Android 关机流程 从kernel到framework
Android6.0关机流程
Android系统关机有如下方式：1.定时关机、2.命令行输入reboot重启、3.长按电源键出现关机对画框等，本文以长按电源键为例来分析基于Android 6.0的高通源码。
长按电源键会启动Android系统的按键消息处理机制。每个activity具有一个phonewindow对象，每个phonewindow对象具有一个DecorView对象，每个DecorVier又被设置到一个ViewRoot对象中(如图一).每个activity创建的时候会通过ViewRoot注册一个inputmanager，然后创建一组对应的事件获取和分发的线程：InputReader 和InputDispatch。当没有事件发生的时候Reader处于轮训状态，Dispatch处于休眠状态。当Reader获取到event的时候，Reader将会唤醒Dispatch，让其分发这个event到当前focus 的activity，然在activity的dispatchkeyEvent中进行处理。我们将关机流程分为PowerKey事件获取、Java层的关机流程分析、Native层的关机流程分析和kernel层的关机流程分析四部分来分析。
Kernel层事件处理
kernel层的事件上传，是指PowerKey按下的事件传递到Framework之前的流程，然后Framework层进行关机的相关操作。
1.pmic8xxx-pwrkey.c-input_report_key
static irqreturn_t pwrkey_press_irq(int irq, void*_pwrkey)
{
struct pmic8xxx_pwrkey*pwrkey = _pwrkey;
if (pwrkey->press== true) {
pwrkey->press = false;
return IRQ_HANDLED;
} else {
pwrkey->press = true;
}
input_report_key(pwrkey->pwr,KEY_POWER, 1);
//PowerKey按下事件，进入input.c中的inputEvent函数
input_sync(pwrkey->pwr);
return IRQ_HANDLED;
}
检测powerkey的按下，开始处理
2.input.c-inputEvent
void input_event(struct input_dev *dev,
unsigned int type, unsigned int code, intvalue)
{
unsigned long flags;
if (is_event_supported(type,dev->evbit, EV_MAX)) {
spin_lock_irqsave(&dev->event_lock,flags);
input_handle_event(dev, type, code, value);
//进入input_handle_event，上下文进行中断锁的操作
spin_unlock_irqrestore(&dev->event_lock,flags);
}
}
进入input_handle_event,然后注册该事件到device，交给Android的消息处理服务进行处理，其中我们开始说的reader读取到该事件。
static void input_handle_event(struct input_dev *dev,
unsigned int type, unsigned int code,int value)
{
int disposition;
disposition = input_get_disposition(dev,type, code, value);
if ((disposition &INPUT_PASS_TO_DEVICE) && dev->event)
dev->event(dev, type, code,value);
//event 处理
if (!dev->vals)
return;
if (disposition &INPUT_PASS_TO_HANDLERS) {
struct input_value *v;
if (disposition &INPUT_SLOT) {
v =&dev->vals[dev->num_vals++];
v->type = EV_ABS;
v->code = ABS_MT_SLOT;
v->value =dev->mt->slot;
}
v = &dev->vals[dev->num_vals++];
v->type = type;
v->code = code;
v->value = value;
}
if (disposition &INPUT_FLUSH) {
if (dev->num_vals >= 2)
input_pass_values(dev,dev->vals, dev->num_vals);
dev->num_vals = 0;
} else if (dev->num_vals >=dev->max_vals - 2) {
dev->vals[dev->num_vals++]= input_value_sync;
input_pass_values(dev,dev->vals, dev->num_vals);
dev->num_vals = 0;
}
}
inputread在读取到有keyboard事件上报后，会调用到keydispatch的notifykey，紧接着调用interceptKeyBeforeQueueing，最终返回到phonewindowmanager. interceptKeyBeforeQueueing(kernel相关的内容待更新、消息服务内容待更新)
kernel层工作 总结：
1.powerkey事件存储
2.消息服务读取powerkey事件
3.消息服务将keyevent进行传递
Java层关机
3.Phonewindowmanager.java-interceptKeyBeforeQueueing
public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
…
final boolean interactive = (policyFlags & FLAG_INTERACTIVE) != 0;
final boolean down = event.getAction() == KeyEvent.ACTION_DOWN;
final boolean canceled = event.isCanceled();
final int keyCode = event.getKeyCode();
…
// Handle special keys.
switch (keyCode) {
…
case KeyEvent.KEYCODE_POWER: {
result &=~ACTION_PASS_TO_USER;
isWakeKey = false; // wake-upwill be handled separately
if (down) {
interceptPowerKeyDown(event, interactive);
//进入interceptPowerKeyDown，上文处理各种消息来源，以及特殊按键功能
} else {
interceptPowerKeyUp(event,interactive, canceled);
}
break;
}
if (useHapticFeedback) {
performHapticFeedbackLw(null, HapticFeedbackConstants.VIRTUAL_KEY, false);
}
if (isWakeKey) {
wakeUp(event.getEventTime(),mAllowTheaterModeWakeFromKey,android.policy:KEY");
}
return result;
}
该方法主要完成各种按键消息的处理，包括按下电源键与音量下键进行抓屏、来电时按电源键启动静音模式等。在该方法根据条件处理按下电源键后的特殊任务，然后调用interceptPowerKeyDown进行进一步的处理。
4. interceptPowerKeyDown方法
private voidinterceptPowerKeyDown(KeyEvent event, boolean interactive) {
// 持有锁
if(!mPowerKeyWakeLock.isHeld()) {
mPowerKeyWakeLock.acquire();
}
// 多次按下，只处理一次
if(mPowerKeyPressCounter != 0) {
mHandler.removeMessages(MSG_POWER_DELAYED_PRESS);
}
// Detect userpressing the power button in panic when an application has
// taken overthe whole screen.
