From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35594) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wkrq2-0002qJ-2g for qemu-devel@nongnu.org; Thu, 15 May 2014 05:20:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Wkrpu-0006cj-I0 for qemu-devel@nongnu.org; Thu, 15 May 2014 05:20:30 -0400 Received: from cantor2.suse.de ([195.135.220.15]:39406 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wkrpu-0006bj-9J for qemu-devel@nongnu.org; Thu, 15 May 2014 05:20:22 -0400 Message-ID: <537486D2.1060609@suse.de> Date: Thu, 15 May 2014 11:20:18 +0200 From: =?ISO-8859-1?Q?Andreas_F=E4rber?= MIME-Version: 1.0 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> <20140515090449.2db0cbe0@bahia.local> In-Reply-To: <20140515090449.2db0cbe0@bahia.local> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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: Greg Kurz , Amit Shah Cc: Kevin Wolf , Fam Zheng , Stefan Hajnoczi , Juan Quintela , "Michael S. Tsirkin" , Alexander Graf , qemu-devel@nongnu.org, Anthony Liguori , Paolo Bonzini Am 15.05.2014 09:04, schrieb Greg Kurz: > 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: >>>>> Since each virtio device is streamed in its own section, the idea i= s to >>>>> stream subsections between the end of the device section and the st= art >>>>> of the next sections. This allows an older QEMU to complain and exi= t >>>>> 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 tha= t >>>> work without this patch. Since backwards migration is not supported upstream, wouldn't it be easiest to just add support for the subsection marker and skipping to the end of section in that downstream? >>>>> All users of virtio_load()/virtio_save() need to be patched because= the >>>>> subsections are streamed AFTER the device itself. IMO this is calling for inversion of control - i.e. let virtio devices call generic load/save functions that then dispatch to device-specific code and let us add common stuff in a central place without forgetting to add calls in some new device. >>>> 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. >> >=20 > 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 kn= ows > 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. There is no ordering guarantee. The state needs to be migrated in the device or bus where it sits, if post-load processing is required; i.e., if it's in VirtIODevice then something like this series, if it were on VirtioBus exclusively (device asking bus for its endianness each time and does not do post-load stuff) then endianness could be migrated as a new bus section. Not sure if that would help the "broken" state though? Would touch on Stefan's alias properties for anything but virtio-mmio. Regards, Andreas --=20 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imend=F6rffer; HRB 16746 AG N=FCrnbe= rg