+/** v4l2_ctrl_subscribe_fh() - Helper function that subscribes a control event.
+ * @fh: The file handler that subscribed the control event.
+ * @sub: The event to subscribe (type must be V4L2_EVENT_CTRL).
+ * @n: How many events should be allocated? (Passed to v4l2_event_alloc).
+ * Recommended to set to twice the number of controls plus whatever
+ * is needed for other events. This function will set n to
+ * max(n, 2 * fh->ctrl_handler->nr_of_refs).
+ *
+ * A helper function that initializes the fh for events, allocates the
+ * list of events and subscribes the control event.
+ *
+ * Typically called in the handler of VIDIOC_SUBSCRIBE_EVENT in the
+ * V4L2_EVENT_CTRL case.
+ */
+int v4l2_ctrl_subscribe_fh(struct v4l2_fh *fh,
+ struct v4l2_event_subscription *sub, unsigned n);
+