Queries about Net-Filter Hooks !!!

[Peter Teoh]

On Mon, Nov 21, 2011 at 6:39 PM, Kesava Srinivas
<vunnavafuture at gmail.com> wrote:
>
> HI Friends,
> Trying to Play with Net-Filter Hooks and here are my Queries!
>
> 1] While adding a New UDP/IP Header over the received skbuffer from NetFilter Module;need to fill the UDP Check-sum. Please let me know ; if there is any Kernel Function which we can use to do this Job ??? OR Do I need to write our own Function to calculate the Check-sum ???
>

just u need, just write your own checksum.   the kernel is highly
optimized.   everytime there is a change in bytes anywere in IP
packet, the existing checksum will be used to calculate the new
checksum incrementally.   so for your case, if u start with no
checksum, just calculate one by setting the checksum to zero first,
calculate checksum, then fill the checksum with the calculated
checksum.

IP ad TCP each has its own checksum BTW.

> 2] Once after adding New Headers to the received skbuffer ; am trying to return NF_ACCEPT. My Understanding was that ; the newly expanded skbuffer with added Headers will be again taken my Net-Filter Hooks Module and will deliver back to the net device. rt? OR Was there some thing more that I should do ; to send the new skbuffer to the device ??
>
don't understand???
> Looking forward for the reply !!
>
> -Thanks in Advance,
> VKS
>
>
>
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--
Regards,
Peter Teoh