Softap热点原理分析
Android4.1.2
设置中开关：
packages/apps/Settings/src/com/android/settings/TetherSettings.java
|----private void startTethering()
| |----mWifiApEnabler.setSoftapEnabled(true);
packages/apps/Settings/src/com/android/settings/wifi/WifiApEnabler.java
|----public void setSoftapEnabled(boolean enable)
| |----mWifiManager.setWifiApEnabled(null, enable)
框架：
frameworks/base/wifi/java/android/net/wifi/WifiManager.java
|----public boolean setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled)
| |----mService.setWifiApEnabled(wifiConfig, enabled);
IWifiManager.aidl
|----void setWifiApEnabled(in WifiConfiguration wifiConfig, boolean enable);
frameworks/base/services/java/com/android/server/WifiService.java
|----public void setWifiApEnabled(WifiConfiguration wifiConfig, boolean enabled)
| |----mWifiStateMachine.setWifiApEnabled(wifiConfig, enabled);
frameworks/base/wifi/java/android/net/wifi/WifiStateMachine.java
|----public void setWifiApEnabled(WifiConfiguration wifiConfig, boolean enable)
| |----sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_AP_STATE_ENABLING, 0));
| |----sendMessage(obtainMessage(CMD_START_AP, wifiConfig));
斗胆分析一下状态机的运作
WifiStateMachine 继承于StateMachine, 而在WifiStateMachine中未有对sendMessage方法的复写，所以实现是使用父类的实现：
/**
* Enqueue a message to this state machine.
*/
public final void sendMessage(int what) {
// mSmHandler can be null if the state machine has quit.
if (mSmHandler == null) return;
mSmHandler.sendMessage(obtainMessage(what));
}
/**
* Enqueue a message to this state machine.
*/
public final void sendMessage(int what, Object obj) {
// mSmHandler can be null if the state machine has quit.
if (mSmHandler == null) return;
mSmHandler.sendMessage(obtainMessage(what,obj));
}
/**
* Enqueue a message to this state machine.
*/
public final void sendMessage(Message msg) {
// mSmHandler can be null if the state machine has quit.
if (mSmHandler == null) return;
mSmHandler.sendMessage(msg);
}
可见，mSmHandler的定义是类SmHandler， 继承于Handler， SmHandler对handleMessage进行了复写，所以对于消息的接收处理应该是在SmHandler的handleMessage中：
/**
* Handle messages sent to the state machine by calling
* the current state's processMessage. It also handles
* the enter/exit calls and placing any deferred messages
* back onto the queue when transitioning to a new state.
*/
@Override
public final void handleMessage(Message msg) {
if (mDbg) Log.d(TAG, "handleMessage: E msg.what=" + msg.what);
/** Save the current message */
mMsg = msg;
if (mIsConstructionCompleted) { //正常的操作
/** Normal path */
processMsg(msg);
} else if (!mIsConstructionCompleted &&
(mMsg.what == SM_INIT_CMD) && (mMsg.obj == mSmHandlerObj)) { //初始化操作
/** Initial one time path. */
mIsConstructionCompleted = true;
invokeEnterMethods(0);
} else {
throw new RuntimeException("StateMachine.handleMessage: " +
"The start method not called, received msg: " + msg);
}
performTransitions(); //应用改变
if (mDbg) Log.d(TAG, "handleMessage: X");
}
processMsg(msg)：
/**
* Process the message. If the current state doesn't handle
* it, call the states parent and so on. If it is never handled then
* call the state machines unhandledMessage method.
