Android WIFI 框架分析

一、Android WIFI模块初始化

上文Android讲到在SystemServer中实例化了ConnectivityService，接着的便是WIFI初始化：
frameworks/base/services/java/com/android/server/ConnectivityService.java
ConnectivityService 的构造函数会创建WifiService，

if (DBG) Log.v(TAG, "Starting Wifi Service.");
      WifiStateTracker wst = new WifiStateTracker(context, mHandler);
      WifiService wifiService = new WifiService(context, wst);
      ServiceManager.addService(Context.WIFI_SERVICE, wifiService);

WifiStateTracker 会创建WifiMonitor 接收来自底层的事件，WifiService 和WifiMonitor 是整个模块的核心。WifiService 负责启动关闭wpa_supplicant、启动关闭WifiMonitor 监视线程和把命令下发给wpa_supplicant，而WifiMonitor 则负责从wpa_supplicant 接收事件通知。
具体流程图如下：

二、WIFI模块启动

WirelessSettings 在初始化的时候配置了由WifiEnabler 来处理Wifi 按钮 WirelessSettings 在初始化的时候配置了由WifiEnabler 来处理Wifi 按钮

Packages\apps\settings\src\com\android\settings\WirelessSettings.java
protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.wireless_settings);
        initToggles();
        mAirplaneModePreference = (CheckBoxPreference) findPreference(KEY_TOGGLE_AIRPLANE);
    }
private void initToggles() {
    …………
    mWifiEnabler = new WifiEnabler(
                this, (WifiManager) getSystemService(WIFI_SERVICE),
                (CheckBoxPreference) wifiPreference);
…………
}

当用户按下Wifi 按钮后，Android 会调用WifiEnabler 的onPreferenceChange，再由WifiEnabler调用WifiManager 的setWifiEnabled 接口函数，通过AIDL，实际调用的是WifiService 的setWifiEnabled 函数，WifiService 接着向自身发送一条MESSAGE_ENABLE_WIFI 消息，在处理该消息的代码中做真正的使能工作：
首先装载WIFI 内核模块（该模块的位置硬编码为"/system/lib/modules/libertas_sdio.ko" ），
然后启动wpa_supplicant （ 配置文件硬编码为"/data/misc/wifi/wpa_supplicant.conf"），再通过WifiStateTracker 来启动WifiMonitor 中的监视线程。
WifiEnabler.java

public boolean onPreferenceChange(Preference preference, Object value) {
        // Turn on/off Wi-Fi
        setWifiEnabled((Boolean) value);        
    }
private void setWifiEnabled(final boolean enable) {
        if (!mWifiManager.setWifiEnabled(enable)) {
        }
    }  

WifiManager.java
 public boolean setWifiEnabled(boolean enabled) {
            return mService.setWifiEnabled(enabled);
    }
 IWifiManager mService;
 interface IWifiManager{
    …………
    boolean startScan(boolean forceActive);
    boolean setWifiEnabled(boolean enable);
 …………
 }

IWifiManger.aidl编译后生成了IWifiManger.java，并生成IWifiManger.Stub（服务器端抽象类）和IWifiManger.Stub.Proxy（客户端代理实现类）。WifiService通过继承IWifiManger.Stub实现，而客户端通过getService()函数获取IWifiManger.Stub.Proxy（即Service的代理类），将其作为参数传递给WifiManger，供其与WifiService通信时使用。
WifiService.java

public boolean setWifiEnabled(boolean enable) {
…………
sendEnableMessage(enable, true, Binder.getCallingUid());
…………
}
private void sendEnableMessage(boolean enable, boolean persist, int uid) {
Message msg = Message.obtain(mWifiHandler,
(enable ? MESSAGE_ENABLE_WIFI : MESSAGE_DISABLE_WIFI),
(persist ? 1 : 0), uid);
msg.sendToTarget();
}
public void handleMessage(Message msg) {
switch (msg.what) {
case MESSAGE_ENABLE_WIFI:
setWifiEnabledBlocking(true, msg.arg1 == 1, msg.arg2);
case MESSAGE_START_WIFI:
mWifiStateTracker.restart();
case MESSAGE_DISABLE_WIFI:
setWifiEnabledBlocking(false, msg.arg1 == 1, msg.arg2);
case MESSAGE_STOP_WIFI:
mWifiStateTracker.disconnectAndStop();
break;
}
}
}
private boolean setWifiEnabledBlocking(boolean enable, boolean persist, int uid) {
if (enable) {
if (!WifiNative.loadDriver()) {
setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);
}
if (!WifiNative.startSupplicant()) {
WifiNative.unloadDriver();
setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);
}
registerForBroadcasts();
mWifiStateTracker.startEventLoop();
} else {
………………
}
// Success!
setWifiEnabledState(eventualWifiState, uid);
}
private void setWifiEnabledState(int wifiState, int uid) {
// Broadcast
final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);
}
JNI android_net_wifi_wifi.cpp
// ----------------------------------------------------------------------------

