dup2: Remove check for dup2, unless supporting old obsolete platforms.

* modules/dup2-obsolete: New file.
* m4/dup2-obsolete.m4: New file.
* m4/dup2.m4 (gl_FUNC_DUP2): Don't check whether dup2 exists if
gl_FUNC_DUP2_OBSOLETE is not also defined.
* modules/dup2 (Depends-on): Add dup2-obsolete.
* doc/posix-functions/dup2.texi: Mention module dup2-obsolete.

ChangeLog

@@ -1,3 +1,13 @@
+2011-04-25  Bruno Haible  <bruno@clisp.org>
+
+	dup2: Remove check for dup2, unless supporting old obsolete platforms.
+	* modules/dup2-obsolete: New file.
+	* m4/dup2-obsolete.m4: New file.
+	* m4/dup2.m4 (gl_FUNC_DUP2): Don't check whether dup2 exists if
+	gl_FUNC_DUP2_OBSOLETE is not also defined.
+	* modules/dup2 (Depends-on): Add dup2-obsolete.
+	* doc/posix-functions/dup2.texi: Mention module dup2-obsolete.
+
 2011-04-25  Bruno Haible  <bruno@clisp.org>
 
 	strnlen: Avoid memchr related link error on old obsolete platforms.

doc/posix-functions/dup2.texi

@@ -4,9 +4,9 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/dup2.html}
 
-Gnulib module: dup2
+Gnulib module: dup2 or dup2-obsolete
 
-Portability problems fixed by Gnulib:
+Portability problems fixed by either Gnulib module @code{dup2} or @code{dup2-obsolete}:
 @itemize
 @item
 This function always returns 0 for success on some platforms:
@@ -34,7 +34,10 @@ This function returns @code{EMFILE} instead of @code{EBADF} for
 extremely large targets, which interferes with using
 @code{dup2(fd,fd)==fd)} as the minimal @code{EBADF} filter:
 FreeBSD 6.1, Cygwin 1.5.
+@end itemize
 
+Portability problems fixed by Gnulib module @code{dup2-obsolete}:
+@itemize
 @item
 This function is missing on some older platforms.
 @end itemize

m4/dup2-obsolete.m4

@@ -0,0 +1,11 @@
+# dup2-obsolete.m4 serial 1
+dnl Copyright (C) 2011 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_DUP2_OBSOLETE],
+[
+  dnl The real code is in dup2.m4.
+  :
+])

m4/dup2.m4

@@ -8,11 +8,17 @@ AC_DEFUN([gl_FUNC_DUP2],
 [
   AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
   AC_REQUIRE([AC_CANONICAL_HOST])
-  AC_CHECK_FUNCS_ONCE([dup2 fcntl])
-  if test $ac_cv_func_dup2 = no; then
-    HAVE_DUP2=0
-    AC_LIBOBJ([dup2])
-  else
+  m4_ifdef([gl_FUNC_DUP2_OBSOLETE], [
+    AC_CHECK_FUNCS_ONCE([dup2])
+    if test $ac_cv_func_dup2 = no; then
+      HAVE_DUP2=0
+      AC_LIBOBJ([dup2])
+    fi
+  ], [
+    AC_DEFINE([HAVE_DUP2], [1], [Define to 1 if you have the 'dup2' function.])
+  ])
+  AC_CHECK_FUNCS_ONCE([fcntl])
+  if test $HAVE_DUP2 = 1; then
     AC_CACHE_CHECK([whether dup2 works], [gl_cv_func_dup2_works],
       [AC_RUN_IFELSE([
          AC_LANG_PROGRAM([[#include <unistd.h>

modules/dup2

@@ -7,6 +7,7 @@ m4/dup2.m4
 
 Depends-on:
 unistd
+dup2-obsolete
 
 configure.ac:
 gl_FUNC_DUP2

modules/dup2-obsolete

@@ -0,0 +1,28 @@
+Description:
+dup2() function for old platforms.
+
+Status:
+obsolete
+
+Notice:
+This module is obsolete.
+
+Files:
+m4/dup2-obsolete.m4
+
+Depends-on:
+dup2
+
+configure.ac:
+gl_FUNC_DUP2_OBSOLETE
+
+Makefile.am:
+
+Include:
+<unistd.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Bruno Haible