, 2007  11:08 -0500, Eric Sandeen wrote:
> Andreas Dilger wrote:
> > I'd like to see the actual corruption, to find out why the hash-type
> > check didn't find it.  If it is because LDISKFS_DX_HASH_LEGACY hash
> > type is zero, I think we can disable that hash type, and people will
> > just have to run "e2fsck -fD" to reindex to a new type.  This hasn't
> > been on for a long, long time.
> 
> So far I haven't been able to find it in any of the images provided.
> 
> We may have to dual-boot windows & run the crummy driver for a while to
> track it down, if we care enough.
> 
> Which reminds me, what do you think of the wording in the ext3_warning I
> added - is "corruption" appropriate?  The other warnings aren't quite so
> stark... hmm maybe we should  add "have you been running a binary-only
> driver for windows?"  :)

It would be interesting to check if mounting a dir_index filesystem on
linux with ext2 has the same problem.  It _should_ have been that 
if rec_len % 4 == 0 (i.e. any valid dirent) we would fail the hash_version
check, but we left in the DX_HASH_LEGACY (0) and that check is blown.
The unused_flags & 1 is only hit for a dirent with DT_FIFO (no good).
The remaining check is indirect_levels > 1, which should be hit for
any dirent with name_len > 1 (i.e. most, but not all).

So, I think you could reproduce this in linux by making an indexed directory
in ext3/4, mounting it as ext2, and then creating a 1-character filename
in the directory, or any length filename and then deleting it.

In addition to your extra check, I think we should remove DX_HASH_LEGACY
check, to catch this more easily.  If (hash_version % 4 == 0) the warning
shouldn't even be printed.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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