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>

drivers/input/input.c

@@ -219,10 +219,24 @@ void input_release_device(struct input_handle *handle)
 
 int input_open_device(struct input_handle *handle)
 {
+	struct input_dev *dev = handle->dev;
+	int err;
+
+	err = down_interruptible(&dev->sem);
+	if (err)
+		return err;
+
 	handle->open++;
-	if (handle->dev->open)
-		return handle->dev->open(handle->dev);
-	return 0;
+
+	if (!dev->users++ && dev->open)
+		err = dev->open(dev);
+
+	if (err)
+		handle->open--;
+
+	up(&dev->sem);
+
+	return err;
 }
 
 int input_flush_device(struct input_handle* handle, struct file* file)
@@ -235,10 +249,17 @@ int input_flush_device(struct input_handle* handle, struct file* file)
 
 void input_close_device(struct input_handle *handle)
 {
+	struct input_dev *dev = handle->dev;
+
 	input_release_device(handle);
-	if (handle->dev->close)
-		handle->dev->close(handle->dev);
+
+	down(&dev->sem);
+
+	if (!--dev->users && dev->close)
+		dev->close(dev);
 	handle->open--;
+
+	up(&dev->sem);
 }
 
 static void input_link_handle(struct input_handle *handle)
@@ -415,6 +436,8 @@ void input_register_device(struct input_dev *dev)
 
 	set_bit(EV_SYN, dev->evbit);
 
+	init_MUTEX(&dev->sem);
+
 	/*
 	 * If delay and period are pre-set by the driver, then autorepeating
 	 * is handled by the driver itself and we don't do it in input.c.

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;