Reviewed by: bde

Changes to support building with _POSIX_SOURCE set to 199309L:

1. Add sys/_posix.h to handle those preprocessor defs that POSIX
says have effects when defined before including any header files;

2. Change POSIX4_VISIBLE back to _POSIX4_VISIBLE

3. Add _POSIX4_VISIBLE_HISTORICALLY for pre-existing BSD features now
defined in POSIX.  These show up when:

_POSIX_SOURCE and _POSIX_C_SOURCE are not set or
_POSIX_C_SOURCE is set >= 199309L

and vanish when:

_POSIX_SOURCE is set or _POSIX_C_SOURCE is < 199309L.

4. Explain these in man 9 posix4;

5. Include _posix.h and conditionalize on new feature test.

1 files changed, 5 insertions, 13 deletions

diff --git a/sys/posix4/posix4.h b/sys/posix4/posix4.h
index 5037b03..99ba882 100644
--- a/sys/posix4/posix4.h
+++ b/sys/posix4/posix4.h
@@ -33,22 +33,14 @@
  *
  */
 
-#if defined(_POSIX_VERSION) && _POSIX_VERSION >= 199309L
+#include <sys/_posix.h>
+
+#ifdef _POSIX4_VISIBLE
+
 #include <sys/param.h>
 #include <sys/ioccom.h>
 #include <sched.h>
 
-/*
- * This defines POSIX4_VISIBLE to indicate posix4 extensions should show up.
- * You should test this when you add a posix4 extension to a header
- * that exists in POSIX.1.  Try "man 9 posix4".
- */
-
-#if !defined(_POSIX_C_SOURCE) || \
- defined(_POSIX_C_SOURCE) && _POSIX_C_SOURCE >= 199309L
-#define POSIX4_VISIBLE
-#endif
-
 /* 
  *
  * March 1, 1998: Details from here on change and this header file
@@ -296,5 +288,5 @@ int kmunlock(int *, void *, const void *, size_t );
 	{ "timer_max", CTLTYPE_INT }, \
 }
 
-#endif /* _POSIX_VERSION >= 199309L */
+#endif /* _POSIX4_VISIBLE */
 #endif /* _POSIX4_POSIX4_H_ */