内核网卡参数设置：devinet_ioctl()

devinet_ioctl() 根据用户空间提供的ifreq参数和cmd操作对网卡进行设置或参数的获取
cmd：大体分为两种，即set和get
p.s. 有意思的是，用户空间的ifreq指针指向的参数需要拷贝到内存空间中，让后函数才能对参数进行解读和分析。
        copy_from_user(&ifr, arg, sizeof(struct ifreq)

struct ifreq {
    char ifr_name[IFNAMSIZ];
    union
    {
        struct sockaddr ifru_addr;
        struct sockaddr ifru_dstaddr;
        struct sockaddr ifru_broadaddr;
        struct sockaddr ifru_netmask;
        struct sockaddr ifru_hwaddr;
        short int ifru_flags;
        int ifru_ivalue;
        int ifru_mtu;
        struct ifmap ifru_map;
        char ifru_slave[IFNAMSIZ]; /* Just fits the size */
        char ifru_newname[IFNAMSIZ];
        __caddr_t ifru_data;
    } ifr_ifru;
};

int devinet_ioctl(unsigned int cmd, void *arg)
{
    struct ifreq ifr;
    struct sockaddr_in *sin = (struct sockaddr_in *)&ifr.ifr_addr;
    struct in_device *in_dev;
    struct in_ifaddr **ifap = NULL;
    struct in_ifaddr *ifa = NULL;
    struct net_device *dev;
    char *colon;
    int ret = 0;

    /*
     *    Fetch the caller's info block into kernel space
     */

    if (copy_from_user(&ifr, arg, sizeof(struct ifreq)))
        return -EFAULT;
    ifr.ifr_name[IFNAMSIZ-1] = 0;

    colon = strchr(ifr.ifr_name, ':');
    if (colon)
        *colon = 0;

#ifdef CONFIG_KMOD
    dev_load(ifr.ifr_name);
#endif

    switch(cmd) {        //根據cmd對參數進行檢查
    case SIOCGIFADDR:    /* Get interface address */
    case SIOCGIFBRDADDR:    /* Get the broadcast address */
    case SIOCGIFDSTADDR:    /* Get the destination address */
    case SIOCGIFNETMASK:    /* Get the netmask for the interface */
        /* Note that this ioctls will not sleep,
           so that we do not impose a lock.
           One day we will be forced to put shlock here (I mean SMP)
         */
        memset(sin, 0, sizeof(*sin));
        sin->sin_family = AF_INET;
        break;

    case SIOCSIFFLAGS:
        if (!capable(CAP_NET_ADMIN))
            return -EACCES;
        break;
    case SIOCSIFADDR:    /* Set interface address (and family) */
    case SIOCSIFBRDADDR:    /* Set the broadcast address */
    case SIOCSIFDSTADDR:    /* Set the destination address */
    case SIOCSIFNETMASK:     /* Set the netmask for the interface */
        if (!capable(CAP_NET_ADMIN))
            return -EACCES;
        if (sin->sin_family != AF_INET)
            return -EINVAL;
        break;
    default:
        return -EINVAL;
    }
    //鎖
    dev_probe_lock();
    rtnl_lock();
    //獲取設備名對應的設備的數據結構（描述一個設備）
    if ((dev = __dev_get_by_name(ifr.ifr_name)) == NULL) {
        ret = -ENODEV;
        goto done;
    }

    if (colon)
        *colon = ':';

    if ((in_dev=__in_dev_get(dev)) != NULL) {                //查找對應的設備名
        for (ifap=&in_dev->ifa_list; (ifa=*ifap) != NULL; ifap=&ifa->ifa_next)
            if (strcmp(ifr.ifr_name, ifa->ifa_label) == 0)
                break;
    }

    if (ifa == NULL && cmd != SIOCSIFADDR && cmd != SIOCSIFFLAGS) {
        ret = -EADDRNOTAVAIL;
        goto done;
    }

    switch(cmd) {                                            //在對應的設備上進行操作
        case SIOCGIFADDR:    /* Get interface address */        //獲取IP
            sin->sin_addr.s_addr = ifa->ifa_local;
            goto rarok;

