Re: [PATCH 05/98] exynos_drm.h: use __u64 from linux/types.h

["Christian König" <christian.koenig@amd.com>]

Yeah, completely agree with Linus on the visibility problem and that's 
exactly the reason why we don't include <stdint.h> in the kernel header 
and expect userspace to define the ISO types somewhere.

But using the types from "include/linux/types.h" and especially 
including it into the uapi headers doesn't make the situation better, 
but rather worse.

With this step we not only make the headers depend on another header 
that isn't part of the uapi, but also pollute the user space namespace 
with __sXX and __uXX types which aren't defined anywhere else.

Regards,
Christian.

On 01.06.2015 10:56, Russell King - ARM Linux wrote:
> On Mon, Jun 01, 2015 at 10:20:10AM +0200, Christian König wrote:
>> Using types that differs on 32-bit and 64-bit machines for a kernel
>> interface is indeed a rather bad idea. This not only includes longs, but
>> pointers as well.
> [cut standard stdint.h types argument which we've heard before]
>
> You need to read Linus' rant on this subject:
>
>   From: Linus Torvalds <torvalds@osdl.org>
>   Subject: Re: [RFC] Splitting kernel headers and deprecating __KERNEL__
>   Date: Mon, 29 Nov 2004 01:30:46 GMT
>
>   Ok, this discussion has gone on for too long anyway, but let's make it
>   easier for everybody. The kernel uses u8/u16/u32 because:
>
>           - the kernel should not depend on, or pollute user-space naming.
>             YOU MUST NOT USE "uint32_t" when that may not be defined, and
>             user-space rules for when it is defined are arcane and totally
>             arbitrary.
>
>           - since the kernel cannot use those types for anything that is
>             visible to user space anyway, there has to be alternate names.
>             The tradition is to prepend two underscores, so the kernel would
>             have to use "__uint32_t" etc for its header files.
>
>           - at that point, there's no longer any valid argument that it's a
>             "standard type" (it ain't), and I personally find it a lot more
>             readable to just use the types that the kernel has always used:
>             __u8/__u16/__u32. For stuff that is only used for the kernel,
>             the shorter "u8/u16/u32" versions may be used.
>
>   In short: having the kernel use the same names as user space is ACTIVELY
>   BAD, exactly because those names have standards-defined visibility, which
>   means that the kernel _cannot_ use them in all places anyway. So don't
>   even _try_.
>