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

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Message-ID: <20061119205711.GE3078@ftp.linux.org.uk>
Date:	Sun, 19 Nov 2006 20:57:11 +0000
From:	Al Viro <viro@....linux.org.uk>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Andi Kleen <ak@...e.de>, Jeff Mahoney <jeffm@...e.com>,
	lkml <linux-kernel@...r.kernel.org>, reiserfs-dev@...esys.com,
	sam@...nborg.org
Subject: Re: reiserfs NET=n build error

On Sun, Nov 19, 2006 at 11:04:33AM -0800, Randy Dunlap wrote:
> 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.
> >
> >-Andi
> 
> That argues for having only one version of it (in a lib.; my preference)
> -or- Every module having its own local copy/version of it.  :(

Wrong.  csum_partial() result is defined modulo 0xffff and it's basically
"whatever's convenient as intermediate for this architecture".

reiserfs use of it is just plain broken.  net/* is fine, since all
final uses are via csum_fold() or equivalents.

Note that reiserfs use is broken in another way: it takes fixed-endian value
and feeds it to cpu_to_le32().  IOW, even if everything had literally the
same csum_partial(), the value it shits on disk would be endian-dependent.

As for net/*, with proper types it's pretty straightforward.  See
davem's net-2.6.20 for that...
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