Re: netif_rx

[Ed Co <edityacomm_knb@xxxxxxxxx>]

Hi;

This may require some hacking but in order to isolate
which layer is causing the error; you can use the
*_INC_STATS hook. basically these are macros that are
called when an error occurs in the transmit/receive
path(I guess to inform via SNMP). The inputpath uses
the INC_STATS_BH hook; so tcp uses the
TCP_INC_STATS_BH and IP uses the IP_INC_STATS_BH hook.
So put  a printk in this macro whenever this gets
called; you will know whether the packets is getrting
dropped at the IP or the TCP layer. Then using the
__FUNCTION__, __LINE__ and __FILE__; you can get the
exact place in the code that is dropping the packet.

Let me know if this works...

regards
Ed

--- aksingh@xxxxxxxxxxx wrote:
> 
> 
> 
> 
> Hi,
> 
>  I am trying to spoof a packet, I have written a
> kernel module, once it
> gets a modified TCP packet(source and dest
> interchanged, ack seq
> interchanged) it calls netif_rx (skb) to inject this
> into the routing path.
> but I am unable to make this packet reach the
> correct socket. Any clues on
> this, can I check some kernel stats to know where
> and why the packet is
> being dropped.
> The various reasons cld be :
> 
> 1. incorrect tcp or ip check sums, i calculate both
> myself
> 2. in the skb->dev field i set the value to the
> value of skb->dev field of
> any incoming valid packet :
>  when i get the first packet on netfilter pre
> routing hook -- i do a
> memcpy(&my_net_dev, skb->dev, sizeof(struct
> net_device));
>  then for the modified TCP packet i set
> skb->dev=&my_net_dev. So maybe it
> gets dropped cos of some problem here(or is there
> any obvious problem here
> ?)
> 
> so how do i isolate the problem ? any clues ??
> 
> thanks
> Amit
> 
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