控制網卡開啟和關閉的C代碼

#include <features.h>  #include <sys/types.h>  #include <sys/socket.h>  #include <sys/ioctl.h>  #include <netinet/in.h>  #include <net/if.h>  #include <net/if_arp.h>  #include <stdio.h>  #include <errno.h>  #include <fcntl.h>  #include <ctype.h>  #include <stdlib.h>  #include <string.h>  #include <unistd.h>  #include <netdb.h>  static int clr_flag(char *ifname, short flag)  {          struct ifreq ifr;          int fd,skfd;          /* Create a channel to the NET kernel. */          if ((skfd = socket(AF_INET,SOCK_DGRAM ,0)) < 0) {                  perror("socket");                  exit(1);          }          fd = skfd;          strncpy(ifr.ifr_name, ifname, IFNAMSIZ);          if (ioctl(fd, SIOCGIFFLAGS, &ifr) < 0) {                  fprintf(stderr, "%s: unknown interface: %s\n",                                   ifname, strerror(errno));                  return -1;          }          strncpy(ifr.ifr_name, ifname, IFNAMSIZ);          if(flag == 1)                ifr.ifr_flags &= ~IFF_UP;        else if(flag == 2)                ifr.ifr_flags |= IFF_UP;           if (ioctl(fd, SIOCSIFFLAGS, &ifr) < 0) {                  perror("SIOCSIFFLAGS");                  return -1;          }          return (0);  }int main(int argc,char **argv){        clr_flag("eth0",1);        sleep(4);        clr_flag("eth0",2);        return 0;}