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Tue, 7 Jul 2020 16:06:37 +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 E819410013D7; Tue, 7 Jul 2020 16:06:36 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 733F31132922; Tue, 7 Jul 2020 18:06:13 +0200 (CEST) From: Markus Armbruster To: qemu-devel@nongnu.org Subject: [PATCH v4 02/45] error: Improve error.h's big comment Date: Tue, 7 Jul 2020 18:05:30 +0200 Message-Id: <20200707160613.848843-3-armbru@redhat.com> In-Reply-To: <20200707160613.848843-1-armbru@redhat.com> References: <20200707160613.848843-1-armbru@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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 Received-SPF: pass client-ip=207.211.31.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 00:46:09 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" 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 --- 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!