docs: public static void record_IOclose( long start_ns, long start_io_ms, int r_w, long size, int flavor ) {
      long block_ns = System.nanoTime() - start_ns;
      long io_ms = System.currentTimeMillis() - start_io_ms;
      // First long word going out has sender-port and a 'bad' control packet
      long b0 = UDP.udp.i_o.ordinal(); // Special flag to indicate io-record and not a rpc-record
      b0 |= H2O.SELF._key.udp_port()<<8;
      b0 |= flavor<<24;           // I/O flavor; one of the Value.persist backends
      b0 |= io_ms<<32;            // msec from start-to-finish, including non-i/o overheads
      record2(H2O.SELF,block_ns,true,r_w,0,b0,size);
    }