Hi,

I am looking for a way to exchange messages/data between kernel module and userspace app. How can i do that ?

What i want to do is that the kernel module is outputting data constantly. I want that data to be displayed to the user. The user can run a process which connects to the kernel module and displays what kernel module is outputting. Secondly, i want the user to be able to send data/command to the kernel module to control its behavior.

Any help on how i can achieve this or any links that explain the same would be appreciated.

Thank You

Well, I'm not even close to being an expert, but implementing a syscall in the kernel module would be the key. iptables / netfilter for example uses a predefined structure to pass the whole data to the kernel. This leads to problems on some architectures but might still be worthwhile checking out.

There is no necessity for "a user to run a process which connects to the kernel module" as output can be provided through /proc easily (for instance 'netstat' reading /proc/net/snmp).


Depends on what needs to be written. If it's like flipping a boolean (like /proc/sys/net/ipv4/ip_forward) then a sysctl key could do. Else, building on janoszen reply, see for instance how 'iptables' handles providing instructions to the Netfilter framework ('man 7 netlink', http://people.redhat.com/nhorman/papers/netlink.pdf). BTW I'm no expert either ;-p

Just use /proc in both directions - the kernel module is responsible for creating any "files" needed, and can respond in need.

Functions like copy_to_user and copy_from_user are available for copying data to and from user space and kernel space.
Kindly search for usage documentations on the net.