usbsacm_fifo_flush_locked
ret = usbsacm_fifo_flush_locked(acmp, port_num, dir);
static int usbsacm_fifo_flush_locked(usbsacm_state_t *, uint_t, int);
rval = usbsacm_fifo_flush_locked(acmp, port_num, DS_TX | DS_RX);