From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58990) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dKiYK-0005DV-Qv for qemu-devel@nongnu.org; Tue, 13 Jun 2017 05:56:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dKiYG-00055q-TW for qemu-devel@nongnu.org; Tue, 13 Jun 2017 05:56:00 -0400 Date: Tue, 13 Jun 2017 10:55:50 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170613095549.GC2096@work-vm> References: <149685579678.12025.9278446121024037161.stgit@bahia.lan> <149685584629.12025.14875914798241845062.stgit@bahia.lan> <20170608040857.GV13397@umbus.fritz.box> <20170608115410.2e7a2511@bahia.ttt.fr.ibm.com> <20170612142456.GJ18542@umbus> <20170613093359.4567ba94@bahia.ttt.fr.ibm.com> <20170613080631.GB30171@umbus> <20170613104003.233e21d5@bahia.ttt.fr.ibm.com> <20170613090002.GA2096@work-vm> <20170613112150.7f64171c@bahia.ttt.fr.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170613112150.7f64171c@bahia.ttt.fr.ibm.com> Subject: Re: [Qemu-devel] [PATCH v3 5/5] spapr: fix migration of ICPState objects from/to older QEMU List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz Cc: David Gibson , qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Cedric Le Goater , Juan Quintela * Greg Kurz (groug@kaod.org) wrote: > On Tue, 13 Jun 2017 10:00:03 +0100 > "Dr. David Alan Gilbert" wrote: > > > * Greg Kurz (groug@kaod.org) wrote: > > > On Tue, 13 Jun 2017 16:06:31 +0800 > > > David Gibson wrote: > > > > > > > On Tue, Jun 13, 2017 at 09:33:59AM +0200, Greg Kurz wrote: > > > [...] > > > > > > > > > +static void pre_2_10_vmstate_register_dummy_icp(sPAPRMachineState *spapr, int i) > > > > > > > > > +{ > > > > > > > > > + bool *flag = &spapr->pre_2_10_ignore_icp[i]; > > > > > > > > > + > > > > > > > > > + g_assert(!*flag); > > > > > > > > > > > > > > > > Apart from this assert(), you never seem to test the values in the > > > > > > > > pre_2_10_ignore_icp() array, so it seems a bit pointless. > > > > > > > > > > > > > > > > > > > > > > There's the opposite check in pre_2_10_vmstate_unregister_dummy_icp(). > > > > > > > But I agree it isn't really useful... but more because of paranoia :) > > > > > > > > > > > > I'm all for paranoid assert()s if they can be made using data readily > > > > > > to hand. Adding a data structure just for the purpose of making an > > > > > > assert() later, not so much. > > > > > > > > > > > > > > > > It is also passed as opaque argument to vmstate_register(), where it is > > > > > used as a key when calling vmstate_unregister(). I could possibly pass > > > > > (void *) i instead, but I'm not a big fan of hijacking pointer arguments > > > > > to pass numbers. > > > > > > > > Ah, I see your point. Creating an array, purely to generate arbitrary > > > > pointers is also kind of ugly, though. Really the cpu_index / XICS > > > > server number makes sense to identify the vmstate, but it looks like > > > > vmstate_unregister() doesn't take that. > > > > > > > > > > Indeed... what about adding a vmstate_unregister_by_instance_id() then ? > > > > > > Cc'ing Juan and David. > > > > So what's the problem with a (void *)i ? > > https://stackoverflow.com/questions/8618637/what-does-it-mean-to-convert-int-to-void-or-vice-versa > > > It's simple, as long as you're > > not actually using the opaque anywhere it's easy. > > > > but as you say, since the opaque isn't used anywhere, it is probably > okay to pass (void *) i. Yes, I don't think we're ever casting back from the (void *) to an int so it feels pretty safe to me. > > > Note from a quick glance at your patch; will this work migrating > > from this 2.10 -> 2.9 ? Are your dummy vmstate's really good enough for > > the 2.9 ? > > > > Yeah but I need to add some comments as David suggested. > > The idea is that 2.9 used to create a bunch of objects at machine init, > that only get used when CPUs are plugged. With 2.10, these objects are > now created under the CPUs. When migrating from 2.10 to 2.9, we only need > to send the real objects. The dummy vmstate entries don't send anything > (.needed always returns false) since the corresponding objects in 2.9 aren't > being used and still have their default state. > OK, that'll probably work. Dave > > Dave > > > > > > > -- > > > Greg > > > > > > -- > > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK