From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41224) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Whycm-000197-2B for qemu-devel@nongnu.org; Wed, 07 May 2014 05:58:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Whych-0003Um-4k for qemu-devel@nongnu.org; Wed, 07 May 2014 05:58:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52264) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Whycg-0003Uc-Qu for qemu-devel@nongnu.org; Wed, 07 May 2014 05:58:47 -0400 Date: Wed, 7 May 2014 12:57:34 +0300 From: "Michael S. Tsirkin" Message-ID: <20140507095734.GB12259@redhat.com> References: <1398271069-22057-1-git-send-email-dgilbert@redhat.com> <5357EF56.4010703@redhat.com> <20140423171622.GG2516@work-vm> <5357FCA9.8040801@redhat.com> <20140423175410.GA28308@redhat.com> <53580D27.2080507@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53580D27.2080507@redhat.com> Subject: Re: [Qemu-devel] [RFC PATCH v2 00/16] visitor+BER migration format List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: quintela@redhat.com, qemu-devel@nongnu.org, stefanb@linux.vnet.ibm.com, mdroth@linux.vnet.ibm.com, agraf@suse.de, aliguori@amazon.com, afaerber@suse.de, "Dr. David Alan Gilbert" On Wed, Apr 23, 2014 at 12:57:43PM -0600, Eric Blake wrote: > On 04/23/2014 11:54 AM, Michael S. Tsirkin wrote: > > On Wed, Apr 23, 2014 at 11:47:21AM -0600, Eric Blake wrote: > >> On 04/23/2014 11:16 AM, Dr. David Alan Gilbert wrote: > >>> The one thing that the environment variable does make nice and easy, > >>> for dev, is using it with existing test setups - e.g. running virt-test > >>> in BER mode or existing mode. > >> Hmm. Maybe a compromise - an environment variable determines the default > >> state of the QMP capability (for use in running the testsuite in one > >> mode or the other for all tests that don't explicitly set a mode), but > >> the QMP command still allows toggling the state at runtime (the > >> environment variable doesn't lock us out from changing away from the > >> startup default). > > > > Eric, could you explain the need for the runtime thing? > > I thought I did - when migrating across machines to what we know is an > older qemu, we want the old migration format; but when migrating to a > file to be reloaded by the current (or newer) qemu, we want the new > format since it is more robust. It's more robust for adding new functionality/new machine types but for old one I think we can assume it describes it sufficiently. > But libvirt can't know up front whether > the user starting a qemu instance has plans down the road of calling > 'virsh save' (migrate to file) or 'virsh migrate' (migrate across > machines) first. > > On the other hand, you have a point that upstream tends to not care > about migration from new qemu to old (that's one of the value-added > tasks of downstream distros), and that we could merely get away with > using the -m machine name as the witness of which form to use, with no > need for an environment variable or any other runtime switch. > > -- > Eric Blake eblake redhat com +1-919-301-3266 > Libvirt virtualization library http://libvirt.org >