03_wireless网络系统

linux无线网络系统

Cfg80211

下面是网络的对cfg80211的描述： cfg80211 is the Linux 802.11 configuration API. cfg80211 replaces Wireless-Extensions. nl80211 is used to configure a cfg80211 device and is used for kernel <–> userspace communication. Wireless extensions is now in maintenance mode, no new features will be added to it, we'll only fix bugs for it. cfg80211 is now feature-par complete with wireless-extensions, it actually has a lot more features that are simply not available and will never be available through wireless extensions. When implementing a cfg80211 driver wireless extensions support is still provided automatically for you through cfg80211 through CONFIG_CFG80211_WEXT. Distributions no longer needing wireless extensions can remove this and are encouraged to do so. cfg80211 also provides full regulatory support, this is done through wireless-regdb and the usage of CRDA. All new Linux wireless drivers should be written targeting either cfg80211 for fullmac devices or mac80211 for softmac devices. 参考：http://wireless.kernel.org/en/developers/Documentation/cfg80211

关键数据结构： 头文件：

Cfg80211.h (include\\net)：cfg80211 is the configuration API for 802.11 devices in Linux. It bridges userspace and drivers, and offers some utility functionality associated with 802.11 Core.h (net\\wireless)：Wireless configuration interface internals.

Nl80211.h (include\\linux)：定义的netlink接口函数（接收netlink命令，发送netlink事件） Regulatory.h (include\\net)：regulatory support structures。

数据结构：

struct cfg80211_registered_device ：设备注册的时用，包含注册的struct cfg80211_ops，供上层应用通过nl80211_ops供上层应用调用.包含了struct wiphy结构实体。

struct net_device ：The DEVICE structure,网络设备结构，网卡名，包含了共享内核资源，中断号，网卡操作函数接口：（struct net_device_ops *netdev_ops，struct ethtool_ops *ethtool_ops，），设备地址，广播地址，net__namespace, sys文件结构，协议相关设备（struct wireless_dev，struct in_device，struct inet6_dev）。等等

struct wireless_dev ：wireless device state：包含struct wiphy，接口类型（AP.STA,AD-HOC,P2P-GO, P2P-GC,），网络设备指针（struct net_device*），SME状态，ssid,

支持的信道类型（enum nl80211_channel_type）， cfg80211连接状态（struct cfg80211_conn），

struct wiphy：wireless hardware description。定义在Cfg80211.h (include\\net)，

struct cfg80211_ops mac80211_config_ops：无线设备驱动需要实现的函数功能，在cfg80211驱动层通过struct genl_ops nl80211_ops[]供调用。 struct genl_ops nl80211_ops[]：通过genl_register_family_with_ops函数注册的netlink接口操作数组。接收wpa_supplicant下发的命令。

struct ieee80211_ops:具体芯片驱动实现的功能，如TI驱动为：struct ieee80211_ops wl1271_ops。

Cfg80211注册的class

参考代码：

static struct device_attribute ieee80211_dev_attrs[] = { __ATTR_RO(index), __ATTR_RO(macaddress), __ATTR_RO(address_mask), __ATTR_RO(addresses), __ATTR_RO(name), {} };

struct class ieee80211_class = { .name = \ .owner = THIS_MODULE, .dev_release = wiphy_dev_release, .dev_attrs = ieee80211_dev_attrs, #ifdef CONFIG_HOTPLUG .dev_uevent = wiphy_uevent, #endif .suspend = wiphy_suspend, .resume = wiphy_resume, .ns_type = &net_ns_type_operations, .namespace = wiphy_namespace, };

int wiphy_sysfs_init(void) { return class_register(&ieee80211_class); }

注册class：是为了绑定无线网络设备与cfg80211关系。参考sysfs中class的作用：根据device类型来区分。

struct class ieee80211_class的属性在具体的设备中生效

这里生效的是底层调用了struct wiphy *wiphy_new()函数来实现的。 #define PHY_NAME \

struct wiphy *wiphy_new(const struct cfg80211_ops *ops, int sizeof_priv) { static int wiphy_counter;

}

rdev = kzalloc(alloc_size, GFP_KERNEL);

dev_set_name(&rdev->wiphy.dev, PHY_NAME \device_initialize(&rdev->wiphy.dev);

rdev->wiphy.dev.class = &ieee80211_class; rdev->wiphy.dev.platform_data = rdev; return &rdev->wiphy;

而wiphy_new可以在mac80211模块(soft MAC)或者无线网卡驱动(full MAC)调用。 下面分别以博通芯片为例说明：soft MAC和full MAC的调用过程。

