From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4B69AC3A59D for ; Fri, 16 Aug 2019 17:43:49 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 26395205F4 for ; Fri, 16 Aug 2019 17:43:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 26395205F4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:58904 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hygGS-0005X6-9P for qemu-devel@archiver.kernel.org; Fri, 16 Aug 2019 13:43:48 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58838) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1hygFY-0004qH-1H for qemu-devel@nongnu.org; Fri, 16 Aug 2019 13:42:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hygFU-0005F5-Oe for qemu-devel@nongnu.org; Fri, 16 Aug 2019 13:42:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49178) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hygFU-0005Ea-Iq for qemu-devel@nongnu.org; Fri, 16 Aug 2019 13:42:48 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 804AD30833B0; Fri, 16 Aug 2019 17:42:47 +0000 (UTC) Received: from localhost (ovpn-116-32.gru2.redhat.com [10.97.116.32]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6CB0387C9; Fri, 16 Aug 2019 17:42:44 +0000 (UTC) Date: Fri, 16 Aug 2019 14:42:41 -0300 From: Eduardo Habkost To: Markus Armbruster Message-ID: <20190816174241.GE3908@habkost.net> References: <20190815183803.13346-1-ehabkost@redhat.com> <20190815183803.13346-4-ehabkost@redhat.com> <87pnl5sks3.fsf@dusky.pond.sub.org> <20190816074932.GK13569@beluga.usersys.redhat.com> <87h86hpae5.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87h86hpae5.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Fri, 16 Aug 2019 17:42:47 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 3/3] pc: Don't make CPU properties mandatory unless necessary X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Yash Mankad , Peter Krempa , Like Xu , "Michael S. Tsirkin" , Erik Skultety , qemu-devel@nongnu.org, Paolo Bonzini , Igor Mammedov , Miroslav Rezanina , "Danilo C. L. de Paula" , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Aug 16, 2019 at 02:22:58PM +0200, Markus Armbruster wrote: > Erik Skultety writes: > > > On Fri, Aug 16, 2019 at 08:10:20AM +0200, Markus Armbruster wrote: > >> Eduardo Habkost writes: > >> > >> > We have this issue reported when using libvirt to hotplug CPUs: > >> > https://bugzilla.redhat.com/show_bug.cgi?id=1741451 > >> > > >> > Basically, libvirt is not copying die-id from > >> > query-hotpluggable-cpus, but die-id is now mandatory. > >> > >> Uh-oh, "is now mandatory": making an optional property mandatory is an > >> incompatible change. When did we do that? Commit hash, please. > >> > >> [...] > >> > > > > I don't even see it as being optional ever - the property wasn't even > > recognized before commit 176d2cda0de introduced it as mandatory. > > Compatibility break. > > Commit 176d2cda0de is in v4.1.0. If I had learned about it a bit > earlier, I would've argued for a last minute fix or a revert. Now we > have a regression in the release. > > Eduardo, I think this fix should go into v4.1.1. Please add cc: > qemu-stable. I did it in v2. > > How can we best avoid such compatibility breaks to slip in undetected? > > A static checker would be nice. For vmstate, we have > scripts/vmstate-static-checker.py. Not sure it's used. I don't think this specific bug would be detected with a static checker. "die-id is mandatory" is not something that can be extracted by looking at QOM data structures. The new rule was being enforced by the hotplug handler callbacks, and the hotplug handler call tree is a bit complex (too complex for my taste, but I digress). We could have detected this with a simple CPU hotplug automated test case, though. Or with a very simple -device test case like the one I have submitted with this patch. This was detected by libvirt automated test cases. It would be nice if this was run during the -rc stage and not only after the 4.1.0 release, though. I don't know details of the test job. Danilo, Mirek, Yash: do you know how this bug was detected, and what we could do to run the same test jobs in upstream QEMU release candidates? -- Eduardo