--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,19 @@
+2011-09-16  Eric Blake  <eblake@redhat.com>
+
+	fdatasync: new module
+	* modules/fsync (Description): Document difference to fdatasync.
+	* modules/fdatasync: New module.
+	* m4/fdatasync.m4 (gl_FUNC_FDATASYNC): New file.
+	* lib/fdatasync.c (fdatasync): Likewise.
+	* m4/unistd_h.m4 (gl_UNISTD_H, gl_UNISTD_H_DEFAULTS): Set up
+	defaults.
+	* modules/unistd (Makefile.am): Set witnesses.
+	* lib/unistd.in.h (fdatasync): Declare.
+	* MODULES.html.sh: Document it.
+	* doc/posix-functions/fdatasync.texi (fdatasync): Likewise.
+	* modules/fdatasync-tests: New test.
+	* tests/test-fdatasync.c: Likewise.
+
 2011-09-16  Eric Blake  <eblake@redhat.com>
 
 	test-fsync: enhance tests

--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -2356,6 +2356,7 @@
   func_module fclose
   func_module fcntl-h
   func_module fcntl
+  func_module fdatasync
   func_module flock
   func_module fopen
   func_module fprintf-posix

--- a/doc/posix-functions/fdatasync.texi
+++ b/doc/posix-functions/fdatasync.texi
@@ -4,15 +4,15 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/fdatasync.html}
 
-Gnulib module: ---
+Gnulib module: fdatasync
 
 Portability problems fixed by Gnulib:
 @itemize
-@end itemize
-
-Portability problems not fixed by Gnulib:
-@itemize
 @item
 This function is missing on some platforms:
 MacOS X 10.5, FreeBSD 6.0, OpenBSD 3.8, Minix 3.1.8, IRIX 5.3, Solaris 2.4, mingw, MSVC 9, Interix 3.5, BeOS.
 @end itemize
+
+Portability problems not fixed by Gnulib:
+@itemize
+@end itemize

new file mode 100644
--- /dev/null
+++ b/lib/fdatasync.c
@@ -0,0 +1,25 @@
+/* Emulate fdatasync on platforms that lack it.
+
+   Copyright (C) 2011 Free Software Foundation, Inc.
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+#include <unistd.h>
+
+int
+fdatasync (int fd)
+{
+  return fsync (fd);
+}

--- a/lib/unistd.in.h
+++ b/lib/unistd.in.h
@@ -484,8 +484,27 @@
 #endif
 
 
+#if @GNULIB_FDATASYNC@
+/* Synchronize changes to a file.
+   Return 0 if successful, otherwise -1 and errno set.
+   See POSIX:2001 specification
+   <http://www.opengroup.org/susv3xsh/fdatasync.html>.  */
+# if !@HAVE_FDATASYNC@
+_GL_FUNCDECL_SYS (fdatasync, int, (int fd));
+# endif
+_GL_CXXALIAS_SYS (fdatasync, int, (int fd));
+_GL_CXXALIASWARN (fdatasync);
+#elif defined GNULIB_POSIXCHECK
+# undef fdatasync
+# if HAVE_RAW_DECL_FDATASYNC
+_GL_WARN_ON_USE (fdatasync, "fdatasync is unportable - "
+                 "use gnulib module fdatasync for portability");
+# endif
+#endif
+
+
 #if @GNULIB_FSYNC@
-/* Synchronize changes to a file.
+/* Synchronize changes, including metadata, to a file.
    Return 0 if successful, otherwise -1 and errno set.
    See POSIX:2001 specification
    <http://www.opengroup.org/susv3xsh/fsync.html>.  */

new file mode 100644
--- /dev/null
+++ b/m4/fdatasync.m4
@@ -0,0 +1,14 @@
+# fdatasync.m4 serial 1
+dnl Copyright (C) 2008-2011 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_FDATASYNC],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_CHECK_FUNCS_ONCE([fdatasync])
+  if test $ac_cv_func_fdatasync = no; then
+    HAVE_FDATASYNC=0
+  fi
+])

--- a/m4/unistd_h.m4
+++ b/m4/unistd_h.m4
@@ -1,4 +1,4 @@
-# unistd_h.m4 serial 58
+# unistd_h.m4 serial 59
 dnl Copyright (C) 2006-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -40,7 +40,7 @@
 # endif
 #endif
     ]], [chown dup2 dup3 environ euidaccess faccessat fchdir fchownat
-    fsync ftruncate getcwd getdomainname getdtablesize getgroups
+    fdatasync fsync ftruncate getcwd getdomainname getdtablesize getgroups
     gethostname getlogin getlogin_r getpagesize getusershell setusershell
     endusershell group_member lchown link linkat lseek pipe pipe2 pread pwrite
     readlink readlinkat rmdir sleep symlink symlinkat ttyname_r unlink unlinkat
@@ -67,6 +67,7 @@
   GNULIB_FACCESSAT=0;            AC_SUBST([GNULIB_FACCESSAT])
   GNULIB_FCHDIR=0;               AC_SUBST([GNULIB_FCHDIR])
   GNULIB_FCHOWNAT=0;             AC_SUBST([GNULIB_FCHOWNAT])
+  GNULIB_FDATASYNC=0;            AC_SUBST([GNULIB_FDATASYNC])
   GNULIB_FSYNC=0;                AC_SUBST([GNULIB_FSYNC])
   GNULIB_FTRUNCATE=0;            AC_SUBST([GNULIB_FTRUNCATE])
   GNULIB_GETCWD=0;               AC_SUBST([GNULIB_GETCWD])
@@ -110,6 +111,7 @@
   HAVE_FACCESSAT=1;       AC_SUBST([HAVE_FACCESSAT])
   HAVE_FCHDIR=1;          AC_SUBST([HAVE_FCHDIR])
   HAVE_FCHOWNAT=1;        AC_SUBST([HAVE_FCHOWNAT])
+  HAVE_FDATASYNC=1;       AC_SUBST([HAVE_FDATASYNC])
   HAVE_FSYNC=1;           AC_SUBST([HAVE_FSYNC])
   HAVE_FTRUNCATE=1;       AC_SUBST([HAVE_FTRUNCATE])
   HAVE_GETDTABLESIZE=1;   AC_SUBST([HAVE_GETDTABLESIZE])

