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worst-case atomic operations:
-----------------------------
unlinking a file:
	changes:
		unallocating all blocks associated.
		unallocating inode associated.
		dir data change
		dir inode change

	12k/meg lost

start_atomic
	date-stamp chagnes?
	changes list?
end_atomic
	segment header contains "atomic" bit.
	"last" changes thrown out if next segment unreadable.
	queue up changes based on last "event" version recorded


block descriptor:
parent | inode or block list? | event #
----------------------------------------
32bit      1 bit                15bit
						== 10 bytes 
	1012k/segment