Linux之虚拟网卡驱动
目录
一、网卡驱动程序框架
二、编写虚拟网卡驱动
2.1 测试直接注册net_device
2.2 提供发包函数
2.3 添加统计信息
2.4 构造假包ping通
一、网卡驱动程序框架
网卡驱动程序时网络驱动程序的一部分，并不是网络驱动程序，网络驱动程序分为很多层，在这里只是最底层，最终会操作到硬件，在硬件上，有硬件相关层的驱动程序，即我们要写的网卡驱动
网卡驱动需要具备收发能力，使数据底层到上层，也能从上层到底层，大多驱动程序都是以面向对象的思想实现，参考真正的网卡驱动程序cs89x0.c，在入口函数中分配了一个net_dev结构体，设置提供发包函数hard_start_xmit函数，在中断中提供收包的功能netif_rx函数，并且注册register_netdev
int __init init_module(void)
{struct net_device *dev = alloc_etherdev(sizeof(struct net_local));
...ret = cs89x0_probe1(dev, io, 1);if (ret)goto out;dev_cs89x0 = dev;return 0;
out:free_netdev(dev);return ret;
}static int __init
cs89x0_probe1(struct net_device *dev, int ioaddr, int modular)
{struct net_local *lp = netdev_priv(dev);static unsigned version_printed;int i;int tmp;unsigned rev_type = 0;int eeprom_buff[CHKSUM_LEN];int retval;...dev->open = net_open;dev->stop = net_close;dev->tx_timeout = net_timeout;dev->watchdog_timeo = HZ;dev->hard_start_xmit = net_send_packet;dev->get_stats = net_get_stats;dev->set_multicast_list = set_multicast_list;dev->set_mac_address = set_mac_address;
#ifdef CONFIG_NET_POLL_CONTROLLERdev->poll_controller = net_poll_controller;
#endifprintk("\n");if (net_debug)printk("cs89x0_probe1() successful\n");retval = register_netdev(dev);...
}static irqreturn_t net_interrupt(int irq, void *dev_id)
{struct net_device *dev = dev_id;struct net_local *lp;int ioaddr, status;...case ISQ_RECEIVER_EVENT:/* Got a packet(s). */net_rx(dev);break;case ISQ_TRANSMITTER_EVENT:lp->stats.tx_packets++;netif_wake_queue(dev);if ((status & TX_OK) == 0) lp->stats.tx_errors++;if (status & TX_LOST_CRS) lp->stats.tx_carrier_errors++;if (status & TX_SQE_ERROR) lp->stats.tx_heartbeat_errors++;if (status & TX_LATE_COL) lp->stats.tx_window_errors++;if (status & TX_16_COL) lp->stats.tx_aborted_errors++;break;
...
}static void
net_rx(struct net_device *dev)
{struct net_local *lp = netdev_priv(dev);struct sk_buff *skb;int status, length;...netif_rx(skb);dev->last_rx = jiffies;lp->stats.rx_packets++;lp->stats.rx_bytes += length;
}
hard_start_xmit和netif_rx之间传输的sk_buff，总体框架如下
| APP:socket | ||
|
----------------------- ----------------------- ----------------------- ----------------------- |
若干层网络协议(纯软件) | |
| 发包函数hard_start_xmit |
|| sk_buff /\ \/ || |
收包函数netif_rx |
| 硬件相关的驱动程序（要提供hard_start_xmit，有数据时，用netif_rx上报） | ||
| 硬件 | ||
写网卡驱动程序：
1. 分配一个net_device结构体
2. 设置:
2.1 发包函数: hard_start_xmit
2.2 收到数据时(在中断处理函数里)用netif_rx上报数据
2.3 其他设置
3. 注册: register_netdev
在cs89x0.c中分配net_dev结构体使用如下，若想自己修改名称，直接使用alloc_netdev函数来分配，ether_setup为默认的设置函数，sizeof_priv为私有数据，alloc_netdev可以多分配出一块内存，其中有指针可以指向这块内存
struct net_device *alloc_etherdev(int sizeof_priv)
{
return alloc_netdev(sizeof_priv, "eth%d", ether_setup);
}
二、编写虚拟网卡驱动
2.1 测试直接注册net_device
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/interrupt.h>
#include <linux/ioport.h>
#include <linux/in.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/bitops.h>
#include <linux/delay.h>#include <asm/system.h>
