AF-XDP（eXpress Data Path）是一种高性能网络数据包处理机制，它允许用户空间程序直接与网络硬件交互，实现零拷贝数据包处理。AF-XDP可以将网络数据包直接映射到用户空间的内存中，从而避免了内核和用户空间之间的数据拷贝。

下面是一个使用AF-XDP的代码示例，其中多个进程可以共享对xsks-map的访问：

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

#define NUM_PROCESSES 4

struct xdp_umem_reg {
    __u32 umem_id;
    __u32 chunk_size;
    __u32 headroom;
};

struct xdp_desc {
    __u64 addr;
    __u32 len;
    __u32 options;
};

struct xdp_ring {
    __u32 producer;
    __u32 consumer;
    __u32 flags;
    __u32 reserved;
    struct xdp_desc desc[];
};

int main() {
    int xsks_fd[NUM_PROCESSES];
    struct xdp_umem_reg umem_reg;
    struct xdp_ring *xsks_ring;
    unsigned int i;

    // 创建AF_XDP套接字并绑定到网络接口
    for (i = 0; i < NUM_PROCESSES; i++) {
        xsks_fd[i] = bpf_create_map(BPF_MAP_TYPE_XSKMAP, sizeof(int), sizeof(int), NUM_PROCESSES, 0);
        if (xsks_fd[i] < 0) {
            printf("Failed to create AF_XDP socket\n");
            return -1;
        }

        struct sockaddr_xdp sxdp;
        memset(&sxdp, 0, sizeof(sxdp));
        sxdp.sxdp_family = AF_XDP;
        sxdp.sxdp_ifindex = if_nametoindex("eth0");
        sxdp.sxdp_queue_id = i;
        sxdp.sxdp_flags = XDP_SHARED_UMEM;

        if (bind(xsks_fd[i], (struct sockaddr *)&sxdp, sizeof(sxdp)) < 0) {
            printf("Failed to bind AF_XDP socket\n");
            return -1;
        }
    }

    // 创建共享的UMEM
    int umem_fd = bpf_create_map(BPF_MAP_TYPE_XSKUMEM, sizeof(int), sizeof(struct xdp_umem_reg), 1, 0);
    if (umem_fd < 0) {
        printf("Failed to create XSKUMEM map\n");
        return -1;
    }

    // 设置UMEM参数
    umem_reg.umem_id = 0;
    umem_reg.chunk_size = XSK_RING_CONS__DEFAULT_NUM_DESCS;
    umem_reg.headroom = XSK_UMEM__DEFAULT_FRAME_SIZE;

    // 创建UMEM
    if (bpf_update_elem(umem_fd, &i, &umem_reg, 0) < 0) {
        printf("Failed to create UMEM\n");
        return -1;
    }

    // 在UMEM上创建XSKS_RING
    for (i = 0; i < NUM_PROCESSES; i++) {
        void *umem_area = mmap(NULL, XSK_UMEM__DEFAULT_FRAME_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
        if (umem_area == MAP_FAILED) {
            printf("Failed to mmap UMEM area\n");
            return -1;
        }

        struct xdp_ring *xsks_ring = mmap(NULL, XSK_RING_CONS__DEFAULT_NUM_DESCS * sizeof(struct xdp_desc), PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
        if (xsks_ring == MAP_FAILED) {
            printf("Failed to mmap XSKS_RING\n");
            return -1;
        }

        // 绑定XSKS_RING到UMEM
        xsks_ring->producer = 0;
        xsks_ring->consumer = 0;
        xsks_ring->flags = 0;

        if (bpf_update_elem(xsks_fd[i], &i, &xsks_ring, 0) < 0) {
            printf("Failed to