AIO-3399-JD4 QT操作LED Qfile权限不够请问是什么问题呢

问题描述及复现步骤:

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
// file.setFileName("/home/firefly/123");
file.setFileName("/sys/class/leds/firefly:yellow:user/brightness");
// system("echo none > /sys/class/leds/firefly:yellow:user/trigger");
}

MainWindow::~MainWindow()
{
delete ui;
}

void MainWindow::on_pushButton_clicked(bool checked)
{
qDebug()<<checked<<endl;
if(!file.exists())
{
qDebug()<<"no led"<<endl;
return ;
}
if(!file.open(QIODevice::WriteOnly))
qDebug()<<file.errorString()<<endl;
QByteArray buf[] = {"0","1"};

if(checked)
{

ui->pushButton->setText("close");
     qDebug()<<"close"<<endl;
    file.write(buf[1]);

}
else
{
ui->pushButton->setText("open");
qDebug()<<"open"<<endl;
file.write(buf[0]);
}
file.close();

}

在终端上 打开文件提示permission denied

尝试 chmod 777没有用

请问是什么问题呢