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=-2.3 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 741C6C2BA1A for ; Fri, 24 Apr 2020 05:28:48 +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 4281020767 for ; Fri, 24 Apr 2020 05:28:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4281020767 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 1jRqsp-0005bH-GW; Fri, 24 Apr 2020 05:28:15 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jRqsn-0005aY-Fq for xen-devel@lists.xenproject.org; Fri, 24 Apr 2020 05:28:13 +0000 X-Inumbo-ID: 63d8c1da-85ec-11ea-83d8-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 63d8c1da-85ec-11ea-83d8-bc764e2007e4; Fri, 24 Apr 2020 05:28:12 +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 DAFB3AD94; Fri, 24 Apr 2020 05:28:10 +0000 (UTC) Subject: Re: [PATCH 1/3] x86/pv: Options to disable and/or compile out 32bit PV support To: Andrew Cooper , Jan Beulich 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: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <68146423-c2cb-0bf4-4bb8-3c89ad17bbcc@suse.com> Date: Fri, 24 Apr 2020 07:28:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <62b51cff-4d6f-690b-371a-e6772ea327ab@citrix.com> Content-Type: text/plain; charset=utf-8; format=flowed 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 23.04.20 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. > > I will absolutely prioritise a more helpful UI over a handful of bytes. What about a kconfig option (defaulting to "yes") enabling this feature? That way an embedded variant can be made smaller while a server one is more user friendly. Juergen