Cfg80211通信接口

1. struct cfg80211_ops ：backend description for wireless configuration。

通过struct wiphy *wiphy_new(const struct cfg80211_ops *ops, int sizeof_priv)来注册。一般是通过mac80211(soft MAC)或者是设备驱动直接调用来注册的函数接口。 2. struct class ieee80211_class = { .name = \ … .dev_attrs = ieee80211_dev_attrs, .ns_type = &net_ns_type_operations, .namespace = wiphy_namespace, };

Sysfs文件系统，组织设备类的通用接口函数。为用户空间提供接口。

3. static struct genl_ops nl80211_ops[] ：用与接收用户层的netlink command，对应

wpa_supplicant drivers_nl80211.c中的函数接口。

4. static int cfg80211_netdev_notifier_call(struct notifier_block *nb, unsigned long state, void

*ndev)：用于监听底层上报的event

5. struct notifier_block nl80211_netlink_notifier:接收底层

6. int genlmsg_unicast(struct net *net, struct sk_buff *skb, u32 pid)：发送nlmsg给上层应用 int genlmsg_multicast_netns(struct net *net, struct sk_buff *skb, u32 pid, unsigned int group, gfp_t flags) 7.

数据帧的传输（这里包括控制帧，管理帧，数据帧）

发送：probe request, probe response;authentication request, authentication response; association request, association response;

实际发送的帧：deauthenticate；disassociate；authenticate；associate；数据帧 接收的帧：

Regulatory domain:

参考：http://wireless.kernel.org/en/developers/Regulatory Regulatory.txt (documentation\\networking)

目前支持两种方式：

1. Keeping regulatory domains in userspace using the CRDA package provided with their distribution，Essentially the kernel will send a udev event when it knows it needs a new regulatory domain. A udev rule can be put in place to trigger crda to send the respective regulatory domain for a specific ISO/IEC 3166 alpha2。Userspace gets a regulatory domain in the kernel by having a userspace agent build it and send it via nl80211.

2. Statically compiled regulatory database To account for this situation, a configuration option has been provided (i.e. CONFIG_CFG80211_INTERNAL_REGDB). With this option enabled, the wireless database information contained in net/wireless/db.txt is used to generate a data structure encoded in net/wireless/regdb.c.

Essentially the kernel will send a udev event when it knows it needs a new regulatory domain.

CRDA

CRDA是一个daemon程序（后台守护进程）:根据平台的COUNTRY环境变量，解析regulatory.bin，获取regulatory domain信息，从而发送给驱动。 参考文档：http://wireless.kernel.org/en/developers/Regulatory/CRDA CRDA源代码下载路径：http://github.com/mcgrof/crda 或者http://wireless.kernel.org/download/crda/

由下图可知：CRDA是一个daemon程序（后台守护进程）。会解析regulatory.bin文件。 流程如下：

1. 当内核需要用新的regulatory domain时，会发送一个udev event

2. 上层接收到udev event后，就会触发crda发送相应的regulatory domain 3. CRDA daemon通过getenv函数获取“COUNTRY”环境变量的具体值

4. 解析regulatory.bin文件，搜索与从“COUNTRY”环境变量中的国家信息匹配的值，从而

获取regulatory domain结构的信息。

5. 通过netlink机制发送给nl80211(即cfg80211模块) 注：步骤3至步骤5是CRDA daemon执行的过程 关键技术点:

1. python脚本生成regulatory.bin 2. 解析regulatory.bin

3. netlink发送封装好的信息给cfg80211 4. 数字签名：

struct ieee80211_reg_rule { struct ieee80211_freq_range freq_range; struct ieee80211_power_rule power_rule; uint32_t flags; };

struct ieee80211_regdomain { uint32_t n_reg_rules; char alpha2[2]; uint8_t dfs_region; struct ieee80211_reg_rule reg_rules[]; };

下面是一个例子：

struct ieee80211_regdomain mydriver_jp_regdom = { .n_reg_rules = 3, .alpha2 = \ //.alpha2 = \ .reg_rules = { /* IEEE 802.11b/g, channels 1..14 */ REG_RULE(2412-20, 2484+20, 40, 6, 20, 0), /* IEEE 802.11a, channels 34..48 */ REG_RULE(5170-20, 5240+20, 40, 6, 20, NL80211_RRF_PASSIVE_SCAN), /* IEEE 802.11a, channels 52..64 */ REG_RULE(5260-20, 5320+20, 40, 6, 20, NL80211_RRF_NO_IBSS | NL80211_RRF_DFS),

} };