boolean panic =mImmersiveModeConfirmation.onPowerKeyDown(interactive,
SystemClock.elapsedRealtime(), isImmersiveMode(mLastSystemUiFlags));
if (panic) {
mHandler.post(mHiddenNavPanic);
}
// Latch power key stateto detect screenshot chord.
if (interactive&& !mScreenshotChordPowerKeyTriggered
&& (event.getFlags() & KeyEvent.FLAG_FALLBACK) == 0) {
mScreenshotChordPowerKeyTriggered = true;
mScreenshotChordPowerKeyTime = event.getDownTime();
interceptScreenshotChord();
}
//来电时powerKey，停止响铃
TelecomManagertelecomManager = getTelecommService();
boolean hungUp = false;
if (telecomManager !=null) {
if (telecomManager.isRinging()) {
// Pressing Power while there's a ringing incoming
// call should silence the ringer.
telecomManager.silenceRinger();
} else if ((mIncallPowerBehavior
&Settings.Secure.INCALL_POWER_BUTTON_BEHAVIOR_HANGUP) != 0
&& telecomManager.isInCall() &&interactive) {
// Otherwise, if "Power button ends call" isenabled,
// the Power button will hang up any current active call.
hungUp = telecomManager.endCall();
}
}
mPowerKeyHandled =hungUp || mScreenshotChordVolumeDownKeyTriggered
||mScreenshotChordVolumeUpKeyTriggered;
if (!mPowerKeyHandled) {
if (interactive) {
// When interactive, we're already awake.
// Wait for a long press or for the buttonto be released to decide what to do.
if(hasLongPressOnPowerBehavior()) {
Message msg =mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
msg.setAsynchronous(true);
mHandler.sendMessageDelayed(msg,
ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
}
} else{
wakeUpFromPowerKey(event.getDownTime());
if(mSupportLongPressPowerWhenNonInteractive &&hasLongPressOnPowerBehavior()) {
Message msg =mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
//PowerKey 的事件传递到handler进行处理
msg.setAsynchronous(true);
mHandler.sendMessageDelayed(msg,
ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
mBeganFromNonInteractive = true;
}else {
final int maxCount = getMaxMultiPressPowerCount();
if (maxCount <= 1) {
mPowerKeyHandled = true;
} else {
mBeganFromNonInteractive = true;
}
}
}
}
}
该方法中主要处理电源键按下后的一下情况，比如电源键松开之前一直亮屏、取消多次按键时的超时消息、当设置后按下电源键后结束响铃，挂断电话等。如果电源键按下的处理情况还没有处理时，解会分长按、短按和多次按来进行处理，此处我们只关心长按电源键，因此会进入mHandler.sendMessageDelayed的方法，而mHandler的类型是PolicyHandler，在初始化PhoneWindowManager时对其进行了赋值。调用sendMessageDelayed方法发送消息，最终会在PolicyHandler的handleMessage进行处理该消息。
5.PolicyHandler 函数
private class PolicyHandler extends Handler {
@Override
public voidhandleMessage(Message msg) {
switch(msg.what) {
…
case MSG_POWER_LONG_PRESS:
powerLongPress();
//处理函数进入powerLongPress,上下文中处理不同按键的逻辑
break;
…
}
}
}
该函数很简单，就是处理各种消息，这里大部分都是键盘按键消息，我们关心的长按电源键的消息处理。由源码可知，当PolicyHandler接收到MSG_POWER_LONG_PRESS消息之后，将会进入powerLongPress方法做进一步的处理。
6.powerLongPress 函数
private void powerLongPress() {
final intbehavior = getResolvedLongPressOnPowerBehavior();
switch(behavior) {
…
case LONG_PRESS_POWER_GLOBAL_ACTIONS:
mPowerKeyHandled = true;
if(!performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false)) {
performAuditoryFeedbackForAccessibilityIfNeed();
}
showGlobalActionsInternal();
//进入showGlobalActionsInternal，上下文针对不同的powerkey事件进行处理
break;
caseLONG_PRESS_POWER_SHUT_OFF:
caseLONG_PRESS_POWER_SHUT_OFF_NO_CONFIRM:
mPowerKeyHandled = true;
performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS,false);
sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
mWindowManagerFuncs.shutdown(behavior == LONG_PRESS_POWER_SHUT_OFF);
break;
}
}
在getResolvedLongPressOnPowerBehavior方法中，如果是工厂模式测试时，返回LONG_PRESS_POWER_SHUT_OFF_NO_CONFIRM，否则返回mLongPressOnPowerBehavior成员变量，而该成员变量是在PhoneWindowManager初始化时进行设置
mLongPressOnPowerBehavior =mContext.getResources().getInteger(
com.android.internal.R.integer.config_longPressOnPowerBehavior);
由mLongPressOnPowerBehavior成员变量初始化可知，getResolvedLongPressOnPowerBehavior方法中最终返回的是config_longPressOnPowerBehavior的值，而该值是在/framework/base/core/res/values/config.xml中进行配置的，在该配置文件中将config_longPressOnPowerBehavior属性值配为1代表是全局的动作；0代表不做任何动作；2表示确认后关机；3表示不确认，直接关机，这就是LONG_PRESS_POWER_SHUT_OFF_NO_CONFIRM的值，在工厂模式测试时，不需要确认直接关机。此处我们将会进入全局动作中，即会进入showGlobalActionsInternal方法，进行关机对话框的显示。
7. showGlobalActionsInternal函数
void showGlobalActionsInternal() {
sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
if(mGlobalActions == null) {
mGlobalActions = new GlobalActions(mContext, mWindowManagerFuncs);
}
final booleankeyguardShowing = isKeyguardShowingAndNotOccluded();
mGlobalActions.showDialog(keyguardShowing, isDeviceProvisioned());
//进入showdialog函数，显示关机对话框
if(keyguardShowing) {
// since it took two seconds of long press tobring this up,
// poke the wake lock so they have sometime to see the dialog.
