kernel_ulong_t driver_info; 이 코드가 잘 이해가 안가요 ㅠㅠ

98 struct usb_device_id {
99 /* which fields to match against? */
100 __u16 match_flags;
101
102 /* Used for product specific matches; range is inclusive */
103 __u16 idVendor;
104 __u16 idProduct;
105 __u16 bcdDevice_lo;
106 __u16 bcdDevice_hi;
107
108 /* Used for device class matches */
109 __u8 bDeviceClass;
110 __u8 bDeviceSubClass;
111 __u8 bDeviceProtocol;
112
113 /* Used for interface class matches */
114 __u8 bInterfaceClass;
115 __u8 bInterfaceSubClass;
116 __u8 bInterfaceProtocol;
117
118 /* not matched against */
119 kernel_ulong_t driver_info;
120 };

driver_info가 구조체인데 어떻게 저런 문법이 성립될 수가 있죠??