Re: Linux IP stack on kernel 2.4.18

[Rabeeh Khoury <rabeeh@xxxxxxxxxxxxx>]

I fixed the problems. I'm replying for the record of the mailing list.

Rabeeh Khoury wrote:

> Hi All,
>
> I'm using kernel 2.4.18 and developing an ethernet network interface 
> driver.
> I have two problems that if you may consult me how to solve them -
>
> 1.. How can I adjust the throttling parameter of the IP stack not to 
> drop any packet ? Meantime the IP stack routes 55k packets/sec and all 
> the other it just drops (I can see them by the result of netif_rx). 

echo 50000 > /proc/sys/net/core/netdev_max_backlog

This puts the throttling parameter of the IP stack to 50000, instead of 
300 which is the defaul in kernel 2.4.18 (the default is set in 
net/core/dev.c with the variable 'int netdev_max_backlog = 300;')

> 2.. Routing jumbo packets through IP stack - I send 9K packets in size 
> and IP stack routes the packets but by sending 1K packets in size ! is 
> this possible ? I tripple checked the device driver on receive and 
> transmit and it's ok. Do you know what is the problem ? 

The HW I'v used that generates jumbo packets has put a wrong 
total_length field in the IP header, which made IP stack remove a large 
chunck of the packet. The relevant code that removes the chunck is in 
net/ipv4/ip_input.c -

               /* Our transport medium may have padded the buffer out. 
Now we know it
                * is IP we can trim to the true length of the frame.
                * Note this now means skb->len holds ntohs(iph->tot_len).
                */
               if (skb->len > len) {
                     __pskb_trim(skb, len);
                       if (skb->ip_summed == CHECKSUM_HW)
                               skb->ip_summed = CHECKSUM_NONE;
               }

> Thank you alot,
> Rabeeh