Using a kernel module that sits between the kernel stack and the network driver, I need to put extra headers on all packets going out of Linux. Note this will result in "frames" that are not really Ethernet frames and the network driver HW is being used more as a DMA engine than an Ethernet device.

The headers are larger that any headroom left on the packets. I would like to avoid using skb_realloc_headroom() for performance reasons; is there any way to do this? I originally thought changing NET_SKB_PAD would help, but apparently that is only for Rx packets.

Maybe changing MAX_HEADER will help? It isn't clear though whether this would help for many cases or not....

Thanks,
Zack

Hi Zack,

I am in the exact same situation, have you found a good way to do this ?

I know tcp uses sk->sk_prot->max_header to do this, but not sure if this would be application to all transport protocols. I was not able to confirm this for udp or icmp.

Please let me know if you have concluded anything.

Thanks.

Yea, try setting netdev->hard_header_len in the driver to whatever length you need reserved.