*/
private final void processMsg(Message msg) {
StateInfo curStateInfo = mStateStack[mStateStackTopIndex]; //获取当前状态
if (mDbg) {
Log.d(TAG, "processMsg: " + curStateInfo.state.getName());
}
while (!curStateInfo.state.processMessage(msg)) { //判断该消息是否处理
/**
* Not processed
*/
curStateInfo = curStateInfo.parentStateInfo;
if (curStateInfo == null) {
/**
* No parents left so it's not handled
*/
mSm.unhandledMessage(msg);
if (isQuit(msg)) {
transitionTo(mQuittingState); //设置状态
}
break;
}
if (mDbg) {
Log.d(TAG, "processMsg: " + curStateInfo.state.getName());
}
}
在WifiStateMachine中有很多状态，截取几个来看：
/* Loading the driver */
private State mDriverUnloadedState = new DriverUnloadedState();
/* Driver load/unload failed */
private State mDriverFailedState = new DriverFailedState();
/* Driver loading */
private State mDriverLoadingState = new DriverLoadingState();
/* Driver loaded */
private State mDriverLoadedState = new DriverLoadedState();
以上4个都是关于Wifi驱动加载与卸载的相关状态，每一个都有复写自己的processMessage方法，比如DriverUnloadedState():
@Override
public boolean processMessage(Message message) {
if (DBG) log(getName() + message.toString() + "\n");
switch (message.what) {
case CMD_LOAD_DRIVER:
transitionTo(mDriverLoadingState);
break;
default:
return NOT_HANDLED;
}
return HANDLED;
}
这说明，在状态是“Wifi驱动已经成功卸载”时，系统只响应（handle）CMD_LOAD_DRIVER的消息，也就是驱动加载命令，其他一概不管。很符合逻辑吧。
假设，在打开Wifi热点的时候，驱动就是卸载的（默认状态），那么 sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_AP_STATE_ENABLING, 0));过后会来到这里，也就会将新的状态mDriverLoadingState加入状态栈。随后返回HANDLED，另一种NOT_HANDLED就 不做讨论了。那么现在的流程变成了processMsg(msg) --> transitionTo(mDriverLoadingState) --> performTransitions()，所以在分析performTransitions()之前要先看看transitionTo（实现在父类 StateMachine中）：
/** @see StateMachine#transitionTo(IState) */
private final void transitionTo(IState destState) {
mDestState = (State) destState;
if (mDbg) Log.d(TAG, "transitionTo: destState=" + mDestState.getName());
}
由于State是IState的子类，所以这样的参数传递进去没有问题，mDestState目标状态变成了mDriverLoadingState，然后是performTransitions()（还是在父类StateMachine中）：
/**
* Do any transitions
*/
private void performTransitions() {
/**
* If transitionTo has been called, exit and then enter
* the appropriate states. We loop on this to allow
* enter and exit methods to use transitionTo.
*/
State destState = null;
while (mDestState != null) { //即transitionTo设置的新状态 mDriverLoadingState
if (mDbg) Log.d(TAG, "handleMessage: new destination call exit");
/**
* Save mDestState locally and set to null
* to know if enter/exit use transitionTo.
*/
destState = mDestState;
mDestState = null;
/**
* Determine the states to exit and enter and return the
* common ancestor state of the enter/exit states. Then
* invoke the exit methods then the enter methods.
*/
StateInfo commonStateInfo = setupTempStateStackWithStatesToEnter(destState); //将状态装入临时队列
invokeExitMethods(commonStateInfo); //将该状态之前的所有状态全部退出
int stateStackEnteringIndex = moveTempStateStackToStateStack(); //把临时队列合并至标准队列，并且返回界限值stateStaclEnteringIndex
invokeEnterMethods(stateStackEnteringIndex); //遍历执行自界限值到队列顶部的所有状态的enter方法，如下图所示：
/*
|-------------|
High| stack_x | mStateStackTopIndex
|-------------|
| ..... |
|-------------|
| stack_y | stateStackEnteringIndex 以上都是从Temp临时队列合并来的
|-------------|
| ..... |
|-------------|
Low | stack_1 |
|-------------|
*/
/**
* Since we have transitioned to a new state we need to have
* any deferred messages moved to the front of the message queue
* so they will be processed before any other messages in the
* message queue.
