Hi,
Can anyone tell me what wud be the best way to communicate between kernel and user space?
More precisely, I m trying to capture a packet in kernel and want to forward it to user space program where I wud encapsulate it into another protocol and send away.
Any suggestions or help is highly appreciated. I read about Netlink thing, can someone tell me if its the best way and how should I go about doing it?

Hi -

This simplest way is:
1. Create your own kernel module (it sounds like you're doing this anyway).
2. Implement your own "open(), "close()", "read()" and "write()", etc methods.
3. "Mknod" a special device in "/dev".
4. "Insmod" your kernel driver and executeyour user-space program that uses it

The user-space program could be a background daemon (if you wish); the kernel module could support asynchronous I/O (if you wish).

Two other approaches would be:
/proc # actually, a bit more complicated
... or ...
netlink sockets # http://www.linuxjournal.com/article/7356

Strong suggestions:
1. Get a copy of "Linux Device Drivers, 3rd Ed", Corbett, Rubini, Hartmann
http://www.bookpool.com/sm/0596005903

2. Get a copy of "Linux Kernel Development, 2nd Ed", Robert Love
http://www.bookpool.com/sm/0672327201
<= The two books absolutely complement each other

'Hope that helps .. PSM

PS:
Even though your question is about "networking", you'd probably have better luck posting to the LQ "Non-*nix, Programming" forum instead...

You could have your program liston on some usused port (either directly or via inetd) and use iptables to forward the relevant packets to that port. I wouldn't have thought it would be necessary to write a kernel module.