From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1NbvSF-0000dH-CY
	for qemu-devel@nongnu.org; Mon, 01 Feb 2010 07:32:35 -0500
Received: from [199.232.76.173] (port=40734 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1NbvSE-0000d3-VU
	for qemu-devel@nongnu.org; Mon, 01 Feb 2010 07:32:35 -0500
Received: from Debian-exim by monty-python.gnu.org with spam-scanned (Exim
	4.60) (envelope-from <jamie@shareable.org>) id 1NbvSD-00041D-OG
	for qemu-devel@nongnu.org; Mon, 01 Feb 2010 07:32:34 -0500
Received: from mail2.shareable.org ([80.68.89.115]:49931)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <jamie@shareable.org>) id 1NbvSD-000415-FJ
	for qemu-devel@nongnu.org; Mon, 01 Feb 2010 07:32:33 -0500
Date: Mon, 1 Feb 2010 12:32:25 +0000
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Re: [PATCH] block: Enable fall-back to read-only for
	backing file
Message-ID: <20100201123225.GF20940@shareable.org>
References: <4B65B4B7.2030700@redhat.com> <4B6694C8.4010703@redhat.com>
	<20100201090649.GA20918@lst.de>
	<BBC20A29-FD6E-45EE-89C3-D3524F0CE1FB@suse.de>
	<20100201092756.GA21616@lst.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20100201092756.GA21616@lst.de>
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: Christoph Hellwig <hch@lst.de>
Cc: Kevin Wolf <kwolf@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Naphtali Sprei <nsprei@redhat.com>, Alexander Graf <agraf@suse.de>, Sheng Yang <sheng@linux.intel.com>

Christoph Hellwig wrote:
> On Mon, Feb 01, 2010 at 10:25:52AM +0100, Alexander Graf wrote:
> > We don't know beforehand if a user will use the commit comnand during  
> > tje runtime of the vm.
> > 
> > IMHO it'd be best to always open backing files read only and try to  
> > open them for write access on the commit command. That command can  
> > then fail gaciously.
> 
> That's another option.  Basically this means opening another
> BlockDriverState for the backing device that is writeable inside
> bdrv_commit().

I'd prefer that.  I like having higher confidence that random bugs in
Qemu are unlikely to accidentally modify precious backing files,
except when I've issued an explicit commit command.

-- Jamie