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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id C8B04C05027 for ; Tue, 14 Feb 2023 16:28:59 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pRyAN-0005YN-HF; Tue, 14 Feb 2023 11:28:27 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pRyAL-0005Y9-EC for qemu-devel@nongnu.org; Tue, 14 Feb 2023 11:28:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pRyAJ-0001Br-QV for qemu-devel@nongnu.org; Tue, 14 Feb 2023 11:28:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1676392102; 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=S0ZVXaRCBYB7pBEgKxVGqqouHbOuzBVGJU6Y0FtMXK0=; b=Jl5WOLvMZQ92cBdieVJR5gpGJ6KAokFq0P509k6rTVIvP/JlF86gA1+WkBBa/4PmK/9BI/ uiIUG8GWN+MEPzdokSBo6uI88nVN1ykJWQt+W3W0AiLcVxREBUE/Onw9QAFidGC4xufDUm H2V/NvVqeAZ4B62E7p9MQkzEe3ZRbHc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-631-JinGDt5CPSysq15PrWJxKg-1; Tue, 14 Feb 2023 11:28:19 -0500 X-MC-Unique: JinGDt5CPSysq15PrWJxKg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 74EDB8027FD; Tue, 14 Feb 2023 16:28:18 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4F1F5400D927; Tue, 14 Feb 2023 16:28:18 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 257DE21E6A1F; Tue, 14 Feb 2023 17:28:17 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, eblake@redhat.com, eduardo@habkost.net, pbonzini@redhat.com, marcel.apfelbaum@gmail.com, mst@redhat.com, philmd@linaro.org, den-plotnikov@yandex-team.ru, antonkuchin@yandex-team.ru, "reviewer:Incompatible changes" Subject: Re: [PATCH v4 14/16] qapi: deprecate "device" field of DEVICE_* events References: <20230213140103.1518173-1-vsementsov@yandex-team.ru> <20230213140103.1518173-15-vsementsov@yandex-team.ru> <87bklwoce9.fsf@pond.sub.org> <87fsb8jw7r.fsf@pond.sub.org> Date: Tue, 14 Feb 2023 17:28:17 +0100 In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Tue, 14 Feb 2023 13:59:43 +0000") Message-ID: <87wn4kfbz2.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > On Tue, Feb 14, 2023 at 12:57:28PM +0100, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >> > On Tue, Feb 14, 2023 at 09:54:22AM +0100, Markus Armbruster wrote: >> >> Daniel P. Berrang=C3=A9 writes: >> >>=20 >> >> > On Mon, Feb 13, 2023 at 05:01:01PM +0300, Vladimir Sementsov-Ogievs= kiy wrote: >> >> >> The device field is redundant, because QOM path always include dev= ice >> >> >> ID when this ID exist. >> >> > >> >> > The flipside to that view is that applications configuring QEMU are >> >> > specifying the device ID for -device (CLI) / device_add (QMP) and >> >> > not the QOM path. IOW, the device ID is the more interesting field >> >> > than QOM path, so feels like the wrong one to be dropping. >> >>=20 >> >> QOM path is a reliable way to identify a device. Device ID isn't: >> >> devices need not have one. Therefore, dropping the QOM path would be >> >> wrong. >> >>=20 >> >> > Is there any real benefit to dropping this ?=20 >> >>=20 >> >> The device ID is a trap for the unwary: relying on it is fine until y= ou >> >> run into a scenario where you have to deal with devices lacking IDs. >> > >> > When a mgmt app is configuring QEMU though, it does it exclusively >> > with device ID values. If I add a device "-device foo,id=3Ddev0", >> > and then later hot-unplug it "device_del dev0", it is pretty >> > reasonable to then expect that the DEVICE_DELETED even will then >> > include the ID value the app has been using elsewhere. >>=20 >> The management application would be well advised to use QOM paths with >> device_del, because only that works even for devices created by default >> (which have no ID), and devices the user created behind the management >> application's back. > > If an application is using -nodefaults, then the only devices which > exist will be those which are hardwired into the machine, and they > can't be used with device_del anyway as they're hardwired. Your trust in the sanity of our board code is touching ;) > So the only reason is to cope with devices created secretly by > the users, and that's a hairy enough problem that most apps won't > even try to cope with it. Fair enough. > At least in terms of the device hotplug area, it feels like we're > adding an extra hurdle for apps to solve a problem that they don't > actually face in practice. > > QOM paths are needed in some other QMP commands though, where > there is definite need to refer to devices that are hardwired, > most obviously qom-set/qom-get. Also query-cpus-fast, query-hotpluggable-cpus, and possibly more I missed.