网络设备驱动的注册与注销由 register_netdev( ) 和 unregister_netdev( ) 函数完成，这两个函数的原型为：
/** * register_netdev - register a network device * @dev: device to register * * Take a completed network device structure and add it to the kernel * interfaces. A %NETDEV_REGISTER message is sent to the netdev notifier * chain. 0 is returned on success. A negative errno code is returned * on a failure to set up the device, or if the name is a duplicate. * * This is a wrapper around register_netdevice that takes the rtnl semaphore * and expands the device name if you passed a format string to * alloc_netdev. */ int register_netdev(struct net_device *dev) { int err; rtnl_lock(); err = register_netdevice(dev); rtnl_unlock(); return err; }
/** * unregister_netdev - remove device from the kernel * @dev: device * * This function shuts down a device interface and removes it * from the kernel tables. * * This is just a wrapper for unregister_netdevice that takes * the rtnl semaphore. In general you want to use this and not * unregister_netdevice. */ void unregister_netdev(struct net_device *dev) { rtnl_lock(); unregister_netdevice(dev); rtnl_unlock(); }
这两个函数都接收一个 net_device 结构体指针为参数，可见 net_device 数据结构在网络设备驱动中的核心地位。
net_device 的生成和成员的赋值并不一定要由我们亲自动手逐个完成，可以利用如下宏帮助填充：
#define alloc_netdev(sizeof_priv, name, name_assign_type, setup) \ alloc_netdev_mqs(sizeof_priv, name, name_assign_type, setup, 1, 1) #define alloc_netdev_mq(sizeof_priv, name, name_assign_type, setup, count) \ alloc_netdev_mqs(sizeof_priv, name, name_assign_type, setup, count, count)
#define alloc_etherdev(sizeof_priv) \
alloc_etherdev_mq(sizeof_priv, 1) #define alloc_etherdev_mq(sizeof_priv, count) \
alloc_etherdev_mqs(sizeof_priv, count, count)
alloc_etherdev_mq 宏引用的 alloc_etherdev_mqs( ) 函数的原型为：
/** * alloc_etherdev_mqs - Allocates and sets up an Ethernet device * @sizeof_priv: Size of additional driver-private structure to be allocated * for this Ethernet device * @txqs: The number of TX queues this device has. * @rxqs: The number of RX queues this device has. * * Fill in the fields of the device structure with Ethernet-generic * values. Basically does everything except registering the device. * * Constructs a new net device, complete with a private data area of * size (sizeof_priv). A 32-byte (not bit) alignment is enforced for * this private data area. */ struct net_device *alloc_etherdev_mqs(int sizeof_priv, unsigned int txqs, unsigned int rxqs) { return alloc_netdev_mqs(sizeof_priv, "eth%d", NET_NAME_UNKNOWN, ether_setup, txqs, rxqs); }
alloc_netdev 以及 alloc_netdev_mq 宏引用的 alloc_netdev_mqs( ) 函数的原型为：
/** * alloc_netdev_mqs - allocate network device * @sizeof_priv: size of private data to allocate space for * @name: device name format string * @name_assign_type: origin of device name * @setup: callback to initialize device * @txqs: the number of TX subqueues to allocate * @rxqs: the number of RX subqueues to allocate * * Allocates a struct net_device with private data area for driver use * and performs basic initialization. Also allocates subqueue structs * for each queue on the device. */ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name, unsigned char name_assign_type, void (*setup)(struct net_device *), unsigned int txqs, unsigned int rxqs) { struct net_device *dev; size_t alloc_size; struct net_device *p; BUG_ON(strlen(name) >= sizeof(dev->name)); if (txqs < 1) { pr_err("alloc_netdev: Unable to allocate device with zero queues\n"); return NULL; } #ifdef CONFIG_SYSFS if (rxqs < 1) { pr_err("alloc_netdev: Unable to allocate device