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 257FDC3DA49 for ; Thu, 25 Jul 2024 06:25:35 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sWruJ-0007mE-99; Thu, 25 Jul 2024 02:24:55 -0400 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 1sWruG-0007jT-1N for qemu-devel@nongnu.org; Thu, 25 Jul 2024 02:24:53 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sWruD-0007Kw-8d for qemu-devel@nongnu.org; Thu, 25 Jul 2024 02:24:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1721888687; 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: in-reply-to:in-reply-to:references:references; bh=ZPMaVxL0QqXqcPl3QO8nmEoN+w2zBU0FOWWZV9muy/Q=; b=KnuR6vD6/sNuSnTRHOwZ+m+OOnq4XBvSYyTQ2fRF7C1YAJzWT094bX5e5l1bHXSR+FUUm4 8nZITfKmhyjXKfS9B1nooEzs5FxpygEk8jEHwod5216v6S6q5h3R2COUcXEw/GlXzIGKVy tF40V/MVdbCn9bO3GiLWoc3NtJFlthA= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-332-Sn0Z2CWINm-H1OpxsTF4og-1; Thu, 25 Jul 2024 02:24:43 -0400 X-MC-Unique: Sn0Z2CWINm-H1OpxsTF4og-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8A1ED1955D4B; Thu, 25 Jul 2024 06:24:41 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.65]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BBA52195605A; Thu, 25 Jul 2024 06:24:39 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 9439D21E668F; Thu, 25 Jul 2024 08:24:37 +0200 (CEST) From: Markus Armbruster To: Collin Walling Cc: qemu-s390x@nongnu.org, qemu-devel@nongnu.org, thuth@redhat.com, david@redhat.com, wangyanan55@huawei.com, philmd@linaro.org, marcel.apfelbaum@gmail.com, eduardo@habkost.net, Jiri Denemark Subject: Re: [PATCH v3] target/s390x: filter deprecated properties based on model expansion type In-Reply-To: <9f8023a4-3edd-476f-9243-677138be3921@linux.ibm.com> (Collin Walling's message of "Wed, 24 Jul 2024 15:42:00 -0400") References: <20240719181741.35146-1-walling@linux.ibm.com> <87h6cksk4h.fsf@pond.sub.org> <28ea8260-a411-4651-8e2a-1fcc009f5043@linux.ibm.com> <87bk2nrzou.fsf@pond.sub.org> <9f8023a4-3edd-476f-9243-677138be3921@linux.ibm.com> Date: Thu, 25 Jul 2024 08:24:37 +0200 Message-ID: <87cyn2ugyi.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.136, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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 Collin Walling writes: > On 7/24/24 3:56 AM, Markus Armbruster wrote: >> Collin Walling writes: > Let me try to explain the purpose of @deprecated-props and see if it > helps bring us closer to some semblance of a mutual understanding so we > can work together on a concise documentation for this field. > > s390 has been announcing features as deprecated for some time now, which > was fine as a way to let users know that they should tune their guests > to no longer user these features. Now that we are approaching the > release of generations that will drop these deprecated features > outright, we encounter an issue: if users have not been mindful with > disabling these announced-deprecated-features, then their guests running > on older models will not be able to migrate to machines running on newer > hardware. > > To alleviate this, I've added the @deprecated-props array to the > CpuModelInfo struct, and this field is populated by a > query-cpu-model-expansion* return. It is up the the user/management app > to make use of this data. > > On the libvirt side (currently in development), I am able to easily > retrieve the host-model with a full expansion, parse the > @deprecated-props, and then cache them for later use (e.g. when > reporting the host-model with these features disabled, or enabling a > user to define their domain with deprecated-features disabled via a > convenient XML attribute). > > tl;dr @deprecated-props is only reported via a > query-cpu-model-expansion, and it is up to the user/management app to > figure out what to do with them. Got it. Permit me a digression. In QAPI/QMP, we do something similar: we expose deprecation in introspection (query-qmp-schema), and what to do with the information is up to the management application. We provide one more tool to it: policy for handling deprecated interfaces, set with -compat. It permits "testing the future". See qapi/compat.json for details. Whether such a thing would be usful in your case I can't say. >> On closer examination, more