以下是一个简单的XDPPROG程序示例，它实现了将从eth0接收到的IPv4数据包转发给eth1，并根据内核中的conntrack状态进行地址转换：

#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/if_packet.h>
#include <linux/if_vlan.h>
#include <linux/filter.h>

SEC("xdp")
int xdp_prog(struct xdp_md *ctx) {
    void *data = (void *)(long)ctx->data;
    void *data_end = (void *)(long)ctx->data_end;

    // Parse Ethernet header
    struct ethhdr *eth = data;
    if (data + sizeof(*eth) > data_end) {
        return XDP_DROP;
    }

    // Check if it's an IPv4 packet
    if (eth->h_proto != htons(ETH_P_IP)) {
        return XDP_PASS;
    }

    // Parse IP header
    struct iphdr *ip = data + sizeof(*eth);
    if (data + sizeof(*eth) + sizeof(*ip) > data_end) {
        return XDP_DROP;
    }

    // Check if it's a TCP or UDP packet
    if (ip->protocol != IPPROTO_TCP && ip->protocol != IPPROTO_UDP) {
        return XDP_PASS;
    }

    // Get source and destination addresses and ports
    __be32 src_ip = ip->saddr;
    __be32 dst_ip = ip->daddr;
    __be16 src_port, dst_port;
    if (ip->protocol == IPPROTO_TCP) {
        struct tcphdr *tcp = data + sizeof(*eth) + sizeof(*ip);
        if (data + sizeof(*eth) + sizeof(*ip) + sizeof(*tcp) > data_end) {
            return XDP_DROP;
        }
        src_port = tcp->source;
        dst_port = tcp->dest;
    } else { // UDP
        struct udphdr *udp = data + sizeof(*eth) + sizeof(*ip);
        if (data + sizeof(*eth) + sizeof(*ip) + sizeof(*udp) > data_end) {
            return XDP_DROP;
        }
        src_port = udp->source;
        dst_port = udp->dest;
    }

    // Lookup conntrack state for the packet
    struct nf_conntrack_tuple_hash tuple_hash;
    struct nf_conntrack_tuple tuple;
    memset(&tuple, 0, sizeof(tuple));
    tuple.src.u3.ip = src_ip;
    tuple.dst.u3.ip = dst_ip;
    tuple.src.u.all = (__force __u16)src_port;
    tuple.dst.u.all = (__force __u16)dst_port;
    tuple.protonum = ip->protocol;
    nf_conntrack_init_tuple_hash(&tuple_hash, &tuple, IPPROTO_TCP);
    struct nf_conntrack_tuple_hash *hash;
    hash = nf_conntrack_find_get(ctx, &nf_ct_zone_dflt, &tuple_hash);

    // Check if the packet is a new connection
    if (!hash || !hash->tuple.dst.dir) {
        // Create new conntrack state and update addresses
        struct nf_conn *ct;
        ct = nf_conntrack_alloc(ctx, &nf_ct_zone_dflt, &tuple);
        if (!ct) {
            return XDP_DROP;
        }
        ct->status |= IPS_SRC_NAT;
        ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip = src_ip;
        ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u3.ip = dst_ip;
        ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.all = src_port;
        ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.u.all = dst_port;
        nf_conntrack_hash_insert(hash, ct);
        hash = &ct->tuplehash[IP_CT_DIR_REPLY];
    }

    // Apply NAT address translation
    struct nf_conntrack_tuple *reply_tuple;
    reply_tuple = &hash->tuple;
    __be32 new_src_ip = reply_tuple->src.u3.ip;
    __be16 new_src_port = reply_tuple->src.u.all;
    ip->saddr = new_src_ip;
    if (ip->protocol == IPPROTO_TCP) {
        struct tcphdr *tcp = data + sizeof(*eth) + sizeof(*ip);
        tcp->source = new_src_port;
    } else { // UDP
        struct udphdr *udp = data + sizeof(*eth) + sizeof(*ip);
        udp->source = new_src_port;
    }

    // Update Ethernet header and send packet to eth1
    eth->h_dest[0] = ...; // Destination MAC address of eth1
    eth->h_dest[1] = ...;
    eth->h_dest[2] = ...;
    eth->h_dest[3] = ...;
    eth->h_dest[4] = ...;
    eth->h_dest[5] = ...;
    return bpf_redirect_map(&tx_port_map, 1 /* index of eth1 */, XDP_PASS);
}

注意，这只是一个示例程序，并且可能需要根据实际情况进行调整和改进。在使用此代码之前，请确保您已经了解以下内容：

• XDP的基本原理和概念，包括如何编写XDPPROG程序、如何使用BPF映射等。
• netfilter中的conntrack机制，它可以记录网络连接状态并进行地址转换。
• 数据包的解析和构造，包括如何解析以太网帧、IP数据包和TCP/UDP头部；以及如何构造新的数据包并更新网络协议头部。