我编写了一个程序，如果网络接口发生了变化，需要得到通知，特别是新的一个出现或者已经存在。我的研究带来了netlink及其RTMGRP_LINK信号。这个manpage给出了一个我尚不清楚的例子。
它有这个代码：
memset(&sa, 0, sizeof(sa));
snl.nl_family = AF_NETLINK;
snl.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR;
fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
bind(fd, (struct sockaddr*)&sa, sizeof(sa));
我的理解是这是启用某些信号的初始化部分。我想必须有一个处理事件的处理程序子程序。
我的问题是：
谢谢你的帮助。
以下代码取自here，我添加了逻辑以获取相关接口的名称。
#include <asm/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <net/if.h>
#include <netinet/in.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#define MYPROTO NETLINK_ROUTE
#define MYMGRP RTMGRP_IPV4_ROUTE
int open_netlink()
{
int sock = socket(AF_NETLINK,SOCK_RAW,MYPROTO);
struct sockaddr_nl addr;
memset((void *)&addr, 0, sizeof(addr));
if (sock<0)
return sock;
addr.nl_family = AF_NETLINK;
addr.nl_pid = getpid();
addr.nl_groups = RTMGRP_LINK|RTMGRP_IPV4_IFADDR|RTMGRP_IPV6_IFADDR;
if (bind(sock,(struct sockaddr *)&addr,sizeof(addr))<0)
return -1;
return sock;
}
int read_event(int sockint, int (*msg_handler)(struct sockaddr_nl *,
struct nlmsghdr *))
{
int status;
int ret = 0;
char buf[4096];
struct iovec iov = { buf, sizeof buf };
struct sockaddr_nl snl;
struct msghdr msg = { (void*)&snl, sizeof snl, &iov, 1, NULL, 0, 0};
struct nlmsghdr *h;
status = recvmsg(sockint, &msg, 0);
if(status < 0)
{
/* Socket non-blocking so bail out once we have read everything */
if (errno == EWOULDBLOCK || errno == EAGAIN)
return ret;
/* Anything else is an error */
printf("read_netlink: Error recvmsg: %d\n", status);
perror("read_netlink: Error: ");
return status;
}
if(status == 0)
{
printf("read_netlink: EOF\n");
}
/* We need to handle more than one message per 'recvmsg' */
for(h = (struct nlmsghdr *) buf; NLMSG_OK (h, (unsigned int)status);
h = NLMSG_NEXT (h, status))
{
/* Finish reading */
if (h->nlmsg_type == NLMSG_DONE)
return ret;
/* Message is some kind of error */
if (h->nlmsg_type == NLMSG_ERROR)
{
printf("read_netlink: Message is an error - decode TBD\n");
return -1; // Error
}
/* Call message handler */
if(msg_handler)
{
ret = (*msg_handler)(&snl, h);
if(ret < 0)
{
printf("read_netlink: Message hander error %d\n", ret);
return ret;
}
}
else
{
printf("read_netlink: Error NULL message handler\n");
return -1;
}
}
return ret;
}
static int netlink_link_state(struct sockaddr_nl *nl, struct nlmsghdr *msg)
{
int len;
struct ifinfomsg *ifi;
nl = nl;
ifi = NLMSG_DATA(msg);
char ifname[1024];if_indextoname(ifi->ifi_index,ifname);
printf("netlink_link_state: Link %s %s\n",
/*(ifi->ifi_flags & IFF_RUNNING)?"Up":"Down");*/
ifname,(ifi->ifi_flags & IFF_UP)?"Up":"Down");
return 0;
}
static int msg_handler(struct sockaddr_nl *nl, struct nlmsghdr *msg)
{
struct ifinfomsg *ifi=NLMSG_DATA(msg);
struct ifaddrmsg *ifa=NLMSG_DATA(msg);
char ifname[1024];
switch (msg->nlmsg_type)
{
case RTM_NEWADDR:
if_indextoname(ifi->ifi_index,ifname);
printf("msg_handler: RTM_NEWADDR : %s\n",ifname);
break;
case RTM_DELADDR:
if_indextoname(ifi->ifi_index,ifname);
printf("msg_handler: RTM_DELADDR : %s\n",ifname);
break;
case RTM_NEWLINK:
if_indextoname(ifa->ifa_index,ifname);
printf("msg_handler: RTM_NEWLINK\n");
netlink_link_state(nl, msg);
break;
case RTM_DELLINK:
if_indextoname(ifa->ifa_index,ifname);
printf("msg_handler: RTM_DELLINK : %s\n",ifname);
break;
default:
printf("msg_handler: Unknown netlink nlmsg_type %d\n",
msg->nlmsg_type);
break;
}
return 0;
}
int main(int argc, char *argv[])
{
int nls = open_netlink();
printf("Started watching:\n");
if (nls<0) {
printf("Open Error!");
}
while (1)
read_event(nls, msg_handler);
return 0;
}
#include<stdio.h>
#include <asm/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <net/if.h>
#include <netinet/in.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
static void network_loop(void *data)
{
struct sockaddr_nl addr;
int nls, len, rtl;
char buffer[4096];
struct nlmsghdr *nlh;
struct ifaddrmsg *ifa;
struct rtattr *rth;
if ((nls = socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) == -1)
printf("MY_PROG: socket failure\n");
memset (&addr,0,sizeof(addr));
addr.nl_family = AF_NETLINK;
addr.nl_groups = RTMGRP_IPV4_IFADDR;
if (bind(nls, (struct sockaddr *)&addr, sizeof(addr)) == -1)
printf("MY_PROG:network_loop bind failure\n");
nlh = (struct nlmsghdr *)buffer;
while ((len = recv(nls,nlh,4096,0)) > 0)
{
for (; (NLMSG_OK (nlh, len)) && (nlh->nlmsg_type != NLMSG_DONE); nlh = NLMSG_NEXT(nlh, len))
{
if (nlh->nlmsg_type == RTM_NEWADDR)
printf("MY_PROG:network_loop RTM_NEWADDR\n");
else if (nlh->nlmsg_type == RTM_DELADDR)
printf("MY_PROG:network_loop RTM_DELADDR\n");
else
printf("MY_PROG:network_loop nlmsg_type=%d\n", nlh->nlmsg_type);
if ((nlh->nlmsg_type != RTM_NEWADDR) && (nlh->nlmsg_type != RTM_DELADDR)) continue; /* some other kind of announcement */
ifa = (struct ifaddrmsg *) NLMSG_DATA (nlh);
rth = IFA_RTA (ifa);
rtl = IFA_PAYLOAD (nlh);
for (; rtl && RTA_OK (rth, rtl); rth = RTA_NEXT (rth,rtl))
{
char name[IFNAMSIZ];
uint32_t ipaddr;
if (rth->rta_type != IFA_LOCAL) continue;
ipaddr = * ((uint32_t *)RTA_DATA(rth));
ipaddr = htonl(ipaddr);
printf("MY_PROG:network_loop %s is now %X\n",if_indextoname(ifa->ifa_index,name),ipaddr);
}
}
}
}
main()
{
network_loop("MYPROG");
printf("EXIT main()\n");
}
简单程序，了解Linux系统中的网络变更通知并进行测试。