From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=42797 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PmYkF-0006Ph-4D for qemu-devel@nongnu.org; Mon, 07 Feb 2011 16:35:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PmYkC-00035q-IH for qemu-devel@nongnu.org; Mon, 07 Feb 2011 16:35:37 -0500 Received: from mail-wy0-f173.google.com ([74.125.82.173]:64487) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PmYkC-00035k-5U for qemu-devel@nongnu.org; Mon, 07 Feb 2011 16:35:36 -0500 Received: by wyg36 with SMTP id 36so5275765wyg.4 for ; Mon, 07 Feb 2011 13:35:35 -0800 (PST) Message-ID: <4D505C92.5040904@codemonkey.ws> Date: Mon, 07 Feb 2011 14:56:50 -0600 From: Anthony Liguori MIME-Version: 1.0 References: <20110207160751.GC25106@redhat.com> <4D504925.3000807@codemonkey.ws> <20110207195315.GA28096@redhat.com> In-Reply-To: <20110207195315.GA28096@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: new->old version migration List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Amit Shah , Alex Williamson , qemu list , Juan Quintela On 02/07/2011 01:53 PM, Michael S. Tsirkin wrote: > On Mon, Feb 07, 2011 at 01:33:57PM -0600, Anthony Liguori wrote: > >> On 02/07/2011 10:07 AM, Michael S. Tsirkin wrote: >> >>> New thread stated intentionally, the original patch is Message-ID: >>> <349e93a4cfc6e1effc1b681cae53f805fdb9624e.1296713825.git.amit.shah@redhat.com> >>> >>> On Thu, Feb 03, 2011 at 11:47:08AM +0530, Amit Shah wrote: >>> >>>> Add a compat property for older machine types. When this is used (via >>>> -M pc-0.13, for example), the new flow control mechanisms will not be >>>> used. This is done to keep migration from a machine started with older >>>> type on a pc-0.14+ qemu to an older machine working. >>>> >>>> The property is named 'flow_control' and defaults to on. >>>> >>>> Reported-by: Alex Williamson >>>> Signed-off-by: Amit Shah >>>> >>> So, I think there are two things that need to be agreed on: >>> >>> - Can we commit to support migration from new qemu version to an old one? >>> We haven't in the past but downstreams do want this, >>> so it makes sense to have the infrastructure upstream. >>> >> Only within a stable release series and only when it's possible >> without sacrificing integrity. I know some downstreams disagree >> with this but I don't think this is a business we want to get into. >> >> Regards, >> >> Anthony Liguori >> >>> - The infrastructure/command line option for such support. >>> We have the -M flags to describe the machine that >>> we are running, but that abstracts away guest-visible machine, >>> which the migration format is not. >>> Also, same qemu could migrate to any older version. >>> So I think we would have to add a flag (call it -V for now) >>> to savevm/migrate commands to specify the format to be used. >>> Naturally some machines would be incompatible with >>> specific -V values, that's nothing new. >>> >>> Pls comment. >>> > OK, assuming we want this, let's talk about implementation. > I think that spreading custom flags all over the code like > this patch does would be pretty bad. > > What I'd like to see is a way to > - map stable versions (e.g. machine type if we are going > to tie to that) to savevm format using > some kind of table > - for save callbacks to be able to figure out what > version to use > Why doesn't subsections already solve this problem? Regards, Anthony Liguori