Re: [lwip-users] pbuf chain and packet queue

[address@hidden]

Bernhard 'Gustl' Bauer wrote:
> OOSEQ is turned on.
>    
This fits to your description that you might have missed a packet (from 
the wireshark log). So unless you don't have any other problems, 
treating pbuf chains correctly will do.
> I have a few questions that will help me to understand chaining of pbufs
> better:
>
> Is tot_len always equal the size of all chained pbufs from this pbuf to
> the end?
>    
Yes, and for the last pbuf, len == tot_len.
> Is it correct that splitting one packet on several pbufs can only be
> done by the CS8900 driver?
>    
Yes, but the problem is the name 'packet' here: your tcp receive 
callback gets a pointer to one pbuf which may be a chain. This is not 
necessarily always a packet, but never a packet queue (i.e. for this 
pbuf chain, the last pbuf with len == tot_len will always have next == 
NULL).
> Is there a need to treat a packet queue different than a pbuf chain (of
> one packet)?
>    
Packet queues don't have to be handled by your application or your netif 
driver: they are only used internally in the stack, e.g. for ARP 
queueing or netif loopback queueing. However, such packet queues are 
always splitted (or for tcp streams: combined to one pbuf chain) before 
being passed out of the stack core, as that would be too complicated for 
users, I guess.

Simon