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 141C0C61DA4 for ; Tue, 14 Feb 2023 11:53:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pRtrz-0006nt-3k; Tue, 14 Feb 2023 06:53:11 -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 1pRtrx-0006nQ-6z for qemu-devel@nongnu.org; Tue, 14 Feb 2023 06:53:09 -0500 Received: from mail-wm1-x32a.google.com ([2a00:1450:4864:20::32a]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1pRtrv-0001MT-EG for qemu-devel@nongnu.org; Tue, 14 Feb 2023 06:53:08 -0500 Received: by mail-wm1-x32a.google.com with SMTP id n33so4779500wms.0 for ; Tue, 14 Feb 2023 03:53:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=xA39zz1e17b81sTGADXxoX/nYHcldTppkglokkqhP9o=; b=bJiZJ831UsSc33QAH7JX75Fc+rFySZkImtd9qptkX6zbKP9wKM/oumD1Hp0Wn1T/KB hDnvJumDaSh8pCvn1gV2BJZ3VJv/hZgRr38yruuPJJPv67KhbgrH6eRzLRWP5Chcg0Rx 0qtzPg2re5mwVnsmzEkUiIwDH61cDIW5Ql7Dv3xc6y0Mg82L1A95O1y7KwN6qk1USDQO rB4RLxi7fc3oEB40p1xOyfKMZpOJ13xs0gKdyFFQ8mHcFZsXD8BA7NkOEGzdY1lOUlGZ alamd7S5Kdouzk7j1XKWdzTWBodkjOztth4JpqJvENwV8QrsF1fdvcCw8ckDNNgEFu3z 3S3w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=xA39zz1e17b81sTGADXxoX/nYHcldTppkglokkqhP9o=; b=wp5xbq0loSRcd9sFXfzUmiRXNkkwEl3FdNvOVJrcEGkOxxzXvMtv/PIEFsPm89GCbU ZcuawMhiJIgKEt16OtCNAin9+GKBtm4JFhDPacicvTC9UrQu6yrTo3JGmVfvfba5LGpj dQI/QJNV6TtPa9VLMt/WV5ZakBm8vFULRq37n/czB9HN1ugqqhXKOo0og8B1kqHDcPm8 6BjvWObdud9+MuRkDLlWSiJW5Y01AEMxq2b0MiPykSDmiY1++Jof3uIu2VtziHkk06fj 3zHNvQNZ9zQFQZCtyqgbssRJf1RBz/YaBfvju6xzBG8aP+Vej0GJ2aTgLn/1jZGOLBsZ ZJSw== X-Gm-Message-State: AO0yUKXMcTCyw0JWE23FbWX0iM2yXSTzukWT5pGFHDhPTnYN/sj03eWM Gldo8/z/GRTX4cayoAcM8aodLA== X-Google-Smtp-Source: AK7set9DaH/hwUKBGVEyrR/G6AGn9bhdhjUGHzENeyVl5nvICTaB11S0Muu0VqGQHFc406bCbN/UUw== X-Received: by 2002:a7b:c855:0:b0:3db:742:cfe9 with SMTP id c21-20020a7bc855000000b003db0742cfe9mr2325612wml.34.1676375584400; Tue, 14 Feb 2023 03:53:04 -0800 (PST) Received: from [192.168.30.216] ([81.0.6.76]) by smtp.gmail.com with ESMTPSA id o7-20020a05600c4fc700b003db0ad636d1sm22022496wmq.28.2023.02.14.03.53.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Feb 2023 03:53:04 -0800 (PST) Message-ID: <73444fb8-49a7-fc2f-091e-6f65e916fa58@linaro.org> Date: Tue, 14 Feb 2023 12:53:01 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH v4 14/16] qapi: deprecate "device" field of DEVICE_* events Content-Language: en-US To: Markus Armbruster , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: Peter Krempa , eduardo@habkost.net, antonkuchin@yandex-team.ru, mst@redhat.com, "reviewer:Incompatible changes" , qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy , den-plotnikov@yandex-team.ru, marcel.apfelbaum@gmail.com, pbonzini@redhat.com, eblake@redhat.com References: <20230213140103.1518173-1-vsementsov@yandex-team.ru> <20230213140103.1518173-15-vsementsov@yandex-team.ru> <87bklwoce9.fsf@pond.sub.org> <87ttzojwl7.fsf@pond.sub.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: <87ttzojwl7.fsf@pond.sub.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::32a; envelope-from=philmd@linaro.org; helo=mail-wm1-x32a.google.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.345, RCVD_IN_DNSWL_NONE=-0.0001, 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 On 14/2/23 12:49, Markus Armbruster wrote: > Daniel P. Berrangé writes: > >> On Tue, Feb 14, 2023 at 10:25:22AM +0100, Peter Krempa wrote: >>> On Tue, Feb 14, 2023 at 09:54:22 +0100, Markus Armbruster wrote: >>>> Daniel P. Berrangé writes: >>>> >>>>> On Mon, Feb 13, 2023 at 05:01:01PM +0300, Vladimir Sementsov-Ogievskiy wrote: >>>>>> The device field is redundant, because QOM path always include device >>>>>> 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. >>>> >>>> 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. >>>> >>>>> Is there any real benefit to dropping this ? >>>> >>>> The device ID is a trap for the unwary: relying on it is fine until you >>>> run into a scenario where you have to deal with devices lacking IDs. >>> >>> Note that libvirt's code is still using the 'device' bit rather than QOM >>> path and the fix might not be entirely trivial although should not be >>> too hard. >> >> What's the documented way to construct a QOM path, given only an ID as >> input ? > > QOM paths a gap in our documentation, even though the composition tree > structure has been stable since day one, and is de facto ABI. > > Short answer: "/machine/peripheral/ID". > > Long answer follows. > > We have three "containers" under /machine that serve as parents for > devices: > > * /machine/peripheral/ > > Parent of user-created devices with ID. Children are named "ID". > > Put there by qdev_set_id(), called from qdev_device_add_from_qdict(). > > On "user-created": Nothing stops board code to abuse qdev_set_id() for > onboard devices, directly or indirectly, but it really, really > shouldn't. > > * /machine/peripheral-anon/ > > Parent of user-created devices without ID. Children are named > "device[N]", where N counts up from zero. > > Put there by qdev_set_id(), called from qdev_device_add_from_qdict(). > > Again, abuse by board code is possible, but would be wrong. > > Beware: a particular device's N changes when the set of devices > created before it grows or shrinks. Messing with the machine type can > change it (different onboard devices). > > * /machine/unattached/ > > Surrogate parent of onboard devices created without a parent. > > Put there by device_set_realized() (general case), > qdev_connect_gpio_out_named() (input pins) , memory_region_do_init() > (memory regions), qemu_create_machine() (the main sysbus). > > I believe this container was created as a convenience, so we don't > have to retrofit parents to existing code. Probably abused ever > since. Are you suggesting this is a stable interface and we can not move devices (like from /machine/unattached/ to /machine/peripheral/) without going thru the deprecation process?