KNI (Kernel Network Interface) is one of the approach, used in DPDK, to connect its user space libs with the Linux kernel network stack.

1. DPDK KNI interface
Quick overview

2. High Level Architecture
User space
Kernel space
NIC
App DPDK
Ring
buffers
KNI driver
RX/TX
queues
TCP/IP
stack

3. Kernel space
Data RX path design
TCP/IP
stack
User space
App DPDK lib
FIFO
Thread
Thread
N

4. Data RX path implementation
Kernel space
netif_rx(skb)
TCP/IP
stack
kni_fifo_put()
Kernel module
FIFO
DPDK libSocket
kni_net_rx
kni_fifo_get
dev_alloc_skb
rte_kni_tx_burst()

5. Kernel space
Data TX path
TCP/IP
stack
User space
App DPDK lib
FIFO

6. Data TX path implementation
Kernel space
kni_net_tx()
TCP/IP
stack
kni_fifo_get()
Kernel module
memcpy (FIFO, SKB)
kni_fifo_put
dev_kfree_skb
FIFO
DPDK libSocket
rte_kni_rx_burst()

7. Kernel space
Sample application in a loopback mode
User space
FIFO 2
NIC
port1 port2
Core2Core1
FIFO 1
Thread

8. Sample application in a standard mode
Kernel space
User space
FIFO 2
NIC
port1 port2
Core2Core1
FIFO 1
vEth1vEth0
Thread
ipstack

9. References
Building the Development Kit Binary
DPDK Programmer’s Guide - Kernel NIC Interface
Kernel NIC Interface Sample Application
Getting Started Guide for Linux
DPDK quick start
Huge pages

10. My blog
Learning Network Programming