It is about time to take a step back and describe what I have been
implementing. A tux3 filesystem is a heirarchical structure with a
simple form:

Superblock
Free map (btree)
Free btree index*
Bitmap block or extents*
Volume table (radix tree)
Volume*
Metablock
Log chain*
Version table (radix tree)
Version index block*
Version*
Atime table (btree)
Atime index block*
Atim...