[Click] AGNOSTIC vs. PUSH/PULL

[Eddie Kohler]

Jesse,

We have very few elements that behave as you describe: N inputs and N outputs, 
and all packets from input N are emitted on output N.  For that reason I don't 
think it's worthwhile to change the default push() and pull() behavior. 
simple_action() is after all meant to be simple.

Your element sounds like it wants the following definition:

elementclass Foo {
   ...
   const char *flow_code() const { return "#/#"; }
   ...
   void push(int port, Packet *p) {
      if ((p = simple_action(p)))
          output(port).push(p);
   }
   Packet *pull(int port) {
      Packet *p = input(port).pull();
      if (p)
          p = simple_action(p);
      return p;
   }
};

Note the flow_code().  Without the flow_code(), Click will believe that 
packets arriving on any port could be emitted on any port, and you won't get 
the agnostic behavior you might expect.

Eddie


Jesse Brown wrote:
> All:
> 
> I am currently working on a router config that looks similar to the 
> following:
> 
>   elementclass Monitor {
>      input ->
>      ipc :: IPClassifier (tcp, udp, icmp, -);
>      f :: Foo;
> 
>      ipc[0] -> Print("tcp-in") -> [0]f[0] -> Print("tcp-out") -> output;
>      ipc[1] -> Print("udp-in") -> [1]f[1] -> Print("udp-out") -> output;
>      ipc[2] -> Print("icmp-in") -> [2]f[2] -> Print("icmp-out") -> output;
>      ipc[3] -> Print("other-in") -> [3]f[3] -> Print("other-out") -> 
> output;
>   }
> 
>   FromDevice(eth0, PROMISC true) ->
>      ... ->
>      Monitor ->
>      ... ->
>      Queue -> ToDevice(eth1);
> 
> 
> This is obviously simplified but conveys my point, I think.
> If I define Foo as
>   const char *class_name() const    { return "Foo"; }
>   const char *port_count() const    { return "-/-"; }
>   const char *processing() const    { return AGNOSTIC; }
> 
>   Packet *simple_action(Packet *);
> 
> Then I will always get
> 
>   icmp-in:   98 | 00151715 a8e50015 17163621 08004500 00540000 40004001
>   tcp-out:   98 | 00151715 a8e50015 17163621 08004500 00540000 40004001
> 
> Due to how Element::push behaves.
> 
> In order to have a single copy of this element that can be located 
> anywhere in a router I have to define Foo::simple_action, Foo::pull, and 
> Foo::push. Is there a more standard way to get the behavior I am after? 
> My desired result would look like:
> 
>   icmp-in:   98 | 00151715 a8e50015 17163621 08004500 00540000 40004001
>   icmp-out:   98 | 00151715 a8e50015 17163621 08004500 00540000 40004001
> 
> in the above example.
> 
> Also, is there a reason that both Element::push and Element::pull ignore 
> the port by default? Would the attached patch break existing behavior?
> 
> Thanks,
> 
> Jesse
> 
> 
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