rfd_class_t
rfd_open(char *name, int revoke_ok, rfd_class_t class,
static int rfd_revoke_next(rfd_class_t);
rfd_find_prev_class(rfd_t *rfd, rfd_class_t class)
rfd_revoke_next(rfd_class_t class)
rfd_class_t rfd_class; /* class of descriptor */
int rfd_open(char *, int, rfd_class_t, void(*)(struct rfd *), void *, int,