QT

you cannot mix blocking I/O with Qt's own event handling system. The
followind code skeletton shows how you can react on incoming data on a
RT FIFO using Qt's QSocketNotifier class:
 
At initialization:

1. int K2UDataFifo = open("/dev/rtfX", O_RDONLY | O_NONBLOCK);

2. QSocketNotifier *Data = new QSocketNotifier(K2UDataFifo,
   QSocketNotifier::Read);

3. QObject::connect(Data, SIGNAL(activated(int)),
   &WhateverQObjectShouldReceiveTheSignal, SLOT(YourReadHandler()));

At programm termination:

1. close(K2UDataFifo);

Your read-handler-slot which will be called every time new data is
available:

void WhateverQObjectShouldReceiveTheSignal::YourReadHandler(){
  read(K2UDataFifo, &YourDataStructure, sizeof(YourDataStructure));
  //process your data, ...
}

That is all. For writing data from user to kernel, just use write() as
you would do from any user space application.