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 95609C4332F for ; Wed, 23 Nov 2022 15:38:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238907AbiKWPif (ORCPT ); Wed, 23 Nov 2022 10:38:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239005AbiKWPiN (ORCPT ); Wed, 23 Nov 2022 10:38:13 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C4624942CF; Wed, 23 Nov 2022 07:38:05 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 74841B8216C; Wed, 23 Nov 2022 15:38:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1979BC433B5; Wed, 23 Nov 2022 15:38:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1669217883; bh=fs5VkTgkSMThkRfwYHbvZbd9KBWsoqyzg9ciy8gus2Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=h0ZAf34Hn5punisJHBW8LcbCQTw15cHF2JJX4ocDW62QTgSy6qJjtysjjdNvwu0ox 57RZmpe0+53Ztv/B01KCVB9FOl0MHv8tq8EoRdlsf0O30ZxuR+2QlY2BhD12bWW0TB l8Nw7ylhiySZzmT0dyMoM2hjY9v4O3HQ5H0j6noM= Date: Wed, 23 Nov 2022 16:37:59 +0100 From: Greg Kroah-Hartman To: Matthew Wilcox Cc: Maximilian Luz , 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 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: Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org 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? thanks, greg k-h