Linux下ipconfig分析及C语言实现

在linux下使用ifconfigl命令能很方便的查看网卡与网线是否连通，运行ifconfig eth0命令大致输出如下：

# ifconfig eth0
eth0      Link encap:Ethernet  HWaddr 00:25:35:68:CC:D6
          inet addr:192.168.1.168  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::215:c5ff:fe18:ccd6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:130722 errors:0 dropped:0 overruns:0 frame:0
          TX packets:112560 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:104371099 (99.5 MiB)  TX bytes:20518584 (19.5 MiB)
          Interrupt:16 

其中的RUNNING就表示网卡与网线正常链接，拔掉网线再运行此命令就会发现RUNNING不在了。

    我的目的是用C语言来实现程序，而linux系统提供了popen/pclose进程管道让C和shell很方便的交互，不过使用的时候要注意设置权限，以免造成安全隐患。废话不多说，看下面C代码结合shell命令检测网卡与网线连通状况：
netstat.c 

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

/**********************************************************************
* 函数名称： GetNetStat
* 功能描述： 检测网络链接是否断开
* 输入参数：
* 输出参数： 无
* 返 回 值： 正常链接1,断开返回-1
* 其它说明： 本程序需要超级用户权限才能成功调用ifconfig命令
* 修改日期        版本号     修改人          修改内容
* ---------------------------------------------------------------------
* 2010/04/02      V1.0      eden_mgqw
***********************************************************************/
int GetNetStat( )
{
    char    buffer[BUFSIZ];
    FILE    *read_fp;
    int        chars_read;
    int        ret;

    memset( buffer, 0, BUFSIZ );
    read_fp = popen("ifconfig eth0 | grep RUNNING", "r");
    if ( read_fp != NULL )
    {
        chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
        if (chars_read > 0)
        {
            ret = 1;
        }
        else
        {
            ret = -1;
        }
        pclose(read_fp);
    }
    else
    {
        ret = -1;
    }

    return ret;
}

int main()
{
    int i=0;
    i = GetNetStat();
    printf( "\nNetStat = %d\n", i );
    return 0;
}

下面是编译运行程序的输出结果（正常返回1，断开返回-1）：
# cc netstat.c 
# ./a.out 
NetStat = 1

C语言实现：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <errno.h>
#include <string.h>
#include <ctype.h>

#include <sys/socket.h>
#include <netinet/in.h>
#include <linux/if.h>
#include <linux/sockios.h>
#include <arpa/inet.h>

static void die(const char *s)
{
    fprintf(stderr,"error: %s (%s)\n", s, strerror(errno));
    exit(-1);
}

static void setflags(int s, struct ifreq *ifr, int set, int clr)
{
    if(ioctl(s, SIOCGIFFLAGS, ifr) < 0) die("SIOCGIFFLAGS");
    ifr->ifr_flags = (ifr->ifr_flags & (~clr)) | set;
    if(ioctl(s, SIOCSIFFLAGS, ifr) < 0) die("SIOCSIFFLAGS");
}

static inline void init_sockaddr_in(struct sockaddr_in *sin, const char *addr)
{
    sin->sin_family = AF_INET;
    sin->sin_port = 0;
    sin->sin_addr.s_addr = inet_addr(addr);
}

static void setmtu(int s, struct ifreq *ifr, const char *mtu)
{
    int m = atoi(mtu);
    ifr->ifr_mtu = m;
    if(ioctl(s, SIOCSIFMTU, ifr) < 0) die("SIOCSIFMTU");
}
static void setdstaddr(int s, struct ifreq *ifr, const char *addr)
{
    init_sockaddr_in((struct sockaddr_in *) &ifr->ifr_dstaddr, addr);
    if(ioctl(s, SIOCSIFDSTADDR, ifr) < 0) die("SIOCSIFDSTADDR");
}

static void setnetmask(int s, struct ifreq *ifr, const char *addr)
{
    init_sockaddr_in((struct sockaddr_in *) &ifr->ifr_netmask, addr);
    if(ioctl(s, SIOCSIFNETMASK, ifr) < 0) die("SIOCSIFNETMASK");
}

