From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NDIVr-0004V0-Q5 for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:06:31 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NDIVo-0004Rr-0x for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:06:31 -0500 Received: from [199.232.76.173] (port=58901 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NDIVn-0004Re-NE for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:06:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:29199) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NDIVn-0008Ol-Hp for qemu-devel@nongnu.org; Wed, 25 Nov 2009 09:06:27 -0500 Received: from int-mx03.intmail.prod.int.phx2.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id nAPE6QZh017348 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 25 Nov 2009 09:06:26 -0500 Date: Wed, 25 Nov 2009 16:03:47 +0200 From: "Michael S. Tsirkin" Subject: Re: [Qemu-devel] Re: Live migration protocol, device features, ABIs and other beasts Message-ID: <20091125140347.GA10539@redhat.com> References: <4B0952C9.9010803@redhat.com> <4B0A899F.2090805@codemonkey.ws> <20091124140517.GL2405@redhat.com> <4B0D32F1.3010008@redhat.com> <20091125134021.GC9333@redhat.com> <4B0D385E.4000102@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B0D385E.4000102@redhat.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: dlaor@redhat.com, qemu-devel , Juan Quintela On Wed, Nov 25, 2009 at 02:59:58PM +0100, Gerd Hoffmann wrote: > On 11/25/09 14:40, Michael S. Tsirkin wrote: > >>> We could add a DeviceState->savevm field and make that available as >>> property for devices which need to support multiple versions. Then you >>> we can use the compat properties to switch back to the older format with >>> -M pc-0.10. > >> I'm confused sorry. Of course when you want to migrate to qemu 0.10 >> you must have a compatible machine. And savevm format has nothing >> to do with it IMO, so MSI is orthogonal to this discussion. >> It just shows that it was smart not to save MSI state when >> MSI is not present (/me pats self on the back). >> >> In this thread we were discussing changes like pvclock bug, >> where we change savevm format without changing the machine, >> or almost without changing the machine. > > If 0.12 has this fixed (and thus a new version) and 0.11 hasn't, then > you'll want -M pc-0.11 use the old (buggy) savevm version. You have to > stay bug compatible otherwise you can't migrate to the old buggy version > because the old qemu can't handle the new format. > > Could be implemented via DeviceState->savevm as outlined above. > > cheers, > Gerd There might be many reasons to use -M pc-0.11. Migrating to old qemu is only one of them. We should not force old savevm bugs on all users that use -M pc-0.11. In partucular, I think with time (years) we might drop support for old savevm bugs, but I see no reason not to support old machines indefinitely. -- MST