From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39306) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZAEl0-0006mo-6B for qemu-devel@nongnu.org; Wed, 01 Jul 2015 05:56:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZAEkv-0003OY-Rz for qemu-devel@nongnu.org; Wed, 01 Jul 2015 05:56:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55645) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZAEkv-0003OC-NW for qemu-devel@nongnu.org; Wed, 01 Jul 2015 05:56:37 -0400 From: Juan Quintela In-Reply-To: <1435742217-62246-1-git-send-email-borntraeger@de.ibm.com> (Christian Borntraeger's message of "Wed, 1 Jul 2015 11:16:57 +0200") References: <1435742217-62246-1-git-send-email-borntraeger@de.ibm.com> Date: Wed, 01 Jul 2015 11:56:34 +0200 Message-ID: <87egks19rh.fsf@neno.neno> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH 1/1] s390x/migration: Introduce 2.4 machine Reply-To: quintela@redhat.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger Cc: Alexander Graf , qemu-devel , "Dr. David Alan Gilbert" , Jens Freimann , "Jason J. Herne" , Boris Fiuczynski , Cornelia Huck Christian Borntraeger wrote: First of all Reviewed-by: Juan Quintela For the patch. But one said that, I don't agree with the commint text. > The section footer changes commit f68945d42bab ("Add a protective > section footer") and commit 37fb569c0198 ("Disable section footers > on older machine types") broke migration for any non-versioned > machines. If broke migration for 2.4 -> 2.3 for machines that don't care about compatibility. If they care, they are versioned O:-) Right now ppc & x86. I guess that s390 and arm will follow in due curse. > While one can argue that section footer should be enabled > explicitely for new versions instead of disabled for old ones, > this pinpoints to a problem of s390-ccw-machines: it needs to > be versioned to be compatible with future changes in common > code data structures such as section footers. It is done explicitely the other way around. New way is the default way. If we did it in a special way in the past, we add a switch. If at some point we remove the old machine type for any reason, we don't have to change anything on $latest. Basically the idea here is that (until now) only x86 cared about backwards compatibility, so when a migration changed happened because it was good for any reason, normal devices do changes, and then x86 try to fix the pieces after the fact. That is going to continue, just that now more architectures care, and then we should detect this kind of problems much earlier. > Let's introduce a version scheme for s390-ccw-virtio machines. > We will use the old s390-ccw-virtio name as alias to the latest > version as all existing libvirt XML for the ccw type were expanded > by libvirt to that name. > > The only downside of this patch is, that the old alias s390-ccw > will no longer be available as machines can have only one alias, > but it should not really matter. Should we change to a list? Later, Juan.