Kernel programming - Ext4 and extents contents

Hi there,
I have a problem with Unix kernel programming.
I have to write a program who should output the whole information the EXT4 extents contain. I have found many tutorial and information about how the EXT4 filesystem is working. Also There ar many information about the EXT4 structure but I could not find any information about how can I access the inode structure and get the whole contents of the extents. If anyone there who can help me with this it would be great if he can explain me the way I can do this.

UNIX filesystems: evolution, design ... - Steve D. Pate - Google Knjige