12

I am writing an application that reports attributes of network devices on the local machine. I need the mac address, mtu, link speed and a few others. I'm using udev for this. I've already figured out how to get the mac address and mtu, but not how to get the link speed. I can get it with ethtool from the terminal, but I need a way to get it programmatically.

Does anyone know how I can get the link speed attribute with udev or another library?

StackedCrooked
  • 32,392
  • 40
  • 137
  • 267

2 Answers2

31

You need to use the SIOCETHTOOL ioctl() call. There's a nice introduction to ioctl/SIOCETHTOOL call on LinuxJournal, and the code below (which is not intended to be an example of good C practices!) should show you how to use it to get the speed.

#include <stdio.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <netinet/in.h>
#include <linux/sockios.h>
#include <linux/if.h>
#include <linux/ethtool.h>
#include <string.h>
#include <stdlib.h>

int main (int argc, char **argv)
{
    int sock;
    struct ifreq ifr;
    struct ethtool_cmd edata;
    int rc;

    sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
    if (sock < 0) {
        perror("socket");
        exit(1);
    }

    strncpy(ifr.ifr_name, "eth0", sizeof(ifr.ifr_name));
    ifr.ifr_data = &edata;

    edata.cmd = ETHTOOL_GSET;

    rc = ioctl(sock, SIOCETHTOOL, &ifr);
    if (rc < 0) {
        perror("ioctl");
        exit(1);
    }
    switch (ethtool_cmd_speed(&edata)) {
        case SPEED_10: printf("10Mbps\n"); break;
        case SPEED_100: printf("100Mbps\n"); break;
        case SPEED_1000: printf("1Gbps\n"); break;
        case SPEED_2500: printf("2.5Gbps\n"); break;
        case SPEED_10000: printf("10Gbps\n"); break;
        default: printf("Speed returned is %d\n", edata.speed);
    }

    return (0);
}
Deltik
  • 1,099
  • 9
  • 31
psmears
  • 21,582
  • 4
  • 37
  • 47
  • Thanks! I'll test it tomorrow. (I actually hacked together a working solution by using code snippits from `ethtool`'s source code. It's very similar to this.) – StackedCrooked May 20 '10 at 18:16
  • This gives an "Operation not permitted" error when running as a non-privileged used on RHEL 5/6. Is there a way to get this information without needing root access? – Dave Johansen Mar 02 '13 at 05:09
  • You should use ethtool_cmd_speed(&edata) to get speed response from edata, as there is some high bits that you ignore here. – MappaM Feb 05 '14 at 12:17
  • @MappaM: Good point - I've updated the answer. (When I originally posted this answer, back in 2010, ethtool_cmd_speed() didn't even exist, at least in the distros I was using :) ) – psmears Feb 12 '14 at 15:06
4

You can get the link speed in bit per second using the sysfs interface:

cat /sys/class/net/eth0/speed
1000
yadutaf
  • 6,024
  • 1
  • 32
  • 45