二,Wifi模块解析
1)框架分析
首先,用户程序使用WifiManager类来管理Wifi模块,它能够获得Wifi模块的状态,配置和控制Wifi模块,而所有这些操作都要依赖Wifiservice类来实现。
WifiService和WifiMonitor类是Wifi框架的核心,如图所示。下面先来看看WifiService是什么时候,怎么被创建和初始化的。
在systemServer启动之后,它会创建一个ConnectivityServer对象,这个对象的构造函数会创建一个WifiService的实例,代码如下所示:
framework/base/services/java/com/android/server/ConnectivityService.java
{
……
case ConnectivityManager.TYPE_WIFI:
if (DBG) Slog.v(TAG, "Starting Wifi Service.");
WifiStateTracker wst = new WifiStateTracker(context, mHandler); //创建WifiStateTracker实例
WifiService wifiService = new WifiService(context, wst);//创建WifiService实例
ServiceManager.addService(Context.WIFI_SERVICE, wifiService); //向服务管理系统添加Wifi服务
wifiService.startWifi(); //启动Wifi
mNetTrackers[ConnectivityManager.TYPE_WIFI] = wst;
wst.startMonitoring(); //启动WifiMonitor中的WifiThread线程
……
}
WifiService的主要工作:WifiMonitor和Wpa_supplicant的启动和关闭,向Wpa_supplicant发送命令。
WifiMonitor的主要工作:阻塞监听并接收来自Wpa_supplicant的消息,然后发送给WifiStateTracker。
上面两个线程通过AF_UNIX套接字和Wpa_supplicant通信,在通信过程中有两种连接方式:控制连接和监听连接。它们创建代码如下:
ctrl_conn = wpa_ctrl_open(ifname);
.. .. ..
monitor_conn = wpa_ctrl_open(ifname);
2)Wifi启动流程
(1)使能Wifi
要想使用Wifi模块,必须首先使能Wifi,当你第一次按下Wifi使能按钮时,WirelessSettings会实例化一个WifiEnabler对象,实例化代码如下:
packages/apps/settings/src/com/android/settings/WirelessSettings.java
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
……
CheckBoxPreference wifi = (CheckBoxPreference) findPreference(KEY_TOGGLE_WIFI);
mWifiEnabler = new WifiEnabler(this, wifi);
……
}
WifiEnabler类的定义大致如下,它实现了一个监听接口,当WifiEnabler对象被初始化后,它监听到你按键的动作,会调用响应函数onPreferenceChange(),这个函数会调用WifiManager的setWifiEnabled()函数。
public class WifiEnabler implements Preference.OnPreferenceChangeListener {
……
public boolean onPreferenceChange(Preference preference, Object value) {
boolean enable = (Boolean) value;
……
if (mWifiManager.setWifiEnabled(enable)) {
mCheckBox.setEnabled(false);
……
}
……
}
我们都知道Wifimanager只是个服务代理,所以它会调用WifiService的setWifiEnabled()函数,而这个函数会调用sendEnableMessage()函数,了解android 消息处理机制的都知道,这个函数最终会给自己发送一个MESSAGE_ENABLE_WIFI的消息,被WifiService里面定义的handlermessage()函数处理,会调用setWifiEnabledBlocking()函数。下面是调用流程:
mWifiEnabler.onpreferencechange()=>mWifiManage.setWifienabled()=>mWifiService.setWifiEnabled()=>mWifiService.sendEnableMessage()=>mWifiService.handleMessage()=>mWifiService.setWifiEnabledBlocking().
在setWifiEnabledBlocking()函数中主要做如下工作:加载Wifi驱动,启动wpa_supplicant,注册广播接收器,启动WifiThread监听线程。代码如下:
……
if (enable) {
if (!mWifiStateTracker.loadDriver()) {
Slog.e(TAG, "Failed to load Wi-Fi driver.");
setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);
return false;
}
if (!mWifiStateTracker.startSupplicant()) {
mWifiStateTracker.unloadDriver();
Slog.e(TAG, "Failed to start supplicant daemon.");
setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);
return false;
}
registerForBroadcasts();
mWifiStateTracker.startEventLoop();
……
至此,Wifi使能结束,自动进入扫描阶段。
(2) 扫描AP
当驱动加载成功后,如果配置文件的AP_SCAN = 1,扫描会自动开始,WifiMonitor将会从supplicant收到一个消息EVENT_DRIVER_STATE_CHANGED,调用handleDriverEvent(),然后调用mWifiStateTracker.notifyDriverStarted(),该函数向消息队列添加EVENT_DRIVER_STATE_CHANGED,handlermessage()函数处理消息时调用scan()函数,并通过WifiNative将扫描命令发送到wpa_supplicant。
Frameworks/base/wifi/java/android/net/wifi/WifiMonitor.java
private void handleDriverEvent(String state) {
if (state == null) {
return;
}
if (state.equals("STOPPED")) {
mWifiStateTracker.notifyDriverStopped();
} else if (state.equals("STARTED")) {
mWifiStateTracker.notifyDriverStarted();
} else if (state.equals("HANGED")) {
mWifiStateTracker.notifyDriverHung();
}
}
Frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java
case EVENT_DRIVER_STATE_CHANGED:
switch (msg.arg1) {
case DRIVER_STARTED:
setNumAllowedChannels();
synchronized (this) {
if (mRunState == RUN_STATE_STARTING) {
mRunState = RUN_STATE_RUNNING;
if (!mIsScanOnly) {
reconnectCommand();
} else {
// In some situations, supplicant needs to be kickstarted to
// start the background scanning
scan(true);
}
}
}
break;
上面是启动Wifi时,自动进行的AP的扫描,用户当然也可以手动扫描AP,这部分实现在WifiService里面,WifiService通过startScan()接口函数发送扫描命令到supplicant。
Frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java
public boolean startScan(boolean forceActive) {
enforceChangePermission();
switch (mWifiStateTracker.getSupplicantState()) {
case DISCONNECTED:
case INACTIVE:
case SCANNING:
case DORMANT:
break;
default:
mWifiStateTracker.setScanResultHandling(
WifiStateTracker.SUPPL_SCAN_HANDLING_LIST_ONLY);
break;
}
return mWifiStateTracker.scan(forceActive);
}
然后下面的流程同上面的自动扫描,我们来分析一下手动扫描从哪里开始的。我们应该知道手动扫描是通过菜单键的扫描键来响应的,而响应该动作的应该是WifiSettings类中Scanner类的handlerMessage()函数,它调用WifiManager的startScanActive(),这才调用WifiService的startScan()。
packages/apps/Settings/src/com/android/settings/wifi wifisettings.java
public boolean onCreateOptionsMenu(Menu menu) {
menu.add(Menu.NONE, MENU_ID_SCAN, 0, R.string.wifi_menu_scan)
.setIcon(R.drawable.ic_menu_scan_network);
menu.add(Menu.NONE, MENU_ID_ADVANCED, 0, R.string.wifi_menu_advanced)
.setIcon(android.R.drawable.ic_menu_manage);
return super.onCreateOptionsMenu(menu);
}
当按下菜单键时,WifiSettings就会调用这个函数绘制菜单。如果选择扫描按钮,WifiSettings会调用onOptionsItemSelected()。
packages/apps/Settings/src/com/android/settings/wifi wifisettings.java
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case MENU_ID_SCAN:
if (mWifiManager.isWifiEnabled()) {
mScanner.resume();
}
return true;
case MENU_ID_ADVANCED:
startActivity(new Intent(this, AdvancedSettings.class));
return true;
}
return super.onOptionsItemSelected(item);
}
private class Scanner extends Handler {
private int mRetry = 0;
void resume() {
if (!hasMessages(0)) {
sendEmptyMessage(0);
}
}
void pause() {
mRetry = 0;
mAccessPoints.setProgress(false);
removeMessages(0);
}
@Override
public void handleMessage(Message message) {
if (mWifiManager.startScanActive()) {
mRetry = 0;
} else if (++mRetry >= 3) {
mRetry = 0;
Toast.makeText(WifiSettings.this, R.string.wifi_fail_to_scan,
Toast.LENGTH_LONG).show();
return;
}
mAccessPoints.setProgress(mRetry != 0);
sendEmptyMessageDelayed(0, 6000);
}
}
这里的mWifiManager.startScanActive()就会调用WifiService里的startScan()函数,下面的流程和上面的一样,这里不赘述。
当supplicant完成了这个扫描命令后,它会发送一个消息给上层,提醒他们扫描已经完成,WifiMonitor会接收到这消息,然后再发送给WifiStateTracker。
Frameworks/base/wifi/java/android/net/wifi/WifiMonitor.java
void handleEvent(int event, String remainder) {
switch (event) {
case DISCONNECTED:
handleNetworkStateChange(NetworkInfo.DetailedState.DISCONNECTED, remainder);
break;
case CONNECTED:
handleNetworkStateChange(NetworkInfo.DetailedState.CONNECTED, remainder);
break;
case SCAN_RESULTS:
mWifiStateTracker.notifyScanResultsAvailable();
break;
case UNKNOWN:
break;
}
}
WifiStateTracker将会广播SCAN_RESULTS_AVAILABLE_ACTION消息:
Frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java
public void handleMessage(Message msg) {
Intent intent;
……
case EVENT_SCAN_RESULTS_AVAILABLE:
if (ActivityManagerNative.isSystemReady()) {
mContext.sendBroadcast(new Intent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
}
sendScanResultsAvailable();
setScanMode(false);
break;
……
}
由于WifiSettings类注册了intent,能够处理SCAN_RESULTS_AVAILABLE_ACTION消息,它会调用handleEvent(),调用流程如下所示。
WifiSettings.handleEvent() => WifiSettings.updateAccessPoints() => mWifiManager.getScanResults() => mService.getScanResults() => mWifiStateTracker.scanResults() => WifiNative.scanResultsCommand()……
将获取AP列表的命令发送到supplicant,然后supplicant通过Socket发送扫描结果,由上层接收并显示。这和前面的消息获取流程基本相同。
(3)配置,连接AP
当用户选择一个活跃的AP时,WifiSettings响应打开一个对话框来配置AP,比如加密方法和连接AP的验证模式。配置好AP后,WifiService添加或更新网络连接到特定的AP。
packages/apps/settings/src/com/android/settings/wifi/WifiSetttings.java
public boolean onPreferenceTreeClick(PreferenceScreen screen, Preference preference) {
if (preference instanceof AccessPoint) {
mSelected = (AccessPoint) preference;
showDialog(mSelected, false);
} else if (preference == mAddNetwork) {
mSelected = null;
showDialog(null, true);
} else if (preference == mNotifyOpenNetworks) {
Secure.putInt(getContentResolver(),
Secure.WIFI_NETWORKS_AVAILABLE_NOTIFICATION_ON,
mNotifyOpenNetworks.isChecked() ? 1 : 0);
} else {
return super.onPreferenceTreeClick(screen, preference);
}
return true;
}
配置好以后,当按下“Connect Press”时,WifiSettings通过发送LIST_NETWORK命令到supplicant来检查该网络是否配置。如果没有该网络或没有配置它,WifiService调用addorUpdateNetwork()函数来添加或更新网络,然后发送命令给supplicant,连接到这个网络。下面是从响应连接按钮到WifiService发送连接命令的代码:
packages/apps/settings/src/com/android/settings/wifi/WifiSetttings.java
public void onClick(DialogInterface dialogInterface, int button) {
if (button == WifiDialog.BUTTON_FORGET && mSelected != null) {
forget(mSelected.networkId);
} else if (button == WifiDialog.BUTTON_SUBMIT && mDialog != null) {
WifiConfiguration config = mDialog.getConfig();
if (config == null) {
if (mSelected != null && !requireKeyStore(mSelected.getConfig())) {
connect(mSelected.networkId);
}
} else if (config.networkId != -1) {
if (mSelected != null) {
mWifiManager.updateNetwork(config);
saveNetworks();
}
} else {
int networkId = mWifiManager.addNetwork(config);
if (networkId != -1) {
mWifiManager.enableNetwork(networkId, false);
config.networkId = networkId;
if (mDialog.edit || requireKeyStore(config)) {
saveNetworks();
} else {
connect(networkId);
}
}
}
}
}
Frameworks\base\wifi\java\android\net\wifi\WifiManager.java
public int updateNetwork(WifiConfiguration config) {
if (config == null || config.networkId < 0) {
return -1;
}
return addOrUpdateNetwork(config);
}
private int addOrUpdateNetwork(WifiConfiguration config) {
try {
return mService.addOrUpdateNetwork(config);
} catch (RemoteException e) {
return -1;
}
}
WifiService.addOrUpdateNetwork()通过调用mWifiStateTracker.setNetworkVariable()将连接命令发送到Wpa_supplicant。
(4)获取IP地址
当连接到supplicant后,WifiMonitor就会通知WifiStateTracker。
Frameworks/base/wifi/java/android/net/wifi/WifiMonitor.java
Public void Run(){
if (connectToSupplicant()) {
// Send a message indicating that it is now possible to send commands
// to the supplicant
mWifiStateTracker.notifySupplicantConnection();
} else {
mWifiStateTracker.notifySupplicantLost();
return;
}
……
}
WifiStateTracker发送EVENT_SUPPLICANT_CONNECTION消息到消息队列,这个消息有自己的handlermessage()函数处理,它会启动一个DHCP线程,而这个线程会一直等待一个消息事件,来启动DHCP协议分配IP地址。
frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java
void notifySupplicantConnection() {
sendEmptyMessage(EVENT_SUPPLICANT_CONNECTION);
}
public void handleMessage(Message msg) {
Intent intent;
switch (msg.what) {
case EVENT_SUPPLICANT_CONNECTION:
……
HandlerThread dhcpThread = new HandlerThread("DHCP Handler Thread");
dhcpThread.start();
mDhcpTarget = new DhcpHandler(dhcpThread.getLooper(), this);
……
……
}
当Wpa_supplicant连接到AP后,它会发送一个消息给上层来通知连接成功,WifiMonitor会接受到这个消息并上报给WifiStateTracker。
Frameworks/base/wifi/java/android/net/wifi/WifiMonitor.java
void handleEvent(int event, String remainder) {
switch (event) {
case DISCONNECTED:
handleNetworkStateChange(NetworkInfo.DetailedState.DISCONNECTED, remainder);
break;
case CONNECTED:
handleNetworkStateChange(NetworkInfo.DetailedState.CONNECTED, remainder);
break;
……
}
private void handleNetworkStateChange(NetworkInfo.DetailedState newState, String data) {
String BSSID = null;
int networkId = -1;
if (newState == NetworkInfo.DetailedState.CONNECTED) {
Matcher match = mConnectedEventPattern.matcher(data);
if (!match.find()) {
if (Config.LOGD) Log.d(TAG, "Could not find BSSID in CONNECTED event string");
} else {
BSSID = match.group(1);
try {
networkId = Integer.parseInt(match.group(2));
} catch (NumberFormatException e) {
networkId = -1;
}
}
}
mWifiStateTracker.notifyStateChange(newState, BSSID, networkId);
}
void notifyStateChange(DetailedState newState, String BSSID, int networkId) {
Message msg = Message.obtain(
this, EVENT_NETWORK_STATE_CHANGED,
new NetworkStateChangeResult(newState, BSSID, networkId));
msg.sendToTarget();
}
case EVENT_NETWORK_STATE_CHANGED:
……
configureInterface();
……
private void configureInterface() {
checkPollTimer();
mLastSignalLevel = -1;
if (!mUseStaticIp) { //使用DHCP线程动态IP
if (!mHaveIpAddress && !mObtainingIpAddress) {
mObtainingIpAddress = true;
//发送启动DHCP线程获取IP
mDhcpTarget.sendEmptyMessage(EVENT_DHCP_START);
}
} else { //使用静态IP,IP信息从mDhcpInfo中获取
int event;
if (NetworkUtils.configureInterface(mInterfaceName, mDhcpInfo)) {
mHaveIpAddress = true;
event = EVENT_INTERFACE_CONFIGURATION_SUCCEEDED;
if (LOCAL_LOGD) Log.v(TAG, "Static IP configuration succeeded");
} else {
mHaveIpAddress = false;
event = EVENT_INTERFACE_CONFIGURATION_FAILED;
if (LOCAL_LOGD) Log.v(TAG, "Static IP configuration failed");
}
sendEmptyMessage(event); //发送IP获得成功消息事件
}
}
DhcpThread获取EVENT_DHCP_START消息事件后,调用handleMessage()函数,启动DHCP获取IP地址的服务。
public void handleMessage(Message msg) {
int event;
switch (msg.what) {
case EVENT_DHCP_START:
……
Log.d(TAG, "DhcpHandler: DHCP request started");
//启动一个DHCP client的精灵进程,为mInterfaceName请求分配一个IP地//址
if (NetworkUtils.runDhcp(mInterfaceName, mDhcpInfo)) {
event = EVENT_INTERFACE_CONFIGURATION_SUCCEEDED;
if (LOCAL_LOGD) Log.v(TAG, "DhcpHandler: DHCP request succeeded");
} else {
event = EVENT_INTERFACE_CONFIGURATION_FAILED;
Log.i(TAG, "DhcpHandler: DHCP request failed: " +
NetworkUtils.getDhcpError());
}
……
}
这里调用了一个NetworkUtils.runDhcp()函数,NetworkUtils类是一个网络服务的辅助类,它主要定义了一些本地接口,这些接口会通过他们的JNI层android_net_NetUtils.cpp文件和DHCP client通信,并获取IP地址。
至此,IP地址获取完毕,Wifi启动流程结束。