C语言实现linux网卡连接检测的方法

#include <stdlib.h>#include <stdio.h>#include <string.h>#include <unistd.h>  #include <sys/socket.h>#include <sys/ioctl.h>#include <linux/if.h>#include <linux/mii.h>#include <linux/sockios.h>#include <errno.h>  int get_if_miireg(const char *if_name, int phy_id, int reg_num ){ int fd = -1;  struct ifreq ifr;  struct mii_ioctl_data *mii;  int value;   if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) { perror("socket"); close(fd); return -1;  }  bzero(&ifr, sizeof(ifr)); strncpy(ifr.ifr_name, if_name, IFNAMSIZ-1);  ifr.ifr_name[IFNAMSIZ-1] = 0;   if (ioctl(fd, SIOCGMIIPHY, &ifr) < 0) {  perror("ioctl"); close(fd); return -1;  }  mii = (struct mii_ioctl_data *)&ifr.ifr_data; mii->reg_num = reg_num;//0x01 if (ioctl(fd, SIOCGMIIREG, &ifr) < 0) {  perror("ioctl"); close(fd); return -1; } close(fd); value = ((mii->val_out&0x04)>>2); return value;} int main(int argc, char* argv[]){  int i=0;  if(argc != 2)  {    fprintf(stderr, "usage: %s <ethname>", argv[0]);    return -1;  }   i = get_if_miireg(argv[1],0x10,0x01);  printf( "if_status = %d/n", i );  return 0;}