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 lists1p.gnu.org (lists1p.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 F1243C5AC67 for ; Thu, 6 Aug 2026 18:16:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ws2d2-0002RO-4V; Thu, 06 Aug 2026 14:15:40 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ws2d0-0002RA-ON for qemu-devel@nongnu.org; Thu, 06 Aug 2026 14:15:38 -0400 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 1ws2cy-0000m5-C5 for qemu-devel@nongnu.org; Thu, 06 Aug 2026 14:15:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1786040135; h=from:from:reply-to: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=nmlhGcOu6DFhF6nKnKB75GmDypaZnmvhrljGAkyXVlg=; b=LTUb5V3hQMc3VKVvNoayYyJrqc57gsK2sCrmtXok9r6+NapUO2cT6oiX97Zz1tj2+9v6ZT 63RNH7biMlKqlY4a+u4zAHpstqBnLlpcKIN8nP5MiZl0VjIoN0PgCwfGBm5sB5ShR8jQbl VM/OOemNwSVpnpotKbrTsaeHmRe2hAw= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-581-W2T70IWnOaiZsy_RBjLNAA-1; Thu, 06 Aug 2026 14:15:31 -0400 X-MC-Unique: W2T70IWnOaiZsy_RBjLNAA-1 X-Mimecast-MFC-AGG-ID: W2T70IWnOaiZsy_RBjLNAA_1786040129 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 02F3A18002F8; Thu, 6 Aug 2026 18:15:29 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C442D1956094; Thu, 6 Aug 2026 18:15:25 +0000 (UTC) Date: Thu, 6 Aug 2026 19:15:22 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Pierrick Bouvier Cc: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , qemu-devel@nongnu.org, Nicholas Piggin , Daniel Henrique Barboza , Bernhard Beschow , Anton Johansson , Alistair Francis , Peter Maydell , Alistair Francis Subject: Re: [PATCH 01/27] include/qemu/target-info-qom.h: declare TYPE_TARGET_SPECIFIC interface Message-ID: References: <20260724000948.234657-1-pierrick.bouvier@oss.qualcomm.com> <20260724000948.234657-2-pierrick.bouvier@oss.qualcomm.com> <5bda3566-5ce5-46dc-a281-2cc07a56dc6f@oss.qualcomm.com> <077fc585-a6b8-455a-abdc-fd72e13b8315@oss.qualcomm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <077fc585-a6b8-455a-abdc-fd72e13b8315@oss.qualcomm.com> User-Agent: Mutt/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.852, 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_PASS=-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: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Aug 06, 2026 at 09:38:43AM -0700, Pierrick Bouvier wrote: > On 8/6/2026 7:52 AM, Philippe Mathieu-Daudé wrote: > > On 6/8/26 12:21, Daniel P. Berrangé wrote: > >> On Wed, Aug 05, 2026 at 12:10:27PM -0700, Pierrick Bouvier wrote: > >>> On 8/5/2026 9:53 AM, Daniel P. Berrangé wrote: > >>>> On Wed, Aug 05, 2026 at 09:16:20AM -0700, Pierrick Bouvier wrote: > >>>>> On 8/5/2026 7:05 AM, Daniel P. Berrangé wrote: > >>>>>> On Fri, Jul 24, 2026 at 12:09:21AM +0000, Pierrick Bouvier wrote: > >>>>>>> In the next commits, We'll replace the logic to filter QOM types per > >>>>>>> target from a static one (based on INTERFACES) to a runtime one, > >>>>>>> based > >>>>>>> on is_available() function, that can be overriden per class. > >>>>>>> > >>>>>>> Introduce the new interface we'll use for that. > >>>>>>> > >>>>>>> Signed-off-by: Pierrick Bouvier > >>>>>>> --- > >>>>>>>   include/qemu/target-info-qom.h | 15 +++++++++++++++ > >>>>>>>   target-info-qom.c              |  5 +++++ > >>>>>>>   2 files changed, 20 insertions(+) > >>>>>>> > >>>>>>> diff --git a/include/qemu/target-info-qom.h b/include/qemu/ > >>>>>>> target-info-qom.h > >>>>>>> index 91be415ed33..83eb537333b 100644 > >>>>>>> --- a/include/qemu/target-info-qom.h > >>>>>>> +++ b/include/qemu/target-info-qom.h > >>>>>>> @@ -14,6 +14,21 @@ > >>>>>>>     #define TYPE_TARGET_INFO "target-info" > >>>>>>>   +#define TYPE_TARGET_SPECIFIC "target-specific" > >>>>>>> + > >>>>>>> +typedef struct TargetSpecific TargetSpecific; > >>>>>>> + > >>>>>>> +typedef struct TargetSpecificClass { > >>>>>>> +    InterfaceClass parent_class; > >>>>>>> + > >>>>>>> +    bool (*is_available)(void); > >>>>>>> +} TargetSpecificClass; > >>>>>>> + > >>>>>>> +#define TARGET_SPECIFIC(obj) \ > >>>>>>> +    INTERFACE_CHECK(TargetSpecific, (obj), TYPE_TARGET_SPECIFIC) > >>>>>>> +DECLARE_CLASS_CHECKERS(TargetSpecificClass, TARGET_SPECIFIC, > >>>>>>> +                       TYPE_TARGET_SPECIFIC) > >>>>>> > >>>>>> Looking through the series,I don't really see the point > >>>>>> in this interface.   Why is this not possible to do by > >>>>>> adding 'is_available' to MachineClass.  