Christopher Haster f3578e3250 Removed clamping to block size in ctz linked-list ...

Initially, I was concerned that the number of pointers in the ctz
linked-list could exceed the storage in a block. Long story short
this isn't really possible outside of extremely small block sizes.

Since clamping impacts the layout of files on disk, removing the
block size removed quite a bit of logic and corner cases. Replaced
with an assert on block size during initialization.

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Long story long, the minimum block size needed to store all ctz
pointers in a filesystem can be found with this formula:

B = (w/8)*log2(2^w / (B - 2*(w/8)))

where:
B = block size in bytes
w = pointer width in bits

It's not a very pretty formula, but does give us some useful info
if we apply some math:

min block size:
32 bit ctz linked-list = 104 bytes
64 bit ctz linked-list = 448 bytes

For littlefs, 128 bytes is a perfectly reasonable minimum block size.

2017-10-12 20:31:33 -05:00

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