        case SIOCGIFBRDADDR:    /* Get the broadcast address */
            sin->sin_addr.s_addr = ifa->ifa_broadcast;
            goto rarok;

        case SIOCGIFDSTADDR:    /* Get the destination address */
            sin->sin_addr.s_addr = ifa->ifa_address;
            goto rarok;

        case SIOCGIFNETMASK:    /* Get the netmask for the interface */
            sin->sin_addr.s_addr = ifa->ifa_mask;
            goto rarok;

        case SIOCSIFFLAGS:
            if (colon) {
                if (ifa == NULL) {
                    ret = -EADDRNOTAVAIL;
                    break;
                }
                if (!(ifr.ifr_flags&IFF_UP))
                    inet_del_ifa(in_dev, ifap, 1);
                break;
            }
            ret = dev_change_flags(dev, ifr.ifr_flags);
            break;

        case SIOCSIFADDR:    /* Set interface address (and family) */
            if (inet_abc_len(sin->sin_addr.s_addr) < 0) {
                ret = -EINVAL;
                break;
            }

            if (!ifa) {
                if ((ifa = inet_alloc_ifa()) == NULL) {
                    ret = -ENOBUFS;
                    break;
                }
                if (colon)
                    memcpy(ifa->ifa_label, ifr.ifr_name, IFNAMSIZ);
                else
                    memcpy(ifa->ifa_label, dev->name, IFNAMSIZ);
            } else {
                ret = 0;
                if (ifa->ifa_local == sin->sin_addr.s_addr)
                    break;
                inet_del_ifa(in_dev, ifap, 0);
                ifa->ifa_broadcast = 0;
                ifa->ifa_anycast = 0;
            }

            ifa->ifa_address =
            ifa->ifa_local = sin->sin_addr.s_addr;            //設置IP

            if (!(dev->flags&IFF_POINTOPOINT)) {
                ifa->ifa_prefixlen = inet_abc_len(ifa->ifa_address);
                ifa->ifa_mask = inet_make_mask(ifa->ifa_prefixlen);
                if ((dev->flags&IFF_BROADCAST) && ifa->ifa_prefixlen < 31)
                    ifa->ifa_broadcast = ifa->ifa_address|~ifa->ifa_mask;
            } else {
                ifa->ifa_prefixlen = 32;
                ifa->ifa_mask = inet_make_mask(32);
            }
            ret = inet_set_ifa(dev, ifa);
            break;

        case SIOCSIFBRDADDR:    /* Set the broadcast address */
            if (ifa->ifa_broadcast != sin->sin_addr.s_addr) {
                inet_del_ifa(in_dev, ifap, 0);
                ifa->ifa_broadcast = sin->sin_addr.s_addr;
                inet_insert_ifa(ifa);
            }
            break;

        case SIOCSIFDSTADDR:    /* Set the destination address */
            if (ifa->ifa_address != sin->sin_addr.s_addr) {
                if (inet_abc_len(sin->sin_addr.s_addr) < 0) {
                    ret = -EINVAL;
                    break;
                }
                inet_del_ifa(in_dev, ifap, 0);
                ifa->ifa_address = sin->sin_addr.s_addr;
                inet_insert_ifa(ifa);
            }
            break;

        case SIOCSIFNETMASK:     /* Set the netmask for the interface */

            /*
             *    The mask we set must be legal.
             */
            if (bad_mask(sin->sin_addr.s_addr, 0)) {
                ret = -EINVAL;
                break;
            }

            if (ifa->ifa_mask != sin->sin_addr.s_addr) {
                inet_del_ifa(in_dev, ifap, 0);
                ifa->ifa_mask = sin->sin_addr.s_addr;
                ifa->ifa_prefixlen = inet_mask_len(ifa->ifa_mask);
                inet_insert_ifa(ifa);
            }
            break;
    }
done:
    rtnl_unlock();
    dev_probe_unlock();
    return ret;

rarok:
    rtnl_unlock();
    dev_probe_unlock();
    if (copy_to_user(arg, &ifr, sizeof(struct ifreq)))
        return -EFAULT;
    return 0;
}