#define vlist_init(tree, cmp, update, type, node, key) \
__vlist_init(tree, cmp, update, offsetof(type, key) - offsetof(type, node))
#define vlist_init(tree, cmp, update, type, node, key) \
__vlist_init(tree, cmp, update, offsetof(type, key) - offsetof(type, node))