demonstrate getifaddrs()

ifaddrs.c

#include <linux/if_packet.h>
#include <net/if.h>
#include <netdb.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>

int
main(void)
{
	struct ifaddrs *addrs = NULL;
	struct ifaddrs *entry = NULL;

	if (getifaddrs(&addrs) < 0) {
		perror("getifaddrs");
		exit(1);
	}

	for (entry = addrs; entry != NULL; entry = entry->ifa_next) {
		printf("---\n");

		printf("name:    %s\n", entry->ifa_name);

		{
			printf("flags:  ");
			if (entry->ifa_flags & IFF_UP) {
				printf(" IFF_UP");
			}
			if (entry->ifa_flags & IFF_RUNNING) {
				printf(" IFF_RUNNING");
			}
			if (entry->ifa_flags & IFF_LOOPBACK) {
				printf(" IFF_LOOPBACK");
			}
			printf("\n");
		}

		{
			const char *family;
			if (entry->ifa_addr->sa_family == AF_INET6) {
				family = "AF_INET6";
			} else if (entry->ifa_addr->sa_family == AF_INET) {
				family = "AF_INET";
			} else if (entry->ifa_addr->sa_family == AF_PACKET) {
				family = "AF_PACKET";
			} else {
				family = "(unknown)";
			}
			printf("family:  %s\n", family);
		}

		if (entry->ifa_addr->sa_family == AF_INET || entry->ifa_addr->sa_family == AF_INET6) {
			char host[NI_MAXHOST];
			int result = getnameinfo(
				entry->ifa_addr,
				entry->ifa_addr->sa_family == AF_INET ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6),
				host,
				NI_MAXHOST,
				NULL,
				0,
				NI_NUMERICHOST);
			if (result != 0) {
				fprintf(stderr, "getnameinfo: %s\n", gai_strerror(result));
				exit(1);
			}
			printf("address: %s\n", host);
		} else if (entry->ifa_addr->sa_family == AF_PACKET) {
			struct sockaddr_ll *sll = (struct sockaddr_ll *) entry->ifa_addr;
			unsigned char *mac = sll->sll_addr;
			printf("mac:     %02x:%02x:%02x:%02x:%02x:%02x\n", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
		}
	}

	freeifaddrs(addrs);
	return 0;
}