mPowerManager.userActivity(SystemClock.uptimeMillis(),false);
}
}
该函数中首先调用sendCloseSystemWindows函数，发送由于全局关机动作的原因，最终会调用ActivityManagerService类的closeSystemDialogs函数关闭其他的系统对话框。利用单例模式创建GlobalActions对象，并保存到其成员变量mGlobalActions中，最终会调用GlobalActions的showDialog方法进行显示关机对话框。
8.GlobalActions.java-showdialog 函数
public void showDialog(
boolean keyguardShowing, boolean isDeviceProvisioned) {
mKeyguardShowing =keyguardShowing;
mDeviceProvisioned =isDeviceProvisioned;
if (mDialog != null) {
mDialog.dismiss();
mDialog = null;
// Show delayed, so that the dismiss of the previousdialog completes
mHandler.sendEmptyMessage(MESSAGE_SHOW);
} else {
handleShow();
//进入handleshow，上文处理keyguard是否显示，显示则推迟处理。
}
}
该方法中主要是判断是否会显示keyguard，如果之前已经有全局对话框显示，则发生延迟消息，以便其显示完后最终关闭，如果是第一次启动全局对话框，则会进入handleShow方法中进行处理。
9.handleshow 函数
private void handleShow() {
awakenIfNecessary();
mDialog = createDialog();//创建对话框，并相应点击事件
prepareDialog();//更新各个模式如静音、飞行
// If we only have 1 item and it's a simple press action,just do this action.
if (mAdapter.getCount() == 1
&& mAdapter.getItem(0)instanceof SinglePressAction
&&!(mAdapter.getItem(0) instanceof LongPressAction)) {
((SinglePressAction)mAdapter.getItem(0)).onPress();
} else {
WindowManager.LayoutParams attrs =mDialog.getWindow().getAttributes();
attrs.setTitle("GlobalActions");
mDialog.getWindow().setAttributes(attrs);
mDialog.show();
mDialog.getWindow().getDecorView().setSystemUiVisibility(View.STATUS_BAR_DISABLE_EXPAND);
}
}
在该方法中，首先调用awakenIfNecessary方法进行了屏幕唤醒，然后调用createDialog()创建全局关机对话框，当对话框创建完成后，调用prepareDialog方法进行keyguard窗口风格样式的设置，最后会进行我们全局关机对匡样式进行判断，如果是只有一个item，则会通过onPress方法进行处理，否则会进行系统UI显示的设置。此处我们进入creatDialog方法进行创建全局关机对话框。
10.PowerAction 点击函数
private final class PowerAction extends SinglePressAction
implementsLongPressAction {
…
public void onPress() {
// shutdownby making sure radio and power are handled accordingly.
mWindowManagerFuncs.shutdown(false /* confirm */);
//mWindowManagerFuncs实际上是windowmanagerservice的对象，进入shutdown
}
}
如果长按会进入过PowerAction的onLongPress函数，最后会进入到mWindowManagerFuncs.rebootSafeMode函数中；如果是短按关机Aciton会进入到PowerAction的onPress函数，最后进入到mWindowManagerFuncs.shutDown方法进行处理。在PhoneWindowManager的初始化过程可知，mWindowManagerFuncs被赋值为WindowManagerService，因此会调用WindowManagerService的shutdown方法。
11.windowmanagerservice.java-shutdown 函数
public void shutdown(boolean confirm) {
ShutdownThread.shutdown(mContext,confirm);
//调用shutdownThread的shutdown方法
}
12.shutdownThread.java-shutdown 方法
public static void shutdown(final Context context,boolean confirm) {
mReboot =false;
mRebootSafeMode = false;
Log.d(TAG,"!!! Request to shutdown !!!");
if (mSpew){
StackTraceElement[] stack = new Throwable().getStackTrace();
for(StackTraceElement element : stack)
{
Log.d(TAG, " |----" +element.toString());
}
}
if(SystemProperties.getBoolean("ro.monkey", false)) {
Log.d(TAG, "Cannot request to shutdown when Monkey is running,returning.");
return;
}
shutdownInner(context, confirm);
//进一步调用shutdowninner，上文判断，若在monkey，不进行关机操作
}
在该方法中只是初始化了一些参数,最后由shutdownInner方法进行处理，参数confirm来设置是否要弹出关机对话框。
13.shutdowninner 方法
static void shutdownInner(final Context context, booleanconfirm) {
…
if(confirm) {
…
} else {
beginShutdownSequence(context);
//开始进行关机准备，进入beginShutdownSequence
}
}
在该方法中，会通过传进来的confirm参数来判断是否要显示关机对话框，如果显示会设置关键对话框，如果不显示直接关机，无论显示与否，最后会进入到beginShutdownSequence方法，做进一步的关机处理。
14.beginshutdownsequence 函数
private static void beginShutdownSequence(Contextcontext) {
// Throw up a system dialog to indicate thedevice is rebooting / shutting down.
