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 E4A98606A31C for ; Thu, 12 Nov 2026 07:45:28 +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=OI7hU1Wv Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xRPUC-0007ck-N2; Thu, 12 Nov 2026 02:44:44 -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 1xRPU6-0007bW-I4 for qemu-devel@nongnu.org; Thu, 12 Nov 2026 02:44:38 -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 1xRPU4-0006ek-K5 for qemu-devel@nongnu.org; Thu, 12 Nov 2026 02:44:38 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1794469474; 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=QslGCBPxyZS5ODa03J/suWTZiylSnpDcG5Q6LGtP3lY=; b=OI7hU1Wvu4VKfzUAODhg2VYtUH/N40TRx9CnUtif0ZCJYkII51CQsB5OBBBbHdm72z3n4t t3AUzlzr9ziAOb1QzaPc09xvKmAyDDKiRgckw2AbX8wp7DnnYo4KHN+llz/b/oP8LPpOWH 364U/nFIJSTjsZJXoiR64b/5Dh28qEI= 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-639-jpydFdRgPNm_YAz04Mrh-Q-1; Thu, 12 Nov 2026 02:44:33 -0500 X-MC-Unique: jpydFdRgPNm_YAz04Mrh-Q-1 X-Mimecast-MFC-AGG-ID: jpydFdRgPNm_YAz04Mrh-Q_1794469472 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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BAFEF18002CB; Thu, 12 Nov 2026 07:44:31 +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 3DD3530000D3; Thu, 12 Nov 2026 07:44:31 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id B6BF421E6A04; Thu, 12 Nov 2026 08:44:28 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: qemu-devel@nongnu.org, david@kernel.org, imammedo@redhat.com, peter.maydell@linaro.org Subject: Re: [PATCH 1/7] backends/hostmem: Drop redundant validation of property "size" In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Wed, 11 Nov 2026 12:45:04 +0000") References: <20261111122342.634370-1-armbru@redhat.com> <20261111122342.634370-2-armbru@redhat.com> Date: Thu, 12 Nov 2026 08:44:28 +0100 Message-ID: <87fqx6sdcz.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=170.10.129.124; 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_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=-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 Daniel P. Berrang=C3=A9 writes: > On Wed, Nov 11, 2026 at 01:23:36PM +0100, Markus Armbruster wrote: >> Property "size" is mandatory, and its setter >> host_memory_backend_set_size() rejects value zero. Delete the >> redundant checks for zero in the .alloc() callbacks. >>=20 >> Signed-off-by: Markus Armbruster >> --- >> backends/hostmem-epc.c | 5 ----- >> backends/hostmem-file.c | 4 ---- >> backends/hostmem-memfd.c | 5 ----- >> backends/hostmem-ram.c | 5 ----- >> backends/hostmem-shm.c | 5 ----- >> 5 files changed, 24 deletions(-) > > Reviewed-by: Daniel P. Berrang=C3=A9 > > ...it is a shame this was/is dead code, since the actual error message > from host_memory_backend_set_size() is (IMHO) worse than that from the > unreachable code you're deleting > > $ ./build/qemu-system-x86_64 -object memory-backend-ram,size=3D0,id=3Df= oo > qemu-system-x86_64: property 'size' of memory-backend-ram doesn't take = value '0' Fair point. > as a separate patch I might suggest > > diff --git a/backends/hostmem.c b/backends/hostmem.c > index 173d042be35..f523dce6eb0 100644 > --- a/backends/hostmem.c > +++ b/backends/hostmem.c > @@ -77,8 +77,8 @@ host_memory_backend_set_size(Object *obj, Visitor *= v, const char *name, if (host_memory_backend_mr_inited(backend)) { error_setg(errp, "cannot change property %s of %s ", name, object_get_typename(obj)); return; } if (!visit_type_size(v, name, &value, errp)) { return; > } > if (!value) { > error_setg(errp, > - "property '%s' of %s doesn't take value '%" PRIu6= 4 "'", > - name, object_get_typename(obj), value); > + "cannot create '%s' with a size of 0", > + object_get_typename(obj)); > return; > } > backend->size =3D value; > > so that we get the nicer message: > > $ ./build/qemu-system-x86_64 -object memory-backend-ram,size=3D0,id= =3Dfoo > qemu-system-x86_64: cannot create 'memory-backend-ram' with a size of= 0 Your message assumes that the property is only ever set on behalf of an object creation request. Not true in general, qom-set exists. I believe it's true here due to the host_memory_backend_mr_inited() guard. But that's not entirely obvious, isn't it? Possible phrasings that don't assume this: property 'size' of 'memory-backend-ram' cannot be zero cannot set property 'size' of 'memory-backend-ram' to zero Is one of them good enough? I doubt this error is common. There are enough "doesn't take value" error messages elsewhere to justify a small series of its own.