Kernel to user space communication in linux:
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  3 different ways to communicate between kernel and userspace in Linux:

1) proc file system
2)ioctl
3) netlink
ioctl is the old mechanism. Speciality of netlink is we can send the command as multicast, so that different applications can receive the command.

 
For more refer:

http://people.ee.ethz.ch/~arkeller/linux/kernel_user_space_howto.html