single, comprehensive kernel data types document?

[Daniel.]

Hi John

stdint.h is part of standard headers (C99?), I think you shouldn't use
standard headers for kernel when
there are such "kernel headers" for same proprose. If the developers
created that specific headers for
kernel, they should have a good reason for it.

I have a pertinent question on this topic too,

I've been using *aways* u8, u16, u32 in kernel code (driver code) and
*aways* __u8, __u16, __u32
for code that goes to both (usualy ioctl definition headers). What is
happening here is that __u8 from
userspace is being "casted" to u8 in driver during an ioctl call, is
that a problem? This is the "right
way to do it", right?

Also, LDD3 stats this:

It's important to remember that these types are Linux specific, and
using them hinders porting software to other Unix flavors. Systems
with recent compilers support the C99-standard types, such as uint8_t
and uint32_t; if portability is a concern, those types can be used in
favor of the Linux-specific variety [1].

So using C99 standard types for userspace headers (ioctl headers for
example) are okay!?

[1] http://www.makelinux.net/ldd3/chp-11-sect-2

2016-04-15 9:37 GMT-03:00 John Chludzinski <john.chludzinski at vivaldi.net>:
> Never use stdint.h? Wasn't that the intent of stdint.h ... for kernel
> code? For embedded code?
>
> ---John
>
> On 2016-04-15 08:27, Greg KH wrote:
>> On Fri, Apr 15, 2016 at 08:04:53AM -0400, Robert P. J. Day wrote:
>>>
>>>   is there a single, decent online doc that explains the proper data
>>> types (int16_t, int32_t and so on) to use in kernel code?
>>
>> First off, never use int16_t and friends, that's not ok :)
>>
>> Second, it's simple, use:
>>       u8
>>       u16
>>       u32
>>       u64
>> and friends in kernel code (s8, s16, and so on for signed values.)
>>
>> 'int' is a return type, and for loops and other things that you know
>> will fit in that size.
>>
>>> including the relationship with types to be used in code to be
>>> exported to user space (include/uapi/linux/types.h)?
>>
>> For values that cross the user/kernel boundry, add '__' to the front of
>> the variable:
>>       __u8
>>       __u16
>>       __u32
>> and so on.  NEVER use 'int' or 'long' crossing that boundry, it's not
>> going to work properly.
>>
>> I think one of the chapters in LDD3 describes all of this, you might
>> want to re-read it for the details.
>>
>> hope this helps,
>>
>> greg k-h
>>
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>
>
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