Linux 以编程方式向上/向下接口 kernel

Question

What is the programmatic way of enabling or disabling an interface in kernel space? What should be done?

Answer 1

...by using IOCTL's...

ioctl(skfd, SIOCSIFFLAGS, &ifr);

... with the IFF_UP bit set or unset depending on whether you want bring the interface up or down accordingly, ie:

static int set_if_up(char *ifname, short flags)
{
    return set_if_flags(ifname, flags | IFF_UP);
}

static int set_if_down(char *ifname, short flags)
{
    return set_if_flags(ifname, flags & ~IFF_UP);
}

Code copy-pasted from Linux networking documentation .

Answer 2

Code to bring eth0 up:

int sockfd;
struct ifreq ifr;

sockfd = socket(AF_INET, SOCK_DGRAM, 0);

if (sockfd < 0)
    return;

memset(&ifr, 0, sizeof ifr);

strncpy(ifr.ifr_name, "eth0", IFNAMSIZ);

ifr.ifr_flags |= IFF_UP;
ioctl(sockfd, SIOCSIFFLAGS, &ifr);

Answer 3

int skfd = -1;      /* AF_INET socket for ioctl() calls.*/
int set_if_flags(char *ifname, short flags)
{
    struct ifreq ifr;
    int res = 0;

    ifr.ifr_flags = flags;
    strncpy(ifr.ifr_name, ifname, IFNAMSIZ);

    if ((skfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        printf("socket error %s\n", strerror(errno));
        res = 1;
        goto out;
    }

    res = ioctl(skfd, SIOCSIFFLAGS, &ifr);
    if (res < 0) {
        printf("Interface '%s': Error: SIOCSIFFLAGS failed: %s\n",
            ifname, strerror(errno));
    } else {
        printf("Interface '%s': flags set to %04X.\n", ifname, flags);
    }
out:
    return res;
}
int set_if_up(char *ifname, short flags)
{
    return set_if_flags(ifname, flags | IFF_UP);
}

usage:

set_if_up("eth0", 1);