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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 101E9C4708B for ; Wed, 23 Nov 2022 15:49:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236825AbiKWPtL (ORCPT ); Wed, 23 Nov 2022 10:49:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38460 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238744AbiKWPss (ORCPT ); Wed, 23 Nov 2022 10:48:48 -0500 Received: from mail-ej1-x631.google.com (mail-ej1-x631.google.com [IPv6:2a00:1450:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9033763BB0; Wed, 23 Nov 2022 07:48:47 -0800 (PST) Received: by mail-ej1-x631.google.com with SMTP id f27so43798192eje.1; Wed, 23 Nov 2022 07:48:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=rWol0vfLar2wlbq1lnLcJmfHTOdUxjebNWwkBKe5szA=; b=a/Mi1ENzdoE9EIvB5Ye2ZQm0JoL4Qwgm366qbxZz3HxkBSOnQFKmyQLhpQAjVgu++T iNr990l84OmsE564r2IQu1CRgoA88Wb/mt2CHH78qJtf4q3nQA3U1QKhyeQuy+Q+SYXE oZhRapBFxOxxnkL23W+rryu0Y+MJLd0y4Fe7TRY0xIfc4q+GYKMDxyonVvL6xJoMSchF jLZRHWdmt7Td106aDj/tE2AbjWoHM4ou1ytNrlgQpiTkFQzZfmYOirqXurIcW94gBPGQ 28MGrk0sS5gGlQz9rnrWrp2bEB/SyKW465+JKI8nLKKWqbRcuF/csCfXF+MM71V/+RQ0 Lg2g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rWol0vfLar2wlbq1lnLcJmfHTOdUxjebNWwkBKe5szA=; b=130V0IEan4abqUJ7+xsgyUCBkbo5q7AzSYrEkRByz8PVOJMBYF2MFdadaFLfedP3cZ flNS/6UnFWze5kobFwq6qXwpRSmlTCWHaf5xBHWD7nbOcGM3jP0lp5jMIshISOmL+JWF tFPSp1fFIne8C/J5n/aYOten3JmnovzuKV/R/g0q0vJIilef/VTadAGHTz/7VFwk7jeG AHriIncpMZ+Ya76VF1rXLXf9eT+NDDHOvwh+u5ouIMbjjBkTw9rv7ZZzEaeoUjIZde50 rHrLgeRPNsRsmGBZ0rmetAlwdxDVoprbdZo36bQ38NRye6omZXp2R8BEd3LTD5tYgeWO 2tBg== X-Gm-Message-State: ANoB5pmmI7rOfyBHaelpp8XCtIBJPZHCZn0Doxr3T5m80ul1qsORpvAv qg4UvzXPOqw9LZNTOD8XJ8M= X-Google-Smtp-Source: AA0mqf4DGaq6LxoFCutoUkFiDXs1R0I6U1M0ITumJqqtc2ke50QNhjcw+Z4GMeoZk1Cs/xwOs0ED4Q== X-Received: by 2002:a17:907:c016:b0:7a4:98cc:7c8e with SMTP id ss22-20020a170907c01600b007a498cc7c8emr14564304ejc.48.1669218525781; Wed, 23 Nov 2022 07:48:45 -0800 (PST) Received: from [10.20.0.7] ([37.120.217.162]) by smtp.gmail.com with ESMTPSA id u2-20020a1709061da200b0073ae9ba9ba8sm7295109ejh.3.2022.11.23.07.48.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Nov 2022 07:48:44 -0800 (PST) Message-ID: Date: Wed, 23 Nov 2022 16:48:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a const * Content-Language: en-US To: Greg Kroah-Hartman , Matthew Wilcox Cc: Andy Shevchenko , linux-kernel@vger.kernel.org, Jens Axboe , "Rafael J. Wysocki" , Len Brown , Stefan Richter , Wolfram Sang , Alexandre Belloni , Dmitry Torokhov , Sean Young , Mauro Carvalho Chehab , Rob Herring , Frank Rowand , Hans de Goede , Mark Gross , Vinod Koul , Bard Liao , Pierre-Louis Bossart , Sanyog Kale , Andreas Noever , Michael Jamet , Mika Westerberg , Yehezkel Bernat , Jiri Slaby , Heikki Krogerus , "Martin K. Petersen" , Chaitanya Kulkarni , Ming Lei , Jilin Yuan , Alan Stern , Sakari Ailus , Jason Gunthorpe , Thomas Gleixner , Ira Weiny , Dan Williams , Won Chung , alsa-devel@alsa-project.org, devicetree@vger.kernel.org, linux-acpi@vger.kernel.org, linux-block@vger.kernel.org, linux-i2c@vger.kernel.org, linux-i3c@lists.infradead.org, linux-input@vger.kernel.org, linux-media@vger.kernel.org, linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, linux1394-devel@lists.sourceforge.net, platform-driver-x86@vger.kernel.org References: <20221123122523.1332370-1-gregkh@linuxfoundation.org> <20221123122523.1332370-3-gregkh@linuxfoundation.org> <711d5275-7e80-c00d-0cdc-0f3d52175361@gmail.com> <97be39ed-3cea-d55a-caa6-c2652baef399@gmail.com> From: Maximilian Luz In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org On 11/23/22 16:37, Greg Kroah-Hartman wrote: > On Wed, Nov 