实现原始套接字的基本代码

该代码实现接收所有以太网上的数据报。

    #include <stdio.h>
    #include <string.h>
    #include <sys/types.h>
    #include <sys/socket.h>
    #include <netpacket/packet.h>
    #include <sys/ioctl.h>
    #include <net/if.h>
    #define LEN 2048
    int main(int argc, char **argv)
    {
        int sockfd;
        int len;
        int optval;
        int read_size;
        short type;
        char *p;
        char buf[LEN];
        struct ifreq ifr;
        struct sockaddr_ll sll;
        struct packet_mreq mr;

        memset(buf, 0, LEN);
        memset(&sll, 0, sizeof(sll));
        memset(&ifr, 0, sizeof(ifr));
        memset(&mr, 0, sizeof(mr));
        sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
        if( sockfd < 0 )
        {
            perror("Create socket failed\n");
            return -1;
        }

        strncpy(ifr.ifr_name, "eth0", sizeof(ifr.ifr_name)-1);
        if( ioctl(sockfd, SIOCGIFINDEX, &ifr) < 0 )
        {
            perror("Ioctl SIOCGIFINDEX failed\n");
            close(sockfd);
            return -1;
        }
        sll.sll_family = AF_PACKET;
        sll.sll_ifindex = ifr.ifr_ifindex;
        sll.sll_protocol = htons(ETH_P_ALL);
        if( (ifr.ifr_flags|IFF_UP|IFF_BROADCAST|IFF_RUNNING) != ifr.ifr_flags){
            ifr.ifr_flags |= IFF_UP|IFF_BROADCAST|IFF_RUNNING;
            if( ioctl(sockfd, SIOCSIFFLAGS, &ifr) < 0)
            {
                perror("Ioctl SIOCSIFFLAGS failed\n");
                close(sockfd);
                return -1;
            }
        }

        if( bind(sockfd, (struct sockaddr *)&sll, sizeof(sll)) < 0)
        {
            perror("Bind ETH_P_ALL failed\n");
            close(sockfd);
            return -1;
        }
        if( ioctl(sockfd, SIOCGIFHWADDR, &ifr) < 0 )
        {
            perror("Ioctl SIOCGIFHWADDR failed\n");
            close(sockfd);
            return -1;
        }
        if( ifr.ifr_hwaddr.sa_family == 1 )
        {
            printf("ARP linktype is set to Ethernet\n");
        }
        else
        {
            printf("Unsupported hardware link type %4d\n",ifr.ifr_hwaddr.sa_family);
            close(sockfd);
            return -1;
        }

        mr.mr_ifindex = sll.sll_ifindex;
        mr.mr_type = PACKET_MR_PROMISC;
        if( setsockopt(sockfd, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mr, sizeof(mr)) < 0){
            perror("setsockopt failed\n");
            close(sockfd);
            return -1;
        }
        len = 1;
        read_size = LEN;
        p = buf;
        len = read(sockfd, p, read_size);
        if( len < 0 )
        {
            perror("Read failed\n");
        }
        close(sockfd);
        return 0;
    }