kernel code reading: one chart on rx_ring data structure
kernel code reading: net_rx_action() who process the received packet

net_rx_action() is the working daemon to process the packet received. The
process is go through the poll_list of per-cpu softnet_data, call the
napi_struct->poll for each.

1. __napi_schedule() is used to put the napi_struct on the poll_list
   This function is used in the irq handler of a nic driver.
2. napi_complete() is used to remove the napi_struct off the poll_list
   This is used in the napi_struct->poll or in net_rx_action()
kernel code reading: pci core enable vf

This change just specify where and how PF calculate the VF BAR size.
kernel code test: remove netlink_listener target in makefile

This target is moved to the userspace.
pci core: some questions on pci_assign_unassigned_resources()
kernel code: periodic workqueue

Implement the periodic workqueue by call queue_delayed_work() in workqueue
function.

Also it
1. rename the source code file from workqueue.c to workqueue_test.c
kernel code test: simulate the pci resource assignment

This is part 1, setup the pci hierachy and pick up the resource value
randomly.