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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 5BAE8C33CB2 for ; Wed, 15 Jan 2020 12:16:37 +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 292842072B for ; Wed, 15 Jan 2020 12:16:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="GiC0t1Zy" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 292842072B 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]:52886 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1irhbA-0003Ih-CX for qemu-devel@archiver.kernel.org; Wed, 15 Jan 2020 07:16:36 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:46512) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1irhaE-0002mI-8U for qemu-devel@nongnu.org; Wed, 15 Jan 2020 07:15:39 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1irha9-0005kC-9M for qemu-devel@nongnu.org; Wed, 15 Jan 2020 07:15:37 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:50397 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1irha8-0005id-UK for qemu-devel@nongnu.org; Wed, 15 Jan 2020 07:15:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579090531; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tAiljNb7HsnUxrJZkEsktItBsnScGc/YKcbXQgKbp4s=; b=GiC0t1Zywfei+r/KVQKY/h8YeHeQ+Rm13nIcD3Ro630HdtdEwigLXbnoxmhinCBv/Q0zvu AAmVV4XgZWMkxNC4MUF3HwMENfCjzh0KM1JQ7b6XGK/PAqN5KnkN6+fmo1qUw0QSsEtd9s ++TOfycaeNFn9EkoYI861/yohWDBFUI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-238-jmfrMKFaO2OZQuQD-xVTGA-1; Wed, 15 Jan 2020 07:15:30 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C5D63800A02; Wed, 15 Jan 2020 12:15:28 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-131.ams2.redhat.com [10.36.116.131]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BB0181000329; Wed, 15 Jan 2020 12:15:18 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 484D81138600; Wed, 15 Jan 2020 13:15:17 +0100 (CET) From: Markus Armbruster To: Christophe de Dinechin Subject: Re: Making QEMU easier for management tools and applications References: <1EFEF446-AFEA-429F-B6BA-3206A7C41836@redhat.com> <20200108104306.GC5057@dhcp-200-226.str.redhat.com> <97F153BD-FB8A-46C7-90D0-9E894B9E0292@redhat.com> <20200108133842.GE5057@dhcp-200-226.str.redhat.com> <87d0bmchq0.fsf@dusky.pond.sub.org> <1B253197-5592-472A-AA26-E0614A13C91A@redhat.com> <87o8v52hz9.fsf@dusky.pond.sub.org> <8CF8359B-1E52-4F7A-944E-C1C14FEC4F92@redhat.com> Date: Wed, 15 Jan 2020 13:15:17 +0100 In-Reply-To: <8CF8359B-1E52-4F7A-944E-C1C14FEC4F92@redhat.com> (Christophe de Dinechin's message of "Wed, 15 Jan 2020 10:34:09 +0100") Message-ID: <87r200zzje.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: jmfrMKFaO2OZQuQD-xVTGA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.120 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: Kevin Wolf , Peter Maydell , "Daniel P. Berrange" , "Denis V. Lunev" , Stefan Hajnoczi , qemu-devel , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Paolo Bonzini , John Snow , Dominik Csapak Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Christophe de Dinechin writes: > Thanks a bunch. This clarifies a number of my misconceptions about > how this is currently used. Most notably this one: > >> On 15 Jan 2020, at 10:20, Markus Armbruster wrote: >>=20 >>> We don=E2=80=99t want the QAPI to let arbitrary fields of a QOM object >>> be modified, do we? >>=20 >> We already do: QMP command qom-set. If it breaks your guest, you get to >> keep the pieces. > > Ouch. I certainly did not expect that. > > "It is not what you don=E2=80=99t know that kills you, it is what you kno= w that ain=E2=80=99t so". Do we have a legitimate use for qom-set right now? Hmm, let's check libvirt... aha: * qemuMonitorJSONSetMemoryStatsPeriod() uses it to control virtio-balloon's guest-stats-polling-interval property, in accordance with docs/virtio-balloon-stats.txt. * qemuMonitorJSONSetIOThread() uses it to control iothread's properties poll-max-ns, poll-grow, poll-shrink. Their use with -object is documented (in qemu-options.hx), their use with qom-set is not. Oh well. >>>> http://dreamsongs.com/RiseOfWorseIsBetter.html >>>=20 >>> You know that I positively hate this ;-) >>=20 >> It's been a tough lesson for me, too. > > Not sure I can call it a =E2=80=9Clesson=E2=80=9D. Much like a philosophy= to fight against, IMO. The tough lesson isn't philosophy, it's an observation: "I believe that worse-is-better [...] has better survival characteristics than the-right-thing". >>> Well, I guess we can expand the schema. #ILoveJSON. >>=20 >> Basing the QAPI language on JSON was a poor choice. Not sure that's >> fixable at a reasonable cost. > > Well, at least now I have a slightly better understanding of the related = costs > and trade-offs. Thanks a lot for explaining. You're welcome!