From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1MJZ0l-00010x-8d
	for qemu-devel@nongnu.org; Wed, 24 Jun 2009 16:24:03 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1MJZ0g-0000nv-6v
	for qemu-devel@nongnu.org; Wed, 24 Jun 2009 16:24:02 -0400
Received: from [199.232.76.173] (port=44267 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1MJZ0g-0000ni-3C
	for qemu-devel@nongnu.org; Wed, 24 Jun 2009 16:23:58 -0400
Received: from mail2.shareable.org ([80.68.89.115]:46997)
	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 1MJZ0f-0003Cc-Nh
	for qemu-devel@nongnu.org; Wed, 24 Jun 2009 16:23:57 -0400
Date: Wed, 24 Jun 2009 21:23:53 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] Regression opening read-only cdroms
Message-ID: <20090624202353.GV14121@shareable.org>
References: <4A37896C.8050208@redhat.com>
	<20090616143259.GA29040@shareable.org>
	<20090618123759.GA7041@amd.home.annexia.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20090618123759.GA7041@amd.home.annexia.org>
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: "Richard W.M. Jones" <rjones@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, Avi Kivity <avi@redhat.com>, Christoph Hellwig <hch@lst.de>

Richard W.M. Jones wrote:
> On Tue, Jun 16, 2009 at 03:33:00PM +0100, Jamie Lokier wrote:
> > Avi Kivity wrote:
> > > qemu used to be quite happy opening read-only cdrom images, and I was 
> > > quite happy feeding kvm-autotest a library of read-only iso images.
> > 
> > 1. While we're here, an _option_ to open an image read-only even when
> >    you have write permission would be useful, for those occasions when
> >    you want to boot from some valuable image and be certain you aren't
> >    modifying it - without having to chmod back and forth in
> >    Qemu-wrapper scripts, or copy the image first.
> 
> FWIW we went round the houses on this one for libguestfs and settled
> on using '-drive ...,snapshot=on' instead.  The guest sees the drive
> as writable, and any writes are discarded when libguestfs/qemu quits.

It's fine for CD-ROMs of course.

For disks, there's that slight problem of running out of RAM or disk
space for the /tmp snapshot files.  Better not to write anything.

It'd be nice to enforce it, instead of depending on good behaviour
from the guest.

-- Jamie