From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:58010)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UcXLO-0005Px-Pa
	for qemu-devel@nongnu.org; Wed, 15 May 2013 04:45:56 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UcXLN-0003v6-EC
	for qemu-devel@nongnu.org; Wed, 15 May 2013 04:45:54 -0400
Received: from mail-wi0-x234.google.com ([2a00:1450:400c:c05::234]:41408)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1UcXLN-0003v1-4s
	for qemu-devel@nongnu.org; Wed, 15 May 2013 04:45:53 -0400
Received: by mail-wi0-f180.google.com with SMTP id hn14so1363327wib.13
	for <qemu-devel@nongnu.org>; Wed, 15 May 2013 01:45:52 -0700 (PDT)
Date: Wed, 15 May 2013 10:45:48 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130515084548.GA23423@stefanha-thinkpad.muc.redhat.com>
References: <20130512135934.14853.36568.malonedeb@soybean.canonical.com>
	<20130512211424.14822.35652.malone@gac.canonical.com>
	<51902923.9030305@interlinx.bc.ca>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <51902923.9030305@interlinx.bc.ca>
Subject: Re: [Qemu-devel] [Bug 1179219] Re: segfault in alloc_refcount_block
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: Bug 1179219 <1179219@bugs.launchpad.net>
Cc: qemu-devel@nongnu.org

On Sun, May 12, 2013 at 11:43:31PM -0000, Brian J. Murrell wrote:
> On 13-05-12 05:14 PM, Michael Tokarev wrote:
> > First, having a single qcow2 file open for read-write access by more
> > than one process in unsupported.
> 
> But I don't, if I understand how qcow2 snapshots work.  Let me apologize
> if I was not clear.  Each of the VMs have their own snapshot of the
> common "origin" qcow2 disk.  If I understand correctly in such a
> configuration, only one VM has each snapshot qcow2 open for read-write
> access and they all have the "origin" open read-only, is that correct?
> Surely that must be supported, yes?

$ qemu-img create -f qcow2 -b template.img vm001.qcow2
$ qemu-img create -f qcow2 -b template.img vm002.qcow2
$ qemu-img create -f qcow2 -b template.img vm003.qcow2
$ ...launch vm001-vm002...

This is safe.  The template.img backing file is open read-only.

Did you do anything else?

Stefan