[Olsr-dev] net_outbuffer_push / buffering problem

[Henning Rogge]

On 08/24/2012 02:30 PM, Ferry Huberts wrote:
>
> Hi guys
>
>
> When going through our logs we sometimes see messages like:
>
>> Aug 24 08:07:25 AHR olsrd[22551]: PUD: Could not send to OLSR
>> interface wlan0: there was not enough room in the buffer (size=56, r=0)
>
> This is reported when the pud plugin tries to add a message (of 56 bytes
> in the example) to the output buffer but is unable to because there is
> not enough space in the buffer. (the code is at lib/pud/src/receiver.c:165)
>
> Any ideas how we can avoid this?
>
> Ideally I'd like the buffer to be larger, or to be able to force the
> buffer out when I'm hitting this condition (which could then be done
> automatically).

You cannot make the buffer larger, its limited by the MTU. The problem 
happens if there are already OLSR messages in the outgoing queue to be 
aggregated into a single packet.

The solution is to check if there is enough space... if not, just send 
an OLSR packet before adding your message:

if (pu_size > net_outbuffer_bytes_left(ifp)) {
     net_output(ifp);
}

Of course if your message is too large to fit into an UDP packet 
(including the mandatory 4 byte OLSR packet header), this will not help 
you either.

Henning Rogge

-- 
Diplom-Informatiker Henning Rogge , Fraunhofer-Institut für
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