android WIFI 分析

目录(?)[+]

1. 系统架构
   1. WifiService
   2. WifiMonitor
   3. wpa_supplicant
   4. Wifi驱动模块
   5. Wifi电源管理模块
   6. Wifi工作步骤
   7. Wifi模块代码
2. WifiService和wpa_supplicant启动流程
   1. 21 状态变化
3. 生产时自动打开Wifi

1. 系统架构

        Android WiFi系统引入了wpa_supplicant，它的整个WiFi系统以wpa_supplicant为核心来定义上层用户接口和下层驱动接口。整个WiFi系统架构如下图所示：

   一切尽在上图中，下面将对每部分进行详细分析。

1.1 WifiService   

     由SystemServer启动的时候生成的ConnecttivityService创建，负责启动关闭wpa_supplicant,启动和关闭WifiMonitor线程，把命令下发给wpa_supplicant以及更新WIFI的状态。

     处理其它模块通过IWifiManager接口发送过来的远端WiFi操作。

1.2 WifiMonitor

    负责从wpa_supplicant接收事件通知。

1.3 wpa_supplicant

  1) 读取配置文件
  2) 初始化配置参数，驱动函数
  3) 让驱动scan当前所有的bssid
  4) 检查扫描的参数是否和用户设置的相符
  5) 如果相符，通知驱动进行权限和认证操作
  6) 连上AP

1.4 Wifi驱动模块

     厂商提供的source,主要进行load firware和kernel的wireless进行通信

1.5 Wifi电源管理模块

     主要控制硬件的GPIO和上下电，让CPU和Wifi模组之间通过sdio接口或USB接口通信

1.6 Wifi工作步骤

  1) Wifi启动
  2) 开始扫描
  3) 显示扫描的AP
  4) 配置AP
  5) 连接AP
  6) 获取IP地址
  7) 上网

1.7 Wifi模块代码

   1) Wifi Settings应用程序
       packages/apps/Settings/src/com/android/settings/wifi

   2) Wifi Framework
       frameworks/base/wifi/java/android/net/wifi (UI通过android.net.wifi package
发送命令给wifi.c)

       frameworks/base/core/java/android/net(更高一级的网络管理)
       frameworks/base/services/java/com/android/server

   3) Wifi JNI
       frameworks/base/core/jni/android_net_wifi_Wifi.cpp
   4) Wifi Hardware (wifi管理库)
       hardware/libhardware_legacy/wifi/wifi.c

   5) wpa_supplicant(wifi  tool)

       external/wpa_supplicant8
       (1) wpa_client (生成库libwpaclient.so)

            external/wpa_supplicant_8/wpa_supplicant/src/common/wpa_ctrl.c

       (2) wpa_server (生成守护进程wpa_supplicant)

            external/wpa_supplicant_8/wpa_supplicant/main.c
   6) Wifi kernel
       net/wireless     drivers/wlan_xxx       arch/arm/mach-xxx/wlan_pm.c

2. WifiService和wpa_supplicant启动流程

     WifiService和wpa_supplicant启动流程如下图所示：

 2.1 状态变化

• 加载wifi驱动的状态变化流程如下：

初始状态：mInitialState

                         |
          mDriverUnloadedState

                         |
      mWaitForP2pDisableState

                         |
mDriverLoadingState(其enter中调用WifiNative.loadDriver)

 

• 启动wpa_supplicant的状态变化如下：
   在DriverLoadedState状态的processMessage中调用WifiNative.startSupplicant

3. 生产时自动打开Wifi

在生产时， 默认Wifi是关闭的，如果需要默认打开，可修改wifiservice.java中的如下代码： 

 

/**
 * Check if Wi-Fi needs to be enabled and start
 * if needed
 *
 * This function is used only at boot time
 */
public void checkAndStartWifi() {
    mAirplaneModeOn.set(isAirplaneModeOn());
    mPersistWifiState.set(getPersistedWifiState());
    /* Start if Wi-Fi should be enabled or the saved state indicates Wi-Fi was on */
    boolean wifiEnabled = shouldWifiBeEnabled() || testAndClearWifiSavedState();
    Slog.i(TAG, "WifiService starting up with Wi-Fi " +
            (wifiEnabled ? "enabled" : "disabled"));
    setWifiEnabled(wifiEnabled); //强制设置为true

    mWifiWatchdogStateMachine = WifiWatchdogStateMachine.
           makeWifiWatchdogStateMachine(mContext);

}

/**
 * Check if Wi-Fi needs to be enabled and start
 * if needed
 *
 * This function is used only at boot time
 */
public void checkAndStartWifi() {
    mAirplaneModeOn.set(isAirplaneModeOn());
    mPersistWifiState.set(getPersistedWifiState());
    /* Start if Wi-Fi should be enabled or the saved state indicates Wi-Fi was on */
    boolean wifiEnabled = shouldWifiBeEnabled() || testAndClearWifiSavedState();
    Slog.i(TAG, "WifiService starting up with Wi-Fi " +
            (wifiEnabled ? "enabled" : "disabled"));
    setWifiEnabled(wifiEnabled); //强制设置为true

    mWifiWatchdogStateMachine = WifiWatchdogStateMachine.
           makeWifiWatchdogStateMachine(mContext);