questions on CpuModelInfo emerge. Uses: >> > > I will attempt to expand on each input @model (CpuModelInfo) as if they > were documented in the file. > >> * query-cpu-model-comparison both arguments >> >> Documentation doesn't say how exactly the command uses the members of >> CpuModelInfo, i.e. @name, @props, @deprecated-props. Can you tell me? >> > > Note: Compares ModelA and ModelB. > > Both @models must include @name. @props is optional. @deprecated-props > is ignored. > > @name: the name of the CPU model definition to look up. The definition > will be compared against the generation, GA level, and a static set of > properties of the opposing model. > > @props: a set of additional properties to include in the model's set of > properties to be compared. > > @deprecated-props: ignored. The user should consider these properties > beforehand and decide if these properties should be disabled/omitted on > the respective model. > >> * query-cpu-model-expansion argument @model and return value member >> @model. >> >> The other argument is the expansion type, on which the value of return >> value model.deprecated-props depends, I believe. Fine. >> >> Documentation doesn't say how exactly the command uses the members of >> CpuModelInfo arguments, i.e. @name, @props, @deprecated-props. Can >> you tell me? >> > > The @model must include @name. @props is optional. @deprecated-props > is ignored. > > @name: the name of the CPU model definition to look up. The definition > is associated with a set of properties that will populate the return data. > > @props: a set of additional properties to include in the model's set of > expanded properties. > > @deprecated-props: ignored. The user should consider these properties > beforehand and decide if these properties should be disabled/omitted on > the model. Return value member @model will have @name, may have @props and @deprecated-props. Absent @props is the same as {}. Only x86 uses {}. Absent @deprecated-props is the same as {}. No target uses {}. Can be present only on S390. Aside: returning the same thing in two different ways, like absent and {}, is slightly more complex than necessary. But let's ignore that here. >> * query-cpu-model-baseline both arguments and return value member >> @model. >> >> Same, except we don't have an expansion type here. So same question, >> plus another one: how does return value model.deprecated-props behave? >> > > Note: Creates a baseline model based on ModelA and ModelB. > > The @models must include @name. @props is optional. @deprecated-props > is ignored. > > @name: the name of the CPU model definition to look up. The definition, > GA level, and a static set of properties will be used to determine the > maximum model between ModelA and ModelB. > > @props: a set of additional properties to include in the model's set of > properties to be baselined. > > @deprecated-props: ignored. The user should consider these properties > beforehand and decide if these properties should be disabled/omitted on > the respective model. Return value member @model is just like in query-cpu-model-expansion. Unlike query-cpu-model-expansion, we don't have an expansion type. The value of @deprecated-props depends on the expansion type. Do we assume a type? Which one? >> If you can't answer my questions, we need to find someone who can. >> > > Hopefully this provides clarity on how CpuModelInfo and its respective > fields are used in each command. @David should be able to fill in any > missing areas / expand / offer corrections. > >> [...] This helps, thanks! Arguments that are silently ignored is bad interface design. Observe: when CpuModelInfo is an argument, @deprecated-props is always ignored. When it's a return value, absent means {}, and it can be present only for certain targets (currently S390). The reason we end up with an argument we ignore is laziness: we use the same type for both roles. We can fix that easily: { 'struct': 'CpuModel', 'data': { 'name': 'str', '*props': 'any' } } { 'struct': 'CpuModelInfo', 'base': 'CpuModel', 'data': { '*deprecated-props': ['str'] } } Use CpuModel for arguments, CpuModelInfo for return values. Since @deprecated-props is used only by some targets, I'd make it conditional, i.e. 'if': 'TARGET_S390X'. Thoughts?