Add a function to determine an interface's link-layer address.

kernel.c

@@ -58,6 +58,45 @@ kernel_ll_addresses(char *ifname, int ifindex,
     return j;
 }
 
+/* Determine an interface's hardware address, in modified EUI-64 format */
+int
+if_eui64(char *ifname, int ifindex, unsigned char *eui)
+{
+    int s, rc;
+    struct ifreq req;
+    unsigned char *mac;
+
+    s = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
+    if(s < 0) return -1;
+    memset(&req, 0, sizeof(req));
+    strncpy(req.ifr_name, ifname, sizeof(req.ifr_name));
+    rc = ioctl(s, SIOCGIFHWADDR, &req);
+    if(rc < 0) {
+        int saved_errno = errno;
+        close(s);
+        errno = saved_errno;
+        return -1;
+    }
+    close(s);
+
+    mac = (unsigned char *)req.ifr_hwaddr.sa_data;
+    /* Check not group and global */
+    if((mac[0] & 1) != 0 || (mac[0] & 2) != 0) {
+        errno = ENOENT;
+        return -1;
+    }
+
+    eui[0] = mac[0] ^ 2;
+    eui[1] = mac[1];
+    eui[2] = mac[2];
+    eui[3] = 0xFF;
+    eui[4] = 0xFE;
+    eui[5] = mac[3];
+    eui[6] = mac[4];
+    eui[7] = mac[5];
+    return 1;
+}
+
 /* Like gettimeofday, but should return monotonic time.  If POSIX clocks
    are not available, falls back to gettimeofday. */
 int

kernel.h

@@ -61,4 +61,5 @@ int kernel_addresses(char *ifname, int ifindex,
                      struct kernel_route *routes, int maxroutes);
 int kernel_ll_addresses(char *ifname, int ifindex,
                         unsigned char (*addresses)[16], int maxaddr);
+int if_eui64(char *ifname, int ifindex, unsigned char *eui);
 int gettime(struct timeval *tv);