*/ moveDeferredMessageAtFrontOfQueue(); //将所有延迟消息再次发送到队列顶部，随后清除延迟消息队列。 }
/**
* After processing all transitions check and
* see if the last transition was to quit or halt.
*/
if (destState != null) { //以下检查状态是否是需求退出或挂起的，是则进行相应处理
if (destState == mQuittingState) {
cleanupAfterQuitting();
} else if (destState == mHaltingState) {
/**
* Call halting() if we've transitioned to the halting
* state. All subsequent messages will be processed in
* in the halting state which invokes haltedProcessMessage(msg);
*/
mSm.halting();
}
}
}
看了好多子函数，有点晕晕的。看得出来这个performTransitions()是对所有状态进行处理的关键节点，可能同一时间会受到很多 Message，而这些Message所携带的不同状态会被加入到一个临时队列中，然后会将标准队列顶端到此状态之前的所有状态都退出（也就是触发 exit()），并设置为非活跃，然后剔除。之后会将临时队列合并入标准队列，取得一个界限值，从界限值到队列顶端依次激活（触发enter()）。其实 在sendMessage的同时，还有一种消息处理方式就是deferMessage，是对消息的延迟发送，最终会将消息加入到一个延迟消息队列 mDeferredMessages中，每次的performTransitions()都会对延迟消息队列进行重新发送并且清空它的队列。最后，还会检 测一下是否有特殊的状态需要处理，如退出和挂起。
回到正题
WifiStateMachine.java
应该关注一下mDriverLoadingState了，前边看到这是一个DriverLoadingState()，enter()的主要内容是一个工作线程:
new Thread(new Runnable() {
public void run() {
mWakeLock.acquire(); //整个过程需要wakelock保护
//enabling state
switch(message.arg1) {
case WIFI_STATE_ENABLING: //打开WIFI
setWifiState(WIFI_STATE_ENABLING);
break;
case WIFI_AP_STATE_ENABLING: //打开WIFI AP
setWifiApState(WIFI_AP_STATE_ENABLING);
break;
}
if(mWifiNative.loadDriver()) { // 加载Wifi驱动，WifiNative.java --> core/jni /android_net_wifi_Wifi.cpp --> hardware/libhardware_legacy/wifi.c 就是 insmod xxx.ko，也许带参数blablabla
if (DBG) log("Driver load successful");
sendMessage(CMD_LOAD_DRIVER_SUCCESS);
} else {
loge("Failed to load driver!");
switch(message.arg1) {
case WIFI_STATE_ENABLING:
setWifiState(WIFI_STATE_UNKNOWN);
break;
case WIFI_AP_STATE_ENABLING:
setWifiApState(WIFI_AP_STATE_FAILED);
break;
}
sendMessage(CMD_LOAD_DRIVER_FAILURE);
}
mWakeLock.release();
}
}).start();
}
而这里可以快速的复习一下前边的流程，加载成功后会sendMessage(CMD_LOAD_DRIVER_SUCCESS)，失败了就会发送 CMD_LOAD_DRIVER_FAILURE。当前的状态就是mDriverLoadingState，所以是DriverLoadingState 的processMessage来处理这两个消息了：
@Override
public boolean processMessage(Message message) {
if (DBG) log(getName() + message.toString() + "\n");
switch (message.what) {
case CMD_LOAD_DRIVER_SUCCESS:
transitionTo(mDriverLoadedState);
break;
case CMD_LOAD_DRIVER_FAILURE:
transitionTo(mDriverFailedState);
break;
case CMD_LOAD_DRIVER:
case CMD_UNLOAD_DRIVER:
case CMD_START_SUPPLICANT:
case CMD_STOP_SUPPLICANT:
case CMD_START_AP:
