This is an interview question. I had written device driver for a char device so I know that code structure looks like this struct file_operations something { .owner=my_device_open; .read=my_device_read; .close=my_device_close; .write=my_device_write; } When the device driver is active then in /dev/mydevice you can actually read and write into it. But what I was not clear is how an application will read or write to this device. I know insmod will insert the module to kernel,and register_chrdev(); will register the driver in kernel but how will application program communicate with this driver. My answer was In unix it simply opens the device node as a file and sends/receives data and commands from it. But he was expecting some thing more complex.