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 E60DFCD98E4 for ; Tue, 16 Jun 2026 16:44:08 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wZWtB-0001hd-0c; Tue, 16 Jun 2026 12:43:49 -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 1wZWt8-0001gp-Rg for qemu-devel@nongnu.org; Tue, 16 Jun 2026 12:43:46 -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 1wZWt7-0002Bv-7P for qemu-devel@nongnu.org; Tue, 16 Jun 2026 12:43:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1781628223; 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=ePpdY+5KphUB9g0JAZw709yvKIEar2RAnrbS2KtJajM=; b=dgFKLegNBb+Am3V4kuH4co3nbivTf9aPnPAWDJneJr1fJnvHor3fPtKW0bJSZXsoNBUrM8 6aMXJDcRXQJ4GuCbxEc1JS74DPupfhtNreVDqi/iqMF6KLcW/Mel61QYAPTF6LptG9YnUn Ts6AEap27suNXwvv4+3En2iyee89hEU= 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-207-Q76XmsxkNbW9Y3VO5jp9iA-1; Tue, 16 Jun 2026 12:43:40 -0400 X-MC-Unique: Q76XmsxkNbW9Y3VO5jp9iA-1 X-Mimecast-MFC-AGG-ID: Q76XmsxkNbW9Y3VO5jp9iA_1781628218 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 68E6E1805C06; Tue, 16 Jun 2026 16:43:38 +0000 (UTC) Received: from redhat.com (unknown [10.44.49.111]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 93918180034F; Tue, 16 Jun 2026 16:43:32 +0000 (UTC) Date: Tue, 16 Jun 2026 17:43:29 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Maydell Cc: qemu-devel@nongnu.org, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Pierrick Bouvier , Peter Xu , =?utf-8?B?SGVydsOp?= Poussineau , Alex =?utf-8?Q?Benn=C3=A9e?= , "Michael S. Tsirkin" , Akihiko Odaki , Aurelien Jarno , Fabiano Rosas , Paolo Bonzini , BALATON Zoltan , Mark Cave-Ayland , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [RFC 2/7] qom: deprecated embedding object structs within other objects Message-ID: References: <20260616155554.264412-1-berrange@redhat.com> <20260616155554.264412-3-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 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: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H3=0.001, RCVD_IN_MSPIKE_WL=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 Tue, Jun 16, 2026 at 05:15:22PM +0100, Peter Maydell wrote: > On Tue, 16 Jun 2026 at 16:56, Daniel P. Berrangé wrote: > > > > The QOM APIs currently allow objects to be either allocated directly > > on the heap, or statically embedded inside the struct of another object. > > > > For the latter QOM has logic to avoid calling 'free' on the object when > > finalizers complete, however, this is not sufficient to make the > > practice safe. > > > > Users of QOM expect that if they call "object_ref" to acquire their own > > reference, then object will never be freed as long as they hold it. > > > > This expectation is broken when an instance is embedded, as the "owner" > > object's may be finalized, which frees the memory that is storing the > > embedded QOM instance, even if its ref-count is still live. > > > > Worse still is that a user of a QOM object cannot easily tell if the > > instance they're using is embedded or directly heap allocated. > > > > Mark the APIs for embedding objects as deprecated as the first step > > towards removal of this flawed design concept. All objects must now > > be directly heap allocated going forward, and existing usage must be > > incrementally converted. > > I think if you mark an API that we call in 800+ places and 150+ files > as deprecated, mostly what will happen is nobody ever turns on the > --enable-deprecated option because the output will be full of noise... That is a challenge. The baseline is that developers have no visibility of use of deprecated APIs at all, and we barely even document them. My thought is that even if --enable-deprecated is rarely enabled, at least having QEMU_DEPRECATED visible in the header files is a red flag for developers to look elsewhere for their solution. 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 :|