public boolean setWifiEnabled(boolean enable) {
…………
sendEnableMessage(enable, true, Binder.getCallingUid());
    …………
}
private void sendEnableMessage(boolean enable, boolean persist, int uid) {
        Message msg = Message.obtain(mWifiHandler,
                                     (enable ? MESSAGE_ENABLE_WIFI : MESSAGE_DISABLE_WIFI),
                                     (persist ? 1 : 0), uid);
        msg.sendToTarget();
    }
public void handleMessage(Message msg) {
            switch (msg.what) {
                case MESSAGE_ENABLE_WIFI:
                    setWifiEnabledBlocking(true, msg.arg1 == 1, msg.arg2);
                case MESSAGE_START_WIFI:                  
                    mWifiStateTracker.restart(); 
               case MESSAGE_DISABLE_WIFI:                 
                    setWifiEnabledBlocking(false, msg.arg1 == 1, msg.arg2);              
                case MESSAGE_STOP_WIFI:
                    mWifiStateTracker.disconnectAndStop();
                    break;
            }
        }
    }
private boolean setWifiEnabledBlocking(boolean enable, boolean persist, int uid) {
if (enable) {
            if (!WifiNative.loadDriver()) {               
                setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);
            }
            if (!WifiNative.startSupplicant()) {
                WifiNative.unloadDriver();             
                setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);
            }
            registerForBroadcasts();
            mWifiStateTracker.startEventLoop();
        } else {
  ………………
  }
    // Success!       
        setWifiEnabledState(eventualWifiState, uid);
}
private void setWifiEnabledState(int wifiState, int uid) {
 // Broadcast
        final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);
}
 JNI android_net_wifi_wifi.cpp
// ----------------------------------------------------------------------------

/*
* JNI registration.
*/
static JNINativeMethod gWifiMethods[] = {
    /* name, signature, funcPtr */
    { "loadDriver", "()Z",  (void *)android_net_wifi_loadDriver },   
    { "startSupplicant", "()Z",  (void *)android_net_wifi_startSupplicant },   
    { "scanResultsCommand", "()Ljava/lang/String;", (void*) android_net_wifi_scanResultsCommand },      
    { "reconnectCommand", "()Z",  (void *)android_net_wifi_reconnectCommand },  
    { "scanCommand", "(Z)Z", (void*) android_net_wifi_scanCommand },
}

/*
* JNI registration.
*/
static JNINativeMethod gWifiMethods[] = {
/* name, signature, funcPtr */
{ "loadDriver", "()Z", (void *)android_net_wifi_loadDriver },
{ "startSupplicant", "()Z", (void *)android_net_wifi_startSupplicant },
{ "scanResultsCommand", "()Ljava/lang/String;", (void*) android_net_wifi_scanResultsCommand },
{ "reconnectCommand", "()Z", (void *)android_net_wifi_reconnectCommand },
{ "scanCommand", "(Z)Z", (void*) android_net_wifi_scanCommand },
}
1）static jboolean

static jboolean android_net_wifi_loadDriver(JNIEnv* env, jobject clazz)
{
    return (jboolean)(::wifi_load_driver() == 0);
}

android_net_wifi_loadDriver(JNIEnv* env, jobject clazz)
{
return (jboolean)(::wifi_load_driver() == 0);
}
2）static jboolean android_net_wifi_startSupplicant(JNIEnv* env, jobject clazz)

static jboolean android_net_wifi_startSupplicant(JNIEnv* env, jobject clazz)
{
    return (jboolean)(::wifi_start_supplicant() == 0);
}

{
return (jboolean)(::wifi_start_supplicant() == 0);
}
3）

WifiStateTracker.java
mWifiStateTracker.startEventLoop();
public void startEventLoop() {
        mWifiMonitor.startMonitoring();
    }
//WifiMonitor.java
public void startMonitoring() {
        new MonitorThread().start();
    }

WifiStateTracker.java
mWifiStateTracker.startEventLoop();
public void startEventLoop() {
mWifiMonitor.startMonitoring();
}
//WifiMonitor.java
public void startMonitoring() {
new MonitorThread().start();
}

当使能成功后，会广播发送WIFI_STATE_CHANGED_ACTION 这个Intent 通知外界WIFI已经成功使能了。// Success!后广播的。

上文讲到WIFI的启动流程，当然接着便扫描热点（AP），然后显示扫描到的AP、配置AP（填写IP地址等信息）、连接AP、获取IP地址、最后就是想要的上网咯！

一、扫描热点（AP）

上文启动WIFI成功后：// Success!