ProgressDialog pd = new ProgressDialog(context);
if(PowerManager.REBOOT_RECOVERY.equals(mRebootReason)) {
mRebootUpdate = new File(UNCRYPT_PACKAGE_FILE).exists();
if(mRebootUpdate) {
pd.setTitle(context.getText(com.android.internal.R.string.reboot_to_update_title));
pd.setMessage(context.getText(
com.android.internal.R.string.reboot_to_update_prepare));
pd.setMax(100);
pd.setProgressNumberFormat(null);
pd.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
pd.setProgress(0);
pd.setIndeterminate(false);
} else{
//Factory reset path. Set the dialog message accordingly.
pd.setTitle(context.getText(com.android.internal.R.string.reboot_to_reset_title));
pd.setMessage(context.getText(
com.android.internal.R.string.reboot_to_reset_message));
pd.setIndeterminate(true);
}
} else {
pd.setTitle(context.getText(com.android.internal.R.string.power_off));
pd.setMessage(context.getText(com.android.internal.R.string.shutdown_progress));
pd.setIndeterminate(true);
}
pd.setCancelable(false);
pd.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
// startthe thread that initiates shutdown
sInstance.mHandler = new Handler() {
};
beginAnimationTime = 0;
booleanmShutOffAnimation = configShutdownAnimation(context);
intscreenTurnOffTime = getScreenTurnOffTime(context);
synchronized (mEnableAnimatingSync) {
if(mEnableAnimating) {
if(mShutOffAnimation) {
Log.d(TAG, "mIBootAnim.isCustBootAnim() is true");
bootanimCust();//播放动画
}else {
pd.show();
sInstance.mProgressDialog = pd;
}
sInstance.mHandler.postDelayed(mDelayDim, screenTurnOffTime);
}
}
if(sInstance.getState() != Thread.State.NEW || sInstance.isAlive()) {
…
} else {
sInstance.start();//进入线程run方法
}
}
该方法主要初始化一些关机操作，比如获取audio，停止启动应用程序播放music等，最后调用ShutdownThread的start函数来启动关机线程，进入到ShutdownThread线程的run方法中。
15.run 函数
public void run() {
BroadcastReceiver br = new BroadcastReceiver() {
@Overridepublic void onReceive(Context context, Intent intent) {
// We don'tallow apps to cancel this, so ignore the result.
actionDone();
}
};
/*
* Write asystem property in case the system_server reboots before we
* get tothe actual hardware restart. If that happens, we'll retry at
* thebeginning of the SystemServer startup.
*/
{
Stringreason = (mReboot ? "1" : "0") + (mRebootReason != null ?mRebootReason : "");
SystemProperties.set(SHUTDOWN_ACTION_PROPERTY, reason);
//记录关机原因
}
/*
* If weare rebooting into safe mode, write a system property
*indicating so.
*/
if(mRebootSafeMode) {
SystemProperties.set(REBOOT_SAFEMODE_PROPERTY, "1");
}
Log.i(TAG,"Sending shutdown broadcast...");
// Firstsend the high-level shut down broadcast.
mActionDone= false;
Intentintent = new Intent(Intent.ACTION_SHUTDOWN);
intent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND);
mContext.sendOrderedBroadcastAsUser(intent,
UserHandle.ALL, null, br, mHandler, 0, null, null);
final long endTime = SystemClock.elapsedRealtime() +MAX_BROADCAST_TIME;
synchronized (mActionDoneSync) {
while(!mActionDone) {
long delay = endTime - SystemClock.elapsedRealtime();
if(delay <= 0) {
Log.w(TAG, "Shutdown broadcast timedout");
break;
}
try{
mActionDoneSync.wait(delay);
}catch (InterruptedException e) {
}
}
}
Log.i(TAG,"Shutting down activity manager...");
//关闭activitymanager
finalIActivityManager am =
ActivityManagerNative.asInterface(ServiceManager.checkService("activity"));
if (am !=null) {
try {
am.shutdown(MAX_BROADCAST_TIME);
} catch(RemoteException e) {
}
}
Log.i(TAG,"Shutting down package manager...");
//关闭packagemanager
finalPackageManagerService pm = (PackageManagerService)
ServiceManager.getService("package");
if (pm !=null) {
pm.shutdown();
}
String shutDownFile = null;
//showShutdownAnimation() is called from here to sync
//music andanimation properly
if(checkAnimationFileExist()) {
lockDevice();
showShutdownAnimation();
if(!isSilentMode()
&& (shutDownFile = getShutdownMusicFilePath()) != null) {
isShutdownMusicPlaying= true;
shutdownMusicHandler.obtainMessage(0, shutDownFile).sendToTarget();
}
}
Log.i(TAG,"wait for shutdown music");
final longendTimeForMusic = SystemClock.elapsedRealtime() + MAX_BROADCAST_TIME;
synchronized (mActionDoneSync) {
while(isShutdownMusicPlaying) {
long delay = endTimeForMusic - SystemClock.elapsedRealtime();
if(delay <= 0) {
Log.w(TAG, "play shutdown music timeout!");
break;
}
try{
mActionDoneSync.wait(delay);
}catch (InterruptedException e) {
}
}
if(!isShutdownMusicPlaying) {
Log.i(TAG, "play shutdown music complete.");
}
}
//关闭通信相关内容
// Shutdownradios.