case CMD_STOP_AP:
case CMD_START_DRIVER:
case CMD_STOP_DRIVER:
case CMD_SET_SCAN_MODE:
case CMD_SET_SCAN_TYPE:
case CMD_SET_COUNTRY_CODE:
case CMD_SET_FREQUENCY_BAND:
case CMD_START_PACKET_FILTERING:
case CMD_STOP_PACKET_FILTERING:
deferMessage(message);
break;
default:
return NOT_HANDLED;
}
return HANDLED;
}
由此可见，加载成功后状态就变为mDriverLoadedState,失败了状态就是mDriverFailedState。回到DriverLoadingState的enter，setWifiApState：
private void setWifiApState(int wifiApState) {
final int previousWifiApState = mWifiApState.get();
try {
if (wifiApState == WIFI_AP_STATE_ENABLED) { //WIFI AP已经打开，则电池状态开始记录Wifi相关
mBatteryStats.noteWifiOn();
} else if (wifiApState == WIFI_AP_STATE_DISABLED) { //WIFI AP已经关闭，则电池状态对WIFI的记录关闭
mBatteryStats.noteWifiOff();
}
} catch (RemoteException e) {
loge("Failed to note battery stats in wifi");
}
// Update state
mWifiApState.set(wifiApState); //设置WIFI AP的状态，原子状态
if (DBG) log("setWifiApState: " + syncGetWifiApStateByName());
//将状态消息发送至WifiManager进行进一步处理。终于脱离了状态机，回到WifiManager了。
final Intent intent = new Intent(WifiManager.WIFI_AP_STATE_CHANGED_ACTION);
intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
intent.putExtra(WifiManager.EXTRA_WIFI_AP_STATE, wifiApState);
intent.putExtra(WifiManager.EXTRA_PREVIOUS_WIFI_AP_STATE, previousWifiApState);
mContext.sendStickyBroadcast(intent);
}
PS：通过sendBroadcast中发出的intent在Reciever注册后才能正确收到，未注册的时候不能被接收，即使后面再次注册上也无法接受到。而sendStickyBroadcast发出的Intent当Reciever注册后就能收到Intent，即使注册发生在广播之后。也就是说sendStickyBroadcast安全性更高，能够保证广播不会丢失，而sendBroadcast有一定危险。
好 的，分析了这么久，只是有一条sendMessage(obtainMessage(CMD_LOAD_DRIVER, WIFI_AP_STATE_ENABLING, 0))，发送出状态广播给别人获取，在系统中一个很好的例子是桌面电源控件对这个状态进行接收，可以直观的理解为当ing的状态时某按钮是不可用的。
然后才是真正的开启动作：
sendMessage(obtainMessage(CMD_START_AP, wifiConfig));
假设加载成功，当前状态变成了mDriverLoadedState，那么去DriverLoadedState的processMessage寻找这个Message的处理方法：
case CMD_START_AP:
transitionTo(mSoftApStartingState);
break;
新的状态，mSoftApStartingState:
/* Soft ap is starting up */
private State mSoftApStartingState = new SoftApStartingState();
@Override
public void enter() {
if (DBG) log(getName() + "\n");
EventLog.writeEvent(EVENTLOG_WIFI_STATE_CHANGED, getName());
final Message message = getCurrentMessage();
if (message.what == CMD_START_AP) { //如果进入这个状态而不是打开AP，那么就直接抛出runtime异常，一般来说就是重启了。又一次验证了：不以结婚为目的的谈恋爱都是耍流氓。
final WifiConfiguration config = (WifiConfiguration) message.obj;
if (config == null) {
mWifiApConfigChannel.sendMessage(CMD_REQUEST_AP_CONFIG);
