DNS cleanup

[Hal Murray]

The basic idea is to simplify things.  In the new world, there is only one 
DNS thread.  To do a lookup, the main thread starts a worker thread with a 
pointer to a peer structure.  The worker thread returns the return code and 
answer in global storage and self destructs.  Maybe it raises a signal to 
wakeup the main thread.  When it notices that the answer is ready, the main 
thread processes it including freeing the answer.

Do we want a configure option to build/run without DNS lookups?  Even if we 
don't, we should probably structure the code to support that.


The pool code already scans the peer list and does DNS lookups.  We can piggy 
back on that.

So we need a dummy peer block for the server case.  The peer structure 
already has room for a name - the pool case needs it.  We'll have to add a 
few flags.

The pool case makes another peer slot for each address it adds.  For the 
server case, there is only one address.  I think we can reuse the same peer 
block.  It needs a flag to indicate that the IP Address is valid.


My plan is to delete ntp_intres, ntp_worker, and work_thread,
then add a new module to fill in the gaps.

Eric:
  close_all_except is in libntp/ntp_worker.c
  where should it live?  Or can we get rid of it?
It's only called from ntpdmain.



-- 
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