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Tue, 7 Jul 2020 19:23:34 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 109E41132FD2; Tue, 7 Jul 2020 21:23:32 +0200 (CEST) From: Markus Armbruster To: Eric Blake Subject: Re: [PATCH v4 03/45] error: Document Error API usage rules References: <20200707160613.848843-1-armbru@redhat.com> <20200707160613.848843-4-armbru@redhat.com> Date: Tue, 07 Jul 2020 21:23:32 +0200 In-Reply-To: (Eric Blake's message of "Tue, 7 Jul 2020 13:46:28 -0500") Message-ID: <87y2nv6sej.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) 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 Content-Type: text/plain Received-SPF: pass client-ip=205.139.110.120; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/07 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, Markus Armbruster , qemu-devel@nongnu.org, groug@kaod.org, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Eric Blake writes: > 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/ Yes. >> + * 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, Yes, there are such functions. > 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: What about - when it does not, say 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); >> Thanks!