Android的SAFE MODE（安全模式）

android系统，按住MENU键开机，会安全模式进入系统。
代码位置：

frameworks/policies/base/phone/com/android/internal/policy/impl/PhoneWindowManager.java

收索SAFE MODE 这个tag会看到相关代码。
步骤：在开机动画时，按住MENU键（或者字母S键，方向键的中间键，鼠标左键中的一个）直到开机，会进入安全模式。

得到log如下：

I/WindowManager( 101): SAFE MODE ENABLED (menu=1 s=-1 dpad=-1 trackball=-1)

现象：在机器左小脚显示“安全模式”。

Android5.1:

frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java

public boolean detectSafeMode() {
if (!mInputMonitor.waitForInputDevicesReady(
INPUT_DEVICES_READY_FOR_SAFE_MODE_DETECTION_TIMEOUT_MILLIS)) {
Slog.w(TAG, "Devices still not ready after waiting "
+ INPUT_DEVICES_READY_FOR_SAFE_MODE_DETECTION_TIMEOUT_MILLIS
+ " milliseconds before attempting to detect safe mode.");
}

int menuState = mInputManager.getKeyCodeState(-1, InputDevice.SOURCE_ANY,
        KeyEvent.KEYCODE_MENU);
int sState = mInputManager.getKeyCodeState(-1, InputDevice.SOURCE_ANY, KeyEvent.KEYCODE_S);
int dpadState = mInputManager.getKeyCodeState(-1, InputDevice.SOURCE_DPAD,
        KeyEvent.KEYCODE_DPAD_CENTER);
int trackballState = mInputManager.getScanCodeState(-1, InputDevice.SOURCE_TRACKBALL,
        InputManagerService.BTN_MOUSE);
int volumeDownState = mInputManager.getKeyCodeState(-1, InputDevice.SOURCE_ANY,
        KeyEvent.KEYCODE_VOLUME_DOWN);
mSafeMode = menuState > 0 || sState > 0 || dpadState > 0 || trackballState > 0
        || volumeDownState > 0;
try {
    if (SystemProperties.getInt(ShutdownThread.REBOOT_SAFEMODE_PROPERTY, 0) != 0) {
        mSafeMode = true;
        SystemProperties.set(ShutdownThread.REBOOT_SAFEMODE_PROPERTY, "");
    }
} catch (IllegalArgumentException e) {
}
if (mSafeMode) {
    Log.i(TAG, "SAFE MODE ENABLED (menu=" + menuState + " s=" + sState
            + " dpad=" + dpadState + " trackball=" + trackballState + ")");
} else {
    Log.i(TAG, "SAFE MODE not enabled");
}
mPolicy.setSafeMode(mSafeMode);
return mSafeMode;

}

要把safe mode禁止掉，把mSafeMode赋值为false即可。