linux-kernel - Re: [PATCH 0/2] lio-target: Add support for libcrypto crc32c and crc32-intel offload

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Date:	Mon, 13 Sep 2010 13:40:06 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	Hannes Reinecke <hare@...e.de>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	James Bottomley <James.Bottomley@...e.de>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Richard Sharpe <realrichardsharpe@...il.com>,
	Vasu Dev <vasu.dev@...ux.intel.com>,
	Joe Eykholt <jeykholt@...co.com>
Subject: Re: [PATCH 0/2] lio-target: Add support for libcrypto crc32c and
	crc32-intel offload

On Mon, 2010-09-13 at 15:35 -0500, Mike Christie wrote:
> On 09/13/2010 02:50 PM, Nicholas A. Bellinger wrote:
> >> IE the in-kernel crc32c routines apparently weren't able to
> >> calculate the checksum in an endianness-independent manner.
> >> So a CRC calculated on a BE machine would fail to be validated by a
> >> LE machine and vice versa.
> >>
> >> Has this been fixed / verified?
> >>
> >
> >> From taking a look at crypto/crc32c.c it still appears AFAICT to not be
> > big endian safe.  I was planning to test this patch on some powerpc/ppc
> > hardware with v2.6.36-rc4 in the next days, but it looks like
> > lio-core-2.6.git will need a seperate crypto/crc32c.c patch to function
> > properly on big endian arches.
> >
> 
> There was this bug that was fixed a couple years ago:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=ef19454bd437b2ba14c9cda1de85debd9f383484
> since then I think we have not had problems.

Hi Mike,

Thanks for the pointer on this, I will give it a shot on powerpc and see
what happens.

FYI, I was under the assumption that for BIG_ENDIAN that crc32c() still
needed an bitshift for the returned value.  This is what we had been
doing with our old internal do_crc() code here:

http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=blob;f=drivers/target/lio-target/iscsi_crc.c;hb=83559072b27eb8cd92abb9a3fc9be85018c5db06#l138

AFAICT there is still nothing that makes crypto/crc32c.c big endian
safe, unless I am overlooking something obvious..?

Best,

--nab


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