mtu

#include
#include <string.h>
#include <sys/socket.h>
#include <linux/if.h>
#include <sys/types.h>
#include <linux/types.h>
#include <linux/sockios.h>

#define EPARAM -100
#define ESOCK -1
#define EICTRL -2
#define MAXMTU 10000

int get_mtu(const char *devname)
{
        int fd, ret;
        struct ifreq ifr;

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        if (fd < 0) {
                perror("create socket failure/n");
                return ESOCK;
        }

        strcpy(ifr.ifr_ifrn.ifrn_name, devname);
        ret = ioctl(fd, SIOCGIFMTU, (__u16 *)&ifr);
        if (ret < 0) {
                perror("get mtu failure/n");
                return EICTRL;
        }

        close( fd );
        printf("current mtu : (%u)/n", ifr.ifr_ifru.ifru_mtu);
        return ifr.ifr_ifru.ifru_mtu;
}

int set_mtu(const char *devname, int new_mtu)
{
        int fd, ret;
        struct ifreq ifr;

        if (new_mtu <= 0 || new_mtu > MAXMTU) {
                perror("parameter mtu value exceed range/n");
                return (-1);
        }

        fd = socket(AF_INET, SOCK_DGRAM, 0);
        if (fd < 0) {
                perror("create socket failure/n");
                return ESOCK;
        }

        strcpy(ifr.ifr_ifrn.ifrn_name, devname);
        ret = ioctl(fd, SIOCGIFMTU, (__u16 *)&ifr);
        if (ret < 0) {
                perror("get mtu failure/n");
                return EICTRL;
        }

        ifr.ifr_ifru.ifru_mtu = new_mtu;
        ret = ioctl(fd, SIOCSIFMTU, (__u16 *)&ifr);
        if (ret < 0) {
                perror("set mtu failure/n");
                return EICTRL;
        }

        close(fd);
        return 0;
}

int main(int arg , char *argv[])
{
        get_mtu("eth0");

        set_mtu("eth0", 1500);

        get_mtu("eth0");

        return 0;
}