From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34806) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aWaI9-0000Rv-2m for qemu-devel@nongnu.org; Thu, 18 Feb 2016 20:55:33 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aWaI3-0005t4-Vj for qemu-devel@nongnu.org; Thu, 18 Feb 2016 20:55:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41592) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aWaI3-0005sw-N8 for qemu-devel@nongnu.org; Thu, 18 Feb 2016 20:55:27 -0500 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 4B7048E6EB for ; Fri, 19 Feb 2016 01:55:26 +0000 (UTC) Date: Fri, 19 Feb 2016 09:55:13 +0800 From: Peter Xu Message-ID: <20160219015513.GA17229@pxdev.xzpeter.org> References: <1455428503-2113-1-git-send-email-peterx@redhat.com> <87povy5mim.fsf@blackfin.pond.sub.org> <20160215103440.GC7978@pxdev.xzpeter.org> <87y4amhuz2.fsf@blackfin.pond.sub.org> <20160215152205.GC898@redhat.com> <20160218044056.GL7978@pxdev.xzpeter.org> <20160218165208.vdf4ycsrn3qwxd2x@hawk.localdomain> <1455815421.3968.12.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1455815421.3968.12.camel@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC PATCH 0/2] ARM: add QMP command to query GIC version List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Bolognani Cc: wei@redhat.com, Andrew Jones , libvir-list@redhat.com, qemu-devel@nongnu.org, Markus Armbruster On Thu, Feb 18, 2016 at 06:10:21PM +0100, Andrea Bolognani wrote: > On Thu, 2016-02-18 at 17:52 +0100, Andrew Jones wrote: > > > Is this work on any of our todo list (or anyone has started the > > > prototyping)? > > >=C2=A0 > > > It seems reasonable to provide such a generic interface, rather tha= n > > > adding a "query-gic-capability" for GIC versions only. The problem > > > is that, I am not sure how eagerly we are wanting this GIC > > > interface, and when will this framework be there in QOM. > >=C2=A0 > > We want it eagerly :-) This type of a rabbit hole is likely why Danie= l > > was suggesting we do more in libvirt. I'm still not sure we want to > > probe both kvm and qemu from libvirt though, so I'm still in favor of > > an improved qemu probing method being worked out. > >=C2=A0 > > I don't know what the policy is for deprecating QMP commands, but I > > wonder if we can't introduce a QMP command now, and then, after worki= ng > > out the QOM extensions, we could shift to it, deprecating this QMP > > command and any others that would no longer be needed. >=20 > AFAIK, the current situation of libvirt passing the GIC version to > QEMU and simply reporting in case of failure is not unprecedented > and there are a few cases where probing in advance would simply not > be feasible. >=20 > Any probing code added to libvirt would have to be kept around > forever to ensure compatibility with current QEMU versions, so it > should IMHO be seen as a last resort in case we can't live without > GIC version probing while it's being implemented, properly, in QEMU. If libvirt is the most possible consumer for the new command, I think it might not be too hard to keep the compatibility of all possible versions of QEMU. E.g., after we have got a better way to query GIC version other than query-gic-capability, we can do something like this in libvirt: - try query-gic-capability - if supported -> [got GIC version] - if not supported -> try the new method - if supported -> [got GIC version] - if not supported -> [not support] During the time when QEMU has both methods working (before obsoleting the query-gic-capability QMP command), QEMU will make sure querying in both way will get exactly the same results. Does this work? Thanks. Peter