zfs_btree_create
zfs_btree_create(&bt, zfs_btree_compare, sizeof (uint64_t));
zfs_btree_create(size_tree, compare, size);
zfs_btree_create(&rt->rt_root, compare, size);
zfs_btree_create(size_tree, rt->rt_btree_compare, size);
void zfs_btree_create(zfs_btree_t *, int (*) (const void *, const void *),