linux-kernel - Re: reiserfs NET=n build error

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Message-ID: <4560BAAF.2030202@suse.com>
Date:	Sun, 19 Nov 2006 15:12:31 -0500
From:	Jeff Mahoney <jeffm@...e.com>
To:	Andi Kleen <ak@...e.de>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	lkml <linux-kernel@...r.kernel.org>, reiserfs-dev@...esys.com,
	sam@...nborg.org, Al Viro <viro@....linux.org.uk>
Subject: Re: reiserfs NET=n build error

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Andi Kleen wrote:
>>> I would copy a relatively simple C implementation, like arch/h8300/lib/checksum.c
>> As long as the h8300 version has the same output as the x86 version.
> 
> The trouble is that the different architecture have different output 
> for csum_partial. So you already got a bug when someone wants to move
> file systems.

Yeah, Al Viro noticed that about reiserfs earlier this month. The
problem is that there's really no good fix for it. I was under the
impression that csum_partial would be arch-independent and was in asm/
for performance reasons. The comment in asm-x86_64 indicates that's not
the case, but the comment in asm-i386 still doesn't. I developed the
code on i386. Moving forward we can define an arch-independent hash
function for that and accept the old arch-dependent checksums, but
there's still the issue of old kernels not understanding it on any arch.
Kind of a nice shot to the foot considering the work I put into making
reiserfs endian safe in the 2.4 days.

I'm hoping there's a better solution to be found than creating a
checksum verifier that checks all known versions. :(

- -Jeff

- --
Jeff Mahoney
SUSE Labs
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