} else {
mWifiApConfigChannel.sendMessage(CMD_SET_AP_CONFIG, config);
startSoftApWithConfig(config);
}
} else {
throw new RuntimeException("Illegal transition to SoftApStartingState: " + message);
}
}
OK, config为NULL，又是一个Message：
mWifiApConfigChannel.sendMessage(CMD_REQUEST_AP_CONFIG);
在WifiStateMachine构造的时候对mWifiApConfigChannel设置了handler：
mWifiApConfigChannel.connectSync(mContext, getHandler(), wifiApConfigStore.getMessenger());
WifiApConfigStore.java
CMD_REQUEST_AP_CONFIG的消息处理是在WifiApConfigStore中处理的:
class DefaultState extends State {
public boolean processMessage(Message message) {
switch (message.what) {
case WifiStateMachine.CMD_SET_AP_CONFIG:
case WifiStateMachine.CMD_SET_AP_CONFIG_COMPLETED:
Log.e(TAG, "Unexpected message: " + message);
break;
case WifiStateMachine.CMD_REQUEST_AP_CONFIG:
mReplyChannel.replyToMessage(message,
WifiStateMachine.CMD_RESPONSE_AP_CONFIG, mWifiApConfig);
break;
default:
Log.e(TAG, "Failed to handle " + message);
break;
}
return HANDLED;
}
}
当前WIFI状态机状态为SoftApStartingState，所以回复消息在这里处理：
@Override
public boolean processMessage(Message message) {
if (DBG) log(getName() + message.toString() + "\n");
switch(message.what) {
case CMD_LOAD_DRIVER:
case CMD_UNLOAD_DRIVER:
case CMD_START_SUPPLICANT:
case CMD_STOP_SUPPLICANT:
case CMD_START_AP:
case CMD_STOP_AP:
case CMD_START_DRIVER:
case CMD_STOP_DRIVER:
case CMD_SET_SCAN_MODE:
case CMD_SET_SCAN_TYPE:
case CMD_SET_COUNTRY_CODE:
case CMD_SET_FREQUENCY_BAND:
case CMD_START_PACKET_FILTERING:
case CMD_STOP_PACKET_FILTERING:
case CMD_TETHER_STATE_CHANGE:
deferMessage(message);
break;
case WifiStateMachine.CMD_RESPONSE_AP_CONFIG:
WifiConfiguration config = (WifiConfiguration) message.obj; //设置文件就是WifiApConfigStore中的mWifiApConfig
if (config != null) {
startSoftApWithConfig(config); //如果配置文件存在就继续开启AP
} else {
loge("Softap config is null!"); //如果配置文件为空则开启失败，发送个消息CMD_START_AP_FAILURE，还是在本状态中处理
sendMessage(CMD_START_AP_FAILURE);
}
break;
case CMD_START_AP_SUCCESS:
setWifiApState(WIFI_AP_STATE_ENABLED);
transitionTo(mSoftApStartedState);
break;
case CMD_START_AP_FAILURE:
// initiate driver unload
sendMessage(obtainMessage(CMD_UNLOAD_DRIVER, WIFI_AP_STATE_FAILED, 0)); //卸载驱动，并更改状态为AP开启失败
break;
default:
return NOT_HANDLED;
}
return HANDLED;
}
配置文件
这里的配置文件是通过WifiManager的setWifiApConfiguration接口生成的：
frameworks/base/wifi/java/android/net/wifi/WifiManager.java
/**
* Sets the Wi-Fi AP Configuration.
