Kernel Module programming -> User login with Time

view story

http://stackoverflow.com – I make my first steps in the Kernel Module programming. My first Test File was like in any other language -> A simple "Hello World" with printk(). And that works without problems. Now I want to write a Kernel Module, where I can see which User has logged in (with Time) in the normal Log File or external File.txt. My Problem is, how can I implement this in a Kernel Module? The first thought was maybe I can catch the first process*, if I logged in but my kernel-stuff knowledge is actually low. *(because if the first process started, then must be a User logged in) It would be nice if someone h (HowTos)