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Date: Thu, 25 Nov 2010 10:06:44 +0100
From: Hannes Reinecke <hare@suse.de>
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Subject: Re: [Qemu-devel] Re: [PATCH] scsi-generic: bugfixes for 'SCSIRequest'
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To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, "Nicholas A. Bellinger" <nab@linux-iscsi.org>, Gerd Hoffmann <kraxel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, linux-iscsi-target-dev@googlegroups.com

On 11/25/2010 10:01 AM, Benjamin Herrenschmidt wrote:
> On Thu, 2010-11-25 at 09:50 +0100, Gerd Hoffmann wrote:
>> On 11/25/10 09:46, Benjamin Herrenschmidt wrote:
>>
>>> So far tho, it appears that I can (at least with scsi-disk) rely on
>>> always been eventually called with SCSI_REASON_DONE so my code (and
>>> maybe the usb-msd code too, I haven't verified) relies on that to
>>> complete requests... Is that incorrect ?
>>
>> Yes.
>=20
> Well, so far it works :-) But I suppose I must be lucky.. I must admit
> that it's very unclear how that SCSI "stack" is meant to be used from
> the HBA standpoint.
>=20
> Right now, I've somewhat come up with:
>=20
>   - client request occurs
>   - call device send_command()
>   - if result is 0, assume my complete() was called with=20
>     SCSI_REASON_DONE
>   - else, use sign of result for transfer direction, store the
>     absolute value as the total expected transfer len and call
>     the device scsi_data_read()/write() and wait for complete()
>   - when complete() is called:
>     - if SCSI_REASON_DONE, complete client request
>     - else perform the client "DMA" for "arg" bytes
>     - call the device scsi_data_read()/write() again
>=20
No, this is exactly as I'm expecting the SCSI layer to work.
So from the light of this the patch to scsi-generic is valid.
And it really looks like papering over a bug in the lsi HBA code.

Gerd?

Cheers,

Hannes
--=20
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=C3=BCrnberg
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