ureadc
error = ureadc(c, uio);
if (ureadc(getc(&tp->t_canq), uio) < 0) {
error = ureadc((int)pti->pt_send, uio);
error = ureadc((int)pti->pt_ucntl, uio);
error = ureadc(0, uio);
int ureadc(int c, struct uio *);