rtnl-link-event.c

/* This example is placed in the public domain. */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <libmnl/libmnl.h>
#include <linux/if.h>
#include <linux/if_link.h>
#include <linux/rtnetlink.h>

static int data_attr_cb(const struct nlattr *attr, void *data)
{
        const struct nlattr **tb = data;
        int type = mnl_attr_get_type(attr);

        /* skip unsupported attribute in user-space */
        if (mnl_attr_type_valid(attr, IFLA_MAX) < 0)
                return MNL_CB_OK;

        switch(type) {
        case IFLA_MTU:
                if (mnl_attr_validate(attr, MNL_TYPE_U32) < 0) {
                        perror("mnl_attr_validate");
                        return MNL_CB_ERROR;
                }
                break;
        case IFLA_IFNAME:
                if (mnl_attr_validate(attr, MNL_TYPE_STRING) < 0) {
                        perror("mnl_attr_validate");
                        return MNL_CB_ERROR;
                }
                break;
        }
        tb[type] = attr;
        return MNL_CB_OK;
}

static int data_cb(const struct nlmsghdr *nlh, void *data)
{
        struct nlattr *tb[IFLA_MAX+1] = {};
        struct ifinfomsg *ifm = mnl_nlmsg_get_payload(nlh);

        printf("index=%d type=%d flags=%d family=%d ", 
                ifm->ifi_index, ifm->ifi_type,
                ifm->ifi_flags, ifm->ifi_family);

        if (ifm->ifi_flags & IFF_RUNNING)
                printf("[RUNNING] ");
        else
                printf("[NOT RUNNING] ");

        mnl_attr_parse(nlh, sizeof(*ifm), data_attr_cb, tb);
        if (tb[IFLA_MTU]) {
                printf("mtu=%d ", mnl_attr_get_u32(tb[IFLA_MTU]));
        }
        if (tb[IFLA_IFNAME]) {
                printf("name=%s", mnl_attr_get_str(tb[IFLA_IFNAME]));
        }
        printf("\n");
        return MNL_CB_OK;
}

int main(void)
{
        struct mnl_socket *nl;
        char buf[MNL_SOCKET_BUFFER_SIZE];
        int ret;

        nl = mnl_socket_open(NETLINK_ROUTE);
        if (nl == NULL) {
                perror("mnl_socket_open");
                exit(EXIT_FAILURE);
        }

        if (mnl_socket_bind(nl, RTMGRP_LINK, MNL_SOCKET_AUTOPID) < 0) {
                perror("mnl_socket_bind");
                exit(EXIT_FAILURE);
        }

        ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
        while (ret > 0) {
                ret = mnl_cb_run(buf, ret, 0, 0, data_cb, NULL);
                if (ret <= 0)
                        break;
                ret = mnl_socket_recvfrom(nl, buf, sizeof(buf));
        }
        if (ret == -1) {
                perror("error");
                exit(EXIT_FAILURE);
        }

        mnl_socket_close(nl);

        return 0;
}