A proof of concept for transferring sparse files
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In Baserock, we often need to transfer sparse files across the
network. At the moment we do that by ignoring that they're sparse:
just read the holes as long sequences of zero bytes. That works, but
is inefficient.

This directory contains a couple of scripts: xfer-hole.py and
recv-hole that transfer holes more efficiently. They use the
`SEEK_DATA` and `SEEK_HOLE` options to the `lseek` system call.
xfer-hole.py produces an encoded form of the input file, where holes
are encoded in an efficient way. recv-hole decodes that and reproduces
the original file. The nifty trick is that recv-hole is a pure shell
script, and so will hopefully work on most target systems, instead of
requiring a custom program there.

This is a proof of concept. It is not ready for production use.
I wrote this to prove it's possible.