From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:60158) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QeVfY-0006jA-Mx for qemu-devel@nongnu.org; Wed, 06 Jul 2011 13:13:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QeVfX-0006Pk-6E for qemu-devel@nongnu.org; Wed, 06 Jul 2011 13:13:48 -0400 Received: from mail-pw0-f45.google.com ([209.85.160.45]:44312) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QeVfW-0006Pe-LU for qemu-devel@nongnu.org; Wed, 06 Jul 2011 13:13:46 -0400 Received: by pwi5 with SMTP id 5so39449pwi.4 for ; Wed, 06 Jul 2011 10:13:45 -0700 (PDT) Message-ID: <4E1497C6.4060505@codemonkey.ws> Date: Wed, 06 Jul 2011 12:13:42 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <4E148776.4000805@redhat.com> In-Reply-To: <4E148776.4000805@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] migration: new sections and backward compatibility. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: jes sorensen , Juan Quintela , "qemu-devel@nongnu.org" , Markus Armbruster On 07/06/2011 11:04 AM, Gerd Hoffmann wrote: > Hi folks, > > We'll need to figure a sane way to handle migration to older versions > with new sections, i.e. devices which used to not save state before do now. > > We already have one case in tree: usb. qemu 0.14 saves state for usb-hid > devices and the usb-hub, whereas qemu 0.13 and older don't. You can't > migrate a vm with a usb-tablet from 0.14 to 0.13 because of that even if > you use -M pc-0.13. Because if you did migrate, you would actively break the guest during migration. So why is this a problem? This comes up a lot. We shouldn't enable migration if we know the guest is going to break during migration. That's a feature, not a bug. Regards, Anthony Liguori