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XFS inode containing btree root node  

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mrthaggar
(@mrthaggar)
New Member

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

0x000100010000000000000000

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[1] = [startoff]
1[0]
u3.bmbt.ptrs[1] = 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?

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Posted : 15/04/2019 2:04 pm
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