From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44113) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wkpj3-0002C6-WB for qemu-devel@nongnu.org; Thu, 15 May 2014 03:05:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Wkpiu-0005FO-LI for qemu-devel@nongnu.org; Thu, 15 May 2014 03:05:09 -0400 Received: from e06smtp13.uk.ibm.com ([195.75.94.109]:46818) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wkpiu-0005F7-CW for qemu-devel@nongnu.org; Thu, 15 May 2014 03:05:00 -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, 15 May 2014 08:04:58 +0100 Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 0550B17D805F for ; Thu, 15 May 2014 08:06:04 +0100 (BST) Received: from d06av11.portsmouth.uk.ibm.com (d06av11.portsmouth.uk.ibm.com [9.149.37.252]) by b06cxnps4074.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s4F74sO862914566 for ; Thu, 15 May 2014 07:04:54 GMT Received: from d06av11.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av11.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s4F74seJ009242 for ; Thu, 15 May 2014 01:04:54 -0600 Date: Thu, 15 May 2014 09:04:49 +0200 From: Greg Kurz Message-ID: <20140515090449.2db0cbe0@bahia.local> In-Reply-To: <20140515064635.GB31192@grmbl.mre> References: <20140514154130.10746.1412.stgit@bahia.local> <20140514154137.10746.94708.stgit@bahia.local> <20140515060425.GA31192@grmbl.mre> <20140515062351.GB14456@redhat.com> <20140515064635.GB31192@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 , Stefan Hajnoczi , Juan Quintela , "Michael S. Tsirkin" , Alexander Graf , qemu-devel@nongnu.org, Anthony Liguori , Paolo Bonzini , Andreas =?UTF-8?B?RsOkcmJlcg==?= On Thu, 15 May 2014 12:16:35 +0530 Amit Shah wrote: > On (Thu) 15 May 2014 [09:23:51], Michael S. Tsirkin wrote: > > On Thu, May 15, 2014 at 11:34:25AM +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. > > BTW Greg, do you plan on working on vmstate for virtio? > Yes. > > > > 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. > > > > > > > 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. > > > > This calls for a way for devices to inherit properties from the bus, > > which doesn't exist ATM. > > Fine but let's not hold up this patchset because of this. > > No, only suggestion is to add a migration section in the bus, and then > it's easier to do this in the post-migrate functions for each device > -- so only one new section gets introduced instead of all devices > being modified to send a new subsection. > The main problem I see is that virtio sucks: as you see in patch 8, we have to be careful not to call vring or virtqueue stuff before the device knows its endianness or it breaks... I need to study how the virtio-bus gets migrated to ensure the endian section is streamed before the devices. > 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.