This is a very incomplete reimplementation of the UNIX domain socket driver
that I wrote and added to the www.erlang.org "User Contributions"
collection.

There are two things that this driver can do that the original UNIX
domain socket driver cannot:

	1. It has a "getfd" call so that Erlang can discover the 
	   underlying UNIX file descriptor for the socket.

	2. Has the ability to use BSD-style file descriptor passing
	   to pass file descriptors between Erlang nodes running
	   on the same machine.

The file descriptor passing has been tested under Linux and FreeBSD.  It
should work under Solaris (minor tweaking perhaps necessary?) and any other
platform that supports BSD-style file descriptor passing over UNIX domain
sockets.

To test the file descriptor passing, to the following:

    On machine-A:

	% make			... GNU make is required, sorry!
	% cd test
	% make
	% make test		... optional, but shows some instructions
	% erl -pz ../ebin
	1> file:delete("/tmp/sock").
	2> unixdom_test:tcp_listen(5555, "/tmp/sock").

    On machine-A, but in another login session:

	% cd test
	% erl -pz ../ebin
	1> unixdom_test:receive_fd("/tmp/sock").
	[... some time later ...]
	TCP socket fd 8 received, looping now

    On machine-B:

	% telnet machine-A 5555
	Trying 10.1.1.1...
	Connected to machine-A
	Escape character is '^]'.
	Hello, there!  Please type some stuff:

If someone would like to fix this driver up, they are more than welcome to!
I have only done enough to implement the file descriptor passing.  My
intention was to create a minimal implementation this time, relying on
using gen_tcp:fdopen() or prim_inet:fdopen() to create a full-featured
socket port, rather than trying to re-invent the wheel (including all of
the gadgets, like packet encoding types, that the inets driver currently
supports!).

-Scott
23 February 2004