        setWifiEnabledState(eventualWifiState, uid);
private void setWifiEnabledState(int wifiState, int uid) {
 // Broadcast
        final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);
}

setWifiEnabledState(eventualWifiState, uid);
private void setWifiEnabledState(int wifiState, int uid) {
// Broadcast
final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);
}

当使能成功后，会广播发送WIFI_STATE_CHANGED_ACTION 这个Intent 通知外界WIFI已经成功使能了。WifiLayer 创建的时候就会向Android 注册接收WIFI_STATE_CHANGED_ACTION，因此它会收到该Intent，从而开始扫描。

WifiSetting.java:

protected void onCreate(Bundle savedInstanceState) {
    mWifiLayer.onCreate();
}

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

WifiLayer.java:
public void onCreate() {
        mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
       
        mIntentFilter = new IntentFilter();
        mIntentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
        mIntentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        mIntentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);        
    }
public void onResume() {
        mContext.registerReceiver(mReceiver, mIntentFilter);       
        if (isWifiEnabled()) {
            // Kick start the continual scan
            queueContinuousScan();
        }
    }

protected void onCreate(Bundle savedInstanceState) {
mWifiLayer.onCreate();
}

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

WifiLayer.java:
public void onCreate() {
mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);

mIntentFilter = new IntentFilter();
mIntentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
mIntentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
mIntentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);
}
public void onResume() {
mContext.registerReceiver(mReceiver, mIntentFilter);
if (isWifiEnabled()) {
// Kick start the continual scan
queueContinuousScan();
}
}

以上就是WifiLayer.java注册接收的部分事件。接收部分事件处理有：

private BroadcastReceiver mReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
                handleNetworkStateChanged(
                        (NetworkInfo) intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO),
                        intent.getStringExtra(WifiManager.EXTRA_BSSID));
            } else if (action.equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {
                handleScanResultsAvailable();
            } ……

           else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) {
                handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                        WifiManager.WIFI_STATE_UNKNOWN));
            }           
        }
    };

private BroadcastReceiver mReceiver = new BroadcastReceiver() {
private BroadcastReceiver mReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
handleNetworkStateChanged(
(NetworkInfo) intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO),
intent.getStringExtra(WifiManager.EXTRA_BSSID));
} else if (action.equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {
handleScanResultsAvailable();
}……

else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) {
handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
WifiManager.WIFI_STATE_UNKNOWN));
}
}
};

从可接受的事件看，当WIFI_STATE_CHANGED_ACTION时，对应的处理函数有：

<pre class="cpp" name="code">handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                        WifiManager.WIFI_STATE_UNKNOWN));

private void handleWifiStateChanged(int wifiState) {
   attemptScan();
   …………
 }

public void attemptScan() {
  if (!mWifiManager.startScanActive()) {
            postAttemptScan();
        }
}

WifiManager.java:
public boolean startScanActive() {
 return mService.startScan(true);
}

-------AIDL-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

WifiService.java:
public boolean startScan(boolean forceActive) {
 …………
 return WifiNative.scanCommand(forceActive);
}

---------JNI---------------------------------------------------------------------------------------------------------------------------------------------------------------------------

android_net_wifi_wifi.cpp:
{ "scanCommand", "(Z)Z", (void*) android_net_wifi_scanCommand },
static jboolean android_net_wifi_scanCommand(JNIEnv* env, jobject clazz, jboolean forceActive)
{
 …………
 result = doBooleanCommand("SCAN", "OK");
}
static jboolean doBooleanCommand(const char *cmd, const char *expect)
{
 if (doCommand(cmd, reply, sizeof(reply)) != 0) {
        return (jboolean)JNI_FALSE;
    }
}
static int doCommand(const char *cmd, char *replybuf, int replybuflen)
{
 if (::wifi_command(cmd, replybuf, &reply_len) != 0)
        return -1;
 …………
}
<p>-------<strong>HAL</strong>------------------------------------------------------------------------------------------------------------------------------------------------------------------------</p><strong>wifi.c:</strong>
int wifi_command(const char *command, char *reply, size_t *reply_len)
{
 return <strong>wifi_send_command</strong>(ctrl_conn, command, reply, reply_len);
}
int wifi_send_command(struct wpa_ctrl *ctrl, const char *cmd, char *reply, size_t *reply_len)
{
ret = <strong>wpa_ctrl_request</strong>(ctrl, cmd, strlen(cmd), reply, reply_len, NULL);
…………
}
</pre>

wpa_ctrl.c:int wpa_ctrl_request()在wpa_ctrl.c中其实就是执行SCAN命令。

二、显示扫描的AP

当扫描成后，WifiMonitor 中的MonitorThread 会被执行来出来这个事件：

  void handleEvent(int event, String remainder) {
            switch (event) {   
                case SCAN_RESULTS:
                    mWifiStateTracker.notifyScanResultsAvailable();
->sendEmptyMessage(EVENT_SCAN_RESULTS_AVAILABLE);
    break;
}

