OVERLAY_F_IN_TX
overlay_io_start(odd, OVERLAY_F_IN_TX);
overlay_io_done(odd, OVERLAY_F_IN_TX);
ASSERT(flag == OVERLAY_F_IN_RX || flag == OVERLAY_F_IN_TX);
if (flag & OVERLAY_F_IN_TX)
ASSERT(flag == OVERLAY_F_IN_RX || flag == OVERLAY_F_IN_TX);
if (flag & OVERLAY_F_IN_TX) {
odd->odd_flags &= ~OVERLAY_F_IN_TX;