Simple Bandwidth monitoring in Gnu Linux

bandwidth_monitoring.c

/* 
 * Copyright (c) 2015 Neeraj Sharma. All rights reserved.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <string.h>     /* strncpy() */
#include <stropts.h>    /* ioctl() */
#include <sys/socket.h> /* socket() and friends */
#include <net/if.h>     /* struct ifreq */
#include <sys/ioctl.h>  /* SIOCGIFFLAGS and friends */
#include <linux/if_ether.h> /* ETH_P_ALL */

#define MAX_PACKET_CAPTURE 1000
#define MAX_BUFFER_SIZE 2048     /* lets not read jumbo frames */

int set_in_promiscuous_mode(const char *ifname, int sockfd)
{
  struct ifreq ifrq = {0};
  int ret = 0;

  strncpy(ifrq.ifr_name, ifname, IFNAMSIZ);
  ret = ioctl(sockfd, SIOCGIFFLAGS, &ifrq);
  ifrq.ifr_flags |= IFF_PROMISC;
  ret = ioctl(sockfd, SIOCSIFFLAGS, &ifrq);

  return ret;
}

int bind_sock_to_dev(const char *ifname, int sockfd)
{
  struct ifreq ifrq = {0};
  void *opaque = &ifrq;
  int ret = 0;

  strncpy(ifrq.ifr_name, ifname, IFNAMSIZ);
  ret = setsockopt(
    sockfd, SOL_SOCKET, SO_BINDTODEVICE, opaque, sizeof(ifrq));
  return ret;
}

int main(int argc, char *argv[])
{
  int sockfd = -1;
  char *ifname = NULL;
  int ret = 0;
  ssize_t octets;
  int packet_count = 0;
  const int buffer_len = MAX_BUFFER_SIZE;
  char buffer[buffer_len];

  if (argc != 2) {
    fprintf(stderr, "need the interface name as an argument\n");
    return 1;
  }
  /* lets open a raw socket to read even the ethernet headers */
  sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

  ret = set_in_promiscuous_mode(argv[1], sockfd);
  if (ret < 0) {
    fprintf(stderr, "cannot set interface %s in promiscuous mode\n",
            argv[1]);
    return 2;
  }

  /* Note that the loop can be run in while(1) for
   * infinite monitoring to as deemed useful.
   */
  while (packet_count < MAX_PACKET_CAPTURE) {
    octets = recv(sockfd, buffer, buffer_len, 0);
    if (octets < 0) {
      break;
    }
    /* process the packet and derive bandwidth information along with
     * traffic flow or any other complex statistics based on deep
     * packet inspection.
     */
    ++packet_count;
  }

  close(sockfd);

  return 0;
}