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Netlink实现网卡上下线监控
http://www.cpplive.com/html/1542.html
为了创建一个 netlink socket,用户需要使用如下参数调用 socket():
fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
第一个参数必须是 AF_NETLINK 或 PF_NETLINK,在 Linux 中,它们俩实际为一个东西,它表示要使用netlink,第二个参数必须是SOCK_RAW或SOCK_DGRAM,第三个参数指定netlink协议类型,NETLINK_ROUTE意为“路由守护进程”,绑定该协议创建的fd可以接收到来自内核的路由通知事件(如网路接口eth0上线)。
函数 bind() 用于把一个打开的 netlink socket 与 netlink 源 socket 地址绑定在一起。netlink socket 的地址初始化及绑定如下:
addr.nl_family = AF_NETLINK;
addr.nl_groups = RTNLGRP_LINK; //指定接收路由多播组消息
bind(fd, (struct sockaddr*)&addr, sizeof(addr));
Netlink实现网卡上下线监控的整个过程,完整的C语言实现如下:
#include <sys/types.h>
#include <sys/socket.h>
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <linux/if.h>
#include <string.h>
#define BUFLEN 20480
int main(int argc, char *argv[])
{
int fd, retval;
char buf[BUFLEN] = {0};
int len = BUFLEN;
struct sockaddr_nl addr;
struct nlmsghdr *nh;
struct ifinfomsg *ifinfo;
struct rtattr *attr;
fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &len, sizeof(len));
memset(&addr, 0, sizeof(addr));
addr.nl_family = AF_NETLINK;
addr.nl_groups = RTNLGRP_LINK;
bind(fd, (struct sockaddr*)&addr, sizeof(addr));
retval = read(fd, buf, BUFLEN);
printf("retval = %d \n", retval);
while ((retval = read(fd, buf, BUFLEN)) > 0)
{
for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, retval); nh = NLMSG_NEXT(nh, retval))
{
if (nh->nlmsg_type == NLMSG_DONE)
break;
else if (nh->nlmsg_type == NLMSG_ERROR)
return;
else if (nh->nlmsg_type != RTM_NEWLINK)
continue;
ifinfo = NLMSG_DATA(nh);
printf("%u: %s", ifinfo->ifi_index,
(ifinfo->ifi_flags & IFF_LOWER_UP) ? "up" : "down" );
attr = (struct rtattr*)(((char*)nh) + NLMSG_SPACE(sizeof(*ifinfo)));
len = nh->nlmsg_len - NLMSG_SPACE(sizeof(*ifinfo));
for (; RTA_OK(attr, len); attr = RTA_NEXT(attr, len))
{
if (attr->rta_type == IFLA_IFNAME)
{
printf(" %s", (char*)RTA_DATA(attr));
break;
}
}
printf("\n");
}
}
return 0;
}
运行程序,测试网线拔除/插入,输出如下:
demo_netlink 100% |***************************************************************************************************************************************| 5556 0:00:00 ETA
# ./demo_netlink
retval = 172
12: down eth1
12: down eth1
12: up eth1
12: up eth1
12: up eth1
12: up eth1
12: down eth1
12: down eth1
12: down eth1