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 44970606A88C for ; Wed, 11 Nov 2026 12:17:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=YxJiocIh Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xR7Ft-0007Wb-UN; Wed, 11 Nov 2026 07:16:45 -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 1xR7Ft-0007Vu-15 for qemu-devel@nongnu.org; Wed, 11 Nov 2026 07:16:45 -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 1xR7Fr-0005C7-EZ for qemu-devel@nongnu.org; Wed, 11 Nov 2026 07:16:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1794399402; 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=d+3dNTb5C6Yaz6YPsOrwsde4hWWwrBWk01C5joDfFzs=; b=YxJiocIhCNrvyc5kvSRqiwDZPS5CFirUEd+7bTihF4LOvNnMgS29lCmbUde+5R8iHjxXaf ipJz62DHNjurU0iz18av45fRpj9rKIXMLvFriY9kSUGEUhItK7k0PYeO8OavDuMuC7J6Xb tQlbHhs90ydoh46nJ/KUsJW89VGR6Nk= 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-442-5EuLuomhPwObE-FY1lrdsA-1; Wed, 11 Nov 2026 07:16:41 -0500 X-MC-Unique: 5EuLuomhPwObE-FY1lrdsA-1 X-Mimecast-MFC-AGG-ID: 5EuLuomhPwObE-FY1lrdsA_1794399399 Received: from mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.95]) (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 541D018011E1; Wed, 11 Nov 2026 12:16:39 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.7]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A0CB6588; Wed, 11 Nov 2026 12:16:38 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 5CDA221E6A04; Wed, 11 Nov 2026 13:16:36 +0100 (CET) From: Markus Armbruster To: Peter Maydell Cc: Daniel P. =?utf-8?Q?Berrang=C3=A9?= , qemu-devel@nongnu.org, David Hildenbrand , Igor Mammedov , Paolo Bonzini , Marcelo Tosatti , "Michael S. Tsirkin" , Richard Henderson , Cornelia Huck , Halil Pasic , Eric Farman , qemu-s390x@nongnu.org, =?utf-8?Q?Marc-Andr=C3=A9_Lureau?= Subject: Re: qemu-system-x86_64 appears to have sgx-epc, but not memory-backend-epc In-Reply-To: (Peter Maydell's message of "Fri, 23 Oct 2026 11:44:10 +0100") References: <87zew5j3iv.fsf@pond.sub.org> Date: Wed, 11 Nov 2026 13:16:36 +0100 Message-ID: <87bj7vwokb.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 3.6 on 10.30.177.95 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 Peter Maydell writes: > On Fri, 23 Oct 2026 at 11:21, Daniel P. Berrang=C3=A9 wrote: >> >> On Thu, Oct 22, 2026 at 02:58:16PM +0200, Markus Armbruster wrote: >> > My build of qemu-system-x86_64 has device sgx-epc: >> > >> > --> {"execute": "qom-list-types", "arguments": {"implements": "sgx-ep= c"}} >> > <-- {"return": [{"name": "sgx-epc", "parent": "device"}]} >> > >> > The device as a link property to a memory-backend-epc: >> > >> > --> {"execute": "qom-list-properties", "arguments": {"typename": "sgx= -epc"}} >> > <-- {"return": [... >> > {"name": "memdev", "type": "link"= }, >> > ...]} >> > >> > However, type memory-backend-epc does not exist: > >> 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 ? > > TYPE_MEMORY_BACKEND_MEMFD does the same. I did a quick grep for > "calls to type_register not indented by exactly 4 spaces" and > I think the other cases are "misindented" or "data-driven > type registration" rather than trying to do things conditionally > (but I didn't actually look at all of them, instead making > guesses based on variable names, so maybe there's one or two > more I missed). Alright, I looked. In addition to "misindented" or "data-driven", I found: * register_types() in hostmem-memfd.c registers "memory-backend-memfd" only when a test of memfd_create() succeeds. This is what Peter reported. * virtio_ccw_gpu_register() in hw/s390x/virtio-ccw-gpu.c registers "virtio-gpu-ccw" only when have_virtio_ccw, which is true when hw/s390x/virtio-ccw.c gets compiled into the binary. So it's effectively compile-time conditional. I wish it was literally compile-time conditional, either in meson or using #if. * qemu_console_early_init() in ui/console-vc.c registers "chardev-vc" if it's not already registered. early_dbus_init() in ui/dbus.c, early_gtk_display_init() in ui/gtk.c, and spice_app_display_early_init() in ui/spice-app.c all register it. These are all QemuDisplay .early_init() callbacks. qemu_display_early_init() calls the selected display's .early_init(), if non-null. Because qemu_console_early_init() runs after qemu_display_early_init(), this always registers a "chardev-vc": the active display may register its own, and when it doesn't, we get ui/console-vc.c's. More moving parts than I'd like. I'm going to post patches for backends/hostmem-{epc,memfd}.c. I don't plan to clean up the other two at this time. [...]