From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Lzn7E-0008LS-El
	for qemu-devel@nongnu.org; Fri, 01 May 2009 03:25:00 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Lzn79-0008LF-NW
	for qemu-devel@nongnu.org; Fri, 01 May 2009 03:24:59 -0400
Received: from [199.232.76.173] (port=58524 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Lzn79-0008LC-Gl
	for qemu-devel@nongnu.org; Fri, 01 May 2009 03:24:55 -0400
Received: from mx20.gnu.org ([199.232.41.8]:48761)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <hch@lst.de>) id 1Lzn79-0006dp-4B
	for qemu-devel@nongnu.org; Fri, 01 May 2009 03:24:55 -0400
Received: from verein.lst.de ([213.95.11.210])
	by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from <hch@lst.de>)
	id 1Lzn78-0000bO-3W
	for qemu-devel@nongnu.org; Fri, 01 May 2009 03:24:54 -0400
Date: Fri, 1 May 2009 09:24:49 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support
Message-ID: <20090501072449.GA21867@lst.de>
References: <20090427082606.GA32604@lst.de>
	<200904291237.21558.paul@codesourcery.com>
	<20090430201350.GA30619@lst.de>
	<200904302249.20940.paul@codesourcery.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <200904302249.20940.paul@codesourcery.com>
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.gnu.org/pipermail/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: Paul Brook <paul@codesourcery.com>
Cc: kvm@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, Christian Borntraeger <borntraeger@de.ibm.com>, Hannes Reinecke <hare@suse.de>, Christoph Hellwig <hch@lst.de>

On Thu, Apr 30, 2009 at 10:49:19PM +0100, Paul Brook wrote:
> Only if you emulate a crufty old parallel scsi bus, and that's just silly.
> One of the nice things about scsi is it separates the command set from the 
> transport layer. cf. USB mass-storage, SAS, SBP2(firewire), and probably 
> several others I've forgotten.

It has nothing to do with an SPI bus.  Everything that resembles a SAM
architecture can have multiple LUs per targer, and multiple targers per
initiator port, so we need all the complex queing code, and we need
error handling and and and.  For some really simple ones like USB
mass-storage we might get away with some ad-hoc SCSI CDB generation
instead of real scsi stack, but I would recommend against it.