23, 2022 at 02:52:59PM +0000, Matthew Wilcox wrote: >> On Wed, Nov 23, 2022 at 02:59:00PM +0100, Maximilian Luz wrote: >>> On 11/23/22 14:34, Andy Shevchenko wrote: >>>> On Wed, Nov 23, 2022 at 02:14:31PM +0100, Maximilian Luz wrote: >>>>> On 11/23/22 13:25, Greg Kroah-Hartman wrote: >>>>>> The uevent() callback in struct device_type should not be modifying the >>>>>> device that is passed into it, so mark it as a const * and propagate the >>>>>> function signature changes out into all relevant subsystems that use >>>>>> this callback. >>>> >>>> [...] >>>> >>>>>> -static inline struct ssam_device *to_ssam_device(struct device *d) >>>>>> +static inline struct ssam_device *to_ssam_device(const struct device *d) >>>>>> { >>>>>> return container_of(d, struct ssam_device, dev); >>>>>> } >>>>> >>>>> I am slightly conflicted about this change as that now more or less >>>>> implicitly drops the const. So I'm wondering if it wouldn't be better to >>>>> either create a function specifically for const pointers or to just >>>>> open-code it in the instance above. >>>>> >>>>> I guess we could also convert this to a macro. Then at least there >>>>> wouldn't be an explicit and potentially misleading const-conversion >>>>> indicated in the function signature. >>>> >>>> This is an intermediate step as far as I know since moving container_of to >>>> recognize const is a bit noisy right now. I guess you can find a discussion >>>> on the topic between Greg and Sakari. >>> >>> Thanks! I assume you are referring to the following? >>> >>> https://lore.kernel.org/lkml/4218173bd72b4f1899d4c41a8e251f0d@AcuMS.aculab.com/T/ >>> >>> As far as I can tell this is only a warning in documentation, not >>> compile time (which would probably be impossible?). >>> >>> As I've said I'd be fine with converting the function to a macro (and >>> preferably adding a similar warning like the one proposed in that >>> thread). The point that irks me up is just that, as proposed, the >>> function signature would now advertise a conversion that should never be >>> happening. >>> >>> Having two separate functions would create a compile-time guarantee, so >>> I'd prefer that, but I can understand if that might be considered too >>> noisy in code. Or if there is a push to make container_of() emit a >>> compile-time warning I'd also be perfectly happy with converting it to a >>> macro now as that'd alleviate the need for functions in the future. >> >> Can't we do: >> >> static inline const struct ssam_device *to_ssam_device(const struct device *d) >> { >> return container_of(d, const struct ssam_device, dev); >> } >> > > You could, if you can always handle a const pointer coming out of this > function, but I don't think you can. > > What you might want to do instead, and I'll be glad to do it for all of > the functions like this I change, is to do what we have for struct > device now: > > static inline struct device *__kobj_to_dev(struct kobject *kobj) > { > return container_of(kobj, struct device, kobj); > } > > static inline const struct device *__kobj_to_dev_const(const struct kobject *kobj) > { > return container_of(kobj, const struct device, kobj); > } > > /* > * container_of() will happily take a const * and spit back a non-const * as it > * is just doing pointer math. But we want to be a bit more careful in the > * driver code, so manually force any const * of a kobject to also be a const * > * to a device. > */ > #define kobj_to_dev(kobj) \ > _Generic((kobj), \ > const struct kobject *: __kobj_to_dev_const, \ > struct kobject *: __kobj_to_dev)(kobj) > > > Want me to do the same thing here as well? That looks great! Thanks! I would very much prefer that. Regards, Max