ref: https://doc.dpdk.org/guides/sample_app_ug/skeleton.html

ref: Breaking down the DPDK helloworld Application

ref experiment: DPDK - Running the Basic Forwarding Sample Application example

The functionality is pretty straightforward → it pairs the port in such a way that the data from port 1 is transmitted to port 2, and from port 2 is transmitted to port 1. If there are port 3 and 4, it will manage the exchange of data between them.

(note the distinction between a device and a port before going through this)

The application is run with the command

sudo ~/dpdk/build/examples/dpdk-skeleton -l 1 -n 4

Code Walkthrough

basicfwd.c

main()

#include<stdlib.h>
#include<rte_eal.h>
#include<rte_ethdev.h>

int
main(int argc, char* argv[])
{
	unsigned nb_ports;
	int ret = rte_eal_init(args, argv);
	if ( ret < 0 )
	{
		rte_exit(EXIT_FAILURE, "Error with EAL initialization\\n");
	}
	
	argc -= ret;
	argv += ret; 
	
	nb_ports = rte_eth_dev_count_avail();
	if (nb_ports < 2 || (nb_ports & 1))
	{
		rte_exit(EXIT_FAILURE, "Error: number of ports must be even\\n");
	}
}

The first part of the code uses rte_eal_init to initialize the EAL Layer. The init function returns the number of CLI args it has consumed.

argc -= ret;
argv += ret;

This code subtracts the number of args used by eal layer from argc and moves the argv pointer ahead by that value.

The function rte_eth_dev_count_avail() is defined in rte_ethdev.h and uses the RTE_ETH_FOREACH_DEV to iterate the ports which are usable for the application, and returns the count of those ports.

The if block after that simply checks if the number of ports are even and ≥2.

#include<stdlib.h>
#include<rte_mbuf.h>
#include<rte_eal.h>

#define NUM_MBUFS 8191
#define MBUF_CACHE_SIZE 250
#define BURST_SIZE 32

int 
main(int argc, char* argv[])
{
	struct rte_mempool *mbuf_pool;
	
	mbuf_pool = rte_pktmbuf_pool_create(
								"MBUF_POOL", 
								NUM_MBUFS * nb_ports,
								MBUF_CACHE_SIZE, 
								0, 
								RTE_MBUF_DEFAULT_BUF_SIZE, 
								rte_socket_id()
							);
	if (mbuf_pool == NULL)
		rte_exit(EXIT_FAILURE, "Cannot create mbuf pool\\n");
}