--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2010-09-28  Bruno Haible  <bruno@clisp.org>
+
+	poll-h: Create poll.h on all platforms.
+	* lib/poll.in.h: Use double-inclusion guard. Don't define POLL*,
+	struct pollfd, nfds_t, INFTIM when the system has <poll.h>.
+	* m4/poll_h.m4 (gl_POLL_H): Set HAVE_POLL_H. Invoke
+	gl_CHECK_NEXT_HEADERS. Don't set POLL_H.
+	(gl_REPLACE_POLL_H): Don't set POLL_H.
+	(gl_POLL_H_DEFAULTS): Don't initialize POLL_H.
+	* modules/poll-h (Depends-on): Add include_next.
+	(Makefile.am): Create poll.h unconditionally. Substitute also
+	HAVE_POLL_H, INCLUDE_NEXT, PRAGMA_SYSTEM_HEADER, NEXT_POLL_H.
+
 2010-09-28  Bruno Haible  <bruno@clisp.org>
 
 	Tests for module 'poll-h'.

--- a/lib/poll.in.h
+++ b/lib/poll.in.h
@@ -20,6 +20,17 @@
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
 
 #ifndef _GL_POLL_H
+
+#if __GNUC__ >= 3
+@PRAGMA_SYSTEM_HEADER@
+#endif
+
+/* The include_next requires a split double-inclusion guard.  */
+#if @HAVE_POLL_H@
+# @INCLUDE_NEXT@ @NEXT_POLL_H@
+#endif
+
+#ifndef _GL_POLL_H
 #define _GL_POLL_H
 
 
@@ -28,17 +39,19 @@
 /* The definition of _GL_WARN_ON_USE is copied here.  */
 
 
+#if !@HAVE_POLL_H@
+
 /* fake a poll(2) environment */
-#define POLLIN      0x0001      /* any readable data available   */
-#define POLLPRI     0x0002      /* OOB/Urgent readable data      */
-#define POLLOUT     0x0004      /* file descriptor is writeable  */
-#define POLLERR     0x0008      /* some poll error occurred      */
-#define POLLHUP     0x0010      /* file descriptor was "hung up" */
-#define POLLNVAL    0x0020      /* requested events "invalid"    */
-#define POLLRDNORM  0x0040
-#define POLLRDBAND  0x0080
-#define POLLWRNORM  0x0100
-#define POLLWRBAND  0x0200
+# define POLLIN      0x0001      /* any readable data available   */
+# define POLLPRI     0x0002      /* OOB/Urgent readable data      */
+# define POLLOUT     0x0004      /* file descriptor is writeable  */
+# define POLLERR     0x0008      /* some poll error occurred      */
+# define POLLHUP     0x0010      /* file descriptor was "hung up" */
+# define POLLNVAL    0x0020      /* requested events "invalid"    */
+# define POLLRDNORM  0x0040
+# define POLLRDBAND  0x0080
+# define POLLWRNORM  0x0100
+# define POLLWRBAND  0x0200
 
 struct pollfd
 {
@@ -49,6 +62,14 @@
 
 typedef unsigned long nfds_t;
 
+/* Define INFTIM only if doing so conforms to POSIX.  */
+# if !defined (_POSIX_C_SOURCE) && !defined (_XOPEN_SOURCE)
+#  define INFTIM (-1)
+# endif
+
+#endif
+
+
 #if @GNULIB_POLL@
 # if @REPLACE_POLL@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
@@ -72,10 +93,6 @@
 # endif
 #endif
 
-/* Define INFTIM only if doing so conforms to POSIX.  */
-#if !defined (_POSIX_C_SOURCE) && !defined (_XOPEN_SOURCE)
-#define INFTIM (-1)
-#endif
-
 
 #endif /* _GL_POLL_H */
+#endif /* _GL_POLL_H */

--- a/m4/poll_h.m4
+++ b/m4/poll_h.m4
@@ -13,9 +13,16 @@
   AC_REQUIRE([gl_POLL_H_DEFAULTS])
 
   AC_CHECK_HEADERS_ONCE([poll.h])
-  if test $ac_cv_header_poll_h != yes; then
+  if test $ac_cv_header_poll_h = yes; then
+    HAVE_POLL_H=1
+  else
+    HAVE_POLL_H=0
     gl_REPLACE_POLL_H
   fi
+  AC_SUBST([HAVE_POLL_H])
+
+  dnl <poll.h> is always overridden, because of GNULIB_POSIXCHECK.
+  gl_CHECK_NEXT_HEADERS([poll.h])
 
   dnl Check for declarations of anything we want to poison if the
   dnl corresponding gnulib module is not in use.
@@ -26,8 +33,8 @@
 dnl Unconditionally enables the replacement of <poll.h>.
 AC_DEFUN([gl_REPLACE_POLL_H],
 [
-  AC_REQUIRE([gl_POLL_H_DEFAULTS])
-  POLL_H='poll.h'
+  dnl This is a no-op, because <poll.h> is always overridden.
+  :
 ])
 
 AC_DEFUN([gl_POLL_MODULE_INDICATOR],
@@ -43,7 +50,6 @@
 [
   GNULIB_POLL=0;        AC_SUBST([GNULIB_POLL])
   dnl Assume proper GNU behavior unless another module says otherwise.
-  POLL_H='';            AC_SUBST([POLL_H])
   HAVE_POLL=1;          AC_SUBST([HAVE_POLL])
   REPLACE_POLL=0;       AC_SUBST([REPLACE_POLL])
 ])

--- a/modules/poll-h
+++ b/modules/poll-h
@@ -8,20 +8,25 @@
 Depends-on:
 c++defs
 extensions
+include_next
 warn-on-use
 
 configure.ac:
 gl_POLL_H
 
 Makefile.am:
-BUILT_SOURCES += $(POLL_H)
+BUILT_SOURCES += poll.h
 
 # We need the following in order to create <poll.h> when the system
 # doesn't have one.
 poll.h: poll.in.h $(CXXDEFS_H) $(WARN_ON_USE_H)
 	$(AM_V_GEN)rm -f $@-t $@ && \
 	{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */'; \
-	  sed -e 's|@''GNULIB_POLL''@|$(GNULIB_POLL)|g' \
+	  sed -e 's|@''HAVE_POLL_H''@|$(HAVE_POLL_H)|g' \
+	      -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
+	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
+	      -e 's|@''NEXT_POLL_H''@|$(NEXT_POLL_H)|g' \
+	      -e 's|@''GNULIB_POLL''@|$(GNULIB_POLL)|g' \
 	      -e 's|@''HAVE_POLL''@|$(HAVE_POLL)|g' \
 	      -e 's|@''REPLACE_POLL''@|$(REPLACE_POLL)|g' \
 	      -e '/definitions of _GL_FUNCDECL_RPL/r $(CXXDEFS_H)' \