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

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

On Mon, 2010-09-13 at 11:21 +0200, Hannes Reinecke wrote:
> Nicholas A. Bellinger wrote:
> > From: Nicholas Bellinger <nab@linux-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.

Indeed, this has historically been the case for LIO-Target and
Core-iSCSI.  I noticed the issue with libcrypto while porting the latter
on a old G4 TI-book waaay back during v2.6.10-rc3 days.

> 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.

Thanks for mentioning this point Hannes!

--nab