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：
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; ………… }-------HAL------------------------------------------------------------------------------------------------------------------------------------------------------------------------
wifi.c: int wifi_command(const char *command, char *reply, size_t *reply_len) { return wifi_send_command(ctrl_conn, command, reply, reply_len); } int wifi_send_command(struct wpa_ctrl *ctrl, const char *cmd, char *reply, size_t *reply_len) { ret = wpa_ctrl_request(ctrl, cmd, strlen(cmd), reply, reply_len, NULL); ………… }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