Getting information of network interface in linux

interface.c

#include <linux/types.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/if.h>
#include <linux/kernel.h>
#include <linux/wireless.h>
#include <linux/sockios.h>
#include <linux/ethtool.h>
#include <string.h>
#include <stdio.h>

int main() {
  int s = socket(AF_INET, SOCK_DGRAM, 0);
  struct ifconf ifc;
  int len = 100 * sizeof(struct ifreq);
  char buf[len];
  int e;
  int interface_count;
  char *ptr;

  ifc.ifc_len = len;
  ifc.ifc_buf = buf;
  e = ioctl(s, SIOCGIFCONF, &ifc);
  interface_count = ifc.ifc_len;
  ptr = ifc.ifc_buf;

  // Iterate over interfaces.
  while (interface_count > 0) {
    struct ifreq* ifr = (struct ifreq *)ptr;
    struct ifreq ifr1 = *ifr;
    struct iwreq wrq;
    struct ethtool_cmd ecmd;
    int si = sizeof(struct ifreq);
    e = ioctl(s, SIOCGIFADDR, &ifr1);
    printf("Interface: %s\n", ifr1.ifr_name);

    // Get ethtool information.
    ecmd.cmd = ETHTOOL_GSET;
    ifr->ifr_data = (caddr_t)&ecmd;
    e = ioctl(s, SIOCETHTOOL, ifr);

    // Print ethtool information if available.
    if (e == -1) {
      printf("  [ethtool] cannot get ethtool\n");
    } else {
      printf("  [ethtool] speed: %d\n", (ecmd.speed_hi << 16) | ecmd.speed);
    }

    // Get wireless extension.
    strcpy(wrq.ifr_name, ifr1.ifr_name);
    e = ioctl(s, SIOCGIWRATE, &wrq);
    if (e == -1) {
      printf("  [iwext] cannot get wireless extension\n");
    } else {
      printf("  [iwext] speed: %d\n", wrq.u.bitrate.value);
    }
    interface_count -= si;
    ptr += si;
  }

  close(s);
}