NFQNL_COPY_PACKET

`NFQNL_COPY_PACKET`是一个标志，用于指示内核将数据包复制到用户空间。它是在使用Netfilter队列机制时使用的标志之一。当使用此标志时，内核将数据包的副本发送到用户空间，以便用户空间应用程序可以对其进行处理。以下是一个使用`NFQNL_COPY_PACKET`标志的示例：

#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <linux/types.h>
#include <linux/netfilter.h>
#include <libnetfilter_queue/libnetfilter_queue.h>

/* Callback function */
static int callback(struct nfq_q_handle *qh, struct nfgenmsg *nfmsg,
                    struct nfq_data *nfa, void *data)
{
    struct nfqnl_msg_packet_hdr *ph;
    u_int32_t id;
    struct nfqnl_msg_packet_hw *hwph;
    u_int8_t *payload;
    int payload_len;

    ph = nfq_get_msg_packet_hdr(nfa);
    if (ph) {
        id = ntohl(ph->packet_id);
        printf("hw_protocol=0x%04x hook=%u id=%u ",
               ntohs(ph->hw_protocol), ph->hook, id);
    }

    hwph = nfq_get_packet_hw(nfa);
    if (hwph) {
        int i, hlen = ntohs(hwph->hw_addrlen);

        printf("hw_src_addr=");
        for (i = 0; i < hlen-1; i++)
            printf("%02x:", hwph->hw_addr[i]);
        printf("%02x ", hwph->hw_addr[hlen-1]);
    }

    payload_len = nfq_get_payload(nfa, &payload);
    if (payload_len >= 0)
        printf("payload_len=%d ", payload_len);

    fputc('\n', stdout);

    /* Copy packet to userspace */
    return nfq_set_verdict(qh, id, NF_ACCEPT, payload_len, payload);
}

int main(int argc, char **argv)
{
    struct nfq_handle *h;
    struct nfq_q_handle *qh;
    struct nfnl_handle *nh;
    int fd;
    int rv;
    char buf[4096] __attribute__ ((aligned));

    printf("opening library handle\n");
    h = nfq_open();
    if (!h) {
        fprintf(stderr, "error during nfq_open()\n");
        exit(1);
    }

    printf("unbinding existing nf_queue handler for AF_INET (if any)\n");
    if (nfq_unbind_pf(h, AF_INET) < 0) {
        fprintf(stderr, "error during nfq_unbind_pf()\n");
        exit(1);
    }

    printf("binding nfnetlink_queue as nf_queue handler for AF_INET\n");
    if (nfq_bind_pf(h, AF_INET) < 0) {
        fprintf(stderr, "error during nfq_bind_pf()\n");
        exit(1);
    }

    printf("binding this socket to queue '0'\n");
    qh = nfq_create_queue(h, 0, &callback, NULL);
    if (!qh) {
        fprintf(stderr, "error during nfq_create_queue()\n");
        exit(1);
    }

    printf("setting copy_packet mode\n");
    if (nfq_set_mode(qh, NFQNL_COPY_PACKET, 0xffff) < 0) {
        fprintf(stderr, "can't set packet_copy mode\n");
        exit(1);
    }

    fd = nfq_fd(h);

    while ((rv = recv(fd, buf, sizeof(buf), 0)) && rv >= 0) {
        printf("pkt received\n");
        nfq_handle_packet(h, buf, rv);
    }

    printf("unbinding from queue 0\n");
    nfq_destroy_queue(qh);

    printf("closing library handle\n");
    nfq_close(h);

    exit(0);
}