[Click] strange Queue behaviour

[Eddie Kohler]

Hi Peter!

It turned out this was a bug in user-level ToDevice.  Here's the relevant patch:


diff -u -u -w -r1.27 todevice.hh
--- elements/userlevel/todevice.hh      8 Oct 2004 21:25:23 -0000       1.27
+++ elements/userlevel/todevice.hh      8 Oct 2004 21:54:13 -0000
@@ -90,7 +90,7 @@
    ~ToDevice();

    const char *class_name() const               { return "ToDevice"; }
-  const char *processing() const               { return AGNOSTIC; }
+  const char *processing() const               { return "a/h"; }
    const char *flags() const                    { return "S2"; }

    int configure_phase() const { return FromDevice::CONFIGURE_PHASE_TODEVICE; }


So what was going on, you ask??  In the configuration with a Queue, ToDevice was 
operating in "full pull mode" -- rather than the intended input=pull, 
output=push -- and Discard (NOT ToDevice) ended up pulling packets off the 
queue.  They went trhough ToDevice as if ToDevice was a Null element, causing 
the "Error on send" printouts; but there hadn't been an Error on send, there'd 
been no *attempt* to send!

So, our bug, fixed now in cvs.  Thanks for reporting it!

Eddie


Peter De Cleyn wrote:
> Hi all,
> 
> While debugging a larger configuration used in userspace, which
> occasionally reported errors when sending packets (packets were
> returned on output 1 of ToDevice whithout further indication of an
> error), I wrote myself the following simple testconfiguration.
> 
> out::Queue()->ToDevice(eth1)->Print("Error on send")->Discard;
> arpq::ARPQuerier(192.168.0.1, 00:0E:0C:37:BF:36);
> 
> FromDevice("eth1")->class::Classifier(12/0806 20/0001, //arp request
>                         12/0806 20/0002, //arp response
>                         12/0800, //ip
>                         -); //other
> 
> class[0]->ARPResponder(192.168.0.1 00:0E:0C:37:BF:36)
>         ->out;
> 
> class[1]->[1]arpq->out;
> 
> class[2]->CheckIPHeader(14)->IPPrint("incoming")->Discard();
> 
> class[3]->Print("Discard")->Discard();
> 
> ICMPPingSource(192.168.0.1, 192.168.0.2, INTERVAL 1)
>         ->arpq; 
> 
> I expected some basic ping behaviour, but the only output I got on screen was:
> 
> Error on send:   42 | ffffffff ffff000e 0c37bf36 08060001 08000604 0001000e
> Error on send:   42 | ffffffff ffff000e 0c37bf36 08060001 08000604 0001000e
> ...
> 
> Which are actually the ARP requests one would expect to be sent before
> the ICMP messages could be sent.
> 
> When I omitted the Queue from the configuration, everything worked fine.
> thus the first line of the configuration became:
> 
> out::ToDevice(eth1)->Print("Error on send")->Discard;
> 
> As the ToDevice did not provided extra output ( looking into the code
> of ToDevice, I expected some messages), I added my own debug output at
> the beginning of send_packet() and push() and noticed that this was
> printed when I didn't use the Queue, but they didn't appear when using
> it. I tried with Queue, SimpleQueue and MSQueue and click versions
> 1.4.1, 1.4pre1 and 1.3pre1. The configuration was also tested with
> different machines, using different types of NICs.
> 
> Could someone point me out what I am missing here?
> 
> thanks a lot for helping me out!
> 
> Peter
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