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Date: Wed, 23 Nov 2022 14:59:00 +0100 From: Maximilian Luz <luzmaximilian@...il.com> To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>, "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, Stefan Richter <stefanr@...6.in-berlin.de>, Wolfram Sang <wsa@...nel.org>, Alexandre Belloni <alexandre.belloni@...tlin.com>, Dmitry Torokhov <dmitry.torokhov@...il.com>, Sean Young <sean@...s.org>, Mauro Carvalho Chehab <mchehab@...nel.org>, Rob Herring <robh+dt@...nel.org>, Frank Rowand <frowand.list@...il.com>, Hans de Goede <hdegoede@...hat.com>, Mark Gross <markgross@...nel.org>, Vinod Koul <vkoul@...nel.org>, Bard Liao <yung-chuan.liao@...ux.intel.com>, Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>, Sanyog Kale <sanyog.r.kale@...el.com>, Andreas Noever <andreas.noever@...il.com>, Michael Jamet <michael.jamet@...el.com>, Mika Westerberg <mika.westerberg@...ux.intel.com>, Yehezkel Bernat <YehezkelShB@...il.com>, Jiri Slaby <jirislaby@...nel.org>, Heikki Krogerus <heikki.krogerus@...ux.intel.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, "Martin K. Petersen" <martin.petersen@...cle.com>, Chaitanya Kulkarni <kch@...dia.com>, Ming Lei <ming.lei@...hat.com>, Jilin Yuan <yuanjilin@...rlc.com>, Alan Stern <stern@...land.harvard.edu>, Sakari Ailus <sakari.ailus@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>, Thomas Gleixner <tglx@...utronix.de>, Ira Weiny <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>, Won Chung <wonchung@...gle.com>, alsa-devel@...a-project.org, devicetree@...r.kernel.org, linux-acpi@...r.kernel.org, linux-block@...r.kernel.org, linux-i2c@...r.kernel.org, linux-i3c@...ts.infradead.org, linux-input@...r.kernel.org, linux-media@...r.kernel.org, linux-serial@...r.kernel.org, linux-usb@...r.kernel.org, linux1394-devel@...ts.sourceforge.net, platform-driver-x86@...r.kernel.org Subject: Re: [PATCH 3/5] driver core: make struct device_type.uevent() take a const * 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. Regards, Max
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