using udev to get physical ethernet device info

udev_example.cxx

/* -----------------------------------------------------------------------------
 * This code is an example of how to use udev on linux to get physical
 * network interfaces and find out information about them
 *
 * compiling:
 *  c++ -std=c++11 udev_example.cxx -o udev_example -ludev
 *
 * ---------------------------------------------------------------------------*/
#include <iostream>
#include <vector>
#include <stdexcept>
#include <libudev.h>

#include <string.h>
#include <unistd.h>
#include <stdlib.h>
#include <libgen.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/sockios.h>
#include <linux/ethtool.h>
#include <linux/wireless.h>

using namespace std;
  
struct Ifx
{
  Ifx(string name, size_t mbps) : name{name}, mbps{mbps} {}
  const string name;
  size_t mbps{0};
};

int main()
{
  vector<Ifx> ixs;

  //initailize udev data structures
  udev *udev = udev_new();
  if(udev == nullptr) { throw runtime_error{"cant create udev"}; }
  udev_enumerate *enumerate = udev_enumerate_new(udev);

  //enumerate all devices in the 'net' subsystem
  udev_enumerate_add_match_subsystem(enumerate, "net");
  udev_enumerate_scan_devices(enumerate);
  udev_list_entry *devices = udev_enumerate_get_list_entry(enumerate);
  udev_list_entry *dev_list_entry;
  udev_list_entry_foreach(dev_list_entry, devices) {

    //get the device path for each found device
    const char *path = udev_list_entry_get_name(dev_list_entry);

    //skip virtual devices
    if(string(path).find("virtual") != string::npos) continue;
    //extract just the name of the device from the path
    path = basename(const_cast<char*>(path));

    //get the link speed capability -- by asking the kernel through an ethtool 
    //ioctl request
    ifreq ifr;
    strncpy(ifr.ifr_name, path, sizeof(ifr.ifr_name));

    ethtool_cmd edata;
    edata.cmd = ETHTOOL_GSET;
    ifr.ifr_data = reinterpret_cast<char*>(&edata);

    int sock = socket(PF_INET, SOCK_DGRAM, 0);
    if(sock < 0) { throw runtime_error{"cant create socket"}; }

    //not worried about wireless cards at the moment
    iwreq iwr;
    strncpy(iwr.ifr_name, path, sizeof(iwr.ifr_name));

    if( ioctl(sock, SIOCGIWNAME, &iwr) == 0 ) 
    { 
      continue; 
    }

    int rc = ioctl(sock, SIOCETHTOOL, &ifr);
    close(sock);
    if(rc < 0 ) 
    { 
      throw runtime_error{"failed to get ethtool data for " + string(path)}; 
    }

    //interpret the speed
    size_t speed{0};
    if(edata.supported & SUPPORTED_10000baseT_Full) { speed = 10000; }
    else if(edata.supported & SUPPORTED_1000baseT_Full) { speed = 1000; }
    else if(edata.supported & SUPPORTED_100baseT_Full) { speed = 100; }
    else if(edata.supported & SUPPORTED_10baseT_Full) { speed = 10; }

    ixs.push_back(Ifx{path, speed});
  }

  udev_enumerate_unref(enumerate);
  udev_unref(udev);

  for(const Ifx & i : ixs)
    cout << i.name << ": " << i.mbps << endl;

}