It would make > >>>>>> the rest of the series simpler and especially avoid the > >>>>>> need to introduced yet more series of macros for defining > >>>>>> machine classes. > >>>>>> > >>>>> > >>>>> We'll need the exact same interface for cpus, and devices also. > >>>>> IMHO, it > >>>>> makes sense to have this in an external interface, instead of > >>>>> forcing it > >>>>> to be present in all cpus/devices/machines. I also considered > >>>>> adding it > >>>>> directly in Object class directly (would be the simplest), but I > >>>>> felt it > >>>>> would be hard to motivate it. > >>>> > >>>> I don't see a need for the common interface across cpus/devices/etc as > >>>> as code that's filtering only cares about the specific types. It also > >>>> definitely doesn't beloong in Object class, but the Object class could > >>>> be changed to make it simpler. > >>>> > >>> > >>> We agree on this. > >>> > >>>> The object_class_get_list() method could get a 'bool > >>>> filter(ObjectClass *cl)' > >>>> callback which could be invoked on each class to filter it. > >>>> > >>>> That said I find it pretty undesirable as an approach that we're > >>>> registering classes that can't then be used in a given situation. > >>>> This has a ripple effect where every bit of code that iterates over > >>>> classes needs changing to add filtering after the fact. It is also > >>>> not great for scalability, as it means every QEMU process will have > >>>> the union of all classes for all targets registered, most of which > >>>> have to be discarded / ignored at runtime. > >>>> > >>> > >>> This is inherent to the nature of having a single binary. > >>> We need to cover those two requirements: > >>> 1. having a filter mechanism (per target) > >>> 2. have all the classes accessible for the heterogeneous machines that > >>> will be coming in the future > >>> > >>> 1. could be covered by what you describe, however, it breaks 2. For > >>> this, you need to be able to register all types by design. > >> > >> > >> Even the heterogeneous machines aren't going to need all the > >> classes from all 30+ targets that QEMU supports. > >> > >> IIUC, the current approach relies on '--target ' to select > >> which target we need. Would the heterogeneous machines not just > >> change that to allow "--target --target ". It still > >> looks like we should be able to significantly limit  what we > >> register for heterogeneous machines. > > > > Heterogeneous binary won't filter anything at runtime (if we want > > to filter components we already have Kconfig at compile time). > > > > "--target " is only needed to have a single binary backward > > compatible. If you use it, you fall back to single architecture > > (our current binaries). If you want anything heterogeneous, you > > can not use it. This will be by design. > > I've been thinking about it yesterday, and we could apply the paradigm > "register only classes that will be used". For heterogeneous machine, > either we'll provide a "none" target, which enables all target, or use > --target aarch64,riscv64, like Daniel proposed. > > I will implement what Daniel asked for v2. > However, please be aware it will be probably be more invasive and > verbose, since we'll need to add macros and stuff to have conditional > type_register_static. > > I would like to avoid doing a change you asked, and have no further > comment after that or something like "it was better before". > Do we agree on this Daniel? That is an unreasonable request - I can't approve of a patch series that doesn't exist yet. I can only say that I don't think the current series is a desirable approach and make suggestions of what I think is (hopefully) a better way. Something else that I didn't consider previously is possible interaction with modules. Much of our use of modules is to make backends loadable, but we've got a few loadable devices too. It seems likely that with the single binary model we'll have greater motivation to make more device & machine code into loadable modules, as people have repeatedly pushed us to have a lower mandatory footprint for QEMU. The loadable modules relies on some metadata defined in the source code alongside the type info. For example static const TypeInfo emulated_card_info = { .name = TYPE_EMULATED_CCID, .parent = TYPE_CCID_CARD, .instance_size = sizeof(EmulatedState), .class_init = emulated_class_initfn, }; module_obj(TYPE_EMULATED_CCID); module_kconfig(USB); In particular it feels like the module_kconfig() and module_arch() metadata have overlap with what you're trying todo in this series. So I wonder if we could generalize the module metadata so that it serves a broader set of use cases. Instead of having to manually write conditional logic in XXX_register_type() methods, perhaps we can do the right thing automatically in type_register() using the metadata we collect from the code ? With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|