with zero RX queues\n"); return NULL; } #endif alloc_size = sizeof(struct net_device); if (sizeof_priv) { /* ensure 32-byte alignment of private area */ alloc_size = ALIGN(alloc_size, NETDEV_ALIGN); alloc_size += sizeof_priv; } /* ensure 32-byte alignment of whole construct */ alloc_size += NETDEV_ALIGN - 1; p = kzalloc(alloc_size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT); if (!p) p = vzalloc(alloc_size); if (!p) return NULL; dev = PTR_ALIGN(p, NETDEV_ALIGN); dev->padded = (char *)dev - (char *)p; dev->pcpu_refcnt = alloc_percpu(int); if (!dev->pcpu_refcnt) goto free_dev; if (dev_addr_init(dev)) goto free_pcpu; dev_mc_init(dev); dev_uc_init(dev); dev_net_set(dev, &init_net); dev->gso_max_size = GSO_MAX_SIZE; dev->gso_max_segs = GSO_MAX_SEGS; dev->gso_min_segs = 0; INIT_LIST_HEAD(&dev->napi_list); INIT_LIST_HEAD(&dev->unreg_list); INIT_LIST_HEAD(&dev->close_list); INIT_LIST_HEAD(&dev->link_watch_list); INIT_LIST_HEAD(&dev->adj_list.upper); INIT_LIST_HEAD(&dev->adj_list.lower); INIT_LIST_HEAD(&dev->all_adj_list.upper); INIT_LIST_HEAD(&dev->all_adj_list.lower); INIT_LIST_HEAD(&dev->ptype_all); INIT_LIST_HEAD(&dev->ptype_specific); dev->priv_flags = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM; setup(dev); dev->num_tx_queues = txqs; dev->real_num_tx_queues = txqs; if (netif_alloc_netdev_queues(dev)) goto free_all; #ifdef CONFIG_SYSFS dev->num_rx_queues = rxqs; dev->real_num_rx_queues = rxqs; if (netif_alloc_rx_queues(dev)) goto free_all; #endif strcpy(dev->name, name); dev->name_assign_type = name_assign_type; dev->group = INIT_NETDEV_GROUP; if (!dev->ethtool_ops) dev->ethtool_ops = &default_ethtool_ops; return dev; free_all: free_netdev(dev); return NULL; free_pcpu: free_percpu(dev->pcpu_refcnt); free_dev: netdev_freemem(dev); return NULL; }
alloc_netdev_mqs( ) 函数生成一个 net_device 结构体，对其成员赋值并返回该结构体的指针。第一个参数为设备私有成员大小，第二个参数为设备名，第三个参数为设备名称来源， 第四个参数为 net_device 的 setup( ) 函数指针，第五、六个参数为要分配的发送和接收子队列的数量。
setup( ) 接收的参数也为 struct net_device 指针，用于预置 net_device 成员的值。
free_netdev( ) 完成与 alloc_netdev( ) 和 alloc_etherdev( ) 函数相反的功能，即释放 net_device 结构体的函数：
/** * free_netdev - free network device * @dev: device * * This function does the last stage of destroying an allocated device * interface. The reference to the device object is released. * If this is the last reference then it will be freed. */ void free_netdev(struct net_device *dev) { struct napi_struct *p, *n; release_net(dev_net(dev)); netif_free_tx_queues(dev); #ifdef CONFIG_SYSFS kvfree(dev->_rx); #endif kfree(rcu_dereference_protected(dev->ingress_queue, 1)); /* Flush device addresses */ dev_addr_flush(dev); list_for_each_entry_safe(p, n, &dev->napi_list, dev_list) netif_napi_del(p); free_percpu(dev->pcpu_refcnt); dev->pcpu_refcnt = NULL; /* Compatibility with error handling in drivers */ if (dev->reg_state == NETREG_UNINITIALIZED) { netdev_freemem(dev); return; } BUG_ON(dev->reg_state != NETREG_UNREGISTERED); dev->reg_state = NETREG_RELEASED; /* will free via device release */ put_device(&dev->dev); }
net_device 结构体的分配 和 网络设备驱动的注册 需在网络设备驱动程序初始化时进行，而 net_device 结构体的释放 和 网络设备驱动的注销 在设备或驱动被移除的时候执行，如下所示：
/* * 网络设备驱动程序的注册和注销 * */ static int xxx_register(void) { ``` /* 分配 net_device 结构体并对其成员赋值 */ xxx_dev = alloc_netdev(sizeof(struct xxx_priv), "sn%d", xxx_init); if (xxx_dev == NULL) ``` /* 分配 net_device 失败 */ /* 注册 net_device 结构体 */ if ((result = register_netdev(xxx_dev))) ``` } static void xxx_unregister(void) { ``` /* 注销 net_device 结构体 */ unregister_netdev(xxx_dev); /* 释放 net_device 结构体 */ free_netdev(xxx_dev); }