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Linux Netlink Socket Example

Posted on 2005-12-17 17:37 幽灵狼 阅读(2329) 评论(0)  编辑 收藏 引用 所属分类: Development

This is a sample program that uses a netlink socket to listen to route change events and prints out some rudimentary information about them. It's very simple and boring, but hopefully useful.

This being a wiki, I also expect everyone to hack on this code and make it nicer, this is pretty hideous, but I want to get on with my real program now. So if you're reading this page your mission (if you choose to accept it) is to clean up the below code a little bit (doesn't need to be much).

See LinuxNetlinkSockets


#include <asm/types.h>

#include <sys/socket.h>
#include <unistd.h>
#include <err.h>
#include <stdio.h>
#include <netinet/in.h>

#include <linux/netlink.h>
#include <linux/rtnetlink.h>

#if 0
//#define MYPROTO NETLINK_ARPD
#define MYMGRP RTMGRP_NEIGH
// if you want the above you'll find that the kernel must be compiled with CONFIG_ARPD, and
// that you need MYPROTO=NETLINK_ROUTE, since the kernel arp code {re,ab}uses rtnl (NETLINK_ROUTE)

#else
#define MYPROTO NETLINK_ROUTE
#define MYMGRP RTMGRP_IPV4_ROUTE
#endif

struct msgnames_t {
int id;
char *msg;
} typenames[] = {
#define MSG(x) { x, #x }
MSG(RTM_NEWROUTE),
MSG(RTM_DELROUTE),
MSG(RTM_GETROUTE),
#undef MSG
{0,0}
};

char *lookup_name(struct msgnames_t *db,int id)
{
static char name[512];
struct msgnames_t *msgnamesiter;
for(msgnamesiter=db;msgnamesiter->msg;++msgnamesiter) {
if (msgnamesiter->id == id)
break;
}
if (msgnamesiter->msg) {
return msgnamesiter->msg;
}
snprintf(name,sizeof(name),"#%i",id);
return name;
}

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 = MYMGRP;
if (bind(sock,(struct sockaddr *)&addr,sizeof(addr))<0)
return -1;
return sock;
}

int read_event(int sock)
{
struct sockaddr_nl nladdr;
struct msghdr msg;
struct iovec iov[2];
struct nlmsghdr nlh;
char buffer[65536];
int ret;
iov[0].iov_base = (void *)&nlh;
iov[0].iov_len = sizeof(nlh);
iov[1].iov_base = (void *)buffer;
iov[1].iov_len = sizeof(buffer);
msg.msg_name = (void *)&(nladdr);
msg.msg_namelen = sizeof(nladdr);
msg.msg_iov = iov;
msg.msg_iovlen = sizeof(iov)/sizeof(iov[0]);
ret=recvmsg(sock, &msg, 0);
if (ret<0) {
return ret;
}
printf("Type: %i (%s)\n",(nlh.nlmsg_type),lookup_name(typenames,nlh.nlmsg_type));
printf("Flag:");
#define FLAG(x) if (nlh.nlmsg_type & x) printf(" %s",#x)
FLAG(NLM_F_REQUEST);
FLAG(NLM_F_MULTI);
FLAG(NLM_F_ACK);
FLAG(NLM_F_ECHO);
FLAG(NLM_F_REPLACE);
FLAG(NLM_F_EXCL);
FLAG(NLM_F_CREATE);
FLAG(NLM_F_APPEND);
#undef FLAG
printf("\n");
printf("Seq : %i\n",nlh.nlmsg_seq);
printf("Pid : %i\n",nlh.nlmsg_pid);
printf("\n");
return 0;
}

int main(int argc, char *argv[])
{ int nls = open_netlink();
if (nls<0) {
err(1,"netlink");
}
while (1)
read_event(nls);
return 0;
}
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