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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 2A678C433E0 for ; Wed, 8 Jul 2020 21:29:03 +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 E622A206DF for ; Wed, 8 Jul 2020 21:29:02 +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="WlBhawCW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E622A206DF 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]:57668 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jtHck-0001GD-4p for qemu-devel@archiver.kernel.org; Wed, 08 Jul 2020 17:29:02 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:33812) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jtHb1-0007LI-I7 for qemu-devel@nongnu.org; Wed, 08 Jul 2020 17:27:15 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:26069 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 1jtHax-0001tz-9g for qemu-devel@nongnu.org; Wed, 08 Jul 2020 17:27:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594243630; 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=BjTg3TYDvdYubEwxieaVivSeO+RKPrnPp3dzxX5R0A8=; b=WlBhawCWwvrLn+fW+PwLdIGN6A8WT5r/L1mOPMNW0/EAu8EjThHPiMovBSn8olAhG9DIfW l5XlL+R0jqv7Pgz3t97fUc+8wZiEmF+8lpUtV0Kx9A+BRiIozYn4J5ly9JCZ0KA1+ldBJ4 KxQSYZx5QwNucXGRnOsrYq7yMmc4EgY= 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-205-EP-ACS0fOG-j34OrZwhnZw-1; Tue, 07 Jul 2020 17:25:07 -0400 X-MC-Unique: EP-ACS0fOG-j34OrZwhnZw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6EDBA18FE861; Tue, 7 Jul 2020 21:25:06 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-143.ams2.redhat.com [10.36.112.143]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3DC9B60CC0; Tue, 7 Jul 2020 21:25:06 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id BEF2C1132922; Tue, 7 Jul 2020 23:25:03 +0200 (CEST) From: Markus Armbruster To: qemu-devel@nongnu.org Subject: [PULL 02/53] error: Improve error.h's big comment Date: Tue, 7 Jul 2020 23:24:12 +0200 Message-Id: <20200707212503.1495927-3-armbru@redhat.com> In-Reply-To: <20200707212503.1495927-1-armbru@redhat.com> References: <20200707212503.1495927-1-armbru@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 17:25:10 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=unavailable autolearn_force=no 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: Greg Kurz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Add headlines to the big comment. Explain examples for NULL, &error_abort and &error_fatal argument better. Tweak rationale for error_propagate_prepend(). Signed-off-by: Markus Armbruster Message-Id: <20200707160613.848843-3-armbru@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Greg Kurz --- include/qapi/error.h | 51 +++++++++++++++++++++++++++++++------------- 1 file changed, 36 insertions(+), 15 deletions(-) diff --git a/include/qapi/error.h b/include/qapi/error.h index e8960eaad5..6d079c58b7 100644 --- a/include/qapi/error.h +++ b/include/qapi/error.h @@ -15,6 +15,8 @@ /* * Error reporting system loosely patterned after Glib's GError. * + * = Creating errors = + * * Create an error: * error_setg(&err, "situation normal, all fouled up"); * @@ -27,6 +29,8 @@ * error_setg(&err, "invalid quark\n" // WRONG! * "Valid quarks are up, down, strange, charm, top, bottom."); * + * = Reporting and destroying errors = + * * Report an error to the current monitor if we have one, else stderr: * error_report_err(err); * This frees the error object. @@ -40,6 +44,30 @@ * error_free(err); * Note that this loses hints added with error_append_hint(). * + * Call a function ignoring errors: + * foo(arg, NULL); + * This is more concise than + * Error *err = NULL; + * foo(arg, &err); + * error_free(err); // don't do this + * + * Call a function aborting on errors: + * foo(arg, &error_abort); + * This is more concise and fails more nicely than + * Error *err = NULL; + * foo(arg, &err); + * assert(!err); // don't do this + * + * Call a function treating errors as fatal: + * foo(arg, &error_fatal); + * This is more concise than + * Error *err = NULL; + * foo(arg, &err); + * if (err) { // don't do this + * error_report_err(err); + * exit(1); + * } + * * Handle an error without reporting it (just for completeness): * error_free(err); * @@ -47,6 +75,11 @@ * reporting it (primarily useful in testsuites): * error_free_or_abort(&err); * + * = Passing errors around = + * + * Errors get passed to the caller through the conventional @errp + * parameter. + * * Pass an existing error to the caller: * error_propagate(errp, err); * where Error **errp is a parameter, by convention the last one. @@ -54,11 +87,10 @@ * Pass an existing error to the caller with the message modified: * error_propagate_prepend(errp, err, * "Could not frobnicate '%s': ", name); - * - * Avoid - * error_propagate(errp, err); + * This is more concise than + * error_propagate(errp, err); // don't do this * error_prepend(errp, "Could not frobnicate '%s': ", name); - * because this fails to prepend when @errp is &error_fatal. + * and works even when @errp is &error_fatal. * * Create a new error and pass it to the caller: * error_setg(errp, "situation normal, all fouled up"); @@ -70,15 +102,6 @@ * handle the error... * } * - * Call a function ignoring errors: - * foo(arg, NULL); - * - * Call a function aborting on errors: - * foo(arg, &error_abort); - * - * Call a function treating errors as fatal: - * foo(arg, &error_fatal); - * * Receive an error and pass it on to the caller: * Error *err = NULL; * foo(arg, &err); @@ -86,8 +109,6 @@ * handle the error... * error_propagate(errp, err); * } - * where Error **errp is a parameter, by convention the last one. - * * Do *not* "optimize" this to * foo(arg, errp); * if (*errp) { // WRONG! -- 2.26.2