shutdownRadios(MAX_RADIO_WAIT_TIME);
// ShutdownMountService to ensure media is in a safe state
IMountShutdownObserver observer = newIMountShutdownObserver.Stub() {
public void onShutDownComplete(int statusCode) throwsRemoteException {
Log.w(TAG, "Result code " + statusCode + " fromMountService.shutdown");
actionDone();
}
};
Log.i(TAG,"Shutting down MountService");
//关闭挂载服务
// Setinitial variables and time out time.
mActionDone= false;
final longendShutTime = SystemClock.elapsedRealtime() + MAX_SHUTDOWN_WAIT_TIME;
synchronized (mActionDoneSync) {
try {
final IMountService mount = IMountService.Stub.asInterface(
ServiceManager.checkService("mount"));
if(mount != null) {
mount.shutdown(observer);
}else {
Log.w(TAG, "MountService unavailable for shutdown");
}
} catch(Exception e) {
Log.e(TAG, "Exception during MountService shutdown", e);
}
while(!mActionDone) {
long delay = endShutTime - SystemClock.elapsedRealtime();
if(delay <= 0) {
Log.w(TAG, "Shutdown wait timed out");
break;
}
try{
mActionDoneSync.wait(delay);
}catch (InterruptedException e) {
}
}
}
//进入rebootorshutdown函数
rebootOrShutdown(mReboot, mRebootReason);
}
该函数中主要完成创建接收关机的广播，设置关机原因，关闭ActivityManagerService、PackagerManagerService、MountServie等，最后进入rebootOrshutDown进行关机操作。
16.rebootorshutdown 函数
public staticvoid rebootOrShutdown(boolean reboot, String reason) {
deviceRebootOrShutdown(reboot, reason);
//检查厂商的关机处理
if (reboot){
Log.i(TAG, "Rebooting, reason: " + reason);
PowerManagerService.lowLevelReboot(reason);
Log.e(TAG, "Reboot failed, will attempt shutdown instead");
} else if(SHUTDOWN_VIBRATE_MS > 0) {
//vibrate before shutting down
//关机震动
Vibrator vibrator = new SystemVibrator();
try {
vibrator.vibrate(SHUTDOWN_VIBRATE_MS, VIBRATION_ATTRIBUTES);
} catch(Exception e) {
//Failure to vibrate shouldn't interrupt shutdown. Just log it.
Log.w(TAG, "Failed to vibrate during shutdown.", e);
}
//vibrator is asynchronous so we need to wait to avoid shutting down too soon.
try {
Thread.sleep(SHUTDOWN_VIBRATE_MS);
} catch(InterruptedException unused) {
}
}
// Shutdownpower
Log.i(TAG,"Performing low-level shutdown...");
PowerManagerService.lowLevelShutdown();
//进入lowlevelshutdown函数
}
在该方法中，首先调用deviceRebootOrShutdown方法来查找OEM关机相关类，然后判断是否是重启，如果重启PowerManagerService.lowLevelReboot方法进行重启；否则如果是关机前有震动，则会创建Vibrator对象，并调用其vibrate方法执行震动操作，最后进入到PowerManagerService.lowLevelShutdown方法中执行关机操作。
17.powermanagerservice.java- lowLevelShutdown 函数
public static void lowLevelShutdown() {
SystemProperties.set("sys.powerctl", "shutdown");
//设置关机属性值，进入systemproperties.set函数
}
在该方法中调用，SystemProperties.set方法，修改sys.powerctl的属性值为shutdown
18. SystemProperties.java-set 函数
public static void set(String key, String val) {
//判断传入值的合法性
if(key.length() > PROP_NAME_MAX) {
throw newIllegalArgumentException("key.length > " + PROP_NAME_MAX);
}
if (val !=null && val.length() > PROP_VALUE_MAX) {
thrownew IllegalArgumentException("val.length > " +
PROP_VALUE_MAX);
}
native_set(key, val);
//调用底层native_set函数
}
该方法比较简单，只是判断了一下key和value的长度后，就进入本地方法native_set中。
Java层工作总结：
1.PhoneWindowManger负责接收由InputManagerService的发放的按键信息，本例中将会获取长
按Power键信息。
2.PolicyHandler发送长按Power键信息，并在其handleMessage方法中做相应的处理。
3.PhoneWindowManger的powerLongPress处理长按Power键的不同情况，1代表是全局的动作；
0代表不做任动作；2表示确认后关机；3表示不确认，直接关机。
4.GlobalActionsDialog调用createDialog创建关键对话框，将关机选择、重启选择、飞行模
式选择以封装的Action对象添加在适配器列表中。封装完成Action后就是创建关机对话框，采用MyAdapter适配器保存这些匹配。
5.WindowManagerService的shutDown方法，最终会进入到shutDownThread线程的rebootOrs
hutDown方法成关机操作。
6.最后进入到PowerManagerServie的lowLevelShutdown方法，进入到SystemProperties.se
