Add scaffolding for feature tests that will be used by our include files.

Inspired by similar macros in FreeBSD.  OK miod@

1 files changed, 151 insertions, 1 deletions

diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
index 1c90d8ee2ae..323108c1953 100644
--- a/sys/sys/cdefs.h
+++ b/sys/sys/cdefs.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cdefs.h,v 1.15 2005/05/19 18:32:51 hshoexer Exp $	*/
+/*	$OpenBSD: cdefs.h,v 1.16 2005/05/24 22:28:02 millert Exp $	*/
 /*	$NetBSD: cdefs.h,v 1.16 1996/04/03 20:46:39 christos Exp $	*/
 
 /*
@@ -179,4 +179,154 @@
 #define	__extension__
 #endif
 
+/*
+ * "The nice thing about standards is that there are so many to choose from."
+ * There are a number of "feature test macros" specified by (different)
+ * standards that determine which interfaces and types the header files
+ * should expose.
+ *
+ * Because of inconsistencies in these macros, we define our own
+ * set in the private name space that end in _VISIBLE.  These are
+ * always defined and so headers can test their values easily.
+ * Things can get tricky when multiple feature macros are defined.
+ * We try to take the union of all the features requested.
+ *
+ * The following macros are guaranteed to have a value after cdefs.h
+ * has been included:
+ *	__POSIX_VISIBLE
+ *	__XPG_VISIBLE
+ *	__ISO_C_VISIBLE
+ *	__OPENBSD_VISIBLE
+ */
+
+/*
+ * X/Open Portability Guides and Single Unix Specifications.
+ * _XOPEN_SOURCE				XPG3
+ * _XOPEN_SOURCE && _XOPEN_VERSION = 4		XPG4
+ * _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED = 1	XPG4v2
+ * _XOPEN_SOURCE == 500				XPG5
+ * _XOPEN_SOURCE == 520				XPG5v2
+ * _XOPEN_SOURCE == 600				POSIX 1003.1-2001 with XSI
+ *
+ * The XPG spec implies a specific value for _POSIX_C_SOURCE.
+ */
+#ifdef _XOPEN_SOURCE
+# if (_XOPEN_SOURCE - 0 >= 600)
+#  define __XPG_VISIBLE		600
+#  undef _POSIX_C_SOURCE
+#  define _POSIX_C_SOURCE	200112L
+# elif (_XOPEN_SOURCE - 0 >= 520)
+#  define __XPG_VISIBLE		520
+#  undef _POSIX_C_SOURCE
+#  define _POSIX_C_SOURCE	199506L
+# elif (_XOPEN_SOURCE - 0 >= 500)
+#  define __XPG_VISIBLE		500
+#  undef _POSIX_C_SOURCE
+#  define _POSIX_C_SOURCE	199506L
+# elif (_XOPEN_SOURCE_EXTENDED - 0 == 1)
+#  define __XPG_VISIBLE		420
+# elif (_XOPEN_VERSION - 0 >= 4)
+#  define __XPG_VISIBLE		400
+# else
+#  define __XPG_VISIBLE		300
+# endif
+#endif
+
+/*
+ * POSIX macros, these checks must follow the XOPEN ones above.
+ *
+ * _POSIX_SOURCE == 1		1003.1-1988 (superseded by _POSIX_C_SOURCE)
+ * _POSIX_C_SOURCE == 1		1003.1-1990
+ * _POSIX_C_SOURCE == 2		1003.2-1992
+ * _POSIX_C_SOURCE == 199309L	1003.1b-1993
+ * _POSIX_C_SOURCE == 199506L   1003.1c-1995, 1003.1i-1995,
+ *				and the omnibus ISO/IEC 9945-1:1996
+ * _POSIX_C_SOURCE == 200112L   1003.1-2001
+ *
+ * The POSIX spec implies a specific value for __ISO_C_VISIBLE, though
+ * this may be overridden by the _ISOC99_SOURCE macro later.
+ */
+#ifdef _POSIX_C_SOURCE
+# if (_POSIX_C_SOURCE - 0 >= 200112)
+#  define __POSIX_VISIBLE	200112
+#  define __ISO_C_VISIBLE	1999
+# elif (_POSIX_C_SOURCE - 0 >= 199506)
+#  define __POSIX_VISIBLE	199506
+#  define __ISO_C_VISIBLE	1990
+# elif (_POSIX_C_SOURCE - 0 >= 199309)
+#  define __POSIX_VISIBLE	199309
+#  define __ISO_C_VISIBLE	1990
+# elif (_POSIX_C_SOURCE - 0 >= 2)
+#  define __POSIX_VISIBLE	199209
+#  define __ISO_C_VISIBLE	1990
+# else
+#  define __POSIX_VISIBLE	199009
+#  define __ISO_C_VISIBLE	1990
+# endif
+#elif defined(_POSIX_SOURCE)
+# define __POSIX_VISIBLE	198808
+#  define __ISO_C_VISIBLE	0
+#endif
+
+/*
+ * _ANSI_SOURCE means to expose ANSI C89 interfaces only.
+ * If the the user defines it in addition to one of the POSIX or XOPEN
+ * macros, assume the POSIX/XOPEN macro(s) should take precedence.
+ */
+#if defined(_ANSI_SOURCE) && !defined(__POSIX_VISIBLE) && \
+    !defined(__XPG_VISIBLE)
+# define __POSIX_VISIBLE	0
+# define __XPG_VISIBLE		0
+# define __ISO_C_VISIBLE	1990
+#endif
+
+/*
+ * _ISOC99_SOURCE and __STDC_VERSION__ override any of the other macros since
+ * they are non-exclusive.
+ */
+#if defined(_ISOC99_SOURCE) || (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901)
+# undef __ISO_C_VISIBLE
+# define __ISO_C_VISIBLE	1999
+#endif
+
+/*
+ * Finally deal with BSD-specific interfaces that are not covered
+ * by any standards.  We expose these when one of the POSIX or XPG
+ * macros is not defined or if the user explicitly asks for them.
+ */
+#if !defined(_OPENBSD_SOURCE) && \
+   (defined(_ANSI_SOURCE) || defined(__XPG_VISIBLE) || defined(__POSIX_VISIBLE))
+# define __OPENBSD_VISIBLE	0
+#endif
+
+/*
+ * __STRICT_ANSI__ (gcc -ansi) overrides everything else.
+ */
+#ifdef __STRICT_ANSI__
+# undef __POSIX_VISIBLE
+# define __POSIX_VISIBLE	0
+# undef __XPG_VISIBLE
+# define __XPG_VISIBLE		0
+# undef __ISO_C_VISIBLE
+# define __ISO_C_VISIBLE	1990
+# undef __OPENBSD_VISIBLE
+# define __OPENBSD_VISIBLE	0
+#endif
+
+/*
+ * Default values.
+ */
+#ifndef __XPG_VISIBLE
+# define __XPG_VISIBLE		600
+#endif
+#ifndef __POSIX_VISIBLE
+# define __POSIX_VISIBLE	200112
+#endif
+#ifndef __ISO_C_VISIBLE
+# define __ISO_C_VISIBLE	1999
+#endif
+#ifndef __OPENBSD_VISIBLE
+# define __OPENBSD_VISIBLE	1
+#endif
+
 #endif /* !_CDEFS_H_ */