EVENT_MAX_DEV
minor = ida_alloc_max(&event_ida, EVENT_MAX_DEV-1, GFP_KERNEL);
ret = alloc_chrdev_region(&dev_num, 0, EVENT_MAX_DEV, EVENT_DEV_NAME);
unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);
unregister_chrdev_region(MKDEV(event_major, 0), EVENT_MAX_DEV);