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 X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9E26C54FCB for ; Mon, 27 Apr 2020 15:38:34 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id B4B5520656 for ; Mon, 27 Apr 2020 15:38:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Qf+Zl6zg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B4B5520656 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51871 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jT5q5-0002xj-Om for qemu-devel@archiver.kernel.org; Mon, 27 Apr 2020 11:38:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:39490) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jT5oV-0000zO-1b for qemu-devel@nongnu.org; Mon, 27 Apr 2020 11:36:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jT5oT-0007dD-OB for qemu-devel@nongnu.org; Mon, 27 Apr 2020 11:36:54 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:57385 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jT5oT-0007c3-4s for qemu-devel@nongnu.org; Mon, 27 Apr 2020 11:36:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588001811; 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=ihZD/jqVN/p9dTPL/nOV9Z5F8BiTzerDtIyvU5zRP3o=; b=Qf+Zl6zgqsrP1BoSMN9uklWFrdBoUL1N3XpYffi6CH/kTKRi0n0CrMQJjsnep5dkhTYdtQ 3Cy6+IzJV42dW/cIIpySQE+DUWjg91NJG/ViKVatgDBDn8eF/SgZE9BdqaxCcapcCWkREQ 9k598lGMtSp9LV94V4IsT1X5uQX0NaU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-439-glOh4eyFNWmA0z7TE3JB6g-1; Mon, 27 Apr 2020 11:36:50 -0400 X-MC-Unique: glOh4eyFNWmA0z7TE3JB6g-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1668E800685; Mon, 27 Apr 2020 15:36:49 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-113-6.ams2.redhat.com [10.36.113.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A49D35D9DA; Mon, 27 Apr 2020 15:36:48 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 2273611358BC; Mon, 27 Apr 2020 17:36:47 +0200 (CEST) From: Markus Armbruster To: qemu-devel@nongnu.org Subject: Re: Questionable aspects of QEMU Error's design References: <87o8sblgto.fsf@dusky.pond.sub.org> <87blo7heag.fsf@dusky.pond.sub.org> Date: Mon, 27 Apr 2020 17:36:47 +0200 In-Reply-To: <87blo7heag.fsf@dusky.pond.sub.org> (Markus Armbruster's message of "Sat, 04 Apr 2020 09:59:35 +0200") Message-ID: <87blndey9c.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.81; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/26 23:33:12 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Vladimir Sementsov-Ogievskiy , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Markus Armbruster writes: > Markus Armbruster writes: > >> QEMU's Error was patterned after GLib's GError. Differences include: > [...] >> * Return value conventions >> >> Common: non-void functions return a distinct error value on failure >> when such a value can be defined. Patterns: >> >> - Functions returning non-null pointers on success return null pointer >> on failure. >> >> - Functions returning non-negative integers on success return a >> negative error code on failure. >> >> Different: GLib discourages void functions, because these lead to >> awkward error checking code. We have tons of them, and tons of >> awkward error checking code: >> >> Error *err =3D NULL; >> frobnicate(arg, &err); >> if (err) { >> ... recover ... >> error_propagate(errp, err); >> } >> >> instead of >> >> if (!frobnicate(arg, errp)) >> ... recover ... >> } >> >> Can also lead to pointless creation of Error objects. >> >> I consider this a design mistake. Can we still fix it? We have more >> than 2000 void functions taking an Error ** parameter... >> >> Transforming code that receives and checks for errors with Coccinelle >> shouldn't be hard. Transforming code that returns errors seems more >> difficult. We need to transform explicit and implicit return to >> either return true or return false, depending on what we did to the >> @errp parameter on the way to the return. Hmm. > [...] > > To figure out what functions with an Error ** parameter return, I used > Coccinelle to find such function definitions and print the return types. > Summary of results: > > 2155 void > 873 signed integer > 494 pointer > 153 bool > 33 unsigned integer > 6 enum > --------------------- > 3714 total > > I then used Coccinelle to find checked calls of void functions (passing > &error_fatal or &error_abort is not considered "checking" here). These > calls become simpler if we make the functions return a useful value. I > found a bit under 600 direct calls, and some 50 indirect calls. > > Most frequent direct calls: > > 127 object_property_set_bool > 27 qemu_opts_absorb_qdict > 16 visit_type_str > 14 visit_type_int > 10 visit_type_uint32 > > Let's have a closer look at object_property_set() & friends. Out of > almost 1000 calls, some 150 are checked. While I'm sure many of the > unchecked calls can't actually fail, I am concerned some unchecked calls > can. > > If we adopt the convention to return a value that indicates success / > failure, we should consider converting object.h to it sooner rather than > later. > > Please understand these are rough numbers from quick & dirty scripts. FYI, I'm working on converting QemuOpts, QAPI visitors and QOM. I keep running into bugs. So far: [PATCH v2 for-5.1 0/9] qemu-option: Fix corner cases and clean up [PATCH for-5.1 0/5] qobject: Minor spring cleaning [PATCH v2 00/14] Miscellaneous error handling fixes [PATCH 0/4] Subject: [PATCH 0/4] smbus: SPD fixes [PATCH 0/3] fuzz: Probably there is a better way to do this [PATCH v2 00/15] qapi: Spring cleaning [PATCH 00/11] More miscellaneous error handling fixes I got another one coming for QOM and qdev before I can post the conversion. Vladimir, since the conversion will mess with error_propagate(), I'd like to get it in before your auto-propagation work.