From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39537) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WkpUU-0008Ca-L7 for qemu-devel@nongnu.org; Thu, 15 May 2014 02:50:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WkpUL-0008SF-BQ for qemu-devel@nongnu.org; Thu, 15 May 2014 02:50:06 -0400 Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:58822) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WkpUL-0008S0-2V for qemu-devel@nongnu.org; Thu, 15 May 2014 02:49:57 -0400 Received: from /spool/local by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 15 May 2014 07:49:55 +0100 Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 931221B08070 for ; Thu, 15 May 2014 07:50:08 +0100 (BST) Received: from d06av05.portsmouth.uk.ibm.com (d06av05.portsmouth.uk.ibm.com [9.149.37.229]) by b06cxnps3075.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s4F6nrQ31311040 for ; Thu, 15 May 2014 06:49:53 GMT Received: from d06av05.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av05.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s4F6nrwq000407 for ; Thu, 15 May 2014 00:49:53 -0600 Date: Thu, 15 May 2014 08:49:48 +0200 From: Greg Kurz Message-ID: <20140515084948.47870ce2@bahia.local> In-Reply-To: <20140515060425.GA31192@grmbl.mre> References: <20140514154130.10746.1412.stgit@bahia.local> <20140514154137.10746.94708.stgit@bahia.local> <20140515060425.GA31192@grmbl.mre> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH RFC 1/8] virtio: add subsections to the migration stream List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Amit Shah Cc: Kevin Wolf , Fam Zheng , Anthony Liguori , "Michael S. Tsirkin" , Juan Quintela , Alexander Graf , qemu-devel@nongnu.org, Stefan Hajnoczi , Paolo Bonzini , Andreas =?UTF-8?B?RsOkcmJlcg==?= On Thu, 15 May 2014 11:34:25 +0530 Amit Shah wrote: > On (Wed) 14 May 2014 [17:41:38], Greg Kurz wrote: > > There is a need to add some more fields to VirtIODevice that should be > > migrated (broken status, endianness). The problem is that we do not > > want to break compatibility while adding a new feature... This issue has > > been addressed in the generic VMState code with the use of optional > > subsections. As a *temporary* alternative to port the whole virtio > > migration code to VMState, this patch mimics a similar subsectionning > > ability for virtio. > > > > Since each virtio device is streamed in its own section, the idea is to > > stream subsections between the end of the device section and the start > > of the next sections. This allows an older QEMU to complain and exit > > when fed with subsections: > > > > Unknown savevm section type 5 > > Error -22 while loading VM state > > Please make this configurable -- either via configure or device > properties. That avoids having to break existing configurations that > work without this patch. > Hmmm... you mean we support migration from a newer QEMU to an older one ? > > All users of virtio_load()/virtio_save() need to be patched because the > > subsections are streamed AFTER the device itself. > > Since all have the same fixup, I'm wondering if a new section can be > added to the virtio-bus itself, which gets propagated to all devices > upon load in the dest. > That would be nice if possible. I will have a closer look. > Amit > Thanks. -- Gregory Kurz kurzgreg@fr.ibm.com gkurz@linux.vnet.ibm.com Software Engineer @ IBM/Meiosys http://www.ibm.com Tel +33 (0)562 165 496 "Anarchy is about taking complete responsibility for yourself." Alan Moore.