Android wifi Enable之后扫描流程

流程框架图

通常我们在设备开启wifi之后，等会会自动扫描出周围的热点。

下面看下自动扫描周围热点的流程

代码流程

1. ClientModeManager.ClientModeStateMachine

• ClientModeStateMachine 由CMD_START 转换到StartedState
• StartedState 状态机，在更新wifiState时，发送广播 WifiManager.WIFI_STATE_CHANGED_ACTION ， 通知WifiTracker 开始进行Scan

frameworks/opt/net/wifi/service/java/com/android/server/wifi/ClientModeManager.java
public boolean processMessage(Message message) {
    .... 
    mClientInterfaceName = mWifiNative.setupInterfaceForClientMode
    ....
    transitionTo(mStartedState); //跳转到 StartedState
}

private class StartedState extends State {
  ...
   private void onUpChanged(boolean isUp) {
   .... 
   sendScanAvailableBroadcast(true);
    mWifiStateMachine.setOperationalMode(WifiStateMachine.CONNECT_MODE,
    // 发 WifiManager.WIFI_STATE_CHANGED_ACTION 广播通知 wifiTracker 启动startScan
     updateWifiState(WifiManager.WIFI_STATE_ENABLED,WifiManager.WIFI_STATE_ENABLING); 
   }
}

2. WifiTracker.BroadcastReceiver --> wifiManager.StartScan

• WifiTracker 广播监听到WifiManager.WIFI_STATE_CHANGED_ACTION ，开启wifiManager.StartScan

frameworks/base/packages/SettingsLib/src/com/android/settingslib/wifi/WifiTracker.java
public void onReceive(Context context, Intent intent) {
	if (WifiManager.WIFI_STATE_CHANGED_ACTION.equals(action))
	{
	updateWifiState(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,WifiManager.WIFI_STATE_UNKNOWN));
}
}
private void updateWifiState(int state) {
	1. WifiManager.WIFI_STATE_ENABLED
		mScanner.resume();
	2.wifi 非enabled 则 mScanner.pause();
}
public void handleMessage(Message message) {
    .. 
    mWifiManager.startScan(); // 开启Wifi Scan 
}

3. wifiManager.StartScan --> WifiServiceImpl --> ScanRequestProxy.StartScan

• 获取mWifiScanner 实例
• 检查 调用者UID ， apk package 是否有权限进行Scan，如无则直接放回
• Create a worksource using the caller’s UID.
• Create the scan settings.
• 初始化Scan 的band 为DFS，是否Scan 隐藏的AP
• mWifiScanner 发起StartScan

frameworks/opt/net/wifi/service/java/com/android/server/wifi/ScanRequestProxy.java
public boolean startScan(int callingUid, String packageName){
	retrieveWifiScannerIfNecessary();
	...
	// Create a worksource using the caller's UID.
        WorkSource workSource = new WorkSource(callingUid);
	   // Create the scan settings.
        WifiScanner.ScanSettings settings = new WifiScanner.ScanSettings();
          // always do full scans
        settings.band = WifiScanner.WIFI_BAND_BOTH_WITH_DFS;
        settings.reportEvents = WifiScanner.REPORT_EVENT_AFTER_EACH_SCAN
                | WifiScanner.REPORT_EVENT_FULL_SCAN_RESULT;
	mWifiScanner.startScan(settings, new ScanRequestProxyScanListener(), workSource);
}

4. WifiScanner.startScan --> WifiScaningServiceImpl.ClientHandler.handleMessage

• 发送scan 请求[CMD_START_SINGLE_SCAN ] to WifiScaningServiceImpl 处理

frameworks/base/wifi/java/android/net/wifi/WifiScanner.java
public void startScan(ScanSettings settings, ScanListener listener, WorkSource workSource) {
	scanParams.putParcelable(SCAN_PARAMS_SCAN_SETTINGS_KEY, settings);
	scanParams.putParcelable(SCAN_PARAMS_WORK_SOURCE_KEY, workSource);
	mAsyncChannel.sendMessage(CMD_START_SINGLE_SCAN, 0, key, scanParams);
}

5. WifiScanner.startScan --> WifiScaningServiceImpl.ClientHandler.handleMessage

• 先进行有效Scan检查
• 当前正在Scanning，如为有效的(活)scaning，标志为ActiveScans，否则标志为PendingScans
• 当前非Scanning，标志为PendingScans，开启一次新的Scan – tryToStartNewScan()
• 非有效Scan，上报错误Failed

frameworks/opt/net/wifi/service/java/com/android/server/wifi/scanner/WifiScanningServiceImpl.java
 class DriverStartedState extends State {
 	case WifiScanner.CMD_START_SINGLE_SCAN:
 	    .... 一大堆code （其实就干了几件事情，见上面描述）
 	   ....
 	   tryToStartNewScan();
 }

6. WifiScaningServiceImpl.tryToStartNewScan – WifiNative.scan

• WifiScaningServiceImpl 到WifiScannerImpl
• WifiScannerImpl 再到WificondScannerImpl
• WificondScannerImpl最终到WifiNative ， 可见与Android N 相比，O、P 的Scan变化太大，但是其套路还是不变，就是上面的环节无论是如何地进行封装，最后还是给到WifiNative 来处理

frameworks/opt/net/wifi/service/java/com/android/server/wifi/scanner/WifiScanningServiceImpl.java
void tryToStartNewScan() {
	....
	mScannerImpl.startSingleScan(settings, this);
}

frameworks/opt/net/wifi/service/java/com/android/server/wifi/scanner/WifiScannerImpl.java
public abstract boolean startSingleScan(WifiNative.ScanSettings settings,WifiNative.ScanEventHandler eventHandler);

frameworks/opt/net/wifi/service/java/com/android/server/wifi/scanner/WificondScannerImpl.java
 public boolean startSingleScan(WifiNative.ScanSettings settings,    WifiNative.ScanEventHandler eventHandler) {
  ....
   freqs = allFreqs.getScanFreqs();
    success = mWifiNative.scan(mIfaceName, settings.scanType, freqs, hiddenNetworkSSIDSet);
 }

7. WifiNative.scan --> WificondControl

• WifiNative 转到 WificondControl
• WificondControl 通过binder 到wificond
• wificond 开始初步的scan 任务 （scannerImpl.scan）
• scannerImpl 传到scan_utils
• scan_utils 通过netlink 将 NL80211_CMD_TRIGGER_SCAN传递wpa_supplicant(driver_nl80211_event.c)
• driver_nl80211_event 将cmd下到wlan drv 里，开始了真正的干活 – scanning

frameworks/opt/net/wifi/service/java/com/android/server/wifi/WifiNative.java
public boolean scan( @NonNull String ifaceName, int scanType, Set freqs, Set hiddenNetworkSSIDs) {
mWificondControl.scan(ifaceName, scanType, freqs, hiddenNetworkSSIDs);
}

frameworks/opt/net/wifi/service/java/com/android/server/wifi/WificondControl.java
  public boolean scan(@NonNull String ifaceName, int scanType, Set freqs,Set hiddenNetworkSSIDs)
{
   ..  
   scannerImpl.scan(settings); 
}

system/connectivity/wificond/scanning/scanner_impl.cpp
Status ScannerImpl::scan(const SingleScanSettings& scan_settings, bool* out_success) {
	
	scan_utils_->Scan(interface_index_, request_random_mac, scan_type,ssids, freqs, &error_code)； // 
}
system/connectivity/wificond/scanning/scan_utils.cpp
bool ScanUtils::Scan(uint32_t interface_index,
                     bool request_random_mac,
                     int scan_type,
                     const vector>& ssids,
                     const vector& freqs,
                     int* error_code) {
  NL80211Packet trigger_scan(
      netlink_manager_->GetFamilyId(),
      NL80211_CMD_TRIGGER_SCAN,
      netlink_manager_->GetSequenceNumber(),
      getpid());
  
  if (scan_flags) {
    trigger_scan.AddAttribute(
        NL80211Attr(NL80211_ATTR_SCAN_FLAGS,
                              scan_flags));
  }
  // We are receiving an ERROR/ACK message instead of the actual
  // scan results here, so it is OK to expect a timely response because
  // kernel is supposed to send the ERROR/ACK back before the scan starts.
  vector> response;
  if (!netlink_manager_->SendMessageAndGetAckOrError(trigger_scan,
                                                     error_code)) {
    // Logging is done inside |SendMessageAndGetAckOrError|.
    return false;
  }
}

8. 扫描结果回传

• 具体与scan 执行流恰为逆向，可参见上面的整体框架图
• 这里简单说明下，当wlan drv 完成scan 之后
• 由 wificond 直接给到WificondControl，
• WificondControl.OnScanResultReady 上报 WifiMonitor
• WifiMonitor -> WificondScannerImpl -> WifiScaningServiceImpl->
• WifiScaningServiceImpl ->WifiService --> WifiTraker --> WifiSettings 刷新扫描结果