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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 14F28C433E0 for ; Tue, 7 Jul 2020 18:47:33 +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 DA24D20708 for ; Tue, 7 Jul 2020 18:47:32 +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="Nw+mqNq2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA24D20708 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]:54604 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jsscu-0007o1-5j for qemu-devel@archiver.kernel.org; Tue, 07 Jul 2020 14:47:32 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42098) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jssc5-0006dq-VV for qemu-devel@nongnu.org; Tue, 07 Jul 2020 14:46:41 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:39147 helo=us-smtp-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 1jssc4-0007QX-AX for qemu-devel@nongnu.org; Tue, 07 Jul 2020 14:46:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594147599; 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=QwMJFZ2WOW0WrqA0Cu0I4c4uL0mnSfnqiJyaxPX4AEI=; b=Nw+mqNq2EMynVY+zo7utfd+d8QofjGLx2k2/mPJgfDYuOdJ465Eoq+XEdr77IqCrkvdTN4 uLEOHXDc47cm+vU/RBUhAIx1VZDu/fbZOBiNOBT1JTM+P8Kw/cHu15JsOflWrYE0Z9+fs9 fjzXn/R0KETiQurgKkGloSTWiMuZ0DE= 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-168-HkfduuMeN6WPK45o0NnRUQ-1; Tue, 07 Jul 2020 14:46:35 -0400 X-MC-Unique: HkfduuMeN6WPK45o0NnRUQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 396471B18BC1; Tue, 7 Jul 2020 18:46:30 +0000 (UTC) Received: from [10.3.115.46] (ovpn-115-46.phx2.redhat.com [10.3.115.46]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9719A797E0; Tue, 7 Jul 2020 18:46:28 +0000 (UTC) Subject: Re: [PATCH v4 03/45] error: Document Error API usage rules To: Markus Armbruster , qemu-devel@nongnu.org References: <20200707160613.848843-1-armbru@redhat.com> <20200707160613.848843-4-armbru@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Tue, 7 Jul 2020 13:46:28 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200707160613.848843-4-armbru@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=eblake@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 06:04:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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@linaro.org, vsementsov@virtuozzo.com, berrange@redhat.com, ehabkost@redhat.com, qemu-block@nongnu.org, groug@kaod.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/7/20 11:05 AM, Markus Armbruster wrote: > This merely codifies existing practice, with one exception: the rule > advising against returning void, where existing practice is mixed. > > When the Error API was created, we adopted the (unwritten) rule to > return void when the function returns no useful value on success, > unlike GError, which recommends to return true on success and false on > error then. > > Make the rule advising against returning void official by putting it > in writing. This will hopefully reduce confusion. > > Update the examples accordingly. > > The remainder of this series will update a substantial amount of code > to honor the rule. > > Signed-off-by: Markus Armbruster > Reviewed-by: Eric Blake > Reviewed-by: Vladimir Sementsov-Ogievskiy > Reviewed-by: Greg Kurz > --- > @@ -95,14 +122,12 @@ > * Create a new error and pass it to the caller: > * error_setg(errp, "situation normal, all fouled up"); > * > - * Call a function and receive an error from it: > - * Error *err = NULL; > - * foo(arg, &err); > - * if (err) { > + * Call a function, receive an error from it, and pass it to caller maybe s/to caller/to the caller/ > + * when the function returns a value that indicates failure, say false: > + * if (!foo(arg, errp)) { > * handle the error... > * } > - * > - * Receive an error and pass it on to the caller: > + * when it doesn't, say a void function: Hmm. It looks like you have a single sentence "Call a function... when the function returns", but this line now makes it obvious that you have a single prefix: "Call a function, ...and pass it to the caller:" with two choices "when the function returns" and "when it doesn't". I'm not sure if there is a nicer way to typeset it, adding yet another ":" at the end of the line looks odd. The idea behind the text is fine, I'm just trying to paint the bikeshed to see if there is a better presentation. > * Error *err = NULL; > * foo(arg, &err); > * if (err) { > @@ -120,6 +145,19 @@ > * foo(arg, errp); > * for readability. > * > + * Receive an error, and handle it locally > + * when the function returns a value that indicates failure, say false: > + * Error *err = NULL; > + * if (!foo(arg, &err)) { > + * handle the error... > + * } > + * when it doesn't, say a void function: It helps that you have repeated the same pattern as above. But that means if you change the layout, both groupings should have the same layout. Maybe: Intro for a task: - when the function returns... - when it doesn't Also, are there functions that have a return type other than void, but where the return value is not an indication of error? If there are, then the "say a void function" clause makes sense (but we should probably recommend against such functions); if there are not, then "say a void function" reads awkwardly. Maybe: - when it does not, because it is a void function: > + * Error *err = NULL; > + * foo(arg, &err); > + * if (err) { > + * handle the error... > + * } > + * > * Receive and accumulate multiple errors (first one wins): > * Error *err = NULL, *local_err = NULL; > * foo(arg, &err); > -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org