From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:60288)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1ZRw8O-0001rH-Ae
	for qemu-devel@nongnu.org; Wed, 19 Aug 2015 01:42:00 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <paolo.bonzini@gmail.com>) id 1ZRw8N-00012K-LK
	for qemu-devel@nongnu.org; Wed, 19 Aug 2015 01:42:00 -0400
Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
References: <55D3EFF4.7030004@cn.fujitsu.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <55D41714.6030903@redhat.com>
Date: Tue, 18 Aug 2015 22:41:40 -0700
MIME-Version: 1.0
In-Reply-To: <55D3EFF4.7030004@cn.fujitsu.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] Block: don't do copy-on-read in
	before_write_notifier
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: Wen Congyang <wency@cn.fujitsu.com>, qemu-devl <qemu-devel@nongnu.org>, qemu block <qemu-block@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>, Jeff Cody <jcody@redhat.com>, Kevin Wolf <kwolf@redhat.com>

On 18/08/2015 19:54, Wen Congyang wrote:
> We will copy data in before_write_notifier to do backup.
> It is a nested I/O request, so we cannot do copy-on-read.

Can you explain why?  What is the bug that this is fixing?

Paolo

> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>