static void setaddr(int s, struct ifreq *ifr, const char *addr)
{
    init_sockaddr_in((struct sockaddr_in *) &ifr->ifr_addr, addr);
    if(ioctl(s, SIOCSIFADDR, ifr) < 0) die("SIOCSIFADDR");
}

int main(int argc, char *argv[])
{
    struct ifreq ifr;
    int s;
    unsigned int addr, mask, flags;
    char astring[20];
    char mstring[20];
    char *updown, *brdcst, *loopbk, *ppp, *running, *multi;

    argc--;
    argv++;

    if(argc == 0) return 0;

    memset(&ifr, 0, sizeof(struct ifreq));
    strncpy(ifr.ifr_name, argv[0], IFNAMSIZ);
    ifr.ifr_name[IFNAMSIZ-1] = 0;
    argc--, argv++;

    if((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        die("cannot open control socket\n");
    }

    if (argc == 0) {
        if (ioctl(s, SIOCGIFADDR, &ifr) < 0) {
            perror(ifr.ifr_name);
            return -1;
        } else
            addr = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr.s_addr;

        if (ioctl(s, SIOCGIFNETMASK, &ifr) < 0) {
            perror(ifr.ifr_name);
            return -1;
        } else
            mask = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr.s_addr;

        if (ioctl(s, SIOCGIFFLAGS, &ifr) < 0) {
            perror(ifr.ifr_name);
            return -1;
        } else
            flags = ifr.ifr_flags;

        sprintf(astring, "%d.%d.%d.%d",
                addr & 0xff,
                ((addr >> 8) & 0xff),
                ((addr >> 16) & 0xff),
                ((addr >> 24) & 0xff));
        sprintf(mstring, "%d.%d.%d.%d",
                mask & 0xff,
                ((mask >> 8) & 0xff),
                ((mask >> 16) & 0xff),
                ((mask >> 24) & 0xff));
        printf("%s: ip %s mask %s flags [", ifr.ifr_name,
               astring,
               mstring
               );

        updown =  (flags & IFF_UP)           ? "up" : "down";
        brdcst =  (flags & IFF_BROADCAST)    ? " broadcast" : "";
        loopbk =  (flags & IFF_LOOPBACK)     ? " loopback" : "";
        ppp =     (flags & IFF_POINTOPOINT)  ? " point-to-point" : "";
        running = (flags & IFF_RUNNING)      ? " running" : "";
        multi =   (flags & IFF_MULTICAST)    ? " multicast" : "";
        printf("%s%s%s%s%s%s]\n", updown, brdcst, loopbk, ppp, running, multi);
        return 0;
    }

    while(argc > 0) {
        if (!strcmp(argv[0], "up")) {
            setflags(s, &ifr, IFF_UP, 0);
        } else if (!strcmp(argv[0], "mtu")) {
            argc--, argv++;
            if (!argc) {
                errno = EINVAL;
                die("expecting a value for parameter \"mtu\"");
            }
            setmtu(s, &ifr, argv[0]);
        } else if (!strcmp(argv[0], "-pointopoint")) {
            setflags(s, &ifr, IFF_POINTOPOINT, 1);
        } else if (!strcmp(argv[0], "pointopoint")) {
            argc--, argv++;
            if (!argc) {
                errno = EINVAL;
                die("expecting an IP address for parameter \"pointtopoint\"");
            }
            setdstaddr(s, &ifr, argv[0]);
            setflags(s, &ifr, IFF_POINTOPOINT, 0);
        } else if (!strcmp(argv[0], "down")) {
            setflags(s, &ifr, 0, IFF_UP);
        } else if (!strcmp(argv[0], "netmask")) {
            argc--, argv++;
            if (!argc) {
                errno = EINVAL;
                die("expecting an IP address for parameter \"netmask\"");
            }
            setnetmask(s, &ifr, argv[0]);
        } else if (isdigit(argv[0][0])) {
            setaddr(s, &ifr, argv[0]);
            setflags(s, &ifr, IFF_UP, 0);
        }
        argc--, argv++;
    }
    return 0;
}