DPDK中的Switch Representation主要是针对网络交换机的数据平面进行优化。它包括两个主要部分：流表规则匹配和动作执行。

下面是一个简单例子，展示了如何使用DPDK的Switch Representation来实现基本的流表规则匹配和动作执行：

#include <rte_ethdev.h>
#include <rte_flow.h>

// 定义流表项结构体
struct flow_item {
    uint64_t src_mac;
    uint64_t dst_mac;
    uint16_t ether_type;
    uint32_t ip_src;
    uint32_t ip_dst;
    uint8_t ip_proto;
    uint16_t tcp_src_port;
    uint16_t tcp_dst_port;
};

// 定义动作结构体
struct flow_action {
    uint8_t set_vlan;
    uint16_t vlan_id;
    uint16_t output_port;
};

// 配置流表规则
static struct rte_flow *
configure_flow_rule(struct flow_item *item, struct flow_action *action) {
    struct rte_flow_error err;
    struct rte_flow_attr attr = {};
    struct rte_flow_item pattern[7] = {};
    struct rte_flow_action actions[3] = {};
    struct rte_flow *flow = NULL;

    // 配置流表属性
    attr.ingress = 1;

    // 配置流表匹配项
    pattern[0].type = RTE_FLOW_ITEM_TYPE_ETH;
    pattern[0].spec = &item->src_mac;
    pattern[0].mask = &full_mask;

    pattern[1].type = RTE_FLOW_ITEM_TYPE_ETH;
    pattern[1].spec = &item->dst_mac;
    pattern[1].mask = &full_mask;

    pattern[2].type = RTE_FLOW_ITEM_TYPE_VLAN;
    pattern[2].spec = &item->ether_type;
    pattern[2].mask = &vlan_mask;

    pattern[3].type = RTE_FLOW_ITEM_TYPE_IPV4;
    pattern[3].spec = &item->ip_src;
    pattern[3].mask = &full_mask;

    pattern[4].type = RTE_FLOW_ITEM_TYPE_IPV4;
    pattern[4].spec = &item->ip_dst;
    pattern[4].mask = &full_mask;

    pattern[5].type = RTE_FLOW_ITEM_TYPE_TCP;
    pattern[5].spec = &item->ip_proto;
    pattern[5].mask = &tcp_mask;

    pattern[6].type = RTE_FLOW_ITEM_TYPE_TCP;
    pattern[6].spec = &item->tcp_src_port;
    pattern[6].mask = &port_mask;

    // 配置动作
    actions[0].type = RTE_FLOW_ACTION_TYPE_OF_SET_VLAN_VID;
    actions[0].conf = &action->vlan_id;

    actions[1].type = RTE_FLOW_ACTION_TYPE_OF_PUSH_VLAN;
    actions[1].conf = &vlan_ethertype;

    actions[2].type = RTE_FLOW_ACTION_TYPE_DROP;

    // 创建流表规则
    flow = rte_flow_create(port_id, &attr, pattern, actions, &err);
    if (flow == NULL) {
        printf("Failed to create flow rule: %s\n", err.message);
        return NULL;
    }

    return flow;
}

// 执行流表规则
static void
execute_flow_rule(struct rte_flow *flow, struct rte_mbuf *pkt) {
    int ret;

    // 匹配包并执行动作
    ret = rte_flow_validate(port_id, NULL, &pkt->packet_type, flow);
    if (ret == 0) {
        rte_flow_apply(port_id, NULL, &pkt->packet_type, flow);
    }
}

// 初始化端口
static void
initialize_port(uint16_t port_id) {
    int ret;
    struct rte_eth_conf port_conf = {};

    // 配置端口属性
    port_conf.rxmode.max_rx_pkt_len = RTE_ETHER_MAX_LEN;
    port_conf.txmode.mq_mode = ETH_MQ_TX_NONE;

    // 初始化端口
    ret = rte_eth_dev_configure(port_id, num_queues, num_queues, &port_conf);
    if (ret < 0) {
        printf("Failed to configure port %u: %s\n", port_id, strerror(-ret));
        exit(1);
    }

    // 启动端口
    ret = rte_eth_dev_start(port_id);
    if (ret < 0) {
        printf("Failed to start port %u: %s\n", port_id, strerror(-ret));
        exit(1);
    }
}

int
main(int argc, char **argv)
{
    uint16_t port_id = 0;
    struct rte_mbuf *pkt;
    struct flow_item item = {};
    struct flow_action action = {};
    struct rte_flow *flow = NULL;

    // 初始化DPDK环境
    rte_eal_init(argc, argv);

    // 初始化端口
    initialize_port(port_id);

    // 配置流表规则
    item.src_mac = 0xb8e856a2c7e4;
    item.dst_mac = 0x30b5c2a9d68d;
    item.ether_type = RTE_BE16(ETHER_TYPE_VLAN);
    item.ip_src = RTE_IPV4(192, 168, 0, 1);
    item.ip_dst = RTE_IPV4(192, 168, 0, 2);
    item.ip_proto = IPPROTO_TCP;
    item.tcp_src_port = RTE_BE16(80);
    item.tcp_dst_port = RTE_BE16(1234);

    action.set_vlan = 1;
    action.vlan_id = RTE_BE16(201);
    action.output_port = 1;

    flow = configure_flow_rule(&item, &action);

    // 接收数据包并执行流表规则
    while (1) {
        pkt = rte_pktmbuf_alloc(mbuf_pool);
        if (pkt == NULL) {
            printf("Failed to allocate packet buffer\n");
            continue;
        }

        rte_eth_rx_burst(port_id, 0, &pkt, 1);

        execute_flow_rule(flow, pkt);

        rte_pktmbuf_free(pkt);
    }

    return 0;
}

这个例子展示了如何使用DPDK的Flow API来配置流表规则和执行动作。在这个例子中，我们定义了一个flow_item结构体，指定了要匹配的数据包字段，以及一个flow_action结构体，指定了匹配成功后要执行的动作。然后我们调用configure_flow_rule函数来配置流表规则，并且在execute_flow_rule函数中检查是否有数据包与流表规则匹配，如果匹配，则执行指定的动作。

需要注意的是，这只是一个简单的例子，实际上在实现交换机数据平面时还需要考虑很多其他因素，如高性能、可伸缩性、安全等。