how to control the DE2 buttons

Hello everyone,I have a problem when I want to control the DE2 buttons in uclinux.I have already added the "nios pio button" when I configed the kernel ,and the button device has been added in uclinux .But I don't how to write an application to get the key number when I press one button on the DE2 board,because I can't understand the "button_read "function in "altera_pio_button.c".

Would anyone can give me an example or some advices ? Thank you in advance.