Re: filtering packtes before OS takes care about them

[Asim Shankar <asimshankar@gmail.com>]

> In my case, I'll need to intercept all outgoing IP packets and change
> them (including L2 frame) before they are passed to the network
> interface driver.
> The reverse operation is applied to incoming IP Packets in the destination host.
> I didnt investigate the packet_type example you provided but I hope I
> will be able to used for the purposes I explained.

If the type field of the struct packet_type you register ==
htons(ETH_P_ALL), then your packet handling function will be added to
the head of the ptype_all list.

As a result, it will see all incoming and outgoing packets - incoming
will be delivered to your function from netif_receive_skb() before the
IP/other packet handlers get to see it and outgoing packets will be
delivered from dev_queue_xmit() (which calls dev_queue_xmit_nit())
just before the packet is queued for sending by the NIC. This may work
for you.

I'm assuming all outgoing packets go through dev_queue_xmit(), though
that may not always be the case (someone more knowledgeable would have
to explain this).

Regards,

-- Asim