Re: [lwip-users] ARP problem (CONFIRMED 0.7.0 BUG)

[Leon Woestenberg]

On Wed, 4 Feb 2004 12:09:46 +0800, "stephen" <address@hidden> said:
> Hi:
> 
>     I am porting lwIP to a very compact RTOS.
>     Is there document for porting guide or port instructions?
>     Really appreciate if you can provide any information.
>     I will make porting instructions if I can port lwIP to my platform
>     successfully.
>
Check out the contrib ports. Unfortunately, documentation in lwIP is
either
absent, outdated.

The best documentation is to be found in the source code, as
JavaDoc/Doxygen
stuff.

We would welcome any specific or non-specific porting guide.
 
>     One problem is about handling ARP request in etharp.c(lwIP version
>     0.7)
>         line 550 => hdr->shwaddr.addr[i] = ethaddr->addr[i];
>         line 586 => update_arp_entry(netif, &(hdr->sipaddr),
>         &(hdr->shwaddr), ARP_INSERT_FLAG);
> 
>     Looks like "hdr->shwaddr" was changed before ARP table being update.
>     Is that correct?
>
Wow. Yes. Bug Alert.

>     Thank you!
>
I think you found a bug introduced through re-ordering the ARP workings.
This bug _may_ have caused the performance loss someone else noted.

The fix is as follows: Move this piece of etharp.c code above the switch
statement (directly above it).

---
  /* add or update entries in the ARP cache */
  if (for_us) {
    /* insert IP address in ARP cache (assume requester wants to talk to
    us)
     * we might even send out a queued packet to this host */
    update_arp_entry(netif, &(hdr->sipaddr), &(hdr->shwaddr),
    ARP_INSERT_FLAG);
  /* request was not directed to us, but snoop anyway */
  } else {
    /* update or insert the source IP address in the cache */
    update_arp_entry(netif, &(hdr->sipaddr), &(hdr->shwaddr), 0);
    /* update or insert the destination IP address pair in the cache */
    update_arp_entry(netif, &(hdr->dipaddr), &(hdr->dhwaddr), 0);
  }
---

I do not have development tools available here. I'll fix this if no-one
else has, tonight or tomorrow.

Thanks,

Leon.

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