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

[David Haas]

Tony,

You are right. Good catch! I did a fair amount of testing and did'nt see 
a problem, but I guess it would manifest itself as a slow memory leak 
and then only if there is more than one frame on the arp queue (which in 
my case is not that likely). I corrected my version.

David.


Mountifield, Tony wrote:

> 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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