kdmsg_state_cmp
RB_GENERATE(kdmsg_state_tree, kdmsg_state, rbnode, kdmsg_state_cmp);
int kdmsg_state_cmp(kdmsg_state_t *state1, kdmsg_state_t *state2);
RB_PROTOTYPE(kdmsg_state_tree, kdmsg_state, rbnode, kdmsg_state_cmp);