A Sensible File System.

There must be no limit to the size of a file beyond the obvious
limits imposed by the size of the disc.

Free blocks must be properly managed so that when a file is deleted
the blocks it occupied are available for re-use.

Access to the data in a file must be efficient.

Do not use contiguous allocation.

Once a file has been created, it must be possible to add data to it
at any time, without limit.

Directories are just like any other file, but with a special data format.

Files have tags in their metadata so that the system will know at
least whether they are directories or regular data files.


Required operations, provided as a library of functions:
   Create a file
   Open an existing file
   Delete a file
   Create a directory
   Write N bytes to a file
   Read N bytes from a file
   Set file position (so, for example, the next write will be
                      appended to the end).