--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2013-09-26  Eric Blake  <eblake@redhat.com>
+
+	getdtablesize: work around cygwin issue
+	* m4/getdtablesize.m4 (gl_FUNC_GETDTABLESIZE): Detect problem.
+	* modules/getdtablesize (configure.ac): Build replacement.
+	* m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Set up a witness.
+	* modules/unistd (Makefile.am): Expose the witness.
+	* lib/unistd.in.h (getdtablesize): Declare replacement.
+	* lib/getdtablesize.c (rpl_getdtablesize): Work around it.
+	* tests/test-getdtablesize.c (main): Test it.
+	* doc/glibc-functions/getdtablesize.texi (getdtablesize): Document it.
+
 2013-09-25  Mats Erik Andersson  <gnu@gisladisker.se>
 
 	pmccabe2html: escaping of special characters

--- a/doc/glibc-functions/getdtablesize.texi
+++ b/doc/glibc-functions/getdtablesize.texi
@@ -9,6 +9,11 @@
 @item
 This function is missing on some platforms:
 mingw, MSVC 9.
+
+@item
+This function does not represent the true @code{RLIMIT_NOFILE} soft
+limit on some platforms:
+Cygwin 1.7.25.
 @end itemize
 
 Portability problems not fixed by Gnulib:

--- a/lib/getdtablesize.c
+++ b/lib/getdtablesize.c
@@ -22,11 +22,11 @@
 
 #if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
 
-#include <stdio.h>
+# include <stdio.h>
 
-#include "msvc-inval.h"
+# include "msvc-inval.h"
 
-#if HAVE_MSVC_INVALID_PARAMETER_HANDLER
+# if HAVE_MSVC_INVALID_PARAMETER_HANDLER
 static int
 _setmaxstdio_nothrow (int newmax)
 {
@@ -44,10 +44,11 @@
 
   return result;
 }
-# define _setmaxstdio _setmaxstdio_nothrow
-#endif
+#  define _setmaxstdio _setmaxstdio_nothrow
+# endif
 
-/* Cache for the previous getdtablesize () result.  */
+/* Cache for the previous getdtablesize () result.  Safe to cache because
+   Windows also lacks setrlimit.  */
 static int dtablesize;
 
 int
@@ -83,4 +84,24 @@
   return dtablesize;
 }
 
+#elif HAVE_GETDTABLESIZE
+
+# include <sys/resource.h>
+# undef getdtablesize
+
+int
+rpl_getdtablesize(void)
+{
+  /* To date, this replacement is only compiled for Cygwin 1.7.25,
+     which auto-increased the RLIMIT_NOFILE soft limit until it
+     hits the compile-time constant hard limit of 3200.  Although
+     that version of cygwin supported a child process inheriting
+     a smaller soft limit, the smaller limit is not enforced, so
+     we might as well just report the hard limit.  */
+  struct rlimit lim;
+  if (!getrlimit (RLIMIT_NOFILE, &lim) && lim.rlim_max != RLIM_INFINITY)
+    return lim.rlim_max;
+  return getdtablesize ();
+}
+
 #endif

--- a/lib/unistd.in.h
+++ b/lib/unistd.in.h
@@ -654,10 +654,19 @@
 #if @GNULIB_GETDTABLESIZE@
 /* Return the maximum number of file descriptors in the current process.
    In POSIX, this is same as sysconf (_SC_OPEN_MAX).  */
-# if !@HAVE_GETDTABLESIZE@
+# if @REPLACE_GETDTABLESIZE@
+#  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
+#   undef getdtablesize
+#   define getdtablesize rpl_getdtablesize
+#  endif
+_GL_FUNCDECL_RPL (getdtablesize, int, (void));
+_GL_CXXALIAS_RPL (getdtablesize, int, (void));
+# else
+#  if !@HAVE_GETDTABLESIZE@
 _GL_FUNCDECL_SYS (getdtablesize, int, (void));
+#  endif
+_GL_CXXALIAS_SYS (getdtablesize, int, (void));
 # endif
-_GL_CXXALIAS_SYS (getdtablesize, int, (void));
 _GL_CXXALIASWARN (getdtablesize);
 #elif defined GNULIB_POSIXCHECK
 # undef getdtablesize

