(start), (arg), struct io_conn *), \
typesafe_cb_preargs(void, void *, (finish), (arg), \
struct io_conn *), \
(arg))
struct io_conn *io_duplex_(struct io_conn *conn,
(start), (arg), struct io_conn *), \
typesafe_cb_preargs(void, void *, (finish), (arg), \
struct io_conn *), \
(arg))
struct io_conn *io_duplex_(struct io_conn *conn,