linux-kernel - [rfc] headers_check cleanups break the whole world

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Date:	Tue, 24 Feb 2009 22:25:53 -0500
From:	Kyle McMartin <kyle@...radead.org>
To:	mingo@...hat.com
Cc:	dwmw2@...radead.org, linux-kernel@...r.kernel.org, hpa@...or.com
Subject: [rfc] headers_check cleanups break the whole world

[names omitted to protect the innocent, hpa@ on the CC wrt klibc maybe
  using these? ]

Hi,

Commits like

    headers_check fix: foo.h

    fix the following 'make headers_check' warnings:
      usr/include/linux/foo.h:29: include of <linux/types.h> is preferred
      usr/include/linux/foo.h:102: found __[us]{8,16,32,64} type without

have proved problematic...

I've had to point out at least two userspace fixes[1] for a variety of
reasons that these patches exacerbated. Note however that I didn't say
they were wrong.

The reason for this is you cannot intermix glibc header <sys/*.h>
includes with <linux/*.h> includes for most things without defining the
__KERNEL_STRICT_NAMES guard. If you fail to define this, you end up
with multiple definitions of things like dev_t.

Software was able to get by, because things that used the headers, dvb for
example were not getting <linux/types.h> into the include chain, because
they were using <asm/types.h> directly.

I propose we invert that logic, so the presumable libc that makes use of
the <linux/types.h> header can just define that it wants these types.
(test __KERNEL__ as well so the kernel doesn't need a pointless
#define.)

If this isn't tenable, how about moving the {,__}[su]{8,16,32,64}
integer types into their own header, so we can avoid this mess ever
occuring in the future. I'm sure the janitors can have a field day with
that... :)

That said, who exactly is the userspace consumer for those
	typedef __kernel_dev_t	dev_t;
defines? Can we just include them all in #ifdef __KERNEL__?

Thoughts?

cheers, Kyle

1. Ok, one of them was libcap playing utterly stupid games with
<linux/capability.h> and header guards, but it was exacerbated by a
similar patch...

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