this module deals with packets: sending, receiving, queueing
and some basic interpretation (e.g it excludes datagram
error packets at the moment).

the packet queueing mechanism was originally introduced when
samba dealt with responses by sending a packet, receiving
packets and queueing all packets that didn't match up with
the response expected. this is fine in a single-thread
environment, but samba now deals with response packets by
queueing the responses. to some extent, therefore, this
queue_packet mechanism is redundant.


/*************************************************************************
  send_mailslot_reply()
  *************************************************************************/

this function is responsible for sending a MAILSLOT packet.

it will _not_ send packets to the pseudo WINS subnet's address of 
255.255.255.255: this would be disastrous.

each packet sent out has a unique transaction identifier. this is done
so that responses can be matched later with the original purpose for
the packet being sent out in the first place.


/*************************************************************************
  listen_for_packets()
  *************************************************************************/

this function is responsible for reading NMB and DGRAM packets, and then
queueing them. it will normally time-out for NMBD_SELECT_LOOP seconds, but
if there is an election currently running or we are expecting a response
then this time is reduced to 1 second.

note: the time-out period needs refining to the millisecond level.


/*************************************************************************
  queue_packet()
  *************************************************************************/

this function is responsible for queueing any NMB and DGRAM packets passed
to it. these packets will be removed from the queue in run_packet_queue().


/*************************************************************************
  run_packet_queue()
  *************************************************************************/

this function is responsible for taking a packet off the queue, 
identifying whether it is an NMB or a DGRAM packet, processing
it accordingly and deleting it. this process continues until
there are no more packets on the queue.


/*************************************************************************
  process_nmb()
  *************************************************************************/

this function receives a packet identified as a netbios packet.
it further identifies whether it is a response or a query packet.
by identifying the type of packet (name registration, query etc)
process_nmb() will call the appropriate function to deal with the
type of packet received.


/*************************************************************************
  process_dgram()
  *************************************************************************/

this function is responsible for identifying whether the datagram
packet received is a browser packet or a domain logon packet. it
also does some filtering of certain types of packets (e.g it
filters out error packets).


/*************************************************************************
  reply_netbios_packet()
  *************************************************************************/

this function is responsible for sending a reply to another NetBIOS
packet from another host. it can be used to send a reply to a name
registration, name release, name query or name status request.

the reply can be either a positive or a negative one.


/*************************************************************************
  initiate_netbios_packet()
  *************************************************************************/

this function is responsible for construction a netbios packet and sending
it. if the packet has not had a unique transaction id allocated to it,
then initiate_netbios_packet() will give it one.


/*************************************************************************
  update_name_trn_id()
  *************************************************************************/

this function is responsible for allocating unique transaction identifiers
for each new packet sent on the network.