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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 96C8CC2BA1A for ; Fri, 24 Apr 2020 06:11:43 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 6444B20767 for ; Fri, 24 Apr 2020 06:11:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6444B20767 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jRrYa-0001DK-12; Fri, 24 Apr 2020 06:11:24 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jRrYZ-0001DF-Gw for xen-devel@lists.xenproject.org; Fri, 24 Apr 2020 06:11:23 +0000 X-Inumbo-ID: 6b9a08ec-85f2-11ea-9466-12813bfff9fa Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 6b9a08ec-85f2-11ea-9466-12813bfff9fa; Fri, 24 Apr 2020 06:11:22 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id B07F5ADEB; Fri, 24 Apr 2020 06:11:20 +0000 (UTC) Subject: Re: [PATCH 1/3] x86/pv: Options to disable and/or compile out 32bit PV support To: Andrew Cooper References: <20200417155004.16806-1-andrew.cooper3@citrix.com> <20200417155004.16806-2-andrew.cooper3@citrix.com> <5dc9dbd9-fbeb-46ef-4d4e-7916c3219bb3@suse.com> <4e732f90-1d5f-7ae5-0f02-6b313a381df7@citrix.com> <6b4e5b50-51f7-566f-2a18-4bb5f4f43d59@suse.com> <62b51cff-4d6f-690b-371a-e6772ea327ab@citrix.com> From: Jan Beulich Message-ID: Date: Fri, 24 Apr 2020 08:11:20 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <62b51cff-4d6f-690b-371a-e6772ea327ab@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Xen-devel , Wei Liu , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 23.04.2020 19:35, Andrew Cooper wrote: > On 21/04/2020 07:02, Jan Beulich wrote: >> On 20.04.2020 20:05, Andrew Cooper wrote: >>> On 20/04/2020 15:05, Jan Beulich wrote: >>>> I'm in particular >>>> concerned that we may gain a large number of such printk()s over >>>> time, if we added them in such cases. >>> The printk() was a bit of an afterthought, but deliberately avoiding the >>> -EINVAL path was specifically not. >>> >>> In the case that the user tries to use `pv=no-32` without CONFIG_PV32, >>> they should see something other than >>> >>> (XEN) parameter "pv=no-32" unknown! >> Why - to this specific build of Xen the parameter is unknown. > > Because it is unnecessarily problematic and borderline obnoxious to > users, as well as occasional Xen developers. > > "you've not got the correct CONFIG_$X for that to be meaningful" is > specifically useful to separate from "I've got no idea". > >>> I don't think overloading the return value is a clever move, because >>> then every parse function has to take care of ensuring that -EOPNOTSUPP >>> (or ENODEV?) never clobbers -EINVAL. >> I didn't suggest overloading the return value. Instead I >> specifically want this to go the -EINVAL path. >> >>> We could have a generic helper which looks like: >>> >>> static inline void ignored_param(const char *cfg, const char *name, >>> const char *s, const char *ss) >>> { >>>     printk(XENLOG_INFO "%s disabled - ignoring '%s=%*.s' setting\n", >>> cfg, name, s, (int)(ss - s)); >>> } >>> >>> which at least would keep all the users consistent. >> Further bloating the binary with (almost) useless string literals. >> I'd specifically like to avoid this. > > I don't accept that as a valid argument. > > We're talking about literally tens of bytes (which will merge anyway, so > 0 in practice), and a resulting UI which helps people get out of > problems rather than penalises them for having gotten into a problem to > begin with. How will they merge? The different instances of the format string above may/should, yes, but the different "CONFIG_xyz" literals the callers pass won't, for example. > I will absolutely prioritise a more helpful UI over a handful of bytes. This "a handful of bytes doesn't matter" attitude has lead to imo unacceptable growth of various software packages over the years. Anyway - I don't want to block this change over this argument, so I'm willing to ack a patch with the helper introduced (and preferably the "CONFIG_" part of the cfg arguments moved into the helper's format string), as long as we plan to then make consistent use of the helper everywhere. That said, I don't immediately see what would be passed for "cfg" in some of parse_iommu_param()'s cases. Jan