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Date: Wed, 23 Nov 2022 23:24:23 +0000 From: Barnabás Pőcze <pobrn@...tonmail.com> To: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Cc: Jason Gunthorpe <jgg@...pe.ca>, Matthew Wilcox <willy@...radead.org>, Maximilian Luz <luzmaximilian@...il.com>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 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>, "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>, 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 * Hi 2022. november 23., szerda 20:06 keltezéssel, Greg Kroah-Hartman írta: > On Wed, Nov 23, 2022 at 02:25:59PM -0400, Jason Gunthorpe wrote: > > > On Wed, Nov 23, 2022 at 07:10:49PM +0100, Greg Kroah-Hartman wrote: > > > > > On Wed, Nov 23, 2022 at 05:49:36PM +0000, Matthew Wilcox wrote: > > > > > > > On Wed, Nov 23, 2022 at 01:29:56PM -0400, Jason Gunthorpe wrote: > > > > > > > > > #define generic_container_of(in_type, in, out_type, out_member) \ > > > > > _Generic(in, \ > > > > > const in_type *: ((const out_type *)container_of(in, out_type, out_member)), \ > > > > > in_type *: ((out_type *)container_of(in, out_type, out_member)) \ > > > > > ) > > > > > > > > There's a neat trick I found in seqlock.h: > > > > > > > > #define generic_container_of(in_t, in, out_t, m) \ > > > > _Generic(*(in), \ > > > > const in_t: ((const out_t *)container_of(in, out_t, m)), \ > > > > in_t: ((out_t *)container_of(in, out_type, m)) \ > > > > ) > > > > > > > > and now it fits in 80 columns ;-) > > > > > > Nice trick! Dropping the inline functions is a bit different, let me > > > see if that still gives a sane error if we pass an incorrect type or > > > mess with the const * the wrong way. I'll run some tests tomorrow > > > afternoon... > > > > The errors in some cases are very verbose, but it is somewhat > > understandable - the worst is when _Generic fails to match anything, > > but also at least clang partially expanded container_of and it throws > > other assertions too. > > > > I also wonder if this could just be rolled into the normal > > container_of. > > > I think we might be able to now, my previous attempts with inline > functions prevented that. I'll beat on that tomorrow... > > > in_type would have to be derived like: > > > > in_type = typeof((out_type *)NULL)->out_member) > > > > But I don't know if you can use typeof in a generic type matching expression.. > > > Maybe that is what threw me before, I can't remember. I do know we > tried a number of different attempts, can't recall the failed ones... > I am sorry I haven't followed the previous discussion, but has something like the following been considered? #define container_of2(ptr, type, member) \ _Generic((ptr), \ typeof_member(const type, member) *: container_of((ptr), const type, member), \ const void *: container_of((ptr), const type, member), \ default: container_of((ptr), type, member) \ ) This is not perfect by any means, but I believe it is a reasonable improvement. It only really works reliably if the member type and the specified `type` in the arguments are unqualified, but I believe that should cover the majority of cases. I have tried to build an x86-64 defconfig with this and there are numerous const violations, but I haven't seen any false positives. > [...] Regards, Barnabás Pőcze
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