USB: define usb_bus_type and register on startup

drivers/usb/core/usb.c

@@ -2757,12 +2757,16 @@ struct list_head *usb_bus_get_list(void)
 }
 #endif
 
+struct bus_type usb_bus_type = {
+	name:	"usb",
+};
 
 /*
  * Init
  */
 static int __init usb_init(void)
 {
+	bus_register(&usb_bus_type);
 	usb_major_init();
 	usbfs_init();
 	usb_hub_init();
@@ -2775,6 +2779,7 @@ static int __init usb_init(void)
  */
 static void __exit usb_exit(void)
 {
+	put_bus(&usb_bus_type);
 	usb_major_cleanup();
 	usbfs_cleanup();
 	usb_hub_cleanup();

include/linux/usb.h

@@ -713,6 +713,8 @@ struct usb_driver {
 	/* void (*resume)(struct usb_device *dev); */
 };
 
+extern struct bus_type usb_bus_type;
+
 /*
  * use these in module_init()/module_exit()
  * and don't forget MODULE_DEVICE_TABLE(usb, ...)