- File meta-data is stored using memory pools.  These use, at the moment,
  wired kernel memory, which is not acceptable because it is easy to turn
  the system unstable by exhausting it.  Therefore, a pool allocator that
  uses anonymous memory has to be written.

- Optimize for speed and memory usage.  Nodes are still quite big; their
  size should be reduced if possible.  But most importantly, the algorithm
  used to resize anonymous memory objects in regular files is extremely
  inefficient.

- Verify that file holes work (they should, but must be checked).  Add a
  regression test for this feature.

- NFS support is broken.  The readdir operation does not work until wcc is
  disabled (which happens as soon as doing a `touch foo' over the NFS
  mount point).  Furthermore, the system crashes if a file is created on the
  original file system and is read through NFS; the system spits a panic
  about busy pages.

- Fix and complete code marked with `XXX' and `TODO' tags.