ext3_group_desc structure or ext4_group_desc structure ??

[ssurampu]

I am writing my own code understand ext4 layout.

I have created a partition on 64 bit rhel6 machine and reated ext4 file system.

Created around 20,000 file.

My code is able to read superblock and able show inodes per group is 8192k
all information is maching wiht dumpe2fs output.

But when I started reading group descriptor table (structure ext4_group_desc) , I am not able to get group desc table successfully. Only first entry i.e. group desc table entry 0 is showing valid values.
Hence I could able to read Inodes upto 8192 (inodes per group desc) only.

But If read group desc table in form of ext3_group_desc structure (which is of less size) I could able to use all table entries to read all inodes.

It seems I need to put some condition when to use ext4_group_desc and when to use only ext3_group_desc for ext4 file system.

I read for 64 bit those new *_hi filed are added but as per my able issue I can see it is not the case.

Could somebody help me exact structure I need to read for ext4 and what are the cases I need to consider.
When I should use new ext4_Group_desc and when I should fall back and read only size of ext3_group_desc.

Please help me.

[Lakshmipathi]

I am writing my own code understand ext4 layout.

If your goal is to understand ext4 layout - Not writing ext4 application using ext2lib.
I think ,ext3/ext4 dev mailing list is the appropriate place to ask these question.