* @return {@code true} if the operation succeeded, {@code false} otherwise
*
* @hide Dont open yet
*/
public boolean setWifiApConfiguration(WifiConfiguration wifiConfig) {
try {
mService.setWifiApConfiguration(wifiConfig);
return true;
} catch (RemoteException e) {
return false;
}
}
mService为IWifiManager，该接口定义如下：
void setWifiApConfiguration(in WifiConfiguration wifiConfig);
而实现为WifiService
public class WifiService extends IWifiManager.Stub
/**
* see {@link WifiManager#setWifiApConfiguration(WifiConfiguration)}
* @param wifiConfig WifiConfiguration details for soft access point
*/
public void setWifiApConfiguration(WifiConfiguration wifiConfig) {
enforceChangePermission();
if (wifiConfig == null)
return;
mWifiStateMachine.setWifiApConfiguration(wifiConfig);
}
真是的实现有抛给了WifiStateMachine：
public void setWifiApConfiguration(WifiConfiguration config) {
mWifiApConfigChannel.sendMessage(CMD_SET_AP_CONFIG, config);
}
消息交给WifiApConfigStore处理，而
WifiApConfigStore(Context context, Handler target) {
super(TAG, target.getLooper());
mContext = context;
addState(mDefaultState);
addState(mInactiveState, mDefaultState);
addState(mActiveState, mDefaultState);
setInitialState(mInactiveState);
}
WifiApConfigStore在构造的时候分mDefaultState分配了两个子状态mInactiveState, mActiveState, 初始化状态为mInactiveState。
class InactiveState extends State {
public boolean processMessage(Message message) {
switch (message.what) {
case WifiStateMachine.CMD_SET_AP_CONFIG:
mWifiApConfig = (WifiConfiguration) message.obj;
transitionTo(mActiveState); //触发ActiveState.enter()
break;
default:
return NOT_HANDLED;
}
return HANDLED;
}
}
class ActiveState extends State {
public void enter() {
new Thread(new Runnable() {
public void run() {
writeApConfiguration(mWifiApConfig);
sendMessage(WifiStateMachine.CMD_SET_AP_CONFIG_COMPLETED);
}
}).start();
}
writeApConfiguration实现：
private void writeApConfiguration(final WifiConfiguration config) {
DataOutputStream out = null;
try {
out = new DataOutputStream(new BufferedOutputStream(
new FileOutputStream(AP_CONFIG_FILE)));
out.writeInt(AP_CONFIG_FILE_VERSION);
out.writeUTF(config.SSID);
int authType = config.getAuthType();
out.writeInt(authType);
if(authType != KeyMgmt.NONE) {
out.writeUTF(config.preSharedKey);
}
} catch (IOException e) {
Log.e(TAG, "Error writing hotspot configuration" + e);
} finally {
if (out != null) {
try {
out.close();
} catch (IOException e) {}
}
}
}
默认文件路径即为/misc/wifi/softap.conf，写好配置文件后发送WifiStateMachine.CMD_SET_AP_CONFIG_COMPLETED，自己发自己收了：
public boolean processMessage(Message message) {
switch (message.what) {
//TODO: have feedback to the user when we do this
//to indicate the write is currently in progress
case WifiStateMachine.CMD_SET_AP_CONFIG:
deferMessage(message);
break;
case WifiStateMachine.CMD_SET_AP_CONFIG_COMPLETED: //修改完后切换状态到InactiveState
transitionTo(mInactiveState);
break;
default:
return NOT_HANDLED;
}
return HANDLED;
}
这样配置文件就配置完了，结果是保存在mWifiConfig中的。
带着配置文件开启AP
frameworks/base/wifi/java/android/net/wifi/WifiStateMachine.java startSoftApWithConfig
/* Current design is to not set the config on a running hostapd but instead
* stop and start tethering when user changes config on a running access point
*
* TODO: Add control channel setup through hostapd that allows changing config
* on a running daemon
*/
private void startSoftApWithConfig(final WifiConfiguration config) {
// start hostapd on a seperate thread
new Thread(new Runnable() {
public void run() {
try {
mNwService.startAccessPoint(config, mInterfaceName, SOFTAP_IFACE);
} catch (Exception e) {
loge("Exception in softap start " + e);
try {
mNwService.stopAccessPoint(mInterfaceName);
mNwService.startAccessPoint(config, mInterfaceName, SOFTAP_IFACE);
} catch (Exception e1) {
loge("Exception in softap re-start " + e1);
sendMessage(CMD_START_AP_FAILURE);
return;
}
}
if (DBG) log("Soft AP start successful");
sendMessage(CMD_START_AP_SUCCESS);
}
}).start();
}
逻辑就是尝试开启，如果发生错误就尝试重启，如果再错误就承认失败，发送失败状态，如果没错误就发送成功的消息。关键在mNwService的startAccessPoint方法中。
config, mInterfaceName, SOFTAP_IFACE
这三个参数：config为传递下来的配置文件，SOFTAP_IFACE为字符串wl0.1，mInterfaceName为WifiStateMachine构造时传递下来的参数，而这个构造动作由WifiService构造的时候发起：
WifiService(Context context) {
mContext = context;
mInterfaceName = SystemProperties.get("wifi.interface", "wlan0");
mWifiStateMachine = new WifiStateMachine(mContext, mInterfaceName);
mWifiStateMachine.enableRssiPolling(true);
...
