hammer2_chain_cmp
int hammer2_chain_cmp(hammer2_chain_t *chain1, hammer2_chain_t *chain2);
RB_PROTOTYPE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);
RB_GENERATE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);
n = hammer2_chain_cmp(chain, focus);
int hammer2_chain_cmp(hammer2_chain_t *chain1, hammer2_chain_t *chain2);
RB_PROTOTYPE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);
RB_GENERATE(hammer2_chain_tree, hammer2_chain, rbnode, hammer2_chain_cmp);