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SubjectRe: include/linux/xattr.h: how much userpace visible?
Date
On Feb 26, 2007, at 19:10:16, H. Peter Anvin wrote:
> Christoph Hellwig wrote:
>> What's the problem of exposing all these APIs unconditionally?
>> glibcs should either use all information from the linux/ headers
>> or nothing at all, but not depend on hiding some bits.
>
> It's not always that simple. In particular, in some files there
> might be typedefs or structure tags that step on libc's namespace
> (but are useful to other libcs), but ABI constants that are
> universally useful.
>
> One way to deal with the particular issue of structure tags which
> is probably even more useful is:
>
> #if defined(__KERNEL__) || defined(__KERNEL_EXPORT_STRUCTURES)
> # define __kstruct_stat stat
> #endif
>
> struct __kstruct_stat {
> /* ...foo... */
> };
>
> ... which lets the libc export it into whatever namespace it wants
> by #defining __kstruct macros accordingly.

Not a bad idea, but it could use some extra error checking to make
sure that somebody remembers to "#define __kstruct_foo" before
"#include <linux/foo.h>" (perhaps indirectly through linux/bar.h).
Maybe something like this (plays nice with the very-basic unifdef
parsing too):

#ifdef __KERNEL__
# define __kstruct_stat stat
# define __kstruct_foo foo
# define __kstruct_bar bar
#endif

#ifdef __LINUX_KERNEL_EXPORT
# define __kstruct_stat stat
# define __kstruct_foo foo
# define __kstruct_bar bar
#endif

#ifndef __kstruct_stat
# error "Missing definition of __kstruct_stat, please insert:"
# error " #define __kstruct_stat <name-for-stat-struct>"
# error "into your C file before '#include <linux/foo.h>'"
#endif
struct __kstruct_stat {
}

Someone who wanted to keep the name __kstruct_stat could of course
"#define __kstruct_stat __kstruct_stat" easily.

Cheers,
Kyle Moffett

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