From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1NDIZm-0006ux-Ad
	for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:10:34 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1NDIZg-0006qL-TJ
	for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:10:33 -0500
Received: from [199.232.76.173] (port=42165 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1NDIZg-0006qD-O4
	for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:10:28 -0500
Received: from mx1.redhat.com ([209.132.183.28]:1762)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <kraxel@redhat.com>) id 1NDIZg-0000OY-My
	for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:10:28 -0500
Received: from int-mx04.intmail.prod.int.phx2.redhat.com
	(int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.17])
	by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id nAPEAR1G019061
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK)
	for <qemu-devel@nongnu.org>; Wed, 25 Nov 2009 09:10:27 -0500
Message-ID: <4B0D3AC8.20704@redhat.com>
Date: Wed, 25 Nov 2009 15:10:16 +0100
From: Gerd Hoffmann <kraxel@redhat.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: Live migration protocol, device features,	ABIs
	and other beasts
References: <4B0952C9.9010803@redhat.com> <m3my2d4euy.fsf@neno.neno>
	<4B0A899F.2090805@codemonkey.ws> <m3my2dwcpk.fsf@neno.neno>
	<20091124140517.GL2405@redhat.com> <m3vdh0t35s.fsf@neno.neno>
	<20091124143523.GQ2405@redhat.com> <4B0D3441.8010307@redhat.com>
	<20091125134220.GD9333@redhat.com>
In-Reply-To: <20091125134220.GD9333@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
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: "Michael S. Tsirkin" <mst@redhat.com>
Cc: dlaor@redhat.com, qemu-devel <qemu-devel@nongnu.org>, Juan Quintela <quintela@redhat.com>

   Hi,

>> Doesn't work.  If you have a qemu 0.11 machine, a virtio nic and your
>> guest uses MSI-X you simply can't migrate to qemu 0.10.  End of story.
>> If you want to be able to migrate to 0.10 you have to start in 0.10
>> compat mode with MSI-X disabled.  So IMHO it does makes sense to tie the
>> savevm format to -M pc-<version>.
>>
>> cheers,
>>    Gerd
>
> MSI-X is an orthogonal issue, let's not mix it in.

It isn't.  I was making that point with feature=MSI-X.  The same 
argument is true for any other feature:  If $feature is new in qemu 
$newversion and you are using it you can't migrate to qemu $oldversion 
which hasn't $feature.  The versioned machine types turn $feature in 
$newversion, so migration to $oldversion could work.

cheers,
   Gerd