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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 48A88C6FA82 for ; Thu, 22 Sep 2022 12:59:57 +0000 (UTC) Received: from localhost ([::1]:51638 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1obLo3-0004HQ-Dz for qemu-devel@archiver.kernel.org; Thu, 22 Sep 2022 08:59:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34936) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1obLXO-00087F-Ck for qemu-devel@nongnu.org; Thu, 22 Sep 2022 08:42:42 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:49720) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1obLXK-0008FC-R8 for qemu-devel@nongnu.org; Thu, 22 Sep 2022 08:42:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1663850555; 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=UDTAZdvpItgJ9ui7UP2S0rwgUJEyQZLEGuYGGwttXl0=; b=AQ1Xm10XH0kbJK+/T4HOtyh2n+alpmLsu6TUZ6h7XlLIW0HO+bqSLzUTPlAKO+lPJOyeT4 Vd7fgyrzUXRhx95uM5KmxzhxuYRF8Qz11ZZEQAuq77FeFyjPcdqMCbgOUQf9dhgzkCDNDZ +z20czqQw/iD0tigFdoy5uJaC52L0x8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-91-U6LlkQb5MmGFRFJTtDxJUQ-1; Thu, 22 Sep 2022 08:42:31 -0400 X-MC-Unique: U6LlkQb5MmGFRFJTtDxJUQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6C4B8185A7A4; Thu, 22 Sep 2022 12:42:31 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.163]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3520E492B13; Thu, 22 Sep 2022 12:42:31 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 4417E21E6900; Thu, 22 Sep 2022 14:42:28 +0200 (CEST) From: Markus Armbruster To: Claudio Fontana Cc: Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Paolo Bonzini , Richard Henderson , Kevin Wolf , qemu-devel@nongnu.org, dinechin@redhat.com, Gerd Hoffmann , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [PATCH v4 2/3] module: add Error arguments to module_load_one and module_load_qom_one References: <20220908183012.17667-1-cfontana@suse.de> <20220908183012.17667-3-cfontana@suse.de> <877d23ekj0.fsf@pond.sub.org> <76775f64-e49a-1c3c-0d73-10d93eff34e4@amsat.org> <87y1ucdirx.fsf@pond.sub.org> <878rmc54cw.fsf@pond.sub.org> <87leqb4ul9.fsf@pond.sub.org> <5f5921fe-6d4f-490b-4328-702a45973bbc@suse.de> Date: Thu, 22 Sep 2022 14:42:28 +0200 In-Reply-To: <5f5921fe-6d4f-490b-4328-702a45973bbc@suse.de> (Claudio Fontana's message of "Thu, 22 Sep 2022 11:43:15 +0200") Message-ID: <87bkr7mvgr.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Claudio Fontana writes: > On 9/22/22 11:38, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >>> On Thu, Sep 22, 2022 at 08:07:43AM +0200, Markus Armbruster wrote: >>>> Ease of use matters, too. When sticking to the rule leads to awkward >>>> code, we should stop and think. Should we deviate from the rule? Or >>>> can we avoid that by tweaking the interface? >>>> >>>> Philippe's proposed interface sticks to the rule. >>> >>> The cost is that when you see a function dosomething(true|false) as >>> a reader you often have no idea what the effect of true vs false is >>> on the behaviour of that function. You resort to looking at the >>> API docs and/or code. This is where C would really benefit from >>> having named parameters like as dosomething(ignore_errors=3Dtrue|false) >>> is totally obvious. Anyway, I digress. >>=20 >> Right. Quoting myself: "If having to pass a flag turns out to to be a >> legibility issue, we can have wrapper functions." :) > > There is something more fundamental that seems to be missed by most in th= is conversation, > ie the distinction between the normal execution path and the error path. > > >>=20 >>>> Another interface that does: return -1 for error, 0 for module not fou= nd >>>> (no error), and 1 for loaded. >>> >>> IMHO this pattern is generally easier to understand when looking at >>> the callers, as the fatal error scenario is always clear. >>> >>> That said I would suggest neither approach as the public facing >>> API. Rather stop trying to overload 3 states onto an error reporting >>> pattern that inherantly wants to be 2 states. Instead just have >>> distinct methods >>=20 >> Like these: >>=20 >>> bool module_load_one(const char *prefix, const char *name, Error *err= p) >>> bool module_try_load_one(const char *prefix, const char *name, Error = *errp) >>> >>> other names are available for the second, eg module_load_one_optional() >>=20 >> module_load_one_if_there()? > > And what do you do with the caller that needs to _know_ whether the modul= e was "there" or not? > > This is losing this information along the way, and the callers NEED it. > > I really invite, with no offense intended, None taken! > to read the hunks of my patch = and the callers, > there are occasions where we need to _know_ if the module was there or no= t, and act depending on the context. > > The information about "bool is_there" needs to be passed to the caller. If you have callers that need to distinguish between not found, found but bad, found and good, then return three distinct values. I proposed to return -1 for found but bad (error), 0 for not found (no error), and 1 for loaded (no error). >> By the way, the "one" in "module_load_one" & friends feels redundant. >> When I see "module_load", I assume it loads one module. > > there is a module_load_all. Libc has fcloseall() and fclose(). Clear enough, isn't it? [...]