kernel code reading: hcall vector match

This one highlight the hcall vector which is used to match between guest and
hypervisor.
kernel code test: show up in /dev for a char device

Generally, I know for a device we need to use mknod to make it shown up in
/dev. While this maybe not convenient for users.

Here I found one piece of code to create this device file under /dev
automatically.
Merge branch 'local_copy' into kernel