Re: need help understanding header file organization

[Geoff Keating <geoffk at geoffk dot org>]

> Date: Wed, 06 Mar 2002 17:11:14 -0800
> From: george anzinger <george@mvista.com>

> I am attempting to add the system call stubs for posix timers to the
> library.  I have set it up so the stubs replace the library routines
> conditioned on the __NR_<call name> being defined.  I think I have this
> under control, BUT...
> 
> The system calls have need of slightly different defines for some of the
> CLOCK_  and other constants in the header files.  One way of doing this
> is to condition the values again on __NR_<call name> being defined.  Is
> this a "ok" way to do this or is there some other preferred method.

This is really not a good idea.  glibc needs to have the same API no
matter what kernel happens to be installed (consider a system that
switches between an older and a newer kernel version).  If the API
should be modified, the best way to do this is to:

- Provide old versions of the routines that just translate the
  constants and call the new routines
- The new routines then call either the system call (if it is present)
  or emulate the syscall (for the case of running a new glibc on an
  older kernel).

The detection of whether the syscalls are present should be done at
runtime; for an example, look at libc/sysdeps/unix/sysv/linux/i386/chown.c.

-- 
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>