t方法，将“sys.powerctl”属性设置为“shutdown”最后进入native层完成关机操作。
Native层关机
19.android_os_properties_set.cpp-native_set 函数
static void SystemProperties_set(JNIEnv *env, jobjectclazz,
jstringkeyJ, jstring valJ)
{
int err;
const char*key;
const char*val;
if (keyJ ==NULL) {
jniThrowNullPointerException(env, "key must not be null.");
return ;
}
key = env->GetStringUTFChars(keyJ, NULL);
if (valJ ==NULL) {
val =""; /* NULL pointer notallowed here */
} else {
val =env->GetStringUTFChars(valJ, NULL);
}
err = property_set(key, val);
//调用perperty_set方法，进入native关机
env->ReleaseStringUTFChars(keyJ, key);
if (valJ !=NULL) {
env->ReleaseStringUTFChars(valJ, val);
}
if (err < 0){
jniThrowException(env, "java/lang/RuntimeException",
"failed to set system property");
}
}
20.properties_set.cpp-property_set 函数
int property_set(const char *key, const char *value)
{
return__system_property_set(key, value);
//进一步调用 __system_property_set函数
}
21.system_properties.cpp-__system_property_set 函数
int __system_property_set(constchar *key, const char *value)
{
if (key == 0) return -1;
if (value == 0) value = "";
if (strlen(key) >= PROP_NAME_MAX) return-1;
if (strlen(value) >= PROP_VALUE_MAX)return -1;
prop_msg msg;
//将关机属性的name，value，size 放入到msg中
memset(&msg, 0, sizeof msg);
msg.cmd = PROP_MSG_SETPROP;
strlcpy(msg.name, key, sizeof msg.name);
strlcpy(msg.value, value, sizeofmsg.value);
const int err =send_prop_msg(&msg);
//将msg发送到服务端，property的服务进程在init.c中运行
//触发 关机属性值的设定 调用dopwrctrl
if (err < 0) {
return err;
}
return 0;
}
22.init.rc
on property:sys.powerctl=*
//表示当sys.powerctl被设置成任意值时触发下面的动作
powerctl${sys.powerctl}
init进程是Android系统的第一个进程，是由Linux内核启动。init进程主要作用是两个：一个是解析init.rc以及init{hardware}.rc等rc文件；
onproperty:sys.powerctl=*
powerctl${sys.powerctl}
在init.rc文件主要由以on开头和service开头，分别代表动作和服务；init进程会调用init_parser.c的parse_config函数来解析这些rc文件，最终会生成动作列表和服务列表，动作列表的定义在keywords.h中
int do_powerctl(int nargs, char**args);
#endif
……
KEYWORD(powerctl, COMMAND, 1,do_powerctl)
……
#ifdef __MAKE_KEYWORD_ENUM__
KEYWORD_COUNT,
};
Init进程通过drain_action_queue函数来解析动作列表和服务列表；通过设置init.rc中动作参数从而执行动作列表中对应的函数。另一个是初始化系统属性，init进程可以通过property_init函数初始化系统属性，并通过property_set函数来设置系统属性。并将设置的参数作为参数传入动作列表对应函数的参数中。因此在关机过程Step17中，通过property_set函数，将sys.powerctl属性值设置为“shutdown”，并交个动作列表中对应的函数do_powerctl来处理。
23.bulltins.c –do_powerctl 函数
int do_powerctl(int nargs, char **args)
{
charcommand[PROP_VALUE_MAX];
int res;
int len = 0;
int cmd = 0;
char*reboot_target;
res =expand_props(command, args[1], sizeof(command));
if (res) {
ERROR("powerctl: cannot expand '%s'\n", args[1]);
return-EINVAL;
}
if(strncmp(command, "shutdown", 8) == 0) {
cmd =ANDROID_RB_POWEROFF;
len = 8;
} else if(strncmp(command, "reboot", 6) == 0) {
cmd =ANDROID_RB_RESTART2;
len = 6;
} else {
ERROR("powerctl: unrecognized command '%s'\n", command);
return-EINVAL;
}
if(command[len] == ',') {
reboot_target = &command[len + 1];
} else if(command[len] == '\0') {
reboot_target = "";
} else {
ERROR("powerctl: unrecognized reboot target '%s'\n",&command[len]);
return-EINVAL;
}
returnandroid_reboot(cmd, 0, reboot_target);
//进入android_reboot 函数
}
该函数中首先读取Java层设置的该属性的值，我们设置为“shutdown”，所以会将cmd设置为ANDROID_RB_POWEROFF，长度为8；如果为重启，则cmd设置为ANDROID_RB_RESTART2。否则就是显示命令错误。因此我们知道sys.powerctl属性只有两个值，一个是shutdown(关机)；一个是reboot(重启)。最后将cmd命令作为参数传入android_reboot函数，做最后的关机操作。
24.Android_reboot.c-android_reboot 函数
int android_reboot(int cmd, int flags UNUSED, char *arg)
{
int ret;
sync();
remount_ro();
switch (cmd) {
caseANDROID_RB_RESTART:
ret =reboot(RB_AUTOBOOT);
