From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MERd8-0001m4-DV for qemu-devel@nongnu.org; Wed, 10 Jun 2009 13:30:30 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MERd3-0001lj-SX for qemu-devel@nongnu.org; Wed, 10 Jun 2009 13:30:29 -0400 Received: from [199.232.76.173] (port=56831 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MERd3-0001lg-NC for qemu-devel@nongnu.org; Wed, 10 Jun 2009 13:30:25 -0400 Received: from mx20.gnu.org ([199.232.41.8]:62564) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1MERd3-0000j1-DV for qemu-devel@nongnu.org; Wed, 10 Jun 2009 13:30:25 -0400 Received: from mail.codesourcery.com ([65.74.133.4]) by mx20.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MERd2-00024l-6M for qemu-devel@nongnu.org; Wed, 10 Jun 2009 13:30:24 -0400 From: Paul Brook Subject: Re: [Qemu-devel] [PATCH 05/11] qemu: MSI-X support functions Date: Wed, 10 Jun 2009 18:30:16 +0100 References: <200906101746.06740.paul@codesourcery.com> <20090610170306.GL28601@redhat.com> In-Reply-To: <20090610170306.GL28601@redhat.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200906101830.21537.paul@codesourcery.com> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Carsten Otte , kvm@vger.kernel.org, Rusty Russell , qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, Blue Swirl , Christian Borntraeger , Avi Kivity On Wednesday 10 June 2009, Michael S. Tsirkin wrote: > On Wed, Jun 10, 2009 at 05:46:03PM +0100, Paul Brook wrote: > > > > If you can't create an identical machine from scratch then I don't > > > > consider snapshot/migration to be a useful feature. i.e. as soon as > > > > you shutdown and restart the guest it is liable to break anyway. > > > > > > Why is liable to break? > > > > A VM booted on an old version of qemu and migrated to a new version will > > behave differently to a the same VM booted on a new version of qemu. > > It will behave identically. That's what the patch does: discover > how did the device behave on old qemu, and make it behave the same way > on new qemu. You're missing the point. After doing a live migration from old-qemu to new- qemu, there is no snapshot to load. We need to be able to shutdown the guest, kill qemu (without saving a snapshot), then start qemu with the exact same hardware. If we can't start a new qemu with the same hardware configuration then we should not be allowing migration or loading of snapshots. Paul