Get Serial Port signal From Device in ubuntu

[basilb07]

How to Get Data from external device. device connected via serial port..
i want read device passing value ..
am try to code here

ui->setupUi(this);
    serial.setPortName("/dev/ttyS0");
    serial.setBaudRate(QSerialPort::Baud9600);
    serial.setDataBits(QSerialPort::Data8);
    serial.setParity(QSerialPort::NoParity);
    serial.setStopBits(QSerialPort::OneStop);
    serial.setFlowControl(QSerialPort::NoFlowControl);
    serial.open(QIODevice::ReadWrite);

ui->setupUi(this);
    serial.setPortName("/dev/ttyS0");
    serial.setBaudRate(QSerialPort::Baud9600);
    serial.setDataBits(QSerialPort::Data8);
    serial.setParity(QSerialPort::NoParity);
    serial.setStopBits(QSerialPort::OneStop);
    serial.setFlowControl(QSerialPort::NoFlowControl);
    serial.open(QIODevice::ReadWrite);

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after how to ready port value