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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 36CD1C04A6B for ; Wed, 8 May 2019 09:17:45 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F14E520656 for ; Wed, 8 May 2019 09:17:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F14E520656 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 ([127.0.0.1]:33735 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOIhs-0005Ld-7b for qemu-devel@archiver.kernel.org; Wed, 08 May 2019 05:17:44 -0400 Received: from eggs.gnu.org ([209.51.188.92]:46595) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hOIh5-00054n-UG for qemu-devel@nongnu.org; Wed, 08 May 2019 05:16:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hOIh4-0007OT-KG for qemu-devel@nongnu.org; Wed, 08 May 2019 05:16:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41280) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hOIh4-0007Kq-D9 for qemu-devel@nongnu.org; Wed, 08 May 2019 05:16:54 -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 CE5F6307D971 for ; Wed, 8 May 2019 09:16:52 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-28.ams2.redhat.com [10.36.116.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6D8C7600D4; Wed, 8 May 2019 09:16:52 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id E55331132B35; Wed, 8 May 2019 11:16:50 +0200 (CEST) From: Markus Armbruster To: Eduardo Habkost References: <20190423212246.3542-1-ehabkost@redhat.com> <87imumj1jb.fsf@dusky.pond.sub.org> <20190507161845.GL28722@habkost.net> Date: Wed, 08 May 2019 11:16:50 +0200 In-Reply-To: <20190507161845.GL28722@habkost.net> (Eduardo Habkost's message of "Tue, 7 May 2019 13:18:45 -0300") Message-ID: <87lfzh5mrh.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain 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 [10.5.110.48]); Wed, 08 May 2019 09:16:52 +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 0/3] Export machine type deprecation info through QMP X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mprivozn@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eduardo Habkost writes: > On Tue, May 07, 2019 at 07:07:04AM +0200, Markus Armbruster wrote: >> Eduardo Habkost writes: >> >> > This series adds machine type deprecation information to the >> > output of the `query-machines` QMP command. With this, libvirt >> > and management software will be able to show this information to >> > users and/or suggest changes to VM configuration to avoid >> > deprecated machine types. >> >> This overlaps with something I want to try, namely using Kevin's >> proposed QAPI feature flags for deprecation markings. Let's compare the >> two. >> >> To mark something as deprecated with your patches, you add a >> @support-status member somewhere, where "somewhere" is related to >> "something" by "provides information on". >> >> Example: MachineInfo (returned by query-machines) provides information >> on possible values of -machine parameter type. If -machine was >> QAPIfied, it would provide information on possible values of a QAPI >> object type's member. The type might be anonymous. The member should >> be an enum (we currently use 'str' in MachineInfo). > > QAPIfying -machine, -cpu, and -device would be wonderful. > >> >> Example: say we want to deprecate block driver "vfat", >> i.e. BlockdevDriver member @vfat. Type BlockdevDriver is used in >> multiple places; let's ignore all but BlockdevOptions. We need to add >> @support-status to something that provides information on >> BlockdevDriver, or maybe on BlockdevOptions. There is no ad hoc query >> providing information on either of the two, because QAPI/QMP >> introspection has been sufficient. What now? >> >> Can we add deprecation information to (general) QAPI/QMP introspection > > Yes, we can. I think it's a good idea. But: > >> instead of ad hoc queries? > > I'm not sure about the "instead of" part. I don't want perfect > to be the enemy of done, and I don't want QAPIfication of > -machine to be a requirement to start reporting machine type > deprecation information. Valid point. Still, I believe we should at least try to predict how the pieces we create now would fit with the pieces we plan to create later on. Note that full QAPIfication of -machine isn't necessary to make QAPI feature "deprecated" work for machine types. Turning MachineInfo member @name into an enum, so we can tack "deprecated" onto its values, would suffice. Such a QAPIfication of machine types is still hard: QOM types are defined at compile time just like the QAPI schema, but their definition is distributed, and collected into one place only at run time. I discussed this on slide 39 of my "QEMU interface introspection: From hacks to solutions" talk (KVM Form 2015). Just for device_add, but it's just a special case of QOM. Choices listed there: * Collect drivers at compile time? Hard... * Make QAPI schema dynamic? Hard... * Forgo driver-specific arguments in schema? Defeats introspection... I'd like to add to the last item: Provide QOM introspection on par with QAPI schema introspection The QOM introspection we have (qom-list-types etc. is not on par. Back to exposing machine type deprecation. I'm doubtful your proposed solution can be applied widely. It relies on adding @support-status to something that provides information on whatever is deprecated. The initial use is with a something that is an ad hoc query, namely query-machines. To use it, the management application needs to understand what query-machines' @support-status applies to. Certainly feasible. But I fear every use will be a special case. Furthermore, a suitable ad hoc query need not exist. What then? Create suitable ad hoc queries just for communicating deprecation? Instead, I'd like us to think about a more genral solution. Or perhaps two: one for properly QAPIfied stuff, and one for QOM. >> Kevin's proposed QAPI feature flags[*] extend the QAPI language so that >> struct types can optionally have a list of feature flags, which are >> strings. Struct types suffice for his immediate needs. I'd like to use >> feature flags to mark deprecation by tacking a "deprecated" feature onto >> whatever is deprecated. This obviously needs feature support for >> everything we want to be able to deprecate: commands, and events, as >> well as members of enum and object types. >> >> Example: to deprecate block driver "vfat", add feature "deprecated" to >> BlockdevDriver member @vfat. >> >> Unlike your patches, this does not require finding a "somewhere" that >> provides information on "something". You simply tack "deprecated" right >> onto "something". >> >> Your patches provide more information, however: human-readable messages. > > It also includes a machine-friendly suggested alternative (which > I think is even more important that the human-readable message). I agree we should point to a preferred replacement whenever we deprecate something. We have to do it in documentation. And we generally do, in qemu-deprecated.texi. How useful would doing it in QMP as well be? Depends on what management applications can do with the additional information. > We could extend QAPI introspection to return that if necessary, > right? I'm confident we can come up with *something*. It might kill the neat and simple "use QAPI features to communicate deprecation" idea, though. >> Food for thought :) >> >> >> [*] Hiding in >> Subject: [PATCH 0/4] file-posix: Add dynamic-auto-read-only QAPI feature >> Date: Mon, 8 Apr 2019 16:35:39 +0200 >> Message-Id: <20190408143543.3982-1-kwolf@redhat.com>