DPDK Skeleton代码详读

#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define RX_RING_SIZE 128       //接收环大小
#define TX_RING_SIZE 512       //发送环大小

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

static const struct rte_eth_conf port_conf_default = {
	.rxmode = { .max_rx_pkt_len = ETHER_MAX_LEN }      //用于配置以太网端口的默认结构。
};                  

/* basicfwd.c: Basic DPDK skeleton forwarding example. */

/*
 * Initializes a given port using global settings and with the RX buffers
 * coming from the mbuf_pool passed as a parameter.
 */

/*
        指定网口的队列数，本列中指定的队列
        在tx、rx两个方向上，设置缓冲区
*/




static inline int
port_init(uint8_t port, struct rte_mempool *mbuf_pool)  //初始化网卡配置；
{
	struct rte_eth_conf port_conf = port_conf_default;    //网口配置=默认的网口配置
	const uint16_t rx_rings = 1, tx_rings = 1;             //网口tx、rx队列的个数
	uint16_t nb_rxd = RX_RING_SIZE;                       //为接收环分配的接收描述符数量
	uint16_t nb_txd = TX_RING_SIZE;                       //同上
	int retval;                    //临时变量，返回值
	uint16_t q;

	if (port >= rte_eth_dev_count())           //port号大于可使用的以太网设备总数,则参数有错，退出；
		return -1;

	/* Configure the Ethernet device. */
	retval = rte_eth_dev_configure(port, rx_rings, tx_rings, &port_conf); //设置网卡设备
	if (retval != 0)
		return retval;

	retval = rte_eth_dev_adjust_nb_rx_tx_desc(port, &nb_rxd, &nb_txd);//??????????????????????????????????????
	if (retval != 0)
		return retval;

	/* Allocate and set up 1 RX queue per Ethernet port. */
	for (q = 0; q < rx_rings; q++) {                         //遍历指定网口的所有rx队列
		retval = rte_eth_rx_queue_setup(port, q, nb_rxd,
				rte_eth_dev_socket_id(port), NULL, mbuf_pool); //申请并设置一个收包队列
		if (retval < 0)
			return retval;
	}

	/* Allocate and set up 1 TX queue per Ethernet port. */
	for (q = 0; q < tx_rings; q++) {
		retval = rte_eth_tx_queue_setup(port, q, nb_txd,          //同上
				rte_eth_dev_socket_id(port), NULL);
		if (retval < 0)
			return retval;
	}

	/* Start the Ethernet port. */
	retval = rte_eth_dev_start(port);                //启动网卡
	if (retval < 0)
		return retval;

	/* Display the port MAC address. */
	struct ether_addr addr;
	rte_eth_macaddr_get(port, &addr);          //获取网卡的MAC地址，并打印
	printf("Port %u MAC: %02" PRIx8 " %02" PRIx8 " %02" PRIx8
			   " %02" PRIx8 " %02" PRIx8 " %02" PRIx8 "\n",
			(unsigned)port,
			addr.addr_bytes[0], addr.addr_bytes[1],
			addr.addr_bytes[2], addr.addr_bytes[3],
			addr.addr_bytes[4], addr.addr_bytes[5]);

	/* Enable RX in promiscuous mode for the Ethernet device. */
	rte_eth_promiscuous_enable(port);  //开启设备的混杂模式，允许所有报文进入；

	return 0;
}

//业务函数入口点
//__attribute__((noreturn))用法
//标明函数无返回值
//用来修饰lcore_main函数，标明lcore_main无返回值
*/
/*
//1、检测CPU与网卡是否匹配
//2、建议使用本地CPU就近网卡？？？，不理解
//3、数据接收、发送的while(1)
*/
static __attribute__((noreturn)) void
lcore_main(void)
{
	const uint8_t nb_ports = rte_eth_dev_count(); //网口总数
	uint8_t port;                                 //临时变量，网口号

