From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: Behan Webster <behanw@converseincode.com>,
linux-ext4@vger.kernel.org, Mark Charlebois <charlebm@gmail.com>
Subject: Re: [PATCH] Remove VLAIS usage from JBD2 code
Date: Fri, 9 Nov 2012 15:24:51 -0800 [thread overview]
Message-ID: <20121109232451.GA11827@blackbox.djwong.org> (raw)
In-Reply-To: <20121109231912.GA6444@blackbox.djwong.org>
On Fri, Nov 09, 2012 at 03:19:12PM -0800, Darrick J. Wong wrote:
> On Thu, Nov 08, 2012 at 10:53:07AM -0500, Theodore Ts'o wrote:
> > Hey Darrick,
> >
> > I was looking at this code a bit more closely while applying the
> > revised version of this patch --- and this in particular raised a red
> > flag for me:
> >
> > *(u32 *)desc.ctx = crc;
> > ...
> > return *(u32 *)desc.ctx;
> >
> > Does this raise any byte swapping issues? Looking at how the crc32
> > code in crypto/ works, I'm almost certain this is broken on big-endian
> > systems, and we need to add le32_to_cup() and cpu_to_le32() calls here.
> >
> > Am I missing something?
>
> crc32_[bl]e_generic() in lib/crc32.c contains the appropriate be/le-to-cpu
> conversion calls to ensure that the results are always returned in cpu-endian
> format. The crypto/crc32.c file is basically just a crypto-hash wrapper around
> the lib/crc32.c code, and don't touch the endianness at all. The ext4 code
> receives the results from the crypto code in cpu-endian format and always
> converts it to (or from) little-endian format when accessing disk structures.
>
> As far as e2fsprogs, it leaves the checksums in le format, only converting it
> to cpu-endian format when verifying or setting the checksum.
I forgot to mention -- I tried creating a metadata_csum filesystem on an x86
box. Then I bounced it between that machine and my one remaining ppc32 box,
running a mount/read/write/unmount/fsck script on each bounce. I didn't see
any errors. Sadly, I no longer have anything weirder (sparc64/s390x) to test.
--D
>
> --D
> >
> > - Ted
> --
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prev parent reply other threads:[~2012-11-09 23:24 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-30 18:40 [PATCH] Removing the use of VLAIS from the Linux Kernel Behan Webster
2012-10-30 18:40 ` [PATCH] Remove VLAIS usage from JBD2 code Behan Webster
2012-10-30 19:00 ` Theodore Ts'o
2012-10-30 19:02 ` Behan Webster
2012-10-30 19:13 ` Darrick J. Wong
2012-11-08 15:53 ` Theodore Ts'o
2012-11-09 23:19 ` Darrick J. Wong
2012-11-09 23:24 ` Darrick J. Wong [this message]
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