网卡状态检测函数

news2024/12/23 20:57:00

内核中网卡的开启状态通过__LINK_STATE_START进行标识。网卡开启或关闭时，通过该标识会被置位。

内核专门提供了一个函数用于检测该标志位。函数定义如下：

static inline bool netif_running(const struct net_device *dev)
{
	return test_bit(__LINK_STATE_START, &dev->state);
}

编写内核模块，通过开启和关闭网卡，观察该函数是否符合预期。

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/netdevice.h>
#include <linux/net_namespace.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>

struct net_device *eth;

static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev) {
        kfree_skb(skb);
        return 0;
}

int ndo_open(struct net_device *dev) {
        printk(KERN_ALERT "open\n");
        printk(KERN_ALERT "%d\n",netif_running(dev));
        return 0;
}
int ndo_stop(struct net_device *dev) {
        printk(KERN_ALERT "stop\n");
        printk(KERN_ALERT "%d\n",netif_running(dev));
        return 0;
}

static const struct net_device_ops vnetdev_ops = {
    .ndo_start_xmit        = virt_net_send_packet,
    .ndo_open = ndo_open,
    .ndo_stop = ndo_stop,
};

static void add_self_netdev(void) {
        int result;
        eth = alloc_etherdev(16);
        if (!eth) {
                printk(KERN_ALERT "eth failed\n");
        }
        eth->netdev_ops = &vnetdev_ops;

        memcpy(eth->name,"eth%d",3);
        eth->dev_addr = "abcedf";

        eth->flags |= IFF_NOARP | IFF_UP | IFF_RUNNING;
        eth->features |= NETIF_F_IP_CSUM;
        result = register_netdev(eth);
        if (result) {
                printk(KERN_ALERT "eth register failed\n");
        }
}
static int fishing_init(void) {
        printk(KERN_ALERT "init\n");
        add_self_netdev();
        return 0;
}

static void fishing_exit(void) {
        printk(KERN_ALERT "exit\n");
        unregister_netdev(eth);
        free_netdev(eth);
}

module_init(fishing_init);
module_exit(fishing_exit);


MODULE_LICENSE("GPL");
MODULE_AUTHOR("shakespeare");

Makefile文件：

obj-m += fishing.o

DIR_KERNEL=/lib/modules/$(shell uname -r)/build/
KDIR=/usr/src/linux-headers-$(shell uname -r)/
PWD=$(shell pwd)

all:
        make M=$(PWD) -C $(KDIR) modules

clean:
        rm *.o *.ko *.mod.c *.mod  *.order *.symvers

编译，并加载到内核。

开启网卡或关闭网卡，然后打印内核日志：