I hope this isn't a "I didn't dig quite deep enough" question...
... I'm experimenting with the BIF port_control/3. One of the very
few examples I can find is in inet.erl:ctl_getstat/2, which seems
pretty straightforward. So I'm trying something like this:
sync_cmd2(Port, Cmd, Bytes, Rep) ->
case catch port_control(Port, Cmd, Bytes) of
{'EXIT', _Stuff} -> io:format("XXX sync_cmd2 err clause 1\n"),
{error, einval};
[Rep|Data] -> {ok, Data};
_Error -> io:format("XXX sync_cmd2 err clause 3: ~w\n", [_Error]),
{error, einval}
end.
But it doesn't work. All I get are matches in clause 3, _Error = [],
which causes my experiment to reimplement inet:ll_name/1 to barf.
ll_name(Inet) ->
case sync_cmd2(Inet, ?INET_REQ_NAME, [], ?INET_REP_NAME) of
{ok, [P1, P0 | Addr]} ->
{ok, { bytes_to_ip(Addr), ?u16(P1, P0) }};
Error -> Error
end.
If sync_cmd2(Port, Cmd, Bytes, Rep) starts out as ->
Port ! {self(), {command, [Cmd|Bytes]}},
receive
{Port, {data, [Rep|T]}} -> {ok, T};
%% ... and so on....
... then it works. Also, if I use sync_cmd2(Port, Cmd, Bytes, Rep) ->
port_command(Port, [Cmd|Bytes]),
receive
{Port, {data, [Rep | T]}} -> {ok, T};
%% ... and so on....
... it also works. Am I overlooking something simple?
-Scott