C语言+shell 实现linux网卡状态检测   和  C语言实现linux网卡连接检测 2文的方法各有缺陷，比如有些系统执行ifconfig需要root权限，要不就不支持ioctl(fd, SIOCGMIIPHY, &ifr)这样的操作。以下给出了C语言实现linux网卡连接检测 的改进版实现与C语言+shell 实现linux网卡状态检测 同样的功能。

#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>

#include <ifaddrs.h>
#include <arpa/inet.h> 

#include  <linux/ethtool.h>

int cshell_netlink_status(char *if_name)
{
	char    buffer[BUFSIZ];
	char    cmd[100];
	FILE    *read_fp;
	int        chars_read;
	int        ret =0;

	memset( buffer, 0, BUFSIZ );
	memset( cmd, 0, 100 );
	sprintf(cmd, "ifconfig -a | grep %s",if_name);
	read_fp = popen(cmd, "r");
	if ( read_fp != NULL )
	{
		chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
		pclose(read_fp);

		if (chars_read > 0)
		{
			ret = 1;
		}
		else
		{
			fprintf(stderr, "DEVICE_NONE\r\n");
			return 0;
		}
	}

	if(ret == 1)
	{
		memset( buffer, 0, BUFSIZ );
		memset( cmd, 0, 100 );
		sprintf(cmd, "ifconfig |grep %s",if_name);
		read_fp = popen(cmd, "r");
		if ( read_fp != NULL )
		{
			chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
			pclose(read_fp);

			if (chars_read > 0)
			{
				ret = 2;
			}
			else
			{
				fprintf(stderr, "DEVICE_DOWN\r\n");
			return 1;
			}
		}
	}

	if(ret == 2)
	{
		memset( buffer, 0, BUFSIZ );
		memset( cmd, 0, 100 );
		sprintf(cmd, "ifconfig %s | grep RUNNING |  awk '{print $3}'",if_name);
		read_fp = popen(cmd, "r");
		if ( read_fp != NULL )
		{
		    chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);
		    pclose(read_fp);
			
		    if (chars_read > 0)
		    {
				fprintf(stderr, "DEVICE_LINKED\r\n");
				return 3;
		    }
		    else
		    {
				fprintf(stderr, "DEVICE_UNPLUGGED\r\n");
				return 2;
		    }
		}
	}

	return -1;
}


int c_netlink_status(const char *if_name )
{
	int fd = -1; 
	struct ifreq ifr; 

	struct ifconf ifc;  
	struct ifreq ifrs_buf[100]; 
	int if_number =0;
	int i;


	if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
	{
		fprintf(stderr, "%s: socket error [%d] %s\r\n",if_name, errno, strerror(errno));
		close(fd);
		return -1; 
	}

	ifc.ifc_len = sizeof(ifrs_buf);  
	ifc.ifc_buf = (caddr_t)ifrs_buf;  
	if (ioctl(fd, SIOCGIFCONF, (char *)&ifc) <0)  
	{
		fprintf(stderr, "%s: ioctl SIOCGIFCONF error [%d] %s\r\n",if_name, errno, strerror(errno));
		close(fd);
		return -1; 
	}

	if_number = ifc.ifc_len / sizeof(struct ifreq);
	for(i=0; i< if_number; i++)
	{
		if(strcmp(if_name,ifrs_buf[i].ifr_name ) == 0)
		{
			break;
		}
	}

	if(i >= if_number)
	{
		close(fd);
		fprintf(stderr, "DEVICE_NONE\r\n");
		return 0;
	}
	
	bzero(&ifr, sizeof(ifr));
	strncpy(ifr.ifr_name, if_name, IFNAMSIZ-1); 
	ifr.ifr_name[IFNAMSIZ-1] = 0; 
	if (ioctl(fd, SIOCGIFFLAGS, (char *)&ifr) <0)  
	{
		fprintf(stderr, "%s: ioctl SIOCGIFFLAGS error [%d] %s\r\n",if_name, errno, strerror(errno));
		close(fd);
		return -1; 
	}
#if 1	
	if(!(ifr.ifr_flags & IFF_UP))
	{
		close(fd);
		fprintf(stderr, "DEVICE_DOWN\r\n");
		return 1;
	}
	
	if(!(ifr.ifr_flags & IFF_RUNNING))
	{
		close(fd);
		fprintf(stderr, "DEVICE_UNPLUGGED\r\n");
		return 2 ;
	}

	fprintf(stderr, "DEVICE_LINKED\r\n");
	return 3;

#else
{
	struct ethtool_value edata;
	if(!(ifr.ifr_flags & IFF_UP) || !(ifr.ifr_flags & IFF_RUNNING))
	{
		close(fd);
		fprintf(stderr, "%s: DOWN\r\n",if_name);
		return 1;
	}
	edata.cmd = ETHTOOL_GLINK;
	edata.data = 0;
	ifr.ifr_data = (char *) &edata;
	if(ioctl( fd, SIOCETHTOOL, &ifr ) < 0)
	{
		fprintf(stderr, "%s: ioctl SIOCETHTOOL error [%d] %s\r\n",if_name, errno, strerror(errno));
		close(fd);
		return -1; 
	}

	if(edata.data == 0)
	{
		fprintf(stderr, "DEVICE_UNPLUGGED\r\n");
		return 2; 
	}
	else
	{
		fprintf(stderr, "DEVICE_LINKED\r\n");
		return 3; 
	}
}
#endif
}

int main(int argc, char* argv[])
{
	int i=0;
	if(argc != 2)
	{
		fprintf(stderr, "usage: %s <ethname>\r\n", argv[0]);
		return -1;
	}

	i = cshell_netlink_status(argv[1]);

	printf( "cshell_netlink_status if_status = %d\n", i );

	i = c_netlink_status(argv[1]);
	printf( "c_netlink_status if_status = %d\n", i );

	return 0;
}