Get ethernet address from interface name in FreeBSD

get_eth_addr.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <net/if.h>
#include <net/if_dl.h>
#include <net/ethernet.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <ifaddrs.h>

#define FORMAT_ETH_ADDR "%02x:%02x:%02x:%02x:%02x:%02x"

int get_eth_addr(const char *ifname, struct ether_addr *ethaddr);

int main(void) {
    struct ether_addr ethaddr;

    if(get_eth_addr("em0", &ethaddr) < 0) {
        fprintf(stderr, "get_eth_addr() failed\n");
        exit(EXIT_FAILURE);
    }

    printf("MAC Address: " FORMAT_ETH_ADDR "\n",
            ethaddr.octet[0], ethaddr.octet[1], ethaddr.octet[2],
            ethaddr.octet[3], ethaddr.octet[4], ethaddr.octet[5]);

    return 0;
}

int get_eth_addr(const char *ifname, struct ether_addr *ethaddr)
{
    struct ifaddrs *ifap;
    struct ifaddrs *searcher;
    struct sockaddr_dl *dl_addr;
    int ret = 0;

    if((ret = getifaddrs(&ifap)) < 0) {
        return ret;
    }

    searcher = ifap;

    while(searcher->ifa_next != NULL) {
        if(strcmp(searcher->ifa_name, ifname) &&
                searcher->ifa_addr->sa_family == AF_LINK) {
            dl_addr = (struct sockaddr_dl *)searcher->ifa_addr;
            memcpy(ethaddr->octet, LLADDR(dl_addr), ETHER_ADDR_LEN);
            ret = 0;
            break;
        }
        searcher = searcher->ifa_next;
    }

    if(ret != 0) {
        ret = -1;
    }

    freeifaddrs(ifap);
    return ret;
}