1 /*
2 * Copyright 2011 Daniel Drown
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 * mtu.c - get interface mtu
17 */
18
19 #include <net/if.h>
20 #include <stdlib.h>
21 #include <string.h>
22 #include <sys/ioctl.h>
23 #include <sys/socket.h>
24 #include <sys/types.h>
25 #include <unistd.h>
26
27 #include "mtu.h"
28
29 /* function: getifmtu
30 * returns the interface mtu or -1 on failure
31 * ifname - interface name
32 */
getifmtu(const char * ifname)33 int getifmtu(const char *ifname) {
34 int fd;
35 struct ifreq if_mtu;
36
37 fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
38 if (fd < 0) {
39 return -1;
40 }
41 strncpy(if_mtu.ifr_name, ifname, IFNAMSIZ);
42 if_mtu.ifr_name[IFNAMSIZ - 1] = '\0';
43 if (ioctl(fd, SIOCGIFMTU, &if_mtu) < 0) {
44 close(fd);
45 return -1;
46 }
47 close(fd);
48 return if_mtu.ifr_mtu;
49 }
50