undocumented system call clock_nanosleep

Multiple packages suspected
    manpages-dev
    libc6

The system call "clock_nanosleep" does not have documentation, and I cannot determine if it is supposed to exist or not.

Release: 8.10 Intrepid Ibex
Updated thru March 1 2009
Package versions:
   libc6: 2.8~20080505-0ubuntu9
   manpages-dev: 3.01-1

Expected result: diagnostics about proper usage. Either ENOSYS or EINVAL would have tested if the function in question was defined in the kernel, or a compiler error compalining about clock_nanosleep not being declared

Actual result: a linker error claiming that clock_nanosleep was not defined

test case:

#include <test.h>

int main()
{
    clock_nanosleep(0, 0, 0, 0);
}

What I think should have happened:

If the system call didn't exist, the macro enabling its declaration __USE_XOPEN2K, should not have been defined, and the compiler should have choked instead of the linker.

If the system call does exist, it should have a manpage. If it doesn't, then it shouldn't be declared in the first place.

There is a problem with either

1) The manpages and the libc6 both omitting this function when the time.h file declares it
2) Feature macros that erroneously enable this

I don't know which the case is. The reference to this function in time(7) manpage suggests its existence at large. Whether or not it does, or is supposed to, in my libs and kernel, is unknown.