File.v: implement read/write/alloc/free, but no trunc yet (or any proofs)
File.v: implement read/write/alloc/free, but no trunc yet (or any proofs)

trunc is a little tricky because it requires allocating/freeing blocks

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl