From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40162) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFenl-0001CE-Au for qemu-devel@nongnu.org; Wed, 22 Jun 2016 05:50:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bFenf-00063N-AA for qemu-devel@nongnu.org; Wed, 22 Jun 2016 05:50:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55474) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFenf-00063J-3x for qemu-devel@nongnu.org; Wed, 22 Jun 2016 05:50:23 -0400 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 782997EBBE for ; Wed, 22 Jun 2016 09:50:22 +0000 (UTC) Date: Wed, 22 Jun 2016 10:50:18 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20160622095018.GA2274@work-vm> References: <1466536447-30146-1-git-send-email-dgilbert@redhat.com> <1466578399.16954.22.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1466578399.16954.22.camel@redhat.com> Subject: Re: [Qemu-devel] [PATCH 00/13] virtio migration: Flip outer layer to vmstate List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gerd Hoffmann Cc: qemu-devel@nongnu.org, mst@redhat.com, amit.shah@redhat.com, quintela@redhat.com * Gerd Hoffmann (kraxel@redhat.com) wrote: > Hi, > > > I think the first two patches are the most controversial; > > they remove migration support for old version of virtio-net and virtio-serial; > > (for virtio-net versions prior to 0.11 and for virtio-serial prior to 0.13). > > I'm working on the basis that migration has bit rotted enough so > > that the streams aren't migration compatible for that long back > > on upstream - but if anyone knows otherwise please shout. > > We've gone great lengths to avoid new versions by using subsections > instead for *years*. So if we are going to cut live migration support > from ancient versions now: Can we possibly remove the versioning > altogether? Short answer: no Longer answer: I'm saying we can remove some compatibility from very old versions, especially if we probably lost the compatibility anyway, but we should stick to trying to maintain compatibility where possible. I've just tested an upstream 0.12.5 migration and it doesn't work; /opt/qemu-0.12/bin/qemu-system-x86_64 -cpu core2duo -M pc-0.12 --enable-kvm -m 1G /home/vms/f20-raw.raw -nographic migrating to: 1.1.2, 1.2.2, 2.5.1 all fail with: qemu: warning: error while loading state for instance 0x0 of device 'ram' and I've not dug into why. (Migration to 1.0.1 hangs instead). Given that, there doesn't seem to be any point in trying to maintain compatibility for loading a stream produced by 0.11 for example. As you know, we do jump through hoops downstream to have one very specific 0.12 derivative migrate to our current releases, and yes this patch set means I'm going to have to do a bit more work to make that keep happening in one corner of it. Although if I'm lucky by then if I can get the rest of this code to be using VMState then it'll be much easier to do the 0.12 compatibility code. Dave > cheers, > Gerd > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK