- virtual directories, reading a directory wipes out the
 virtual directory. virtual property in the inode.

- inode contains the qid, inuse, pointers, and virtual
 property.  one pointer each for 3 levels.

? reserve version == -1 to mean a virtual file? makes
 some things easier.

- first inode is always the root.

- adding any virtual entry to a directory makes the
 whole directory virtual.

? how do we keep cfs from swapping?

? how do we resolve access to missing parts when running
 remotely?

? what are default properties of files (ones we haven't
 stat'd)?