break;
caseANDROID_RB_POWEROFF:
ret =reboot(RB_POWER_OFF);
//进入reboot 函数
break;
case ANDROID_RB_RESTART2:
ret =syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
LINUX_REBOOT_CMD_RESTART2, arg);
break;
default:
ret =-1;
}
return ret;
}
该函数首先是做了一些关机重启前的预处理工作，sync()作用是将缓存中的信息写入磁盘，以免程序异常结束导致文件被损坏，linux系统关机前会做几次这样的动作；而remount_ro()作用是强制将文件系统挂载为只读，不再允许任何写入操作，同时会通过检查/proc/mounts的设备状态来确认是否当前的所有写入工作已经完成，这个检查过程是阻塞操作。
cmd参数中ANDROID_RB_RESTART为普通关机，reason为RB_AUTOBOOT；ANDROID_RB_POWEROFF，无需reason，直接调用reboot进行关机；带参数的特殊重启ANDROID_RB_RESTART2，reason 将为默认值-1。本例中是reboot “shutdown”，则在Step18中传入的cmd参数为ANDROID_RB_POWEROFF，则会进入reboot(RB_POWER_OFF)函数进行处理。这些cmd值是在/bionic/libc/include/sys/Reboot.h中
#define RB_AUTOBOOT LINUX_REBOOT_CMD_RESTART
#define RB_HALT_SYSTEM LINUX_REBOOT_CMD_HALT
#define RB_ENABLE_CAD LINUX_REBOOT_CMD_CAD_ON
#define RB_DISABLE_CAD LINUX_REBOOT_CMD_CAD_OFF
#define RB_POWER_OFF LINUX_REBOOT_CMD_POWER_OFF
而LINUX_REBOOT_CMD_XXXX是在/binoic/libc/kernel/uapi/linux/Reboot.h中：我们直接进入到reboot(RB_POWER_OFF)函数中做关机操作。
#define LINUX_REBOOT_CMD_RESTART0x01234567
/* WARNING: DO NOT EDIT,AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define LINUX_REBOOT_CMD_HALT0xCDEF0123
#define LINUX_REBOOT_CMD_CAD_ON0x89ABCDEF
#define LINUX_REBOOT_CMD_CAD_OFF0x00000000
#define LINUX_REBOOT_CMD_POWER_OFF0x4321FEDC
/* WARNING: DO NOT EDIT,AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
#define LINUX_REBOOT_CMD_RESTART20xA1B2C3D4
#defineLINUX_REBOOT_CMD_SW_SUSPEND 0xD000FCE2
#define LINUX_REBOOT_CMD_KEXEC0x45584543
#endif
25.reboot.cpp – reboot 函数
include <unistd.h>
#include <sys/reboot.h>
extern "C" int __reboot(int, int, int, void*);
int reboot(int mode) {
return__reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, NULL);
//表明这是外部定义实现的一个C函数 进入kernel层关机
}
该函数中，调用Kernel层的_reboot函数做进一步分析。该函数在/bionic/libc/bionic/Reboot.cpp文件中。另外，在该文件中有extern"C" int __reboot，该表示在外部文件定义的__reboot函数，并且是以C语言方式进行编译连接，因此__reboot函数是c语言函数。
Native层工作总结 ：
1.采用property_set函数来设置系统属性的值，通过init进程解析init.rc文件的生成的动作
的列表，最终根据传进去的属性值(“shutdown”)，最终调用do_powerctl函数做关机的操作。
2.Android_reboot通cmd命令值做各种操作，cmd参数是在这些cmd值是在/bionic/libc/incl
ude/sys/Reboot.h中
3. 通过reboot中C++函数，最终调用到kernel层__reboot函数做kernel层的关机操作。
Kernel层关机
26.__reboot.s-reboot 函数
#include <private/bionic_asm.h>
ENTRY(__reboot)
mov ip, r7
ldr r7, =__NR_reboot
swi #0
mov r7, ip
cmn r0, #(MAX_ERRNO + 1)
bxls lr
neg r0, r0
b __set_errno_internal
END(__reboot)
发现__reboot函数最终映射到__NR_reboot，而__NR_reboot在文件/development/ndk/platforms/android-19/arch-mips/include/sys/Linux-syscalls.h中定义。
#define__NR_reboot (__NR_SYSCALL_BASE + 88)
其被指定了一个固定的偏移量，其被指定了一个固定的偏移量，在被调用的时候就是通过这个偏移量去内核中寻找对应的入口的，由此可见，内核中一定有着相同的定义，否则将不能成功调用。内核中对syscall偏移量的定义在内核源码中的arch/arm/include/asm/unistd.h，相关信息完全一致。已经找到了内核中的对应映射，那么下一步就要去找寻真正的实现函数了，/Include/asm-generic/unistd.h中可以找到内核对__NR_reboot的syscall函数映射。
/* kernel/sys.c */
#define __NR_setpriority 140
__SYSCALL(__NR_setpriority,sys_setpriority)
#define __NR_getpriority 141
__SYSCALL(__NR_getpriority,sys_getpriority)
#define __NR_reboot 142
__SYSCALL(__NR_reboot, sys_reboot)
由定义可知，__NR_reboot被映射到sys_reboot函数，该函数的定义在/kernel/inlude/linux/syscalls.h中
asmlinkagelong sys_reboot(int magic1, int magic2, unsigned int cmd,void __user *arg);
我们在文件sys.c中没有找到sys_reboot函数，但是发现有这样一个函数SYSCALL_DEFINE4(reboot,int, magic1, int, magic2, unsigned int, cmd, void __user *, arg)参数和sys_reboot函数基本相同，我们/kernel/inlude/linux/syscalls.h文件中有这样的定义：
#define SYSCALL_DEFINE4(name, ...)SYSCALL_DEFINEx(4, _##name, __VA_ARGS__)
#define SYSCALL_DEFINEx(x, sname,...)
