ioctl之获取arp表项

ioctl是跟内核交互的一种方式，网络设计中广泛使用了ioctl函数来和内核协议栈进行交互。其原型为：

int ioctl(int d,int request,...)

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <net/if_arp.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
int main(int argc, char *argv[])
{
int s;
struct arpreq arpreq;
struct sockaddr_in *addr = (struct sockaddr_in*)&arpreq.arp_pa;
unsigned char *hw;
int err = -1;
if(argc < 2){
printf("错误的使用方式,格式为:\nmyarp ip(myarp 127.0.0.1)\n");
return -1;
}
/*建立一个数据报套接字*/
s = socket(AF_INET, SOCK_DGRAM, 0);
if (s < 0)	{
printf("socket() 出错\n");
return -1;
}
/*填充arpreq的成员arp_pa*/
addr->sin_family = AF_INET;
addr->sin_addr.s_addr = inet_addr(argv[1]);
if(addr->sin_addr.s_addr == INADDR_NONE){
printf("IP 地址格式错误\n");
}
/*网络接口为eth1*/
strcpy(arpreq.arp_dev, "eth1");
err = ioctl(s, SIOCGARP, &arpreq);  //<span style="font-family: Arial, Helvetica, sans-serif;">SIOCGARP：获取arp表中的一项，如果没有就会出错</span>
if(err < 0){								/*失败*/
printf("IOCTL 错误\n");
return -1;
}else{/*成功*/
hw = (unsigned char*)&arpreq.arp_ha.sa_data;	/*硬件地址*/
printf("%s:",argv[1]);/*打印IP*/
printf("%02x:%02x:%02x:%02x:%02x:%02x\n",		/*打印硬件地址*/
hw[0],hw[1],hw[2],hw[3],hw[4],hw[5]);
};
close(s);
return 0;
}

运行结果：

[root@localhost 12.6.5]# ./ioctl_arp 10.10.10.2

10.10.10.2:00:50:56:fb:8f:da