From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46923) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZV1sj-0002ik-Ts for qemu-devel@nongnu.org; Thu, 27 Aug 2015 14:26:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZV1se-0002ZG-U5 for qemu-devel@nongnu.org; Thu, 27 Aug 2015 14:26:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38596) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZV1se-0002Z1-NT for qemu-devel@nongnu.org; Thu, 27 Aug 2015 14:26:32 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id 51E73C15CA97 for ; Thu, 27 Aug 2015 18:26:31 +0000 (UTC) Date: Thu, 27 Aug 2015 15:26:29 -0300 From: Eduardo Habkost Message-ID: <20150827182629.GK4230@thinpad.lan.raisama.net> References: <1439939502-4722-1-git-send-email-ehabkost@redhat.com> <20150819095526.GB2332@work-vm> <55D4C813.1070308@redhat.com> <87vbc5qadz.fsf@blackfin.pond.sub.org> <20150825162116.GD25920@redhat.com> <20150827134638-mutt-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150827134638-mutt-send-email-mst@redhat.com> Subject: Re: [Qemu-devel] [PATCH] q35: Remove old machine versions List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Marcel Apfelbaum , Laszlo Ersek , qemu-devel@nongnu.org, Markus Armbruster , Paolo Bonzini , John Snow , "Dr. David Alan Gilbert" On Thu, Aug 27, 2015 at 01:50:10PM +0300, Michael S. Tsirkin wrote: > On Tue, Aug 25, 2015 at 05:21:16PM +0100, Daniel P. Berrange wrote: > > On Mon, Aug 24, 2015 at 11:54:48AM +0200, Markus Armbruster wrote: > > > John Snow writes: > > > > > > > On 08/19/2015 02:55 AM, Dr. David Alan Gilbert wrote: > > > >> * Eduardo Habkost (ehabkost@redhat.com) wrote: > > > >>> Migration with q35 was not possible before commit > > > >>> 04329029a8c539eb5f75dcb6d8b016f0c53a031a, because q35 unconditionally creates > > > >>> an ich9-ahci device, that was marked as unmigratable. So all q35 machines > > > >>> before pc-q35-2.4 were unmigratable, and there's no point in keeping > > > >>> compatibility code for them. > > > >>> > > > >>> Remove all old pc-q35 machine classes and keep only pc-q35-2.4. > > > >> > > > >> But doesn't that mean that anyone who has a machine configured with one > > > >> of those machine types will suddenly find it wont start? > > > >> > > > >> Dave > > > >> > > > > > > > > To some extent, all versions of this board prior to 2.4 should be > > > > considered unsupported and we should discourage their use anyway. > > > > > > > > If you really want, I suppose we could just alias them to 2.4 ... > > > > > > I'd very much prefer an honest "won't start" over a silent change of the > > > machine type. > > > > > > If we really want to bend over backwards for existing uses of these > > > machine types, we could make them error out with "use pc-q35-2.5 > > > instead". Since I don't think they exist outside testing, I wouldn't > > > bother. > > > > Agreed, we should be reporting a hard error for any machine types we > > have deleted. Or if we care about smooth upgrade path then we shouldn't > > be deleting them in the first place. Silently changing the user's > > requested machine type into a different machine type is violating > > the semantics of stable machine types. > > > > Regards, > > Daniel > > The reason we are deleting them is because changes in behaviour are not > user visible implementation details, and live migration is unsupported. > > In other words 2.4 is identical to <2.3 in all respect except live > migration, which didn't work in <2.3 and works in 2.4, that's why > aliasing them is fine. I don't know what you mean by "not user visible implementation details" and "identical in all respect", because I see lots of compat code that implement user-visible differences inside pc_compat_*(), PC_COMPAT_*, pc_q35_*_machine_options() for 2.3 and older. -- Eduardo