btree_write
static void btree_complete_write(struct btree *b, struct btree_write *w)
struct btree_write *w = btree_prev_write(b);
struct btree_write *w = btree_current_write(b);
struct btree_write writes[2];
static inline struct btree_write *btree_current_write(struct btree *b)
static inline struct btree_write *btree_prev_write(struct btree *b)