}
可见，这个mInterfaceName由prop wifi.interface控制，如我们经常能在build.prop中看到wifi.interface=eth0/wlan0等，如果没有会默认给wlan0。
接下来看startAccessPoint的实现（frameworks/base/services/java/com/android/server/NetworkManagementService.java）：
@Override
public void startAccessPoint(
WifiConfiguration wifiConfig, String wlanIface, String softapIface) {
mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
try {
Resources resources = mContext.getResources();
if (resources.getBoolean(com.android.internal.R.bool.config_wifiApFirmwareReload))
wifiFirmwareReload(wlanIface, "AP");
if (resources.getBoolean(com.android.internal.R.bool.config_wifiApStartInterface))
mConnector.execute("softap", "start", wlanIface);
if (wifiConfig == null) {
mConnector.execute("softap", "set", wlanIface, softapIface);
} else {
mConnector.execute("softap", "set", wlanIface, softapIface, wifiConfig.SSID,
getSecurityType(wifiConfig), wifiConfig.preSharedKey);
}
mConnector.execute("softap", "startap");
} catch (NativeDaemonConnectorException e) {
throw e.rethrowAsParcelableException();
}
}
config_wifiApFirmwareReload、config_wifiApStartInterface都是可以用户自定义的xml配置接口，默认在frameworks/base/core/res/res/values/config.xml中，默认如：
<!-- Boolean indicating whether Softap requires reloading AP firmware -->
<bool name="config_wifiApFirmwareReload">true</bool>
<!-- Boolean indicating whether the start command should be called on the wireless interface
when starting the SoftAp -->
<bool name="config_wifiApStartInterface">false</bool>
想关联的几个函数有：
private static String getSecurityType(WifiConfiguration wifiConfig) { //获取网络安全类型
switch (wifiConfig.getAuthType()) {
case KeyMgmt.WPA_PSK:
return "wpa-psk";
case KeyMgmt.WPA2_PSK:
return "wpa2-psk";
default:
return "open";
}
}
/* @param mode can be "AP", "STA" or "P2P" */
@Override
public void wifiFirmwareReload(String wlanIface, String mode) { //根据不同模式装在不同的固件（如果有需要的话）
mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
try {
mConnector.execute("softap", "fwreload", wlanIface, mode);
} catch (NativeDaemonConnectorException e) {
throw e.rethrowAsParcelableException();
}
}
通过以上不难看出，最终都是通过mConnector.execute来执行命令。
/**
* Constructs a new NetworkManagementService instance
*
* @param context Binder context for this service
*/
private NetworkManagementService(Context context) {
mContext = context;
if ("simulator".equals(SystemProperties.get("ro.product.device"))) {
return;
}
mConnector = new NativeDaemonConnector(
new NetdCallbackReceiver(), "netd", 10, NETD_TAG, 160);
mThread = new Thread(mConnector, NETD_TAG);
// Add ourself to the Watchdog monitors.
