linux-kernel - Re: [PATCH] media: do not use C++ style comments in uapi headers

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Message-ID: <20190616154848.GA24837@xo-6d-61-c0.localdomain>
Date:   Sun, 16 Jun 2019 17:48:48 +0200
From:   Pavel Machek <pavel@....cz>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Randy Dunlap <rdunlap@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: do not use C++ style comments in uapi headers

Hi!

> > > In fact, I detected this issue by the following patch:
> > > https://patchwork.kernel.org/patch/10974669/
> > >
> > > When I worked on it, I wondered which
> > > c-dialect flags should be used.
> > >
> > > This code:
> > >
> > > > # Unlike the kernel space, uapi headers are written in more strict C.
> > > > #  - Forbid C++ style comments
> > > > #  - Use '__inline', '__asm__' instead of 'inline', 'asm'
> > > > #
> > > > # -std=c90 (equivalent to -ansi) catches the violation of those.
> > > > # We cannot go as far as adding -Wpedantic since it emits too many warnings.
> > > > #
> > > > # REVISIT: re-consider the proper set of compiler flags for uapi compile-test.
> > > >
> > > > UAPI_CFLAGS := -std=c90 -Wpedantic -Wall -Werror=implicit-function-declaration
> > >
> > > Even "-std=c99 -Wpedantic" emits lots of warnings.
> > >
> > >
> > >
> > > I noticed one more thing.
> > >
> > > There are two ways to define fixed-width type.
> > >
> > > [1] #include <linux/types.h>, __u8, __u16, __u32, __u64
> > >
> > >       vs
> > >
> > > [2] #include <stdint.h>, uint8_t, uint16_t, uint32_t, uint64_t
> > >
> > >
> > > Both are used in UAPI headers.
> > > IIRC, <stdint.h> was standardized by C99.
> > >
> > > So, we have already relied on C99 in user-space too.
> >
> > Just because we have relied on it in the past, does not mean we need to
> > keep relying on it.  I have had numerous complaints over the years from
> > libc authors that our uapi headers are _NOT_ able to be directly
> > consumed by them.  They all end up having to fix things up and include
> > local "sanitized" copies.
> >
> > So any work we can do here to make them more sane and work properly
> > everywhere is a good thing, as right now, they are broken.
> 
> Maybe, we should document UAPI header coding guideline.

> Without To-Don't list,
> people will do anything.

Even better would be a (compile-time) test that checks for problems in the headers...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html