input: Implement input device grabbing so that it is possible to steal

an input device from other handlers and have an exclusive access
to events.

drivers/input/evdev.c

@@ -29,6 +29,7 @@ struct evdev {
 	char name[16];
 	struct input_handle handle;
 	wait_queue_head_t wait;
+	struct evdev_list *grab;
 	struct list_head list;
 };
 
@@ -48,7 +49,8 @@ static void evdev_event(struct input_handle *handle, unsigned int type, unsigned
 	struct evdev *evdev = handle->private;
 	struct evdev_list *list;
 
-	list_for_each_entry(list, &evdev->list, node) {
+	if (evdev->grab) {
+		list = evdev->grab;
 
 		do_gettimeofday(&list->buffer[list->head].time);
 		list->buffer[list->head].type = type;
@@ -57,7 +59,17 @@ static void evdev_event(struct input_handle *handle, unsigned int type, unsigned
 		list->head = (list->head + 1) & (EVDEV_BUFFER_SIZE - 1);
 
 		kill_fasync(&list->fasync, SIGIO, POLL_IN);
-	}
+	} else
+		list_for_each_entry(list, &evdev->list, node) {
+
+			do_gettimeofday(&list->buffer[list->head].time);
+			list->buffer[list->head].type = type;
+			list->buffer[list->head].code = code;
+			list->buffer[list->head].value = value;
+			list->head = (list->head + 1) & (EVDEV_BUFFER_SIZE - 1);
+
+			kill_fasync(&list->fasync, SIGIO, POLL_IN);
+		}
 
 	wake_up_interruptible(&evdev->wait);
 }
@@ -88,6 +100,11 @@ static int evdev_release(struct inode * inode, struct file * file)
 {
 	struct evdev_list *list = file->private_data;
 
+	if (list->evdev->grab == list) {
+		input_release_device(&list->evdev->handle);
+		list->evdev->grab = NULL;
+	}
+
 	evdev_fasync(-1, file, 0);
 	list_del(&list->node);
 
@@ -257,6 +274,22 @@ static int evdev_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
 				return -EFAULT;
 			return 0;
 
+		case EVIOCGRAB:
+			if (arg) {
+				if (evdev->grab)
+					return -EBUSY;
+				if (input_grab_device(&evdev->handle))
+					return -EBUSY;
+				evdev->grab = list;
+				return 0;
+			} else {
+				if (evdev->grab != list)
+					return -EINVAL;
+				input_release_device(&evdev->handle);
+				evdev->grab = NULL;
+				return 0;
+			}
+
 		default:
 
 			if (_IOC_TYPE(cmd) != 'E' || _IOC_DIR(cmd) != _IOC_READ)

drivers/input/input.c

@@ -33,6 +33,8 @@ EXPORT_SYMBOL(input_register_device);
 EXPORT_SYMBOL(input_unregister_device);
 EXPORT_SYMBOL(input_register_handler);
 EXPORT_SYMBOL(input_unregister_handler);
+EXPORT_SYMBOL(input_grab_device);
+EXPORT_SYMBOL(input_release_device);
 EXPORT_SYMBOL(input_open_device);
 EXPORT_SYMBOL(input_close_device);
 EXPORT_SYMBOL(input_accept_process);
@@ -175,9 +177,12 @@ void input_event(struct input_dev *dev, unsigned int type, unsigned int code, in
 	if (type != EV_SYN) 
 		dev->sync = 0;
 
-	list_for_each_entry(handle, &dev->h_list, d_node)
-		if (handle->open)
-			handle->handler->event(handle, type, code, value);
+	if (dev->grab)
+		dev->grab->handler->event(dev->grab, type, code, value);
+	else
+		list_for_each_entry(handle, &dev->h_list, d_node)
+			if (handle->open)
+				handle->handler->event(handle, type, code, value);
 }
 
 static void input_repeat_key(unsigned long data)
@@ -201,6 +206,21 @@ int input_accept_process(struct input_handle *handle, struct file *file)
 	return 0;
 }
 
+int input_grab_device(struct input_handle *handle)
+{
+	if (handle->dev->grab)
+		return -EBUSY;
+
+	handle->dev->grab = handle;
+	return 0;
+}
+
+void input_release_device(struct input_handle *handle)
+{
+	if (handle->dev->grab == handle)
+		handle->dev->grab = NULL;
+}
+
 int input_open_device(struct input_handle *handle)
 {
 	if (handle->dev->pm_dev)
@@ -221,6 +241,7 @@ int input_flush_device(struct input_handle* handle, struct file* file)
 
 void input_close_device(struct input_handle *handle)
 {
+	input_release_device(handle);
 	if (handle->dev->pm_dev)
 		pm_dev_idle(handle->dev->pm_dev);
 	if (handle->dev->close)

include/linux/input.h

@@ -77,6 +77,8 @@ struct input_absinfo {
 #define EVIOCRMFF		_IOW('E', 0x81, int)			/* Erase a force effect */
 #define EVIOCGEFFECTS		_IOR('E', 0x84, int)			/* Report number of effects playable at the same time */
 
+#define EVIOCGRAB		_IOW('E', 0x90, int)			/* Grab/Release device */
+
 /*
  * Event types
  */
@@ -798,6 +800,8 @@ struct input_dev {
 	int (*upload_effect)(struct input_dev *dev, struct ff_effect *effect);
 	int (*erase_effect)(struct input_dev *dev, int effect_id);
 
+	struct input_handle *grab;
+
 	struct list_head	h_list;
 	struct list_head	node;
 };
@@ -888,6 +892,9 @@ void input_unregister_device(struct input_dev *);
 void input_register_handler(struct input_handler *);
 void input_unregister_handler(struct input_handler *);
 
+int input_grab_device(struct input_handle *);
+void input_release_device(struct input_handle *);
+
 int input_open_device(struct input_handle *);
 void input_close_device(struct input_handle *);