#include <asm/io.h>
#include <asm/irq.h>static struct net_device *vnet_dev;static int virt_net_init(void)
{/* 1. 分配一个net_device结构体 */vnet_dev = alloc_netdev(0, "vnet%d", ether_setup);; /* alloc_etherdev *//* 2. 设置 *//* 3. 注册 */register_netdev(vnet_dev);return 0;
}static void virt_net_exit(void)
{unregister_netdev(vnet_dev);free_netdev(vnet_dev);
}module_init(virt_net_init);
module_exit(virt_net_exit);MODULE_AUTHOR("xiaoma"); //可以写入作者信息
MODULE_LICENSE("GPL");编译驱动程序，加载到单板上，其中eth0为网卡DM9000，vnet0则是我们注册的网卡驱动，在没有提供发包函数，在这里能够ping得通自己，说明在网络层纯软件中来回，IP是纯软件的概念，跟硬件无关，当我们ping 3.3.3.4后发出去会调用到hard_start_xmit发包函数，这里没有编写，因此会死机，为什么ping 3.3.3.4的时候从网卡vnet0出去，是因为两者之间处于同一网段，所以当PC机有两个网卡时，最好不要处于同一网段，否则ping一个IP或者访问一个主机的时候，操作系统不知道把数据发给哪个网卡
# insmod virt_net.ko
# ifconfig vnet0 3.3.3.3
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:60:6E:33:44:55
inet addr:192.168.0.19 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1770 errors:0 dropped:0 overruns:0 frame:0
TX packets:720 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2170957 (2.0 MiB) TX bytes:111980 (109.3 KiB)
Interrupt:51 Base address:0xa000lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)vnet0 Link encap:Ethernet HWaddr 00:00:00:00:00:00
inet addr:3.3.3.3 Bcast:3.255.255.255 Mask:255.0.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)# ping 3.3.3.3
PING 3.3.3.3 (3.3.3.3): 56 data bytes
64 bytes from 3.3.3.3: seq=0 ttl=64 time=1.064 ms
64 bytes from 3.3.3.3: seq=1 ttl=64 time=0.463 ms
64 bytes from 3.3.3.3: seq=2 ttl=64 time=0.466 ms
64 bytes from 3.3.3.3: seq=3 ttl=64 time=0.463 ms
64 bytes from 3.3.3.3: seq=4 ttl=64 time=0.461 ms
64 bytes from 3.3.3.3: seq=5 ttl=64 time=0.458 ms
64 bytes from 3.3.3.3: seq=6 ttl=64 time=0.464 ms--- 3.3.3.3 ping statistics ---
7 packets transmitted, 7 packets received, 0% packet loss
round-trip min/avg/max = 0.458/0.548/1.064 ms# ping 3.3.3.4
PING 3.3.3.4 (3.3.3.4): 56 data bytes
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0004000
[00000000] *pgd=00000000
Internal error: Oops: 0 [#1]
Modules linked in: virt_net
CPU: 0 Not tainted (2.6.22.6 #1)
PC is at __init_begin+0x3fff8000/0x30
LR is at dev_hard_start_xmit+0x1a8/0x240 //没有发包函数
pc : [<00000000>] lr : [<c0245798>] psr: 60000013
sp : c035ddd8 ip : c035ddfc fp : c035ddf8
r10: c06cec00 r9 : 04030303 r8 : c03c79b8
r7 : c06cec00 r6 : c07d6780 r5 : c07d6780 r4 : c06cec00
r3 : 00000000 r2 : c06e50a0 r1 : c06cec00 r0 : c07d6780
Flags: nZCv IRQs on FIQs on Mode SVC_32 Segment kernel
Control: c000717f Table: 33ecc000 DAC: 00000017
Process swapper (pid: 0, stack limit = 0xc035c258)
Stack: (0xc035ddd8 to 0xc035e000)
ddc0: c06cec00 00000000
dde0: c07d6780 c06cec2c 03030303 c035de18 c035ddfc c0252680 c0245600 c06cec00
de00: c07d6780 00000000 c07189a0 c035de34 c035de1c c0245994 c02525e0 c06f5160
de20: c07d6140 00000000 c035de44 c035de38 c027ee70 c0245840 c035de64 c035de48
de40: c027eebc c027ee70 03030303 00000000 c06ced30 00000000 c035dea4 c035de68
...