WifiStateTracker.java

public void handleMessage(Message msg) {              
  switch (msg.what) {
               case EVENT_SCAN_RESULTS_AVAILABLE:
                        if (ActivityManagerNative.isSystemReady()) {
                                mContext.sendBroadcast(new   Intent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));       
                     }
}

WifiLayer注册接收SCAN_RESULTS_AVAILABLE_ACTION这个Intent：

private BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
 else if (action.equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION))
       {             

             handleScanResultsAvailable();     

     }
 handleScanResultsAvailable();
       -> list = mWifiManager.getScanResults();
        -> mCallback.onAccessPointSetChanged(ap, true);

handleScanResultsAvailable()中首先会去拿到SCAN的结果（最终是往wpa_supplicant中发送SCAN_RESULT命令并读取返回值来实现的），对每一个扫描返回的AP，WifiLayer会回调WifiSetting的onAccessPointSetChanged函数，从而最终把该AP加到GUI显示列表中。

三、配置AP

当用户在 WifiSettings 界面上选择了一个AP 后，会显示配置AP 参数的一个对话框：

public boolean onPreferenceTreeClick()
          ->showAccessPointDialog(state, AccessPointDialog.MODE_INFO);
                    ->AccessPointDialog dialog   =
                                            new AccessPointDialog(this,    mWifiLayer);
                                     showDialog(dialog);

当用户在AccessPointDialog中选择好加密方式和输入密钥之后，再点击连接按钮，Android就会去连接这个AP。

四、连接AP

在AccessPointDialog.java中点击连接后会执行：

public void onClick(DialogInterface dialog, int which) {
           handleConnect();
   -> mWifiLayer.connectToNetwork(mState);
    ->  // Need WifiConfiguration for the AP
                               WifiConfiguration config = findConfiguredNetwork(state);
                                config = addConfiguration(state, 0);
                                managerEnableNetwork(state, false)
          ->mWifiManager.enableNetwork()
                                         ->mService.enalbeNetwork()
                     ->WifiNative.enableNetworkCommand()  

接下去就JNI { "enableNetworkCommand", "(IZ)Z", (void*)android_net_wifi_enableNetworkCommand},最终就是向wpa_supplicant发送连接命令
五、获取IP地址

当wpa_supplicant成功连接上AP之后,它会向控制通道发送事件通知连接上AP了,从而wifi_wait_for_event函数会接收到该事件，由此WifiMonitor中的MonitorThread会被执行来出来这个事件:

void handleEvent(int event, String remainder) {
       switch (event) {   
              case CONNECTED:
                  handleNetworkStateChange();
                  -> mWifiStateTracker.notifyStateChange(newState, BSSID, networkId);
  ->msg.sendToTarget();
                  break;
}

WifiStateTracker.java

public void handleMessage(Message msg) {         
  switch (msg.what) {              
            case EVENT_NETWORK_STATE_CHANGED:
                       sendNetworkStateChangeBroadcast(mWifiInfo.getBSSID());      
                     }
}

WifiStateTracker中注册的对Wifi相关数据库的观察者if(changed) 则启动：

 private void configureInterface()
   ->  mDhcpTarget.sendEmptyMessage();
 private class DhcpHandler extends Handler
          handleMessage()
              ->switch (msg.what) {
                      case EVENT_DHCP_START:
                              Target.sendEmptyMessage(event);

DhcpHandler会发送EVENT_DHCP_START消息启动DHCP去获取IP地址，当DHCP拿到IP地址之后，会发送EVENT_INTERFACE_CONFIGURATION_SUCCEEDED的消息，然后WifiStateTacker中的handleMessage会处理这样的消息

case EVENT_INTERFACE_CONFIGURATION_SUCCEEDED:
     sendNetworkStateChangeBroadcast(mWifiInfo.getBSSID());
            ->  Intent intent = new Intent(WifiManager.NETWORK_STATE_CHANGED_ACTION);
            -> mContext.sendStickyBroadcast(intent);

这次带上完整的IP地址信息。WifiLayer中注册了此Intent的接受者，会调用handleNetworkStateChanged进行处理。最后就可以自由的上网了