bset_bkey_idx
? bset_bkey_idx(t->data, t->data->keys - bkey_u64s(&t->end))
(void *) bset_bkey_idx(n2, keys) - (void *) n2->start);
bset_bkey_idx(n2, keys),
(void *) bset_bkey_idx(n2, keys));
keys += bkey_u64s(bset_bkey_idx(btree_bset_first(n1),
bset_bkey_idx(btree_bset_first(n1), keys));
keys += bkey_u64s(bset_bkey_idx(btree_bset_first(n1), keys));