--- a/m4/getdtablesize.m4
+++ b/m4/getdtablesize.m4
@@ -1,4 +1,4 @@
-# getdtablesize.m4 serial 4
+# getdtablesize.m4 serial 5
 dnl Copyright (C) 2008-2013 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -7,8 +7,35 @@
 AC_DEFUN([gl_FUNC_GETDTABLESIZE],
 [
   AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST])
   AC_CHECK_FUNCS_ONCE([getdtablesize])
-  if test $ac_cv_func_getdtablesize != yes; then
+  if test $ac_cv_func_getdtablesize = yes; then
+    # Cygwin 1.7.25 automatically increases the RLIMIT_NOFILE soft limit
+    # up to an unchangeable hard limit; all other platforms correctly
+    # require setrlimit before getdtablesize() can report a larger value.
+    AC_CACHE_CHECK([whether getdtablesize works],
+      [gl_cv_func_getdtablesize_works],
+      [AC_RUN_IFELSE([
+        AC_LANG_PROGRAM([[#include <unistd.h>]],
+          [int size = getdtablesize();
+           if (dup2 (0, getdtablesize()) != -1)
+             return 1;
+           if (size != getdtablesize())
+             return 2;
+          ])],
+        [gl_cv_func_getdtablesize_works=yes],
+        [gl_cv_func_getdtablesize_works=no],
+        [case "$host_os" in
+          cygwin*) # on cygwin 1.5.25, getdtablesize() automatically grows
+            gl_cv_func_getdtablesize_works="guessing no" ;;
+          *) gl_cv_func_getdtablesize_works="guessing yes" ;;
+         esac])
+      ])
+    case "$gl_cv_func_getdtablesize_works" in
+      *yes) ;;
+      *) REPLACE_GETDTABLESIZE=1 ;;
+    esac
+  else
     HAVE_GETDTABLESIZE=0
   fi
 ])

--- a/m4/unistd_h.m4
+++ b/m4/unistd_h.m4
@@ -1,4 +1,4 @@
-# unistd_h.m4 serial 66
+# unistd_h.m4 serial 67
 dnl Copyright (C) 2006-2013 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -160,6 +160,7 @@
   REPLACE_FTRUNCATE=0;    AC_SUBST([REPLACE_FTRUNCATE])
   REPLACE_GETCWD=0;       AC_SUBST([REPLACE_GETCWD])
   REPLACE_GETDOMAINNAME=0; AC_SUBST([REPLACE_GETDOMAINNAME])
+  REPLACE_GETDTABLESIZE=0; AC_SUBST([REPLACE_GETDTABLESIZE])
   REPLACE_GETLOGIN_R=0;   AC_SUBST([REPLACE_GETLOGIN_R])
   REPLACE_GETGROUPS=0;    AC_SUBST([REPLACE_GETGROUPS])
   REPLACE_GETPAGESIZE=0;  AC_SUBST([REPLACE_GETPAGESIZE])

--- a/modules/getdtablesize
+++ b/modules/getdtablesize
@@ -7,11 +7,12 @@
 
 Depends-on:
 unistd
+extensions
 msvc-inval      [test $HAVE_GETDTABLESIZE = 0]
 
 configure.ac:
 gl_FUNC_GETDTABLESIZE
-if test $HAVE_GETDTABLESIZE = 0; then
+if test $HAVE_GETDTABLESIZE = 0 || test $REPLACE_GETDTABLESIZE = 1; then
   AC_LIBOBJ([getdtablesize])
   gl_PREREQ_GETDTABLESIZE
 fi
@@ -26,5 +27,5 @@
 LGPLv2+
 
 Maintainer:
-Bruno Haible
+Bruno Haible, Eric Blake
 

--- a/modules/unistd
+++ b/modules/unistd
@@ -137,6 +137,7 @@
 	      -e 's|@''REPLACE_FTRUNCATE''@|$(REPLACE_FTRUNCATE)|g' \
 	      -e 's|@''REPLACE_GETCWD''@|$(REPLACE_GETCWD)|g' \
 	      -e 's|@''REPLACE_GETDOMAINNAME''@|$(REPLACE_GETDOMAINNAME)|g' \
+	      -e 's|@''REPLACE_GETDTABLESIZE''@|$(REPLACE_GETDTABLESIZE)|g' \
 	      -e 's|@''REPLACE_GETLOGIN_R''@|$(REPLACE_GETLOGIN_R)|g' \
 	      -e 's|@''REPLACE_GETGROUPS''@|$(REPLACE_GETGROUPS)|g' \
 	      -e 's|@''REPLACE_GETPAGESIZE''@|$(REPLACE_GETPAGESIZE)|g' \

--- a/tests/test-getdtablesize.c
+++ b/tests/test-getdtablesize.c
@@ -29,6 +29,8 @@
 main (int argc, char *argv[])
 {
   ASSERT (getdtablesize () >= 3);
+  ASSERT (dup2 (0, getdtablesize() - 1) == getdtablesize () - 1);
+  ASSERT (dup2 (0, getdtablesize()) == -1);
 
   return 0;
 }