From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9B460C4332F for ; Wed, 8 Nov 2023 06:51:26 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r0cOX-0002WA-8b; Wed, 08 Nov 2023 01:50:34 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r0cOU-0002Vj-Q2 for qemu-devel@nongnu.org; Wed, 08 Nov 2023 01:50:30 -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 1r0cOT-0008CM-4N for qemu-devel@nongnu.org; Wed, 08 Nov 2023 01:50:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1699426227; 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: in-reply-to:in-reply-to:references:references; bh=HeILgklWo5c/K5HmT4p/bqlFrkeIgX1xE2OrWVAW+Ws=; b=Qlf3edXIfodr+ZX+BB73JT9TxYScE9qklI+NK2Gp8bRZ6NeAYJiQil5nZ14qn15y+c2f92 LGnGH9anIuWm4+iKVy9EBBkru0iYDPYUdwot/6OKlDz99LMhuCtEViKROJ3fOsg9e2zvEE difs07iLSgUmOKYBJiLKPsecPF3rzec= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-333-43ub48PpN62Tmf_dtkd01A-1; Wed, 08 Nov 2023 01:50:26 -0500 X-MC-Unique: 43ub48PpN62Tmf_dtkd01A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id E9CFC3C0E647; Wed, 8 Nov 2023 06:50:25 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BEBE940C6EB9; Wed, 8 Nov 2023 06:50:25 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id C002F21E6A1F; Wed, 8 Nov 2023 07:50:24 +0100 (CET) From: Markus Armbruster To: Kevin Wolf Cc: qemu-devel@nongnu.org, berrange@redhat.com, peter.maydell@linaro.org, pbonzini@redhat.com, philmd@linaro.org Subject: Re: [PATCH v2 11/12] qdev: Make netdev properties work as list elements References: <20231030142658.182193-1-kwolf@redhat.com> <20231030142658.182193-12-kwolf@redhat.com> <87jzr09uxe.fsf@pond.sub.org> Date: Wed, 08 Nov 2023 07:50:24 +0100 In-Reply-To: (Kevin Wolf's message of "Tue, 7 Nov 2023 14:35:12 +0100") Message-ID: <874jhwd9hr.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Kevin Wolf writes: > Am 02.11.2023 um 13:55 hat Markus Armbruster geschrieben: >> Kevin Wolf writes: >> >> > The 'name' parameter of QOM setters is primarily used to specify the name >> > of the currently parsed input element in the visitor interface. For >> > top-level qdev properties, this is always set and matches 'prop->name'. >> > >> > However, for list elements it is NULL, because each element of a list >> > doesn't have a separate name. Passing a non-NULL value runs into >> > assertion failures in the visitor code. >> >> Yes. visitor.h's big comment: >> >> * The @name parameter of visit_type_FOO() describes the relation >> * between this QAPI value and its parent container. When visiting >> * the root of a tree, @name is ignored; when visiting a member of an >> * object, @name is the key associated with the value; when visiting a >> * member of a list, @name is NULL; and when visiting the member of an >> * alternate, @name should equal the name used for visiting the >> * alternate. >> >> > Therefore, using 'name' in error messages is not right for property >> > types that are used in lists, because "(null)" isn't very helpful to >> > identify what QEMU is complaining about. >> >> We get "(null)" on some hosts, and SEGV on others. > > Fair, I can add "(or even a segfault)" to the commit message. > >> Same problem in all property setters and getters (qdev and QOM), I >> presume. The @name parameter looks like a death trap. Thoughts? > > All property setters and getters that abuse @name instead of just > passing it to the visitor. I don't know how many do, but let's see: > > * qdev_prop_size32 uses @name in an error message > > * Array properties themselves use @name in an error message, too > (preexisting) > > * qdev-properties-system.c has more complicated properties, which have > the same problem: drive, chardev, macaddr, netdev (before this patch), > reserved_region, pci_devfn (one error path explicitly considers name > == NULL, but another doesn't), uuid > > * Outside of hw/core/ we may have some problematic properties, too. > I found qdev_prop_tpm, and am now too lazy to go through all devices. > These are probably specialised enough that they are less likely to be > used in arrays. > > We can fix these on top of this series, though we should probably first > figure out what the best way to replace it is to avoid touching > everything twice. Makes sense. >> Any reproducer known before the next patch? > > Not to me. > >> > Change netdev properties to use 'prop->name' instead, which will contain >> > the name of the array property after switching array properties to lists >> > in the external interface. >> >> Points at the entire array property without telling the user which of >> the elements is at fault. Sure better than NULL. I'm not asking you to >> improve the error message further. Mention the error message's lack of >> precision in the commit message? > > Can do. > > At least the input visitor has better ways internally to identify the > currently visited object with full_name(). If other visitor types can do > similar things, maybe extending the public visitor interface to access > the name would be possible? Yes, there's a need for better error reporting around visitors, ideally without doing it in every visitor like the QObject input visitor does. I've thought about it, but only briefly, and without a conclusion. I figure your idea is to provide a visitor method to get a malloced string describing the thing being visited. Might work, but to know for sure, we have to try. This could also help with getting rid of the dangerous @name use we discussed above. Thanks!