u16 * befs_bt_keylen_index (befs_btree_node * node);
Returns a pointer to the start of the key length index array of the B+tree node *node
``The length of all the keys in the node is added to the size of the header and then rounded up to a multiple of four to get the beginning of the key length index'' (p.88, practical filesystem design).
Except that rounding up to 8 works, and rounding up to 4 doesn't.