From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=56002 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1PLXiE-0006OO-I3
	for qemu-devel@nongnu.org; Thu, 25 Nov 2010 04:01:58 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <benh@kernel.crashing.org>) id 1PLXiD-0004pC-8h
	for qemu-devel@nongnu.org; Thu, 25 Nov 2010 04:01:54 -0500
Received: from gate.crashing.org ([63.228.1.57]:50015)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <benh@kernel.crashing.org>) id 1PLXiC-0004p7-Nu
	for qemu-devel@nongnu.org; Thu, 25 Nov 2010 04:01:53 -0500
Subject: Re: [Qemu-devel] Re: [PATCH] scsi-generic: bugfixes for
	'SCSIRequest' conversion
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
In-Reply-To: <4CEE2343.3090505@redhat.com>
References: <1290586723-8724-1-git-send-email-nab@linux-iscsi.org>
	<4CECD36E.50401@suse.de> <4CECD50F.9060501@redhat.com>
	<4CECE609.7080600@suse.de> <4CECEA2A.40008@redhat.com>
	<4CECED12.5020109@suse.de> <1290674774.32570.106.camel@pasglop>
	<4CEE2343.3090505@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Date: Thu, 25 Nov 2010 20:01:44 +1100
Message-ID: <1290675704.32570.114.camel@pasglop>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, "Nicholas A. Bellinger" <nab@linux-iscsi.org>, Hannes Reinecke <hare@suse.de>, Paolo Bonzini <pbonzini@redhat.com>, linux-iscsi-target-dev@googlegroups.com

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.

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.

Right now, I've somewhat come up with:

  - client request occurs
  - call device send_command()
  - if result is 0, assume my complete() was called with 
    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

So far it seems to work with scsi-disk but maybe I miss something in
which case I would very much enjoy being corrected :-)

Cheers,
Ben.