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 DB2A8C2BA1E for ; Mon, 6 Apr 2020 14:09:36 +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 A719D22246 for ; Mon, 6 Apr 2020 14:09:36 +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="giYhbe80" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A719D22246 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]:60724 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jLSRT-0002mF-SL for qemu-devel@archiver.kernel.org; Mon, 06 Apr 2020 10:09:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56226) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jLSNi-0007fq-ND for qemu-devel@nongnu.org; Mon, 06 Apr 2020 10:05:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jLSNg-0008IA-Os for qemu-devel@nongnu.org; Mon, 06 Apr 2020 10:05:41 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:39431 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jLSNg-0008I2-L4 for qemu-devel@nongnu.org; Mon, 06 Apr 2020 10:05:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586181940; 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=Z+4kbNaYKSc37XZ9+Furg1Tl1WS9KYQK9628t6eyCzg=; b=giYhbe80+Qk+X1dgI+1RjV0QmEzPx0wgIC42B1M+FOF1ufHsZrIdzG9ErSg2Bhgym8vgYa cOJswSRgHbTfNgNLZkcrWIn+8Tq75aWvBhZOHVvPkJgKjBBu3ELlIKWUDPlq5Ni99wf87X 5kUMf0EBFKnWsOA7BsWEhsW6A3+a/og= 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-315-xr3WpJeUP1-xHtW-G5EonQ-1; Mon, 06 Apr 2020 10:05:37 -0400 X-MC-Unique: xr3WpJeUP1-xHtW-G5EonQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0AD031005509; Mon, 6 Apr 2020 14:05:36 +0000 (UTC) Received: from localhost (ovpn-116-201.gru2.redhat.com [10.97.116.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id 43D62277B6; Mon, 6 Apr 2020 14:05:33 +0000 (UTC) Date: Mon, 6 Apr 2020 11:05:31 -0300 From: Eduardo Habkost To: Markus Armbruster Subject: Re: Questionable aspects of QEMU Error's design Message-ID: <20200406140531.GE299832@habkost.net> References: <87o8sblgto.fsf@dusky.pond.sub.org> <87blo7heag.fsf@dusky.pond.sub.org> <87sghjfre8.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87sghjfre8.fsf@dusky.pond.sub.org> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/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 , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, Paolo Bonzini , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sat, Apr 04, 2020 at 12:59:27PM +0200, Markus Armbruster wrote: > Markus Armbruster writes: >=20 > > 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 point= er > >> 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 mor= e > >> than 2000 void functions taking an Error ** parameter... > >> > >> Transforming code that receives and checks for errors with Coccinell= e > >> 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 call= s > > can. > > > > If we adopt the convention to return a value that indicates success / > > failure, we should consider converting object.h to it sooner rather tha= n > > later. > > > > Please understand these are rough numbers from quick & dirty scripts. >=20 > Paolo, Daniel, Eduardo, >=20 > Please pick one for QOM: Replying this without reading the whole discussion and context: >=20 > * Do nothing. Looks like >=20 > object_property_set_bool(..., &err); > if (err) { > error_propagate(errp, err); > return; > } >=20 > * Return true on success, false on error. Looks like >=20 I prefer this one. > if (!object_property_set_bool(..., errp)) { > return; > } >=20 > * Return 0 on success, -1 on error. Looks like >=20 > if (object_property_set_bool(..., errp) < 0) { > return; > } >=20 > This is slightly more likely to require line wrapping than the > previous one. --=20 Eduardo