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 C9AD9606A31C for ; Wed, 11 Nov 2026 12:54:32 +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=O/Lfn/zb Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xR7qJ-0004y7-V9; Wed, 11 Nov 2026 07:54:25 -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 1xR7pq-0004wN-0B for qemu-devel@nongnu.org; Wed, 11 Nov 2026 07:53:54 -0500 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 1xR7po-00056H-1L for qemu-devel@nongnu.org; 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Wed, 11 Nov 2026 12:53:45 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9B16E436; Wed, 11 Nov 2026 12:53:44 +0000 (UTC) Date: Wed, 11 Nov 2026 12:53:41 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: qemu-devel@nongnu.org, david@kernel.org, imammedo@redhat.com, peter.maydell@linaro.org Subject: Re: [PATCH 4/7] backends/hostmem-epc: Register QOM type unconditionally Message-ID: References: <20261111122342.634370-1-armbru@redhat.com> <20261111122342.634370-5-armbru@redhat.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261111122342.634370-5-armbru@redhat.com> User-Agent: Mutt/2.4.3 (2026-10-09) X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 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: 5 X-Spam_score: 0.5 X-Spam_bar: / X-Spam_report: (0.5 / 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 On Wed, Nov 11, 2026 at 01:23:39PM +0100, Markus Armbruster wrote: > The example from docs/system/i386/sgx.rst section "Launching a guest" > fails for me like this: > > $ qemu-system-x86_64 -cpu host,+sgx-provisionkey -object memory-backend-epc,id=mem1,size=64M,prealloc=on -M sgx-epc.0.memdev=mem1,sgx-epc.0.node=0 > qemu-system-x86_64: invalid object type: memory-backend-epc > > Device "sgx-epc" has a link property to a "memory-backend-epc" (SgxEPC > member memdev). It's not optional, so we must create a > "memory-backend-epc" to be able to create an "sgx-epc". In the test > shown above, "sgx-epc" exists, but "memory-backend-epc" does not. > > The latter doesn't exist for me, because we register QOM type > "memory-backend-epc" only when we can open /dev/sgx_vepc read/write, > which fails for me. Such conditional registration is unusual and > problematic: > > 1. Management applications use introspection interfaces to find out > what a certain QEMU can do. Conditional type registration makes QOM > introspection results depend on the condition, which generally makes > them valid only for the process that produced them. Undesirable. > > 2. For user-creatable objects like "memory-backend-epc", it also makes > QAPI introspection unreliable: query-qmp-schema claims the type > exists (object-add argument @qom-type accepts "memory-backend-epc") > even when it doesn't. > > Conditional registration actually serves no purpose here, because we > still have to open /dev/sgx_vepc for real when we create the object, > and need and do handle errors then. > > Register unconditionally. The example now fails to create the object, > like this: > > qemu-system-x86_64: can't create 'memory-backend-epc': Could not open '/dev/sgx_vepc': No such file or directory Bonus points - this error message is orders of magnitude more useful to users than qemu-system-x86_64: invalid object type: memory-backend-epc which makes them think their QEMU is built wrong or outdated. > > Signed-off-by: Markus Armbruster > --- > backends/hostmem-epc.c | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) Reviewed-by: Daniel P. Berrangé > > diff --git a/backends/hostmem-epc.c b/backends/hostmem-epc.c > index e1c784249ff..bf5aecdfd45 100644 > --- a/backends/hostmem-epc.c > +++ b/backends/hostmem-epc.c > @@ -62,12 +62,7 @@ static const TypeInfo sgx_epc_backed_info = { > > static void register_types(void) > { > - int fd = qemu_open_old("/dev/sgx_vepc", O_RDWR); > - if (fd >= 0) { > - close(fd); > - > - type_register_static(&sgx_epc_backed_info); > - } > + type_register_static(&sgx_epc_backed_info); > } > > type_init(register_types); > -- > 2.55.0 > 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 :|