user code test: fake arp entry on target
kernel code reading: pci_driver structure
kernel code test: proc file new api

Currently, proc fs use a new api to create it.

This example has a very simple read/write function for reference.
userspace code test: bit operations

Usually, we will face some operation on bits, like
1. whether a number is power of 2
2.whether a number is start with all 1 and end with all 0
3. how many 1s are in a number.

Here I create a store for futher reference.