XFS inode containing btree root node
I'm currently doing some parsing work on XFS, and I'm a bit stuck looking at an inode containing the root of a btree. The inode is for a directory containing several thousand random text files I created.
Looking through the XFS documentation, I can see that that after the inode code, at offset 178 should be a 'xfs_bmdr_block' structure, which shows how many levels and entries there are. However, looking at the data, I'm a bit confused
That's the data representing the entries, so one level, one entry.
But both the entires are zero? I did read something somewhere that they should start at logical offset zero, but of course, I've lost that page so I can't confirm that is correct.
The data highlighted in blue is the actual block address of the directory data, but I don't understand why it's there in the inode? Is it part of an array, or is it just there in slack, and I should just ignore it.
This is the output from xfs_db
u3.bmbt.level = 1
u3.bmbt.numrecs = 1
u3.bmbt.keys = [startoff]
u3.bmbt.ptrs = 4227489
So there's that offset, 4227489 (0x408aA1) and after checking, that's where the actual btree data is for the directory. What I can't figure out is how xfs_db calculated that from an array that contains zero.
Am I completely misunderstanding this?