2.2 提供发包函数
对于真实的网卡，virt_net_send_packet会把skb里的数据通过网卡发送出去
static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev)
{
static int cnt = 0;
printk("virt_net_send_packet cnt = %d\n", ++cnt);
return 0;
}vnet_dev->hard_start_xmit = virt_net_send_packet;
重新加载驱动，ping 3.3.3.4成功，发送了8次，但是重新查看数据信息，TX packets为0
# ifconfig vnet0 3.3.3.3
# ping 3.3.3.4
PING 3.3.3.4 (3.3.3.4): 56 data bytes
virt_net_send_packet cnt = 1
virt_net_send_packet cnt = 2
virt_net_send_packet cnt = 3
virt_net_send_packet cnt = 4
virt_net_send_packet cnt = 5
virt_net_send_packet cnt = 6
virt_net_send_packet cnt = 7
virt_net_send_packet cnt = 8...
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:60:6E:33:44:55
inet addr:192.168.0.19 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3250 errors:0 dropped:0 overruns:0 frame:0
TX packets:900 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2734036 (2.6 MiB) TX bytes:141182 (137.8 KiB)
Interrupt:51 Base address:0xa000lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:10 errors:0 dropped:0 overruns:0 frame:0
TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1120 (1.0 KiB) TX bytes:1120 (1.0 KiB)vnet0 Link encap:Ethernet HWaddr 00:00:00:00:00:00
inet addr:3.3.3.3 Bcast:3.255.255.255 Mask:255.0.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
2.3 添加统计信息
在net_device结构体中有struct net_device_stats stats成员包含了信息
struct net_device_stats
{unsigned long rx_packets; /* total packets received */unsigned long tx_packets; /* total packets transmitted */unsigned long rx_bytes; /* total bytes received */unsigned long tx_bytes; /* total bytes transmitted */unsigned long rx_errors; /* bad packets received */unsigned long tx_errors; /* packet transmit problems */unsigned long rx_dropped; /* no space in linux buffers */unsigned long tx_dropped; /* no space available in linux */unsigned long multicast; /* multicast packets received */unsigned long collisions;/* detailed rx_errors: */unsigned long rx_length_errors;unsigned long rx_over_errors; /* receiver ring buff overflow */unsigned long rx_crc_errors; /* recved pkt with crc error */unsigned long rx_frame_errors; /* recv'd frame alignment error */unsigned long rx_fifo_errors; /* recv'r fifo overrun */unsigned long rx_missed_errors; /* receiver missed packet *//* detailed tx_errors */unsigned long tx_aborted_errors;unsigned long tx_carrier_errors;unsigned long tx_fifo_errors;unsigned long tx_heartbeat_errors;unsigned long tx_window_errors;/* for cslip etc */unsigned long rx_compressed;unsigned long tx_compressed;
};修改hard_start_xmit函数
static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev)
{static int cnt = 0;printk("virt_net_send_packet cnt = %d\n", ++cnt);/* 更新统计信息 */dev->stats.tx_packets++;dev->stats.tx_bytes += skb->len;return 0;
}设置MAC地址，参考cs89x0.c
vnet_dev = alloc_netdev(0, "vnet%d", ether_setup);vnet_dev->dev_addr[0] = 0x08;vnet_dev->dev_addr[1] = 0x89;vnet_dev->dev_addr[2] = 0x89;vnet_dev->dev_addr[3] = 0x89;vnet_dev->dev_addr[4] = 0x89;vnet_dev->dev_addr[5] = 0x11;代码如下：
