linux-ext4 - Re: [PATCH] debugfs: byteswap dirsearch dirent buf on big endian systems

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Message-ID: <20250304193446.GA2803723@frogsfrogsfrogs>
Date: Tue, 4 Mar 2025 11:34:46 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Brian Foster <bfoster@...hat.com>
Cc: linux-ext4@...r.kernel.org
Subject: Re: [PATCH] debugfs: byteswap dirsearch dirent buf on big endian
 systems

On Mon, Mar 03, 2025 at 02:09:05PM -0500, Brian Foster wrote:
> On Thu, Jan 23, 2025 at 08:52:11AM -0500, Brian Foster wrote:
> > fstests test ext4/048 fails on big endian systems due to broken
> > debugfs dirsearch functionality. On an s390x system and 4k block
> > size, the dirsearch command seems to hang indefinitely. On the same
> > system with a 1k block size, the command fails to locate an existing
> > entry and causes the test to fail due to unexpected results.
> > 
> > The cause of the dirsearch failure is lack of byte swapping of the
> > on-disk (little endian) dirent buffer before attempting to iterate
> > entries in the given block. This leads to garbage record and name
> > length values, for example. To resolve this problem, byte swap the
> > directory buffer on big endian systems.
> > 
> > Signed-off-by: Brian Foster <bfoster@...hat.com>
> > ---
> > 
> > Hi all,
> > 
> > I'm not terribly familiar with this code, but this fixes the test and
> > doesn't show any regressions from fstests runs on big or little endian
> > systems. Thanks.
> > 
> 
> Ping... curious if anybody has thoughts on this for dirsearch on big
> endian? Thanks!

It looks correct to /me/... horrors of debugfs, etc. :(

Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>

--D

> 
> Brian
> 
> > Brian
> > 
> >  debugfs/htree.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/debugfs/htree.c b/debugfs/htree.c
> > index a1008150..4ea8f30b 100644
> > --- a/debugfs/htree.c
> > +++ b/debugfs/htree.c
> > @@ -482,6 +482,12 @@ static int search_dir_block(ext2_filsys fs, blk64_t *blocknr,
> >  		return BLOCK_ABORT;
> >  	}
> >  
> > +#ifdef WORDS_BIGENDIAN
> > +	errcode = ext2fs_dirent_swab_in(fs, p->buf, 0);
> > +	if (errcode)
> > +		return BLOCK_ABORT;
> > +#endif
> > +
> >  	while (offset < fs->blocksize) {
> >  		dirent = (struct ext2_dir_entry *) (p->buf + offset);
> >  		errcode = ext2fs_get_rec_len(fs, dirent, &rec_len);
> > -- 
> > 2.47.1
> > 
> > 
> 
>