* NFS intro

xdr_wrapstring, encodes null terminated string
- type of xdr being encoded
- length of string (so receiver can malloc appropriate buf)
- bytes of string in network order
- maybe a null @ end
- simple parity/checksum/CRC @ end

Server calls registerrpc()
- prognum: program number (64 bits)
	defined in /etc/rpc
- versum: version of this protocol/program
- procnum: procedure no. within program
	1 (INIT), 2 (READ_OBJECT), 3 (WRITE_OBJ), 4 (FINISH), ...
- input xdr procedure + void* data
- output xdr procedure + void* data

Every rpc service has its own program number, out of a large space (larger
than 1024 reserved ports).
- every computer runs a special broker called rpcsvc or portmapper

- when client C wants to talk to server S for program P, it asks pormapper
  (on fixed port 111) on host S "what port number does program P runs on
  with version V"

- then client knows which port on S to talk to for service P (and version V).

NULL procedure: useful as liveness "ping" and to measure service RTT