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

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Message-ID: <4C8DED17.6080801@suse.de>
Date:	Mon, 13 Sep 2010 11:21:27 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	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>,
	Mike Christie <michaelc@...wisc.edu>,
	James Bottomley <James.Bottomley@...e.de>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Richard Sharpe <realrichardsharpe@...il.com>,
	Mike Christie <michaelc@...wisc.edu>,
	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

Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@...ux-iscsi.org>
> 
> Greetings all,
> 
> This patch series converts the LIO-Target fabric module from using a legacy
> internal slicing by 1x CRC32C algorithm to the slicing by 1x CRC32C available in
> crc32c.ko, as well as initial support for the Nehalem series crc32c-intel.ko
> instruction offload available since v2.6.27 in late 2008.
> 
> So far this series has been lightly tested with a handful of Open-iSCSI client VMs
> with the optimized crc32c-intel.ko offload case, and there appears to be some
> HeaderDigest failures for one case with RHEL6 B2 x86_64, while Ubuntu i686 on
> v2.6.27 and OpenSuse 11.2 x86_64 on v2.6.31 work as expected with HeaderDigest=CRC32C
> and DataDigest=CRC32C using the offload on the LIO-Target side.
> 
> Currently this patch disables the new iSCSI TPG attribute crc32c_x86_offload
> to force the crc32c.ko slicing by x1 CRC32C algorithm until these compatibility
> issues with existing libcrc32c clients can be properly resolved with the Nehalem
> CRC32C offload instructions running on the LIO-Target side.
> 
Due to a customer issue I had to revisit the CRC32 issue recently.
And according to you the main reason for using your own CRC routines
had been endianness issues.
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?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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