# HG changeset patch
# User Eric Blake <ebb9@byu.net>
# Date 1255145320 21600
# Node ID 3c9981d0d9c3832aeeb7cdb630a807f80cbeb51b
# Parent  a620bedbe9580b226566839dfced8fc694d285eb
dup2: work around FreeBSD 6.1 bug

dup2(1,1000000) needs to fail with EBADF (per POSIX), not
EMFILE, based on our usage of it in other modules.

* m4/dup2.m4 (gl_FUNC_DUP2): Detect bug.
* doc/posix-functions/dup2.texi (dup2): Document it.
Reported by Nelson H. F. Beebe and Jim Meyering.

Signed-off-by: Eric Blake <ebb9@byu.net>

diff --git a/ChangeLog b/ChangeLog
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2009-10-09  Eric Blake  <ebb9@byu.net>
 
+	dup2: work around FreeBSD 6.1 bug
+	* m4/dup2.m4 (gl_FUNC_DUP2): Detect bug.
+	* doc/posix-functions/dup2.texi (dup2): Document it.
+	Reported by Nelson H. F. Beebe and Jim Meyering.
+
 	test-stat-time: port to buggy NFS clients
 	* tests/test-stat-time.c (main) [W32]: Reduce ifdefs.
 	(test_ctime): Also skip test if mtime and ctime are skewed.
diff --git a/doc/posix-functions/dup2.texi b/doc/posix-functions/dup2.texi
--- a/doc/posix-functions/dup2.texi
+++ b/doc/posix-functions/dup2.texi
@@ -25,6 +25,12 @@
 Linux releases between July 2008 and May 2009 (versions 2.6.27 to 2.6.29).
 
 @item
+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.
+
+@item
 This function is missing on some older platforms.
 @end itemize
 
diff --git a/m4/dup2.m4 b/m4/dup2.m4
--- a/m4/dup2.m4
+++ b/m4/dup2.m4
@@ -1,4 +1,4 @@
-#serial 8
+#serial 9
 dnl Copyright (C) 2002, 2005, 2007, 2009 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -15,12 +15,16 @@
   else
     AC_CACHE_CHECK([whether dup2 works], [gl_cv_func_dup2_works],
       [AC_RUN_IFELSE([
-         AC_LANG_PROGRAM([[#include <unistd.h>]],
+         AC_LANG_PROGRAM([[#include <unistd.h>
+#include <errno.h>]],
            [if (dup2 (1, 1) == 0)
               return 1;
             close (0);
             if (dup2 (0, 0) != -1)
-              return 1;
+              return 2;
+            /* Many gnulib modules require POSIX conformance of EBADF.  */
+            if (dup2 (1, 1000000) == -1 && errno != EBADF)
+              return 3;
             return 0;
            ])
         ],
@@ -33,6 +37,8 @@
 	   linux*) # On linux between 2008-07-27 and 2009-05-11, dup2 of a
 	           # closed fd may yield -EBADF instead of -1 / errno=EBADF.
 	     gl_cv_func_dup2_works=no;;
+           freebsd*) # on FreeBSD 6.1, dup2(1,1000000) gives EMFILE, not EBADF.
+	     gl_cv_func_dup2_works=no;;
 	   *) gl_cv_func_dup2_works=yes;;
 	 esac])
       ])