	/*
	 * Check that the port is on the same NUMA node as the polling thread
	 * for best performance.
	 */
	for (port = 0; port < nb_ports; port++)
		if (rte_eth_dev_socket_id(port) > 0 &&
				rte_eth_dev_socket_id(port) !=
						(int)rte_socket_id())           //检测网口和当当前lcore的物理socket的ID是否匹配，即这个网口是不是当前CPU的；
			printf("WARNING, port %u is on remote NUMA node to "
					"polling thread.\n\tPerformance will "
					"not be optimal.\n", port);

	printf("\nCore %u forwarding packets. [Ctrl+C to quit]\n",
			rte_lcore_id());

	/* Run until the application is quit or killed. */
	for (;;) {                   /*运行 直到 应用程序 推出 或 被kill*/
		 /*
		  * 从Eth接收数据包 ，并发送到 ETH上。
                 * 发送顺序为：0 的接收 到 1的 发送，
                 *              1 的接收 到 0的 发送
                 * 每两个端口为一对
          */
		for (port = 0; port < nb_ports; port++) {

			/* Get burst of RX packets, from first port of pair. */
			struct rte_mbuf *bufs[BURST_SIZE];//存储数据包的指针；
			const uint16_t nb_rx = rte_eth_rx_burst(port, 0,   //0是队列的ID；
					bufs, BURST_SIZE);       //BURST_SIZE要取回的包的最大数目。

			if (unlikely(nb_rx == 0))//把这个选择标记成绝少发生的分支：即if(unlikely(x))等价于if(x)，但是它告诉gcc，x取0的可能性比较大。
				continue;

			/* Send burst of TX packets, to second port of pair. */
			const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
					bufs, nb_rx);
			 //*****注意：以上流程为：从x收到的包，发送到x^1口
                        //其中，0^1 = 1, 1^1 = 0
                        //此运算可以达到测试要求的收、发包逻辑


           /* Free any unsent packets. */
           //释放不发送的数据包
           //1、收到nb_rx个包，转发了nb_tx个，剩余nb_rx-nb_tx个
           //2、把剩余的包释放掉

			if (unlikely(nb_tx < nb_rx)) {
				uint16_t buf;
				for (buf = nb_tx; buf < nb_rx; buf++)
					rte_pktmbuf_free(bufs[buf]); //把没有发送的数据包释放掉
			}
		}
	}
}

int main(int argc, char *argv[])
{
	struct rte_mempool *mbuf_pool;           //指向内存池结构的指针变量
	unsigned nb_ports;                       //网口个数
	uint8_t portid;                          //网口号，临时的标记变量

	int ret = rte_eal_init(argc, argv);
	if (ret < 0)
		rte_exit(EXIT_FAILURE, "Error with EAL initialization\n");

	argc -= ret;             //不知道有啥用???????????????????????????
	argv += ret;             //???????????????????????????????????????

	nb_ports = rte_eth_dev_count();
	if (nb_ports < 2 || (nb_ports & 1))
		rte_exit(EXIT_FAILURE, "Error: number of ports must be even\n");

	/* Creates a new mempool in memory to hold the mbufs. */
	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)     //如果有效网口数小于2或有效网口数为奇数0，则出错。奇数不行吗，最后一个网口不用不就行了??????????????
		rte_exit(EXIT_FAILURE, "Cannot create mbuf pool\n");

	/* Initialize all ports. */
	for (portid = 0; portid < nb_ports; portid++)   //端口初始化；
		if (port_init(portid, mbuf_pool) != 0)            //只有等于0，网口初始化才成功
			rte_exit(EXIT_FAILURE, "Cannot init port %"PRIu8 "\n",
					portid);

	if (rte_lcore_count() > 1)
		printf("\nWARNING: Too many lcores enabled. Only 1 used.\n");

	/* Call lcore_main on the master core only. */
	lcore_main();            //执行数据转发函数；

	return 0;
}