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 BB7CE606A33F for ; Thu, 12 Nov 2026 08:13:37 +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=XsFs8+uf Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1xRPvU-00029L-Ju; Thu, 12 Nov 2026 03:12:56 -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 1xRPvS-00028a-Lm for qemu-devel@nongnu.org; Thu, 12 Nov 2026 03:12:54 -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 1xRPvQ-0005I0-Ks for qemu-devel@nongnu.org; Thu, 12 Nov 2026 03:12:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1794471169; h=from:from:reply-to: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=JWAI2Y9ia224WO3jwqbLkRnKp/+jvxkbYe9e8GVmT5Y=; b=XsFs8+ufTLfw5mZ8HgtWitEiXKWac8gE6BqL3Svny7cxvwfUx6j4A9H6cAmTslHLGC56Y1 elC7rtVerut0WE5KiNwo3NZPjVnI9unI+IRPF/EnOa1aeNz4mySt84eORUfyIg4+yuUb99 TJ5K9PMRH+xklj/keUxn+V4sg2rl+4I= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-517-A2qgD0olMYSeFLd-rrcTRg-1; Thu, 12 Nov 2026 03:12:46 -0500 X-MC-Unique: A2qgD0olMYSeFLd-rrcTRg-1 X-Mimecast-MFC-AGG-ID: A2qgD0olMYSeFLd-rrcTRg_1794471165 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E36A11955E85; Thu, 12 Nov 2026 08:12:44 +0000 (UTC) Received: from redhat.com (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 666AE30001B9; Thu, 12 Nov 2026 08:12:43 +0000 (UTC) Date: Thu, 12 Nov 2026 08:12:40 +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 1/7] backends/hostmem: Drop redundant validation of property "size" Message-ID: References: <20261111122342.634370-1-armbru@redhat.com> <20261111122342.634370-2-armbru@redhat.com> <87fqx6sdcz.fsf@pond.sub.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87fqx6sdcz.fsf@pond.sub.org> User-Agent: Mutt/2.4.3 (2026-10-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 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 Thu, Nov 12, 2026 at 08:44:28AM +0100, Markus Armbruster wrote: > Daniel P. Berrangé 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. > >> > >> 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. Berrangé > > > > ...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=0,id=foo > > 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 '%" PRIu64 "'", > > - name, object_get_typename(obj), value); > > + "cannot create '%s' with a size of 0", > > + object_get_typename(obj)); > > return; > > } > > backend->size = value; > > > > so that we get the nicer message: > > > > $ ./build/qemu-system-x86_64 -object memory-backend-ram,size=0,id=foo > > 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. I'm fine with either of those, perhaps mildly leaning towards the second. > There are enough "doesn't take value" error messages elsewhere to > justify a small series of its own. 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 :|