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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 153E1C43331 for ; Thu, 2 Apr 2020 08:50:09 +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 D689E208E4 for ; Thu, 2 Apr 2020 08:50:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JvgGl/T3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D689E208E4 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]:35430 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jJvY8-0004Gm-03 for qemu-devel@archiver.kernel.org; Thu, 02 Apr 2020 04:50:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44765) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jJvVa-0001SL-U2 for qemu-devel@nongnu.org; Thu, 02 Apr 2020 04:47:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jJvVZ-0005jG-Gw for qemu-devel@nongnu.org; Thu, 02 Apr 2020 04:47:30 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:49440 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 1jJvVZ-0005iP-C8 for qemu-devel@nongnu.org; Thu, 02 Apr 2020 04:47:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585817248; 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=iTekKKCPc758a1jnx1olfZfMBfwq/Fz4ZvFrm+PuqcA=; b=JvgGl/T3rgCl2mt9BlW6nFLrxlNE6GZ3fOaxpzIooV00vOBhlKyEIdmcXjUv9Q65XGwJTc KFwi7asZ50wFgrjZzCYgq/U4lQbhTEEObzxtmTlii2BHj88ujVpYHP80y3TdtTgTl6SrqB Yn5e/eLKk3nUWnTfmouHYK5PNoSKHGw= 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-420-BZ6BUx9ZPXKx1jb894-m3g-1; Thu, 02 Apr 2020 04:47:25 -0400 X-MC-Unique: BZ6BUx9ZPXKx1jb894-m3g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 034AE108442D; Thu, 2 Apr 2020 08:47:24 +0000 (UTC) Received: from redhat.com (unknown [10.36.110.55]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4B2285C1B0; Thu, 2 Apr 2020 08:47:22 +0000 (UTC) Date: Thu, 2 Apr 2020 09:47:19 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Subject: Re: Questionable aspects of QEMU Error's design Message-ID: <20200402084719.GB423991@redhat.com> References: <87o8sblgto.fsf@dusky.pond.sub.org> <87sghmbfgc.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87sghmbfgc.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , Vladimir Sementsov-Ogievskiy , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 02, 2020 at 07:54:11AM +0200, Markus Armbruster wrote: > Peter Maydell writes: >=20 > > On Wed, 1 Apr 2020 at 10:03, Markus Armbruster wrot= e: > >> > >> QEMU's Error was patterned after GLib's GError. Differences include: > > > > From my POV the major problem with Error as we have it today > > is that it makes the simple process of writing code like > > device realize functions horrifically boilerplate heavy; > > for instance this is from hw/arm/armsse.c: > > > > object_property_set_link(cpuobj, OBJECT(&s->cpu_container[i]), > > "memory", &err); > > if (err) { > > error_propagate(errp, err); > > return; > > } > > object_property_set_link(cpuobj, OBJECT(s), "idau", &err); > > if (err) { > > error_propagate(errp, err); > > return; > > } > > object_property_set_bool(cpuobj, true, "realized", &err); > > if (err) { > > error_propagate(errp, err); > > return; > > } > > > > 16 lines of code just to set 2 properties on an object > > and realize it. It's a lot of boilerplate and as > > a result we frequently get it wrong or take shortcuts > > (eg forgetting the error-handling entirely, calling > > error_propagate just once for a whole sequence of > > calls, taking the lazy approach and using err_abort > > or err_fatal when we ought really to be propagating > > an error, etc). I haven't looked at 'auto propagation' > > yet, hopefully it will help? >=20 > With that, you can have >=20 > object_property_set_link(cpuobj, OBJECT(&s->cpu_container[i]), > "memory", errp); > if (*errp) { > return; > } > object_property_set_link(cpuobj, OBJECT(s), "idau", errp); > if (*errp) { > return; > } > object_property_set_bool(cpuobj, true, "realized", errp); > if (*errp) { > return; > } >=20 > but you have to add >=20 > ERRP_AUTO_PROPAGATE(); >=20 > right at the beginning of the function. >=20 > It's a small improvement. A bigger one is >=20 > if (object_property_set_link(cpuobj, OBJECT(&s->cpu_container[i])= , > "memory", errp)) { > return; > } > if (object_property_set_link(cpuobj, OBJECT(s), "idau", errp)) { > return; > } > if (object_property_set_bool(cpuobj, true, "realized", errp)) { > return; > } >=20 > This is item "Return value conventions" in the message you replied to. Even better, we can then string the checks together if (object_property_set_link(cpuobj, OBJECT(&s->cpu_container[i]), "memory", errp) || object_property_set_link(cpuobj, OBJECT(s), "idau", errp) || object_property_set_bool(cpuobj, true, "realized", errp)) { return; } =20 Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberrange= :| |: https://libvirt.org -o- https://fstop138.berrange.com= :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange= :|