Input: add semaphore and user count to input_dev structure;

serialize open and close calls and ensure that device's
       open and close methods are only called when first user
       opens it or last user closes it.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

include/linux/input.h

@@ -859,6 +859,10 @@ struct input_dev {
 	int (*erase_effect)(struct input_dev *dev, int effect_id);
 
 	struct input_handle *grab;
+
+	struct semaphore sem;	/* serializes open and close operations */
+	unsigned int users;
+
 	struct device *dev;
 
 	struct list_head	h_list;