From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53093) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YsqWr-0007ks-77 for qemu-devel@nongnu.org; Thu, 14 May 2015 06:38:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YsqWn-0001f4-PS for qemu-devel@nongnu.org; Thu, 14 May 2015 06:38:13 -0400 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:42619) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YsqWn-0001e6-G4 for qemu-devel@nongnu.org; Thu, 14 May 2015 06:38:09 -0400 Received: from /spool/local by e06smtp13.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 14 May 2015 11:38:08 +0100 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id A573617D805A for ; Thu, 14 May 2015 11:38:54 +0100 (BST) Received: from d06av03.portsmouth.uk.ibm.com (d06av03.portsmouth.uk.ibm.com [9.149.37.213]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t4EAc5EL48103500 for ; Thu, 14 May 2015 10:38:05 GMT Received: from d06av03.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av03.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t4EAc4vp007804 for ; Thu, 14 May 2015 04:38:05 -0600 Message-ID: <55547B0B.2090806@de.ibm.com> Date: Thu, 14 May 2015 12:38:03 +0200 From: Christian Borntraeger MIME-Version: 1.0 References: <1431528122-50960-1-git-send-email-cornelia.huck@de.ibm.com> <1431528122-50960-2-git-send-email-cornelia.huck@de.ibm.com> <20150513165438-mutt-send-email-mst@redhat.com> <20150513170335.2d662124.cornelia.huck@de.ibm.com> <20150513180005-mutt-send-email-mst@redhat.com> <55545BAF.4040701@redhat.com> <20150514095651.GA12939@redhat.com> <55547315.9050209@redhat.com> <20150514120542-mutt-send-email-mst@redhat.com> <5554745D.2080808@redhat.com> In-Reply-To: <5554745D.2080808@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , "Michael S. Tsirkin" Cc: Cornelia Huck , qemu-devel@nongnu.org, jjherne@linux.vnet.ibm.com Am 14.05.2015 um 12:09 schrieb Paolo Bonzini: > > > On 14/05/2015 12:07, Michael S. Tsirkin wrote: >>> If you really want that, the hook should be in the virtio device class. >>> Keying on the machine type is almost never the answer, at least upstream. >>> Distros can always override it if they know what they're getting into. >> >> I beg to disagree. Check out PC_COMPAT_ macros. > > I'm talking specifically about migration subsections. None of them are > keyed on the machine type downstream, as far as I know. > >> But if you are saying >> migration with virtio-ccw is just too broken ATM, so we shouldn't care >> about its migration compatibility upstream, then I can buy that. > > Yes, I'm also saying that (and Christian must agree or they would not > have posted this patch). So some background: Migration works most of the time but it will fail if config changes happen (like virtio-balloon). When trying to fix this Jason came up with a patch that added qemu_put_be16(f, vdev->config_vector) in the virtio_ccw save_config. As this does not use vmstates and versions we were not sure about how to ensure compatibility. So Conny came up with this proposal to detect and reject migration from an old (broken) version. Christian