新的环回设备模块在wireshark中不显示跟踪

2024-6-4 • tag-icon

我正在尝试编写一个可以复制环回设备功能的网络设备驱动程序。我修改了可用的代码关联。我正在 Linux 4.8 上进行测试。我删除了与网络命名空间的统计和环回注册相关的代码。为了这变量，我找不到定义，所以现在将其删除。

/* testlo.c */

#include <linux/kernel.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/in.h>

#include <asm/uaccess.h>
#include <asm/io.h>

#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/ethtool.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <linux/if_ether.h> /* For the statistics structure. */
#include <linux/if_arp.h>   /* For ARPHRD_ETHER */
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/percpu.h>
#include <net/net_namespace.h>
#include <linux/u64_stats_sync.h>

/*
 * The higher levels take care of making this non-reentrant (it's
 * called with bh's disabled).
 */
netdev_tx_t loopback_xmit(struct sk_buff *skb,
             struct net_device *dev)
{
    //struct pcpu_lstats *lb_stats;
    int len;

    skb_orphan(skb);

    /* Before queueing this packet to netif_rx(),
     * make sure dst is refcounted.
     */
    skb_dst_force(skb);

    skb->protocol = eth_type_trans(skb, dev);

    len = skb->len;
    if (likely(netif_rx(skb) == NET_RX_SUCCESS)) { }

    printk("Received packet at device driver \n");

    return NETDEV_TX_OK;
}

u32 always_on(struct net_device *dev)
{
    return 1;
}

const struct ethtool_ops loopback_ethtool_ops = {
    .get_link       = always_on,
};

int loopback_dev_init(struct net_device *dev)
{
    return 0;
}

void loopback_dev_free(struct net_device *dev)
{
    free_netdev(dev);
}

const struct net_device_ops loopback_ops = {
    .ndo_init      = loopback_dev_init,
    .ndo_start_xmit= loopback_xmit,
    .ndo_set_mac_address = eth_mac_addr,
};

/*
 * The loopback device is special. There is only one instance
 * per network namespace.
 */
void loopback_setup(struct net_device *dev)
{
    dev->mtu        = 64 * 1024;
    dev->hard_header_len    = ETH_HLEN; /* 14   */
    dev->addr_len       = ETH_ALEN; /* 6    */
    dev->type       = ARPHRD_LOOPBACK;  /* 0x0001*/
    dev->flags      = IFF_LOOPBACK;
    dev->priv_flags     |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
    netif_keep_dst(dev);
    dev->hw_features    = NETIF_F_GSO_SOFTWARE;
    dev->features       = NETIF_F_SG | NETIF_F_FRAGLIST
        | NETIF_F_GSO_SOFTWARE
        | NETIF_F_HW_CSUM
        | NETIF_F_RXCSUM
        | NETIF_F_SCTP_CRC
        | NETIF_F_HIGHDMA
        | NETIF_F_LLTX
        | NETIF_F_NETNS_LOCAL
        | NETIF_F_VLAN_CHALLENGED
        | NETIF_F_LOOPBACK;
    dev->ethtool_ops    = &loopback_ethtool_ops;
    dev->netdev_ops     = &loopback_ops;
    dev->destructor     = loopback_dev_free;
}

struct net_device *global_dev;

/* Setup and register the loopback device. */
int init_dev (void)
{
    struct net_device *dev;
    int err;

    printk ("Init Module\n");

    err = -ENOMEM;
    dev = alloc_netdev(0, "testlo", NET_NAME_UNKNOWN, loopback_setup);
    if (!dev)
        goto out;

    err = register_netdev(dev);
    if (err)
        goto out_free_netdev;

    BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);   
    global_dev = dev; 

    return 0;

out_free_netdev:
    free_netdev(dev);
out:
    return err;
}

void cleanup (void)
{
    printk ("Cleaning Up Module\n");
    unregister_netdev (global_dev);
    return;
}

module_init (init_dev);
module_exit (cleanup);

生成文件：

obj-m += testlo.o

all:
      make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
      make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

一旦我编译代码并插入内核模块，我就可以在列表中看到我的新设备（testlo）ip a。我可以将设备状态设置为启动并为其分配 IP 地址。但是，如果我尝试 ping 该 IP（我确实看到了 ping 响应），则代码的功能loopback_xmit()不会被触发。如果我检查wireshark，当我ping 新设备的IP 时，没有任何痕迹。在默认环回设备 (lo) 中，ping 会127.0.0.1在wireshark 中显示跟踪。

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