From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45842) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xr5Ys-0006Xx-8M for qemu-devel@nongnu.org; Wed, 19 Nov 2014 08:44:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xr5Ym-0007jS-3P for qemu-devel@nongnu.org; Wed, 19 Nov 2014 08:44:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45544) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xr5Yl-0007jB-Rx for qemu-devel@nongnu.org; Wed, 19 Nov 2014 08:44:40 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id sAJDibrj020772 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 19 Nov 2014 08:44:37 -0500 Message-ID: <546C9EC0.5000105@redhat.com> Date: Wed, 19 Nov 2014 14:44:32 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1416254843-16859-1-git-send-email-mst@redhat.com> <1416254843-16859-3-git-send-email-mst@redhat.com> <546AE14E.7060606@redhat.com> <20141118074904.GA19745@redhat.com> <87y4r7o8dh.fsf@elfo.elfo> <20141119093320.GA26119@redhat.com> <87d28jo5yp.fsf@elfo.elfo> <20141119102136.GC26395@redhat.com> <878uj7o4ec.fsf@elfo.elfo> <20141119132851.GA27435@redhat.com> In-Reply-To: <20141119132851.GA27435@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH 2/5] exec: qemu_ram_alloc_device, qemu_ram_resize List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" , Juan Quintela Cc: qemu-devel@nongnu.org, dgilbert@redhat.com On 19/11/2014 14:28, Michael S. Tsirkin wrote: > > > > qemu-2.0 -M pc-2.0 -> qemu-2.2 -M pc-2.0 > > > > what BIOS should the second qemu use? the one that existed on qemu-2.0 > > time or the one that existed on qemu-2.2 time? You can allow for > > bugfixes, but not for big changes like moving where the acpi tables were > > generated, etc, etc. > > > I really think that we should use the BIOS from qemu-2.0 era. And my > > understanding is that you defend that we should use the qemu-2.2 era > > BIOS. > > Not only that. We already do. And we don't intend to change that for 2.2. Am I missing a part of the discussion? When we migrate, the second QEMU uses the BIOS from the first. So: qemu-2.0 -M pc-2.0 -> qemu-2.2 -M pc-2.0 uses 2.0 BIOS qemu-2.2 -M pc-2.0 -> qemu-2.0 -M pc-2.0 uses 2.2 BIOS Both should work, in general. BIOS is rarely the reason for incompatibilities. However, breakage can happen, for example I know that RHEL7 SeaBIOS does not work on RHEL6. RHEL6 SeaBIOS works on RHEL7, but it needs a couple workarounds. Shipping a separate BIOS for different machine types is unrealistic and pointless. It would also be a good terrain for bug reports, unless you also do things like "forbid creating -device megasas-gen2 on 2.1 because it was introduced in 2.2". Remember that libvirt keeps the same machine type for the whole life of a virtual machine definition, even if other parts of the hardware (e.g. disks or NICs) change. Paolo