利用Magic Packet启动电脑

许多电脑支持从网络唤醒，这样的电脑一般从网卡驱动里选择启用Wake up功能，选择Magic Packet启动即可。

比如，我的Atheros网卡就是支持的：

选好这个之后，再记录下网卡的MAC地址，可以使用getmac命令，或者ipconfig。

然后在同局域网另一台电脑上使用Magic Packet Sender软件发包，即可启动电脑。

Magic Packet的包格式很简单，理论上可以在任意网络封包中打包Magic Packet，不过一般选择UDP或IPX。

Magic Packet的格式是，首先包含六个FF，然后是重复十六次待唤醒电脑的MAC。比如上图的封包，就应该是这样：

FF FF FF FF FF FF 20 12 04 24 13 43 20 12 04 24 13 43 ......

所以，它的编码实现是很简单的，下面附上我自己写的Magic Packet发包程序：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

void fill_magic_buf(void *magic_buf, void *mac)
{
        int i;
        char *ptr;

        ptr = magic_buf;
        memset(ptr, 0xFF, 6);
        ptr += 6;

        for(i = 0; i < 16; ++i) {
                memcpy(ptr, mac, 6);
                ptr += 6;
        }
}

void usage(void)
{
        printf("usage...\n");
}

int main(int argc, char **argv)
{
        int s;
        int packet_num = 10;
        char c;

        unsigned char mac[6] = {0x00, 0x1A, 0x92, 0xE5, 0x1B, 0xA7};
        char dstip[256] = "192.168.9.180";
        int port = 9;

        struct sockaddr_in address;
        char magic_buf[6 + 6 * 16] = {0};

        daemon(0,0);    /* run in background */

        while((c = getopt(argc, argv, "d:m:p:")) != -1) {
                switch(c) {
                case 'd':
                        strcpy(dstip, optarg);
                        break;
                case 'm':
                        sscanf(optarg, "%x:%x:%x:%x:%x:%x",
                                (unsigned int*)&mac[0], (unsigned int*)&mac[1],
                                (unsigned int*)&mac[2], (unsigned int*)&mac[3],
                                (unsigned int*)&mac[4], (unsigned int*)&mac[5]);
                        break;
                case 'p':
                        port = atoi(optarg);
                        break;
                default:
                        usage();
                        return -1;
                }
        }

        s = socket(AF_INET, SOCK_DGRAM, 0);

        if (s == -1) {
                perror("Opening socket");
                exit(EXIT_FAILURE);
        }

        memset(&address, 0, sizeof(struct sockaddr_in));
        address.sin_family = AF_INET;
        address.sin_addr.s_addr = inet_addr(dstip);
        address.sin_port = htons(port);

        fill_magic_buf(magic_buf, mac);

        /* ten packets. TODO: use ping to check whether the destination is on or else. */
        while (packet_num-- > 0) {
                if (sendto(s, magic_buf, sizeof(magic_buf), 0,
                     (struct sockaddr *)&address, sizeof(address)) < 0) {
                        printf("sendto\n");
                        exit(EXIT_FAILURE);
                }
                sleep(1);
        }

        exit(EXIT_SUCCESS);
}