despen at verizon
Nov 14, 2009, 1:56 PM
Post #5 of 6
(1560 views)
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David Woodhouse <dwmw2 [at] infradead> writes:
> On Sat, 2009-11-14 at 09:27 -0500, despen [at] verizon wrote:
>>
>> I'm thinking of modifying the source to save a copy of the
>> routing table after it's set up, then periodically getting a new
>> copy and comparing the 2 tables. I'd rather be able to directly
>> detect changes but I don't see any API for that.
>
> Netlink.
Hmm, never heard of it. Just gave it a quick try,
(code below).
What does it do? I found some sample code then added groups
for route add, delete, get, then did some route, route add, route del
commands but got no messages.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <asm/types.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
struct sockaddr_nl sa;
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
void read_msgs( );
int fd;
int main (int argc, char *argv[])
{
int rc;
memset (&sa, 0, sizeof(sa));
sa.nl_family = AF_NETLINK;
sa.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTM_NEWROUTE | RTM_DELROUTE | RTM_GETROUTE;
fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
rc = bind(fd, (struct sockaddr*)&sa, sizeof(sa));
if (rc == -1) {
handle_error("bind");
}
read_msgs();
return 0;
}
void read_msgs(void)
{
int len;
char buf[4096];
struct iovec iov = { buf, sizeof(buf) };
struct msghdr msg = { (void *)&sa, sizeof(sa), &iov, 1, NULL, 0, 0 };
struct nlmsghdr *nh;
printf("enter recvmsg\n");
len = recvmsg (fd, &msg, 0);
printf("got recvmsg");
for (nh = (struct nlmsghdr *) buf;
NLMSG_OK (nh, len);
nh = NLMSG_NEXT (nh, len)) {
/* The end of multipart message. */
if (nh->nlmsg_type == NLMSG_DONE)
return;
if (nh->nlmsg_type == NLMSG_ERROR) {
printf("Error\n");
/* Do some error handling. */
/* Continue with parsing payload. */
}
}
}
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