二：从网卡驱动说起。
以intel 100M 网卡驱动为例简要概述数据包的接收与发送流程。代码见（drivers/net/e100.c）
网卡是属于PCI设备，它的注册跟一般的PCI设备注册没什么两样。
static int __init e100_init_module(void)
{
if(((1 << debug) - 1) & NETIF_MSG_DRV) {
printk(KERN_INFO PFX "%s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
printk(KERN_INFO PFX "%s\n", DRV_COPYRIGHT);
}
//注册PCI
return pci_module_init(&e100_driver);
}
其中e100_driver对应为网卡的pci_driver.
static struct pci_driver e100_driver = {
//驱动对应的名字
.name = DRV_NAME,
//匹配类型
.id_table = e100_id_table,
//侦测函数
.probe = e100_probe,
//移除函数，设备移除时将调用此函数
.remove = __devexit_p(e100_remove),
#ifdef CONFIG_PM
.suspend = e100_suspend,
.resume = e100_resume,
#endif
}
当总数探测到PCI设备符合e100_id_table中的参数时，将会调用e100_probe,开始设备的初始化
在e100_probe中：
static int __devinit e100_probe(struct pci_dev *pdev,
const struct pci_device_id *ent)
{
struct net_device *netdev;
struct nic *nic;
int err;
//分配net_device并为其赋值
//alloc_etherdev为以太网接口的net_device分配函数。它是alloc_netdev的封装函数
if(!(netdev = alloc_etherdev(sizeof(struct nic)))) {
if(((1 << debug) - 1) & NETIF_MSG_PROBE)
printk(KERN_ERR PFX "Etherdev alloc failed, abort.\n");
return -ENOMEM;
}
//对netdev中的函数指针赋初值
netdev->open = e100_open;
netdev->stop = e100_close;
netdev->hard_start_xmit = e100_xmit_frame;
netdev->get_stats = e100_get_stats;
netdev->set_multicast_list = e100_set_multicast_list;
netdev->set_mac_address = e100_set_mac_address;
netdev->change_mtu = e100_change_mtu;
netdev->do_ioctl = e100_do_ioctl;
//支持ethtool工具时有效
SET_ETHTOOL_OPS(netdev, &e100_ethtool_ops);
netdev->tx_timeout = e100_tx_timeout;
netdev->watchdog_timeo = E100_WATCHDOG_PERIOD;
//轮询函数
netdev->poll = e100_poll;
netdev->weight = E100_NAPI_WEIGHT;
#ifdef CONFIG_NET_POLL_CONTROLLER
netdev->poll_controller = e100_netpoll;
#endif
//获得net_device私有数据区，并对其赋值
//私有数据大小是由alloc_etherdev（）参数中指定的
nic = netdev_priv(netdev);
nic->netdev = netdev;
nic->pdev = pdev;
nic->msg_enable = (1 << debug) - 1;
pci_set_drvdata(pdev, netdev);
//启动网卡.为之后DMA，I/O内存映射做准备
//它实际上是对PCI的控制寄存器赋值来实现的
if((err = pci_enable_device(pdev))) {
DPRINTK(PROBE, ERR, "Cannot enable PCI device, aborting.\n");
goto err_out_free_dev;
}
//获取该资源相关联的标志
//如果该设备存在I/O内存，则置IORESOURCE_MEM
if(!(pci_resource_flags(pdev, 0) & IORESOURCE_MEM)) {
DPRINTK(PROBE, ERR, "Cannot find proper PCI device "
"base address, aborting.\n");
err = -ENODEV;
goto err_out_disable_pdev;
}
//对PCI的6个寄存器都会调用资源分配函数进行申请
if((err = pci_request_regions(pdev, DRV_NAME))) {
DPRINTK(PROBE, ERR, "Cannot obtain PCI resources, aborting.\n");
goto err_out_disable_pdev;
}
//探制设备的DMA能力。如果设备支持DMA。pci_set_dma_mask返回0
pci_set_master(pdev);
if((err = pci_set_dma_mask(pdev, 0xFFFFFFFFULL))) {
DPRINTK(PROBE, ERR, "No usable DMA configuration, aborting.\n");
goto err_out_free_res;
}
SET_MODULE_OWNER(netdev);
SET_NETDEV_DEV(netdev, &pdev->dev);
//映射设备对应的I/O。以后对设备寄存器的操作可以直接转换为对内存的操作
nic->csr = ioremap(pci_resource_start(pdev, 0), sizeof(struct csr));
if(!nic->csr) {
DPRINTK(PROBE, ERR, "Cannot map device registers, aborting.\n");
err = -ENOMEM;
goto err_out_free_res;
}
if(ent->driver_data)
nic->flags |= ich;
else
nic->flags &= ~ich;
spin_lock_init(&nic->cb_lock);
spin_lock_init(&nic->cmd_lock);
//设置定时器。
init_timer(&nic->watchdog);
nic->watchdog.function = e100_watchdog;
nic->watchdog.data = (unsigned long)nic;
init_timer(&nic->blink_timer);
nic->blink_timer.function = e100_blink_led;
nic->blink_timer.data = (unsigned long)nic;
//为nic->mem建立线性DMA。只是在支持ethtool的时候才有用
if((err = e100_alloc(nic))) {
DPRINTK(PROBE, ERR, "Cannot alloc driver memory, aborting.\n");
goto err_out_iounmap;
}
//对nic成员赋初值
e100_get_defaults(nic);
e100_hw_reset(nic);
e100_phy_init(nic);
//读取网卡的EEPROM。其中存放着网卡的MAC地址。
//对EEPROM是通过对I/O映射内存的操作实现的，即nic->csr
if((err = e100_eeprom_load(nic)))
goto err_out_free;
//设置netdev->dev_addr
memcpy(netdev->dev_addr, nic->eeprom, ETH_ALEN);
if(!is_valid_ether_addr(netdev->dev_addr)) {
DPRINTK(PROBE, ERR, "Invalid MAC address from "
"EEPROM, aborting.\n");
err = -EAGAIN;
goto err_out_free;
}
/* Wol magic packet can be enabled from eeprom */
if((nic->mac >= mac_82558_D101_A4) &&
(nic->eeprom[eeprom_id] & eeprom_id_wol))
nic->flags |= wol_magic;
pci_enable_wake(pdev, 0, nic->flags & (wol_magic | e100_asf(nic)));
//注册网络设备
if((err = register_netdev(netdev))) {
DPRINTK(PROBE, ERR, "Cannot register net device, aborting.\n");
goto err_out_free;
}
DPRINTK(PROBE, INFO, "addr 0x%lx, irq %d, "
"MAC addr %02X:%02X:%02X:%02X:%02X:%02X\n",
pci_resource_start(pdev, 0), pdev->irq,
netdev->dev_addr[0], netdev->dev_addr[1], netdev->dev_addr[2],
netdev->dev_addr[3], netdev->dev_addr[4], netdev->dev_addr[5]);
return 0;
err_out_free:
e100_free(nic);
err_out_iounmap:
iounmap(nic->csr);
err_out_free_res:
pci_release_regions(pdev);
err_out_disable_pdev:
pci_disable_device(pdev);
err_out_free_dev:
pci_set_drvdata(pdev, NULL);
free_netdev(netdev);
return err;
}
