正常关机流程

/****************************************************************************************/
1.]从long power key到出现关机界面
/****************************************************************************************/
frameworks/base/services/core/java/com/android/server/policy/PhoneWindowManager.java
    public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags) {
            case KeyEvent.KEYCODE_POWER: {
                result &= ~ACTION_PASS_TO_USER;
                isWakeKey = false; // wake-up will be handled separately
                if (down) {
                    interceptPowerKeyDown(event, interactive);
                } else {
                    interceptPowerKeyUp(event, interactive, canceled);
                }
                break;
            }
    }


    private void interceptPowerKeyDown(KeyEvent event, boolean interactive) {
          Message msg = mHandler.obtainMessage(MSG_POWER_LONG_PRESS);
          msg.setAsynchronous(true);
          mHandler.sendMessageDelayed(msg, ViewConfiguration.get(mContext).getDeviceGlobalActionKeyTimeout());
    }


    private class PolicyHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_POWER_LONG_PRESS:
                    powerLongPress();
                    break;
   }
}


    private void powerLongPress() {
        final int behavior = getResolvedLongPressOnPowerBehavior();
        switch (behavior) {
        case LONG_PRESS_POWER_GLOBAL_ACTIONS:
            mPowerKeyHandled = true;
            if (!performHapticFeedbackLw(null, HapticFeedbackConstants.LONG_PRESS, false)) {
                performAuditoryFeedbackForAccessibilityIfNeed();
            }
            showGlobalActionsInternal();
            break;
}
    }


    void showGlobalActionsInternal() {
        sendCloseSystemWindows(SYSTEM_DIALOG_REASON_GLOBAL_ACTIONS);
        if (mGlobalActions == null) {
            mGlobalActions = new GlobalActions(mContext, mWindowManagerFuncs);
        }
        final boolean keyguardShowing = isKeyguardShowingAndNotOccluded();
        mGlobalActions.showDialog(keyguardShowing, isDeviceProvisioned());
        if (keyguardShowing) {
            // since it took two seconds of long press to bring this up,
            // poke the wake lock so they have some time to see the dialog.
            mPowerManager.userActivity(SystemClock.uptimeMillis(), false);
        }
    }


/****************************************************************************************/
2.]按下reboot 按键
调用powermanagerservice的reboot 接口
/****************************************************************************************/
frameworks/base/services/core/java/com/android/server/power/PowerManagerService.java
        /**
         * Reboots the device.
         *
         * @param confirm If true, shows a reboot confirmation dialog.
         * @param reason The reason for the reboot, or null if none.
         * @param wait If true, this call waits for the reboot to complete and does not return.
         */
        @Override // Binder call
        public void reboot(boolean confirm, String reason, boolean wait) {
            mContext.enforceCallingOrSelfPermission(android.Manifest.permission.REBOOT, null);
            if (PowerManager.REBOOT_RECOVERY.equals(reason)) {
                mContext.enforceCallingOrSelfPermission(android.Manifest.permission.RECOVERY, null);
            }


            final long ident = Binder.clearCallingIdentity();
            try {
                shutdownOrRebootInternal(false, confirm, reason, wait);
            } finally {
                Binder.restoreCallingIdentity(ident);
            }
        }


    private void shutdownOrRebootInternal(final boolean shutdown, final boolean confirm,
            final String reason, boolean wait) {
        if (mHandler == null || !mSystemReady) {
            throw new IllegalStateException("Too early to call shutdown() or reboot()");
        }


        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                synchronized (this) {
                    if (shutdown) {
                        ShutdownThread.shutdown(mContext, confirm);
                    } else {
                        ShutdownThread.reboot(mContext, reason, confirm);
                    }
                }
            }
        };


