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 CE9CAC46467 for ; Wed, 23 Nov 2022 14:53:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238054AbiKWOxY (ORCPT ); Wed, 23 Nov 2022 09:53:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52942 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237907AbiKWOxN (ORCPT ); Wed, 23 Nov 2022 09:53:13 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B7E471EEF2; Wed, 23 Nov 2022 06:53:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=d34IWNksyN/fUaMdJSyNyFr5/NYJSUamcGjA6pAMtuA=; b=caDYBku0DlKozdr16VvQx2Pf47 2FemMLhC3IcrPQOUzURzAZnbhstHNQck3oc9tp/PXObEiBO1MfrwTzqTVM4sWneDrW/0ivZt02rfR GJ97qbtKp6invRyg7JlLsZYl3ZG3vWExlD7hzk57S+mKdQTrPuVtfzCSbDoVVJ8FxhHKtoRSJ0jtU XYB3KakhM7UNmV0lB+Oflj6FYMkeTc2cxN2tMw87mvmQsXCHH2Ve1EXgve0TduL0q7RtvwUTii1c5 R8WonwObHfVSic7ZLMDFLvXv3RjVaPGgy5xWCwSrWbCPm+c1AWWTPP+4n4zTi5sjodPbwnBYZMh7x 2Km029GQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1oxr7T-007j3f-RC; Wed, 23 Nov 2022 14:53:00 +0000 Date: Wed, 23 Nov 2022 14:52:59 +0000 From: Matthew Wilcox To: Maximilian Luz Cc: Andy Shevchenko , Greg Kroah-Hartman , 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 Subject: Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a const * Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <97be39ed-3cea-d55a-caa6-c2652baef399@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org 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); }