new file mode 100644
--- /dev/null
+++ b/modules/fdatasync
@@ -0,0 +1,28 @@
+Description:
+fdatasync(2) function: synchronize writes to a file.
+
+Files:
+lib/fdatasync.c
+m4/fdatasync.m4
+
+Depends-on:
+fsync
+unistd
+
+configure.ac:
+gl_FUNC_FDATASYNC
+if test $HAVE_FDATASYNC = 0; then
+  AC_LIBOBJ([fdatasync])
+fi
+gl_UNISTD_MODULE_INDICATOR([fdatasync])
+
+Makefile.am:
+
+Include:
+<unistd.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Eric Blake

new file mode 100644
--- /dev/null
+++ b/modules/fdatasync-tests
@@ -0,0 +1,13 @@
+Files:
+tests/test-fdatasync.c
+tests/signature.h
+tests/macros.h
+
+Depends-on:
+errno
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-fdatasync
+check_PROGRAMS += test-fdatasync

--- a/modules/fsync
+++ b/modules/fsync
@@ -1,5 +1,5 @@
 Description:
-fsync(2) function: synchronize writes to a file.
+fsync(2) function: synchronize writes, including metadata, to a file.
 
 Files:
 lib/fsync.c

--- a/modules/unistd
+++ b/modules/unistd
@@ -39,6 +39,7 @@
 	      -e 's/@''GNULIB_FACCESSAT''@/$(GNULIB_FACCESSAT)/g' \
 	      -e 's/@''GNULIB_FCHDIR''@/$(GNULIB_FCHDIR)/g' \
 	      -e 's/@''GNULIB_FCHOWNAT''@/$(GNULIB_FCHOWNAT)/g' \
+	      -e 's/@''GNULIB_FDATASYNC''@/$(GNULIB_FDATASYNC)/g' \
 	      -e 's/@''GNULIB_FSYNC''@/$(GNULIB_FSYNC)/g' \
 	      -e 's/@''GNULIB_FTRUNCATE''@/$(GNULIB_FTRUNCATE)/g' \
 	      -e 's/@''GNULIB_GETCWD''@/$(GNULIB_GETCWD)/g' \
@@ -82,6 +83,7 @@
 	      -e 's|@''HAVE_FACCESSAT''@|$(HAVE_FACCESSAT)|g' \
 	      -e 's|@''HAVE_FCHDIR''@|$(HAVE_FCHDIR)|g' \
 	      -e 's|@''HAVE_FCHOWNAT''@|$(HAVE_FCHOWNAT)|g' \
+	      -e 's|@''HAVE_FDATASYNC''@|$(HAVE_FDATASYNC)|g' \
 	      -e 's|@''HAVE_FSYNC''@|$(HAVE_FSYNC)|g' \
 	      -e 's|@''HAVE_FTRUNCATE''@|$(HAVE_FTRUNCATE)|g' \
 	      -e 's|@''HAVE_GETDTABLESIZE''@|$(HAVE_GETDTABLESIZE)|g' \

new file mode 100644
--- /dev/null
+++ b/tests/test-fdatasync.c
@@ -0,0 +1,64 @@
+/* Test of fdatasync() function.
+   Copyright (C) 2008-2011 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include "signature.h"
+SIGNATURE_CHECK (fdatasync, int, (int));
+
+#include <errno.h>
+#include <fcntl.h>
+
+#include "macros.h"
+
+int
+main (void)
+{
+  int fd;
+  const char *file = "test-fdatasync.txt";
+
+  if (fdatasync (STDOUT_FILENO) != 0)
+    {
+      ASSERT (errno == EINVAL /* POSIX */
+              || errno == ENOTSUP /* seen on MacOS X 10.5 */
+              || errno == EBADF /* seen on AIX 7.1 */
+              );
+    }
+  errno = 0;
+  ASSERT (fdatasync (-1) == -1);
+  ASSERT (errno == EBADF);
+  fd = open (file, O_WRONLY|O_CREAT|O_TRUNC, 0644);
+  ASSERT (0 <= fd);
+  ASSERT (write (fd, "hello", 5) == 5);
+  ASSERT (fdatasync (fd) == 0);
+  ASSERT (close (fd) == 0);
+#if 0
+  /* POSIX is self-contradictory on whether fdatasync must fail on
+     read-only file descriptors.  Glibc allows it, as does our
+     implementation if fsync allows it.  */
+  fd = open (file, O_RDONLY);
+  ASSERT (0 <= fd);
+  errno = 0;
+  ASSERT (fdatasync (fd) == -1);
+  ASSERT (errno == EBADF);
+  ASSERT (close (fd) == 0);
+#endif
+  ASSERT (unlink (file) == 0);
+
+  return 0;
+}