diff --git a/lib/libc/include/libc_private.h b/lib/libc/include/libc_private.h
index 8c4d72d14093..cf346f1367f0 100644
--- a/lib/libc/include/libc_private.h
+++ b/lib/libc/include/libc_private.h
@@ -228,6 +228,7 @@ enum {
 	INTERPOS_wait6,
 	INTERPOS_ppoll,
 	INTERPOS_map_stacks_exec,
+	INTERPOS_fdatasync,
 	INTERPOS_MAX
 };
 
@@ -318,6 +319,7 @@ int		__sys_clock_gettime(__clockid_t, struct timespec *ts);
 int		__sys_close(int);
 int		__sys_connect(int, const struct sockaddr *, __socklen_t);
 int		__sys_fcntl(int, int, ...);
+int		__sys_fdatasync(int);
 int		__sys_fsync(int);
 __pid_t		__sys_fork(void);
 int		__sys_ftruncate(int, __off_t);
diff --git a/lib/libc/sys/Makefile.inc b/lib/libc/sys/Makefile.inc
index a2be249e7e62..a37c5661c720 100644
--- a/lib/libc/sys/Makefile.inc
+++ b/lib/libc/sys/Makefile.inc
@@ -37,6 +37,7 @@ INTERPOSED = \
 	close \
 	connect \
 	fcntl \
+	fdatasync \
 	fsync \
 	fork \
 	kevent \
diff --git a/lib/libc/sys/fdatasync.c b/lib/libc/sys/fdatasync.c
new file mode 100644
index 000000000000..fed97913d31e
--- /dev/null
+++ b/lib/libc/sys/fdatasync.c
@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2016 The FreeBSD Foundation.
+ * All rights reserved.
+ *
+ * Portions of this software were developed by Konstantin Belousov
+ * under sponsorship from the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice(s), this list of conditions and the following disclaimer as
+ *    the first lines of this file unmodified other than the possible
+ *    addition of one or more copyright notices.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice(s), this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <sys/fcntl.h>
+#include <unistd.h>
+#include "libc_private.h"
+
+int
+fdatasync(int fd)
+{
+
+	return (((int (*)(int))__libc_interposing[INTERPOS_fdatasync])(fd));
+}
diff --git a/lib/libc/sys/interposing_table.c b/lib/libc/sys/interposing_table.c
index 75bb2804b759..1447e42ef238 100644
--- a/lib/libc/sys/interposing_table.c
+++ b/lib/libc/sys/interposing_table.c
@@ -79,6 +79,7 @@ interpos_func_t __libc_interposing[INTERPOS_MAX] = {
 	SLOT(wait6, __sys_wait6),
 	SLOT(ppoll, __sys_ppoll),
 	SLOT(map_stacks_exec, __libc_map_stacks_exec),
+	SLOT(fdatasync, __sys_fdatasync),
 };
 #undef SLOT
 
diff --git a/lib/libthr/thread/thr_syscalls.c b/lib/libthr/thread/thr_syscalls.c
index 712249b1e573..362826ca2f91 100644
--- a/lib/libthr/thread/thr_syscalls.c
+++ b/lib/libthr/thread/thr_syscalls.c
@@ -227,6 +227,20 @@ __thr_fsync(int fd)
 	return (ret);
 }
 
+static int
+__thr_fdatasync(int fd)
+{
+	struct pthread *curthread;
+	int ret;
+
+	curthread = _get_curthread();
+	_thr_cancel_enter2(curthread, 0);
+	ret = __sys_fdatasync(fd);
+	_thr_cancel_leave(curthread, 1);
+
+	return (ret);
+}
+
 /*
  * Cancellation behavior:
  *   Thread may be canceled after system call.
@@ -653,6 +667,7 @@ __thr_interpose_libc(void)
 	SLOT(wait6);
 	SLOT(ppoll);
 	SLOT(map_stacks_exec);
+	SLOT(fdatasync);
 #undef SLOT
 	*(__libc_interposing_slot(
 	    INTERPOS__pthread_mutex_init_calloc_cb)) =
diff --git a/share/man/man3/pthread_testcancel.3 b/share/man/man3/pthread_testcancel.3
index fc412de5b1ae..1dfc96483445 100644
--- a/share/man/man3/pthread_testcancel.3
+++ b/share/man/man3/pthread_testcancel.3
@@ -1,5 +1,5 @@
 .\" $FreeBSD$
-.Dd April 16, 2015
+.Dd August 16, 2016
 .Dt PTHREAD_TESTCANCEL 3
 .Os
 .Sh NAME
@@ -114,6 +114,7 @@ function is a cancellation point if
 .Fa cmd
 is
 .Dv F_SETLKW .
+.It Fn fdatasync
 .It Fn fsync
 .It Fn kevent
 The