From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:54505)
	by lists.gnu.org with esmtp (Exim 4.71) (envelope-from <hch@lst.de>)
	id 1R4ajI-0000lx-NW
	for qemu-devel@nongnu.org; Fri, 16 Sep 2011 11:53:29 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <hch@lst.de>) id 1R4ajC-0000ZE-Fp
	for qemu-devel@nongnu.org; Fri, 16 Sep 2011 11:53:28 -0400
Received: from verein.lst.de ([213.95.11.211]:38412 helo=newverein.lst.de)
	by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from <hch@lst.de>)
	id 1R4ajC-0000YT-8h
	for qemu-devel@nongnu.org; Fri, 16 Sep 2011 11:53:22 -0400
Date: Fri, 16 Sep 2011 17:53:20 +0200
From: Christoph Hellwig <hch@lst.de>
Message-ID: <20110916155320.GA28201@lst.de>
References: <1315628610-28222-1-git-send-email-ronniesahlberg@gmail.com>
	<1315628610-28222-2-git-send-email-ronniesahlberg@gmail.com>
	<20110912091408.GA3465@stefanha-thinkpad.localdomain>
	<20110914143608.GB12218@lst.de>
	<CAJSP0QW-o7fFF25YPY17EXqu_tJcD052aFvSnFKNi6eQsi0dZA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAJSP0QW-o7fFF25YPY17EXqu_tJcD052aFvSnFKNi6eQsi0dZA@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH] This patch adds a new block driver : iSCSI
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/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: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: kwolf@redhat.com, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, qemu-devel@nongnu.org, fujita.tomonori@lab.ntt.co.jp, Ronnie Sahlberg <ronniesahlberg@gmail.com>, Christoph Hellwig <hch@lst.de>

On Wed, Sep 14, 2011 at 04:50:25PM +0100, Stefan Hajnoczi wrote:
> I think in this case it will not make the code nicer.  Since the
> external iSCSI library is based on callbacks it would be necessary to
> write the coroutines<->callbacks adapter functions.  So for example,
> the READ10 command would need a function that can be called in
> coroutine context and yields while libiscsi does the I/O.  When the
> callback is invoked it will re-enter the coroutine.
> 
> The area where coroutines are useful in the block layer is for image
> formats.  We already have common coroutines<->callback adapter
> functions in block.c so it's possible to write sequential code for
> image formats.  They only need access to block layer functions which
> have already been adapted.  But as soon as you interact with a
> callback-based API from the coroutine, then you need to write an
> adapter yourself.

So you plan on keeping the aio interface around forever?  Qemu with two
different I/O pathes was already more than painful enough, I don't
think keeping three, and two of them beeing fairly complex is a good
idea.