Re: [RFC][PATCH 1/2] Create initial kernel ABI header infrastructure

Kyle Moffett
2006-03-26T12:50:43Z

On Mar 26, 2006, at 07:32:31, Arjan van de Ven wrote:
> On Sun, 2006-03-26 at 06:54 -0500, Kyle Moffett wrote:
>> Create initial kernel ABI header infrastructure
>
> it's nice that you picked this one;
> for this you want an arch-generic/stddef32.h and stddef64.h
>
> and have arch-foo just only include the proper generic one..

I plan to add a lot of other definitions to this file later on. For
example different architectures have different notions of what a
__kernel_ino_t is (unsigned int versus unsigned long). I may rename
this file as types.h, but from looking through the code I figure I'll
have enough general purpose declarations about "This architecture has
blah" that a separate stddef.h file will be worth it.

> (and... why do you prefix these with _KABI? that's a mistake imo.
> Don't bother with that. Really. Either these need exporting to
> userspace, but then either use __ as prefix or don't use a prefix.
> But KABI.. No.)

According to the various standards all symbols beginning with __ are
reserved for "The Implementation", including the compiler, the
standard library, the kernel, etc. In order to avoid clashing with
any/all of those, I picked the __KABI_ and __kabi_ prefixes for
uniqueness. In theory I could just use __, but there are problems
with that too. For example, note how the current compiler.h files
redefine __always_inline to mean something kinda different. The GCC
manual says we should be able to write this:

inline __attribute__((__always_inline)) int increment(int x)
{
return x+1;
}

Except when compiling the kernel headers turn that into this (which
obviously doesn't compile):
inline __attribute__((__attribute__((always_inline)))) int increment
(int x)
{
return x+1;
}

As a result, I kinda want to stay away from anything that remotely
looks like a conflicting namespace. Using such a unique namespace
means we can also safely do this if necessary (Since you can't
"typedef struct foo struct bar"):

kabi/foo.h:
struct __kabi_foo {
int x;
int y;
};

linux/foo.h:
#define __kabi_foo foo
#include <kabi/foo.h>

drivers/foo/foo.h:
#include <linux/foo.h>
void func()
{
struct foo = { .x = 1, .y = 2 };
}

Cheers,
Kyle Moffett