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/interrupt.h>
#include <linux/ioport.h>
#include <linux/in.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/bitops.h>
#include <linux/delay.h>#include <asm/system.h>
#include <asm/io.h>
#include <asm/irq.h>static struct net_device *vnet_dev;static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev)
{static int cnt = 0;printk("virt_net_send_packet cnt = %d\n", ++cnt);/* 对于真实的网卡, 把skb里的数据通过网卡发送出去 *//* 更新统计信息 */dev->stats.tx_packets++;dev->stats.tx_bytes += skb->len;return 0;
}static int virt_net_init(void)
{/* 1. 分配一个net_device结构体 */vnet_dev = alloc_netdev(0, "vnet%d", ether_setup);; /* alloc_etherdev *//* 2. 设置 */vnet_dev->hard_start_xmit = virt_net_send_packet;/* 设置MAC地址 */vnet_dev->dev_addr[0] = 0x08;vnet_dev->dev_addr[1] = 0x89;vnet_dev->dev_addr[2] = 0x89;vnet_dev->dev_addr[3] = 0x89;vnet_dev->dev_addr[4] = 0x89;vnet_dev->dev_addr[5] = 0x11;/* 3. 注册 */register_netdev(vnet_dev);return 0;
}static void virt_net_exit(void)
{unregister_netdev(vnet_dev);free_netdev(vnet_dev);
}module_init(virt_net_init);
module_exit(virt_net_exit);MODULE_AUTHOR("xiaoma");
MODULE_LICENSE("GPL");
测试结果如下：
# rmmod virt_net
# insmod virt_net.ko
# ifconfig vnet0 3.3.3.3
# ping 3.3.3.4
PING 3.3.3.4 (3.3.3.4): 56 data bytes
virt_net_send_packet cnt = 1
virt_net_send_packet cnt = 2
virt_net_send_packet cnt = 3
virt_net_send_packet cnt = 4
virt_net_send_packet cnt = 5
virt_net_send_packet cnt = 6--- 3.3.3.4 ping statistics ---
6 packets transmitted, 0 packets received, 100% packet loss
# ifconfig
eth0 Link encap:Ethernet HWaddr 00:60:6E:33:44:55
inet addr:192.168.0.19 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:4684 errors:0 dropped:0 overruns:0 frame:0
TX packets:1023 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3144891 (2.9 MiB) TX bytes:157598 (153.9 KiB)
Interrupt:51 Base address:0xa000lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:16 errors:0 dropped:0 overruns:0 frame:0
TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1792 (1.7 KiB) TX bytes:1792 (1.7 KiB)vnet0 Link encap:Ethernet HWaddr 08:89:89:89:89:11
inet addr:3.3.3.3 Bcast:3.255.255.255 Mask:255.0.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:252 (252.0 B)
2.4 构造假包ping通
假设有IP为3.3.3.4的设备，当我们ping它的时候，会发包(hard_start_xmit)给它，它收到包后会返回数据，有数据时要用(netif_rx)上报，就可以ping通，由于现在是虚拟网卡，并没有真正的网线，也没有3.3.3.4的设备，这里构造假包，直接返回数据，这样我们就可以ping得通
构造一个假的sk_buff,上报，函数自己实现
emulator_rx_packet(skb, dev);
参考cs89x0.c，对于真正的网卡，首先会停止该网卡的队列，把skb的数据写入网卡，释放skb就会有中断产生，数据发送完后会在中断函数唤醒网卡的队列，在这里直接唤醒
/* 对于真实的网卡, 把skb里的数据通过网卡发送出去 */
netif_stop_queue(dev); /* 停止该网卡的队列 */
/* ...... */ /* 把skb的数据写入网卡，这里会操作网卡 *//* 构造一个假的sk_buff,上报 */
emulator_rx_packet(skb, dev);dev_kfree_skb (skb); /* 释放skb */
netif_wake_queue(dev); /* 数据全部发送出去后,唤醒网卡的队列 */
编写emulator_rx_packet，参考LDD3，包中有源目的长度三要素，数据放在skb->data中
static void emulator_rx_packet(struct sk_buff *skb, struct net_device *dev)
