From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E23F7606A322 for ; Mon, 9 Nov 2026 14:30:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=JOEiWCAw Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xQQNp-0005dk-3H; Mon, 09 Nov 2026 09:30:06 -0500 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 1xQQNT-0005T6-1a for qemu-devel@nongnu.org; Mon, 09 Nov 2026 09:29:44 -0500 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 1xQQNR-0003rj-Ba for qemu-devel@nongnu.org; Mon, 09 Nov 2026 09:29:42 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1794234578; 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=VjayitvpK+RuIcoheEEHrCfH68raRoPPvO3X1dCoBmA=; b=JOEiWCAwkFnRFulPGzP7d38UIoHKN41Ac+Ktccr5C7qn99Naypu+3ZJ8ETcP7mxo8ZsJYs hZcrXDMSaVQ1lP2ofvmfwRRxjHozjTwwLp7aLjEL0Qga4IUiaSbMF0BvONWu61pr/7DF64 mnaKK2+Hk9Pwe9f6GsSSeXoLw2p2yuU= Received: from mx-prod-mc-06.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-306-aBPsUiroOiyXU00l20MvAQ-1; Mon, 09 Nov 2026 09:29:34 -0500 X-MC-Unique: aBPsUiroOiyXU00l20MvAQ-1 X-Mimecast-MFC-AGG-ID: aBPsUiroOiyXU00l20MvAQ_1794234573 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A13371800544; Mon, 9 Nov 2026 14:29:33 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.7]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4743230000E5; Mon, 9 Nov 2026 14:29:33 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 0174221E6A04; Mon, 09 Nov 2026 15:29:30 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: qemu-devel@nongnu.org, David Hildenbrand , Igor Mammedov , Paolo Bonzini , Marcelo Tosatti , "Michael S. Tsirkin" , Richard Henderson Subject: Re: qemu-system-x86_64 appears to have sgx-epc, but not memory-backend-epc In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Fri, 23 Oct 2026 11:20:45 +0100") References: <87zew5j3iv.fsf@pond.sub.org> Date: Mon, 09 Nov 2026 15:29:30 +0100 Message-ID: <87qzgu2i45.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 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: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, 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-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Daniel P. Berrang=C3=A9 writes: > On Thu, Oct 22, 2026 at 02:58:16PM +0200, Markus Armbruster wrote: >> My build of qemu-system-x86_64 has device sgx-epc: >>=20 >> --> {"execute": "qom-list-types", "arguments": {"implements": "sgx-epc"= }} >> <-- {"return": [{"name": "sgx-epc", "parent": "device"}]} >>=20 >> The device as a link property to a memory-backend-epc: >>=20 >> --> {"execute": "qom-list-properties", "arguments": {"typename": "sgx-e= pc"}} >> <-- {"return": [... >> {"name": "memdev", "type": "link"}, >> ...]} >>=20 >> However, type memory-backend-epc does not exist: >>=20 >> --> {"execute": "qom-list-types", "arguments": {"implements": "memory-b= ackend"}} >> <-- {"return": [{"name": "memory-backend-ram", "parent": "memory-backen= d"}, {"name": "memory-backend-file", "parent": "memory-backend"}, {"name": = "memory-backend-memfd", "parent": "memory-backend"}, {"name": "memory-backe= nd-shm", "parent": "memory-backend"}]} > > There is some rather dubious code that conditionally registers > the type > > static void register_types(void) > { > int fd =3D qemu_open_old("/dev/sgx_vepc", O_RDWR); > if (fd >=3D 0) { > close(fd); > > type_register_static(&sgx_epc_backed_info); > } > } > > > Normal practice is for types to be unconditionally registered. Do we > have any examples outside of this SGX case where we conditionally > register types ? Should we change this to follow normal practice ? Loosely related: conditional *class* properties. Example: static void memfd_backend_class_init(ObjectClass *oc, const void *data) { HostMemoryBackendClass *bc =3D MEMORY_BACKEND_CLASS(oc); bc->alloc =3D memfd_backend_memory_alloc; if (qemu_memfd_check(MFD_HUGETLB)) { object_class_property_add_bool(oc, "hugetlb", memfd_backend_get_hugetlb, memfd_backend_set_hugetlb); object_class_property_set_description(oc, "hugetlb", "Use huge pages"); object_class_property_add(oc, "hugetlbsize", "uint64", &uint64_type_info, memfd_backend_get_hugetlbsize, memfd_backend_set_hugetlbsize, NULL, NULL); object_class_property_set_description(oc, "hugetlbsize", "Huge pages size (ex: 2M,= 1G)"); } [...] } These properties are also declared in qapi/qom.json if CONFIG_LINUX. QAPI introspection (query-qmp-schema) shows them then. QOM introspection (qom-list-properties etc.) only shows them when the MFD_HUGETLB check succeeded. Feels undesirable to me. Should we instead make them read-only when the check fails?