Watchdog.getInstance().addMonitor(this);
}
mConnector是在构造时生成的NativeDaemonConnector对象，查看一下NativeDaemonConnector的构造过程 （frameworks/base/services/java/com/android/server /NativeDaemonConnector.java）：
NativeDaemonConnector(INativeDaemonConnectorCallbacks callbacks, String socket,
int responseQueueSize, String logTag, int maxLogSize) {
mCallbacks = callbacks;
mSocket = socket;
mResponseQueue = new ResponseQueue(responseQueueSize);
mSequenceNumber = new AtomicInteger(0);
TAG = logTag != null ? logTag : "NativeDaemonConnector";
mLocalLog = new LocalLog(maxLogSize);
}
1.分别在handleMessage和listenToSocket的时候调用回调对象的onEvent和onDaemonConnected方法。而 监听socket的服务被创建后就已经开出一个线程始终监听了。在这里为new NetdCallbackReceiver()；
2.mSocket也就是在NetworkManagementService中始终监听的那个local socket。在这里为netd（/dev/socket/netd）；
3.mResponseQueue是新建了一个命令队列ResponseQueue，传递金的参数responseQueuesize就是这个队列的容量上限。这个子类算上构造在内总共4个方法：
a.构造
b.添加命令
c.移除命令
d.打印队列信息
4.mSequeueceNumber作为指令执行计数器，是个原子量， 防止线程操作混乱；
5.日志标签
6.日志容量
构造完成后，会new出一个线程，这个线程的工作就是调用listenToSocket。最后会使用看门狗来保护这个服务。
回到主线，默认情况下，并有有效的配置文件，打开WIFI AP需要执行两条命令：
mConnector.execute("softap", "fwreload", wlanIface, mode);
mConnector.execute("softap", "set", wlanIface, softapIface, wifiConfig.SSID,
getSecurityType(wifiConfig), wifiConfig.preSharedKey);
逐个分析一下：
固件重载
wlanIface就是prop指定的wifi.interface，默认为wlan0，mode为"AP"，共计四个参数。
这两条命令都会最终执行到这里：
public NativeDaemonEvent[] execute(int timeout, String cmd, Object... args)
throws NativeDaemonConnectorException {
final ArrayList<NativeDaemonEvent> events = Lists.newArrayList();
final int sequenceNumber = mSequenceNumber.incrementAndGet(); //命令计数器加一并返回
final StringBuilder cmdBuilder =
new StringBuilder(Integer.toString(sequenceNumber)).append(' ');
final long startTime = SystemClock.elapsedRealtime(); //返回的是自从系统启动到当前的时间
makeCommand(cmdBuilder, cmd, args); //将所有参数整合成一条命令，放置在cmdBuilder中
final String logCmd = cmdBuilder.toString(); /* includes cmdNum, cmd, args */
log("SND -> {" + logCmd + "}");
cmdBuilder.append('\0'); //给字符串来个尾巴，然后化作真正的字符串sentCmd
final String sentCmd = cmdBuilder.toString(); /* logCmd + \0 */
synchronized (mDaemonLock) {
if (mOutputStream == null) { //mOutputStraem是netd的输出通道
throw new NativeDaemonConnectorException("missing output stream");
} else {
try {
mOutputStream.write(sentCmd.getBytes(Charsets.UTF_8)); //将命令发送出去 netd socket
} catch (IOException e) {
throw new NativeDaemonConnectorException("problem sending command", e);
}
}
}
NativeDaemonEvent event = null;
do {
event = mResponseQueue.remove(sequenceNumber, timeout, sentCmd); //从命令队列中删除已经发送出去的命令
if (event == null) {
loge("timed-out waiting for response to " + logCmd);
throw new NativeDaemonFailureException(logCmd, event);
}
log("RMV <- {" + event + "}");
events.add(event);
} while (event.isClassContinue());
final long endTime = SystemClock.elapsedRealtime();
if (endTime - startTime > WARN_EXECUTE_DELAY_MS) {
loge("NDC Command {" + logCmd + "} took too long (" + (endTime - startTime) + "ms)");
}
if (event.isClassClientError()) {
throw new NativeDaemonArgumentException(logCmd, event);
}
if (event.isClassServerError()) {
throw new NativeDaemonFailureException(logCmd, event);
}
return events.toArray(new NativeDaemonEvent[events.size()]);
}
现在看来，所有命令都是通过netd socket发送出去。但是这个socket是谁来接收呢？
netd Socket
system/netd
[to be continued...]