#define __SYSCALL_DEFINEx(x, name,...) asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));
整合后的结果如下：
#defineSYSCALL_DEFINE4(name, ...) asmlinkagelong sys##_name(__SC_DECL##4(__VA_ARGS__))
可知就是sys_reboot函数，因此我们直接进入到SYSCALL_DEFINE4函数
27. sys.c-SYSCALL_DEFINE4 函数
SYSCALL_DEFINE4(reboot, int, magic1, int, magic2,unsigned int, cmd,
void __user*, arg)
{
structpid_namespace *pid_ns = task_active_pid_ns(current);
charbuffer[256];
int ret = 0;
/* We only trustthe superuser with rebooting the system. */
if(!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))
return-EPERM;
/* For safety,we require "magic" arguments. */
if (magic1 !=LINUX_REBOOT_MAGIC1 ||
(magic2 != LINUX_REBOOT_MAGIC2 &&
magic2 != LINUX_REBOOT_MAGIC2A&&
magic2 !=LINUX_REBOOT_MAGIC2B &&
magic2 != LINUX_REBOOT_MAGIC2C))
return-EINVAL;
/*
* If pid namespaces are enabled and thecurrent task is in a child
* pid_namespace, the command is handled byreboot_pid_ns() which will
* call do_exit().
*/
ret =reboot_pid_ns(pid_ns, cmd);
if (ret)
return ret;
/* Instead oftrying to make the power_off code look like
* halt when pm_power_off is not set do it theeasy way.
*/
if ((cmd ==LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)
cmd =LINUX_REBOOT_CMD_HALT;
mutex_lock(&reboot_mutex);
switch (cmd) {
caseLINUX_REBOOT_CMD_RESTART:
kernel_restart(NULL);
break;
caseLINUX_REBOOT_CMD_CAD_ON:
C_A_D = 1;
break;
caseLINUX_REBOOT_CMD_CAD_OFF:
C_A_D = 0;
break;
caseLINUX_REBOOT_CMD_HALT:
kernel_halt();
do_exit(0);
panic("cannothalt");
caseLINUX_REBOOT_CMD_POWER_OFF:
kernel_power_off();
// kernel 关闭电源
do_exit(0);
break;
caseLINUX_REBOOT_CMD_RESTART2:
if(strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) < 0) {
ret =-EFAULT;
break;
}
buffer[sizeof(buffer)- 1] = '\0';
kernel_restart(buffer);
break;
#ifdef CONFIG_KEXEC
caseLINUX_REBOOT_CMD_KEXEC:
ret =kernel_kexec();
break;
#endif
#ifdef CONFIG_HIBERNATION
caseLINUX_REBOOT_CMD_SW_SUSPEND:
ret =hibernate();
break;
#endif
default:
ret =-EINVAL;
break;
}
mutex_unlock(&reboot_mutex);
return ret;
}
在该函数中，首先检测权限问题，只有超级用户才可以执行重启操作，否则返回权限错误，对应的权限列表在/kernel/include/uapi/linux/Capability.h文件中。CAP_SYS_BOOT的值为22，随后对magicnumber进行了校验。接下来做了一个判断就是如果用户要求关机，而pm_power_off为空，则就把用户的关机命令转化为挂起。pm_power_off的定义位置在/kernel/arch/arm/kernel/Process.c
void (*pm_power_off)(void);
EXPORT_SYMBOL(pm_power_off);
可知pm_power_off为函数指针，而且做了全局操作，整个kernel都可以调用它。最后会调用kernel_power_off函数完成关机操作。
28.kernel_power_off 函数
/* kernel_power_off- power_off the system
*
* Shutdown everything and perform a clean systempower_off.
*/
void kernel_power_off(void)
{
kernel_shutdown_prepare(SYSTEM_POWER_OFF);//准备shutdown
if(pm_power_off_prepare)
pm_power_off_prepare();
migrate_to_reboot_cpu();
syscore_shutdown();
printk(KERN_EMERG"Power down.\n");
kmsg_dump(KMSG_DUMP_POWEROFF);
machine_power_off();//machine关闭电源
}
Kernel层工作总结：
1. 调用syscalldefine 关机
2. 存储相关信息并关闭电源