port_get_data Erlang module function not found

[Inswitch Solutions - Erlang Evaluation]

Module inet_db has the following function used by gen_tcp:send/2 :

lookup_socket(Socket) when port(Socket) ->
    case catch erlang:port_get_data(Socket) of
 Module when atom(Module) ->
     {ok, Module};
 _ ->
     {error, closed}
    end.


- could someone tell me what does bif port_get_data/1 do?
- where can I find a description of all erlang BIF?


Thanks,
Eduardo Figoli

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