hammer_undo
RB_HEAD(hammer_und_rb_tree, hammer_undo);
RB_PROTOTYPE2(hammer_und_rb_tree, hammer_undo, rb_node,
RB_ENTRY(hammer_undo) rb_node;
TAILQ_ENTRY(hammer_undo) lru_entry;
struct hammer_undo undos[HAMMER_MAX_UNDOS];
TAILQ_HEAD(, hammer_undo) undo_lru_list;
struct hammer_undo;
RB_GENERATE2(hammer_und_rb_tree, hammer_undo, rb_node,