return err == syscall.EOPNOTSUPP || err == syscall.ENOPROTOOPT
}

// isUsingMPTCPProto reports whether the socket protocol is MPTCP.
//
// Compared to hasFallenBack method, here only the socket protocol being used is
// checked: it can be MPTCP but it doesn't mean MPTCP is used on the wire, maybe
// a fallback to TCP has been done.
func isUsingMPTCPProto(fd *netFD) bool {

		ch <- err
		return
	}

	if !mptcp {
		ch <- errors.New("incoming connection is not with MPTCP")
		return
	}

	// Also check the method for the older kernels if not tested before
	if hasSOLMPTCP && !isUsingMPTCPProto(tcp.fd) {
		ch <- errors.New("incoming connection is not an MPTCP proto")
		return
	}
}

func dialerMPTCP(t *testing.T, addr string, envVar bool) {
	d := &Dialer{}

	if envVar {