{unsigned char *type;struct iphdr *ih;__be32 *saddr, *daddr, tmp;unsigned char tmp_dev_addr[ETH_ALEN];struct ethhdr *ethhdr;struct sk_buff *rx_skb;// 从硬件读出/保存数据/* 对调"源/目的"的mac地址 */ethhdr = (struct ethhdr *)skb->data;memcpy(tmp_dev_addr, ethhdr->h_dest, ETH_ALEN);memcpy(ethhdr->h_dest, ethhdr->h_source, ETH_ALEN);memcpy(ethhdr->h_source, tmp_dev_addr, ETH_ALEN);/* 对调"源/目的"的ip地址 */ ih = (struct iphdr *)(skb->data + sizeof(struct ethhdr));saddr = &ih->saddr;daddr = &ih->daddr;tmp = *saddr;*saddr = *daddr;*daddr = tmp;//((u8 *)saddr)[2] ^= 1; /* change the third octet (class C) *///((u8 *)daddr)[2] ^= 1;type = skb->data + sizeof(struct ethhdr) + sizeof(struct iphdr);//printk("tx package type = %02x\n", *type);// 修改类型, 原来0x8表示ping*type = 0; /* 0表示reply */ih->check = 0; /* and rebuild the checksum (ip needs it) */ih->check = ip_fast_csum((unsigned char *)ih,ih->ihl);// 构造一个sk_buffrx_skb = dev_alloc_skb(skb->len + 2); //保留2个字节skb_reserve(rx_skb, 2); /* align IP on 16B boundary */ memcpy(skb_put(rx_skb, skb->len), skb->data, skb->len);//环型暖冲区/* Write metadata, and then pass to the receive level */rx_skb->dev = dev;rx_skb->protocol = eth_type_trans(rx_skb, dev);rx_skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */dev->stats.rx_packets++; //更新统计信息dev->stats.rx_bytes += skb->len;// 提交sk_buffnetif_rx(rx_skb);
}对于skb->data，一开始是MAC头，在MAC中有目的MAC，源MAC，还有h_proto，当我们返回数据时，需要把目的和源调换一下位置，MAC头紧接着就是IP头，有源IP和目的IP，同样需要调换，还有check校验码用ip_fast_csum函数来校验，IP头紧接着就是type和数据，type对于0x8原来表示ping包，修改为0表示回复包
| 目的MAC | 源MAC | ... | 源IP | 目的IP | ... | type | 数据 |
struct ethhdr {
unsigned char h_dest[ETH_ALEN]; /* destination eth addr */
unsigned char h_source[ETH_ALEN]; /* source ether addr */
__be16 h_proto; /* packet type ID field */
} __attribute__((packed));ethhdr = (struct ethhdr *)skb->data;
struct iphdr {
#if defined(__LITTLE_ENDIAN_BITFIELD)
__u8 ihl:4,
version:4;
#elif defined (__BIG_ENDIAN_BITFIELD)
__u8 version:4,
ihl:4;
#else
#error "Please fix <asm/byteorder.h>"
#endif
__u8 tos;
__be16 tot_len;
__be16 id;
__be16 frag_off;
__u8 ttl;
__u8 protocol;
__sum16 check;
__be32 saddr;
__be32 daddr;
/*The options start here. */
};ih = (struct iphdr *)(skb->data + sizeof(struct ethhdr));
加上相关标志，才能ping通
vnet_dev->flags |= IFF_NOARP;
vnet_dev->features |= NETIF_F_NO_CSUM;
整体代码：
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/interrupt.h>
#include <linux/ioport.h>
#include <linux/in.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/ip.h> // 添加ip头文件#include <asm/system.h>
#include <asm/io.h>
#include <asm/irq.h>static struct net_device *vnet_dev;static void emulator_rx_packet(struct sk_buff *skb, struct net_device *dev)
{/* 参考LDD3 */unsigned char *type;struct iphdr *ih;__be32 *saddr, *daddr, tmp;unsigned char tmp_dev_addr[ETH_ALEN];struct ethhdr *ethhdr;struct sk_buff *rx_skb;// 从硬件读出/保存数据/* 对调"源/目的"的mac地址 */ethhdr = (struct ethhdr *)skb->data;memcpy(tmp_dev_addr, ethhdr->h_dest, ETH_ALEN);memcpy(ethhdr->h_dest, ethhdr->h_source, ETH_ALEN);memcpy(ethhdr->h_source, tmp_dev_addr, ETH_ALEN);/* 对调"源/目的"的ip地址 */ ih = (struct iphdr *)(skb->data + sizeof(struct ethhdr));saddr = &ih->saddr;daddr = &ih->daddr;tmp = *saddr;*saddr = *daddr;*daddr = tmp;//((u8 *)saddr)[2] ^= 1; /* change the third octet (class C) *///((u8 *)daddr)[2] ^= 1;type = skb->data + sizeof(struct ethhdr) + sizeof(struct iphdr);//printk("tx package type = %02x\n", *type);// 修改类型, 原来0x8表示ping*type = 0; /* 0表示reply */ih->check = 0; /* and rebuild the checksum (ip needs it) */ih->check = ip_fast_csum((unsigned char *)ih,ih->ihl);// 构造一个sk_buffrx_skb = dev_alloc_skb(skb->len + 2);skb_reserve(rx_skb, 2); /* align IP on 16B boundary */ memcpy(skb_put(rx_skb, skb->len), skb->data, skb->len);/* Write metadata, and then pass to the receive level */rx_skb->dev = dev;rx_skb->protocol = eth_type_trans(rx_skb, dev);rx_skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */dev->stats.rx_packets++;dev->stats.rx_bytes += skb->len;// 提交sk_buffnetif_rx(rx_skb);
}static int virt_net_send_packet(struct sk_buff *skb, struct net_device *dev)
{static int cnt = 0;printk("virt_net_send_packet cnt = %d\n", ++cnt);/* 对于真实的网卡, 把skb里的数据通过网卡发送出去 */netif_stop_queue(dev); /* 停止该网卡的队列 *//* ...... */ /* 把skb的数据写入网卡 *//* 构造一个假的sk_buff,上报 */emulator_rx_packet(skb, dev);dev_kfree_skb (skb); /* 释放skb */netif_wake_queue(dev); /* 数据全部发送出去后,唤醒网卡的队列 *//* 更新统计信息 */dev->stats.tx_packets++;dev->stats.tx_bytes += skb->len;return 0;
}static int virt_net_init(void)
{/* 1. 分配一个net_device结构体 */vnet_dev = alloc_netdev(0, "vnet%d", ether_setup);; /* alloc_etherdev *//* 2. 设置 */vnet_dev->hard_start_xmit = virt_net_send_packet;/* 设置MAC地址 */vnet_dev->dev_addr[0] = 0x08;vnet_dev->dev_addr[1] = 0x89;vnet_dev->dev_addr[2] = 0x89;vnet_dev->dev_addr[3] = 0x89;vnet_dev->dev_addr[4] = 0x89;vnet_dev->dev_addr[5] = 0x11;/* 设置下面两项才能ping通 */vnet_dev->flags |= IFF_NOARP;vnet_dev->features |= NETIF_F_NO_CSUM; /* 3. 注册 */register_netdev(vnet_dev);return 0;
}static void virt_net_exit(void)
{unregister_netdev(vnet_dev);free_netdev(vnet_dev);
}module_init(virt_net_init);
module_exit(virt_net_exit);MODULE_AUTHOR("xiaoma");
MODULE_LICENSE("GPL");测试结果：能ping 3.3.3.4并查看统计信息
# rmmod virt_net
# insmod virt_net.ko
# ifconfig vnet0 3.3.3.3
# ping 3.3.3.4
PING 3.3.3.4 (3.3.3.4): 56 data bytes
virt_net_send_packet cnt = 1
64 bytes from 3.3.3.4: seq=0 ttl=64 time=0.838 ms
virt_net_send_packet cnt = 2
64 bytes from 3.3.3.4: seq=1 ttl=64 time=0.518 ms
virt_net_send_packet cnt = 3
64 bytes from 3.3.3.4: seq=2 ttl=64 time=0.504 ms
virt_net_send_packet cnt = 4
64 bytes from 3.3.3.4: seq=3 ttl=64 time=0.442 ms
virt_net_send_packet cnt = 5
64 bytes from 3.3.3.4: seq=4 ttl=64 time=0.502 ms--- 3.3.3.4 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 0.442/0.560/0.838 msifconfig
...
vnet0 Link encap:Ethernet HWaddr 08:89:89:89:89:11
inet addr:3.3.3.3 Bcast:3.255.255.255 Mask:255.0.0.0
UP BROADCAST RUNNING NOARP MULTICAST MTU:1500 Metric:1
RX packets:5 errors:0 dropped:0 overruns:0 frame:0
TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:490 (490.0 B) TX bytes:490 (490.0 B)
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