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 EB61F606A31A for ; Tue, 27 Oct 2026 06:40:49 +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=bAxc7zsR Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xLarS-0004mw-Sh; Tue, 27 Oct 2026 02:40:42 -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 1xLarN-0004ll-D2 for qemu-devel@nongnu.org; Tue, 27 Oct 2026 02:40:37 -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 1xLarK-00012A-Na for qemu-devel@nongnu.org; Tue, 27 Oct 2026 02:40:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1793083232; 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=5z5W3Z46pEbzuofmxiQmotzJ2y3VKzyTvyPnwigDQqk=; b=bAxc7zsRzs1WliroRpbsjYGJ6JF7DBJQ0XmwB3IINo/yGIGLI+RdceeHkqQ/L76+DwocJn GtKBUhDgdKeIgQF4ifeTQv8i6lx1c/sUPR9FCHs/0FW8w0i496y+F84bqxgL0DWBStrROu 7pggW0rG8asrjhvz9o1u2hIWlQ8qG70= 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-157-5ypPBClDNFusxljbORYHvw-1; Tue, 27 Oct 2026 02:40:29 -0400 X-MC-Unique: 5ypPBClDNFusxljbORYHvw-1 X-Mimecast-MFC-AGG-ID: 5ypPBClDNFusxljbORYHvw_1793083228 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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 B93C51800BC6; Tue, 27 Oct 2026 06:40:27 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.2]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5CEFF1800444; Tue, 27 Oct 2026 06:40:27 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id EE20521E6A04; Tue, 27 Oct 2026 07:40:24 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: Peter Maydell , 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 12:07:54 +0100") References: <87zew5j3iv.fsf@pond.sub.org> Date: Tue, 27 Oct 2026 07:40:24 +0100 Message-ID: <87ecdbbq93.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 10.30.177.93 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.339, 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_H5=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=-7.6 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 Fri, Oct 23, 2026 at 11:44:10AM +0100, Peter Maydell wrote: >> 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-= epc"}} >> > > <-- {"return": [{"name": "sgx-epc", "parent": "device"}]} >> > > >> > > The device as a link property to a memory-backend-epc: >> > > >> > > --> {"execute": "qom-list-properties", "arguments": {"typename": "s= gx-epc"}} >> > > <-- {"return": [... >> > > {"name": "memdev", "type": "link"}, >> > > ...]} >> > > >> > > However, type memory-backend-epc does not exist: >>=20 >> > 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 ? >>=20 >> 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). >>=20 >> I guess maybe this is trying to work around the fact that the >> memory backend API doesn't give a backend any place to say >> "this is never going to work" early, because instance_init isn't >> allowed to fail, these objects aren't TYPE_DEVICE so they >> don't have "realize", and so the only other option is >> "fail every alloc call" ? > > The memory backends are all implementing the UserCreatable > interface, which provides a "complete" method where they > could gracefully report lack of the feature via 'errp'. Yes. > This is not obvious since UserCreatable is implemented in > the parent base class, but the subclasses could provide > their own 'complete' impl and chain up the parent impl David, Igor, can you clean this up? Or would you like me to try?