RE: [lwip-devel] Problem with UDP and ARP queuing

[Mountifield, Tony]

OK, I've just looked in more detail at pbuf_queue(). Just before the end 
(pbuf.c:754), it does a pbuf_ref() on the packet being queued, so I think 
etharp_queue() only needs to do a pbuf_ref() when putting the pointer directly 
into the ARP  table, and not when doing a pbuf_queue().

Cheers
Tony

> -----Original Message-----
> From: David Haas [mailto:address@hidden
> Sent: 18 August 2004 16:34
> To: lwip-devel
> Subject: Re: [lwip-devel] Problem with UDP and ARP queuing
> 
> 
> It turns out that
> 
> arp_table[i] = p;
> 
> and
> 
> pbuf_queue(arp_table[i].p, p);
> 
> really do the same thing: put p on the arp_table queue. The 
> reason they 
> are separate is that pbuf_queue() does not handle the case where the 
> queue is empty and therefore the first argument would be zero. If the 
> pbuf is being queued at all, then the arp table has a pointer to the 
> pbuf. Later when it takes the pbuf off the queue it will call 
> pbuf_free() with that pbuf pointer. So it needs to increment the 
> reference count when the pbuf is being queued.
> 
> David.
> 
> 
> Mountifield, Tony wrote:
> 
> >Sorry, wrong "if".
> >
> >You have (effectively):
> >
> >        if (arp_table[i].p == NULL) {
> >            arp_table[i].p = p;
> >        } else {
> >            pbuf_queue(arp_table[i].p, p);
> >        }
> >        pbuf_ref(p);
> >
> >whereas I have:
> >
> >        if (arp_table[i].p == NULL) {
> >            pbuf_ref(p);
> >            arp_table[i].p = p;
> >        } else {
> >            pbuf_queue(arp_table[i].p, p);
> >        }
> >
> >I'm not sure which of the two is correct. It depends whether 
> queueing requires a refcnt increment, and if so, whether 
> pbuf_queue() handles it.


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