fs/fcntl.c                 | 23 +++++++++++++++++++++++
 include/uapi/linux/fcntl.h | 14 ++++++++------
 2 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 54cc85d3338e..1ddb63f70445 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -327,6 +327,25 @@ static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
 	return 0;
 }
 
+/*
+ * Is the file descriptor a dup of the file?
+ */
+static long f_dupfd_query(int fd, struct file *filp)
+{
+	struct fd f = fdget_raw(fd);
+
+	/*
+	 * We can do the 'fdput()' immediately, as the only thing that
+	 * matters is the pointer value which isn't changed by the fdput.
+	 *
+	 * Technically we didn't need a ref at all, and 'fdget()' was
+	 * overkill, but given our lockless file pointer lookup, the
+	 * alternatives are complicated.
+	 */
+	fdput(f);
+	return f.file == filp;
+}
+
 static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 		struct file *filp)
 {
@@ -342,6 +361,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 	case F_DUPFD_CLOEXEC:
 		err = f_dupfd(argi, filp, O_CLOEXEC);
 		break;
+	case F_DUPFD_QUERY:
+		err = f_dupfd_query(argi, filp);
+		break;
 	case F_GETFD:
 		err = get_close_on_exec(fd) ? FD_CLOEXEC : 0;
 		break;
@@ -446,6 +468,7 @@ static int check_fcntl_cmd(unsigned cmd)
 	switch (cmd) {
 	case F_DUPFD:
 	case F_DUPFD_CLOEXEC:
+	case F_DUPFD_QUERY:
 	case F_GETFD:
 	case F_SETFD:
 	case F_GETFL:
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 282e90aeb163..c0bcc185fa48 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -8,6 +8,14 @@
 #define F_SETLEASE	(F_LINUX_SPECIFIC_BASE + 0)
 #define F_GETLEASE	(F_LINUX_SPECIFIC_BASE + 1)
 
+/*
+ * Request nofications on a directory.
+ * See below for events that may be notified.
+ */
+#define F_NOTIFY	(F_LINUX_SPECIFIC_BASE + 2)
+
+#define F_DUPFD_QUERY	(F_LINUX_SPECIFIC_BASE + 3)
+
 /*
  * Cancel a blocking posix lock; internal use only until we expose an
  * asynchronous lock api to userspace:
@@ -17,12 +25,6 @@
 /* Create a file descriptor with FD_CLOEXEC set. */
 #define F_DUPFD_CLOEXEC	(F_LINUX_SPECIFIC_BASE + 6)
 
-/*
- * Request nofications on a directory.
- * See below for events that may be notified.
- */
-#define F_NOTIFY	(F_LINUX_SPECIFIC_BASE+2)
-
 /*
  * Set and get of pipe page size array
  */