OK6410（256M RAM ，1G SLC NAND）Linux-3.8.3驱动（12.1）虚拟网卡1

目的：创建一个最简单的虚拟网卡

网卡驱动程序框架:
app:  socket
--------------------------------------------------
                    ---------------
                    --------------- 若干层网络协议--纯软件
                    ---------------
                    ---------------
       nodo_start_xmit||       /\ 
                      \/       ||  netif_rx   sk_buff
                     ---------------
          硬件相关的驱动程序(要提供ndo_start_xmit, 有数据时要用netif_rx上报)           
--------------------------------------------------
                           硬件           

写网卡驱动程序步骤：
1. 分配一个net_device结构体
2. 设置:
    2.1 在结构体net_device_ops中定义发包函数:nodo_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


代码如下

/*
 * 参考drivers\net\dm9000.c
 */
#include <linux/module.h>
#include <linux/ioport.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/crc32.h>
#include <linux/mii.h>
#include <linux/ethtool.h>
#include <linux/dm9000.h>
#include <linux/delay.h>
#include <linux/platform_device.h>
#include <linux/irq.h>
#include <linux/slab.h>

#include <asm/delay.h>
#include <asm/irq.h>
#include <asm/io.h>

static struct net_device *vnet_dev;

static struct net_device_ops vnet_dev_ops =
{
    /* 2.1 在结构体net_device_ops中定义发包函数:nodo_start_xmit */
};

static int vnet_init(void)
{
    /* 1. 分配一个net_device */
    vnet_dev = alloc_netdev(0, "vnet%d", ether_setup); // alloc_etherdev;

    /* 2. 设置: */

    /* 2.2 其他信息 */


    /* 3. 硬件相关的: request_irq, 在中断函数里得到数据后用netif_rx上报 */

    /* 4. 注册net_device */
    vnet_dev->netdev_ops = &vnet_dev_ops;//必须添加，否则会注册失败
    register_netdev(vnet_dev);


    return 0;
}

static void vnet_exit(void)
{
    unregister_netdev(vnet_dev);
    free_netdev(vnet_dev);
}

module_init(vnet_init);
module_exit(vnet_exit);

MODULE_LICENSE("GPL");

注意：vnet_dev_ops结构体必须添加，否则在开发板insmod驱动时会出现如下错误

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = cfac8000
[00000000] *pgd=5fb21831, *pte=00000000, *ppte=00000000
Internal error: Oops: 17 [#1] ARM
Modules linked in: vnet(O+)
CPU: 0    Tainted: G           O (3.8.3 #82)
PC is at register_netdevice+0x74/0x390
LR is at 0x74656e76
pc : [<c02bbe34>] lr : [<74656e76>] psr: 60000013
sp : cfb6de48 ip : 00000000  fp : 00000001
r10: bf000024  r9 : cfb10760  r8 : bf0000b0
r7 : 00000000  r6 : 00000000  r5 : c04d8308  r4 : cfae5800
r3 : 00000030  r2 : 80000000  r1 : cfb6de25  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
Control: 00c5387d  Table: 5fac8008  DAC: 00000015
Process insmod (pid: 970, stack limit = 0xcfb6c1b0)
Stack: (0xcfb6de48 to 0xcfb6e000)
de40: cfae5a18 c04d8af8 cfb6c000 cfae5800 cfb6c000 c04de000
de60: 00000000 bf0000b0 cfb10760 bf000024 00000001 c02bc164 cfb6c000 bf000054
de80: 00000001 00000000 00000002 c0008658 00000018 00000017 00000017 bf000024
dea0: 00000000 c04dd144 bf0000b0 bf0000f8 00000018 cfac09c0 bf0000bc bf0000bc
dec0: cfb6c000 cfb6df50 00400100 bf0000b0 cfb10760 bf0000f8 00000001 c0059c84
dee0: bf0000bc 00007fff c0057e14 c008dcec d0862000 0000001c 00000020 00000018
df00: bf0001e4 c035a248 00000000 00000000 00000000 00000000 00000000 00000000
df20: 00000000 c008e9e0 000000d2 cfb6df50 0001776b 000eb040 000e1d93 c000eb28
df40: cfb6c000 00000000 00000000 c005a3a8 d0862000 0001776b d08740f8 d0873fc0
df60: d0879668 000001fc 000002fc 00000000 00000000 00000000 0000001e 0000001f
df80: 00000009 00000000 00000006 00000000 cfb6c000 000007cc beb07cc4 00000069
dfa0: 00000080 c000e980 000007cc beb07cc4 000eb040 0001776b 000e1d93 00000000
dfc0: 000007cc beb07cc4 00000069 00000080 beb07cc8 00000000 beb07cc8 00000000
dfe0: 00000001 beb07954 00021ea4 b6e59154 60000010 000eb040 00000000 00000000
[<c02bbe34>] (register_netdevice+0x74/0x390) from [<c02bc164>] (register_netdev+0x14/0x24)
[<c02bc164>] (register_netdev+0x14/0x24) from [<bf000054>] (vnet_init+0x30/0x48 [vnet])
[<bf000054>] (vnet_init+0x30/0x48 [vnet]) from [<c0008658>] (do_one_initcall+0x34/0x178)
[<c0008658>] (do_one_initcall+0x34/0x178) from [<c0059c84>] (load_module+0xb94/0x116c)
[<c0059c84>] (load_module+0xb94/0x116c) from [<c005a3a8>] (sys_init_module+0xc0/0xf4)
[<c005a3a8>] (sys_init_module+0xc0/0xf4) from [<c000e980>] (ret_fast_syscall+0x0/0x30)
Code: ebfffef3 e2506000 ba000008 e594c0d8 (e59c3000)
---[ end trace fb9590d42235a944 ]---
Segmentation fault

具体原理可以参考http://blog.chinaunix.net/uid-28970775-id-3941741.html


测试方法：

1. 加载驱动


2. 配置虚拟网卡的ip：ifconfig vnet0 3.3.3.3


3. 查看：ifconfig，看到新网卡vnet0


4. ping 3.3.3.3，发现可以ping通，说明ip实际是纯软件的概念，在ping本地ip时饶过了底层的网卡驱动，

    因此说明网卡驱动只需要提供发包和收包的功能，并不需要了解那些上层协议


5. ping 3.3.3.4，开发板死机，由于驱动没有提供发包和收包的函数