/****************************************************************************************/
3.]从powermanagerservice到shutdown thread
/****************************************************************************************/
frameworks/base/services/core/java/com/android/server/power/ShutdownThread.java:
    /**
     * Request a clean shutdown, waiting for subsystems to clean up their
     * state etc.  Must be called from a Looper thread in which its UI
     * is shown.
     *
     * @param context Context used to display the shutdown progress dialog.
     * @param reason code to pass to the kernel (e.g. "recovery"), or null.
     * @param confirm true if user confirmation is needed before shutting down.
     */
    public static void reboot(final Context context, String reason, boolean confirm) {
        mReboot = true;
        mRebootSafeMode = false;
        mRebootUpdate = false;
        mRebootReason = reason;
        shutdownInner(context, confirm);
    }
08-15 16:55:49.358   554  2615 W System.err: java.lang.Exception: ShutdownThread: reboot
08-15 16:55:49.359   554  2615 W System.err: at com.android.server.power.ShutdownThread.reboot(ShutdownThread.java:228)
08-15 16:55:49.359   554  2615 W System.err: at com.android.server.power.PowerManagerService$3.run(PowerManagerService.java:2329)
08-15 16:55:49.359   554  2615 W System.err: at android.os.Handler.handleCallback(Handler.java:739)
08-15 16:55:49.359   554  2615 W System.err: at android.os.Handler.dispatchMessage(Handler.java:95)
08-15 16:55:49.359   554  2615 W System.err: at android.os.Looper.loop(Looper.java:148)
08-15 16:55:49.359   554  2615 W System.err: at android.os.HandlerThread.run(HandlerThread.java:61)
08-15 16:55:49.359   554  2615 W System.err: at com.android.server.ServiceThread.run(ServiceThread.java:46)
08-15 16:55:49.360   554  2615 D ShutdownThread: Notifying thread to start shutdown longPressBehavior=1


然后调进了shutdownThread的run函数，栈并没有显示怎样调进去的。


08-15 16:55:49.360   554  2615 D ShutdownThread: Notifying thread to start shutdown longPressBehavior=1
08-15 16:55:49.403   554  2615 D InputDispatcher: channel 'fa020be  (server)' ~ registerInputChannel - monitor=false
08-15 16:55:49.403   554  2615 D InputDispatcher: setInputWindows
08-15 16:55:49.403   554  2615 D InputDispatcher: Focus left window: Window{8e3e186 u0 GlobalActions}
08-15 16:55:49.403   554  2615 D InputDispatcher: Focus entered window: Window{fa020be u0 android}
08-15 16:55:49.408   554  5868 W System.err: java.lang.Exception: shutdownThread: run
08-15 16:55:49.408   554  5868 W System.err: at com.android.server.power.ShutdownThread.run(ShutdownThread.java:384)


/****************************************************************************************/
4.]从shutdown thread再到powermanager service的lowlevel
/****************************************************************************************/
run -> rebootOrShutdown(mContext, mReboot, mRebootReason);
    public static void rebootOrShutdown(final Context context, boolean reboot, String reason) {
        deviceRebootOrShutdown(reboot, reason);
        if (reboot) {
            Log.i(TAG, "Rebooting, reason: " + reason);
            PowerManagerService.lowLevelReboot(reason);
            Log.e(TAG, "Reboot failed, will attempt shutdown instead");
}
        // Shutdown power
        Log.i(TAG, "Performing low-level shutdown...");
        PowerManagerService.lowLevelShutdown();
    }
这里又调入：PowerManagerService
    public static void lowLevelReboot(String reason) {
        if (reason == null) {
            reason = "";
        }
        if (reason.equals(PowerManager.REBOOT_RECOVERY)) {
            // If we are rebooting to go into recovery, instead of
            // setting sys.powerctl directly we'll start the
            // pre-recovery service which will do some preparation for
            // recovery and then reboot for us.
            SystemProperties.set("ctl.start", "pre-recovery");
        } else {
            SystemProperties.set("sys.powerctl", "reboot," + reason);
        }
    }


/****************************************************************************************/
5.]触发property:sys.powerctl改变对应的处理函数
/****************************************************************************************/
SystemProperties.set(sys.powerctl, xxx);


sys.powerctl属性触发开关在init.rc定义
on property:sys.powerctl=* powerctl ${sys.powerctl}


我们来解读这句话，on property:sys.powerctl=*表示当属性sys.powerctl设置为任何值是都会跑到这里，
触发动作是powerctl ${sys.powerctl},这个动作的意思是调用powerctl指令，并把sys.powerctl的值传给它。
powerctl指令在init进程会执行。
从下面的表可知，powerctl对应的操作是do_powerctl
[system/core/init/keywords.h]
KEYWORD(powerctl, COMMAND, 1, do_powerctl)


do_powerctl的实现
代码如下：
[system/core/init/builtins.c]
int do_powerctl(int nargs, char **args) { ....  return android_reboot(cmd, 0, reboot_target); }


它调用android_reboot()函数，实现如下：
[system/core/libcutils/android_reboot.c]