Casting sock to inet_timewait_sock

Hello, When casting sock to inet_timewait_sock ([1]) it is assumed that sock points to a structure of type inet_timewait_sock. Is there a way to check if a sock struct wraps around a inet_timewait_sock struct? thanks, Daniel. [1] http://lxr.linux.no/linux+v2.6.37/include/net/inet_timewait_sock.h#L189