android去除安全模式

问题：android长按power，出现关机、重启、飞行模式界面，长按关机会提示是否进入安全模式，现在需要去除这个功能。

在识别长按的是否返回可以解决该问题。
现在说一下我的改法：
在首次开机后，会在/data/system/users/目录下面生成0.xml（本机）和userlist.xml（游客）两个文件，这两个xml文件就会有一些UserManager里面的功能限制，安全模式就在这其中。

/**
     * Specifies if the user is not allowed to reboot the device into safe boot mode.
     * This can only be set by device owners and profile owners on the primary user.
     * The default value is false.
     *
     * 
Key for user restrictions.
     * 
Type: Boolean
     * @see DevicePolicyManager#addUserRestriction(ComponentName, String)
     * @see DevicePolicyManager#clearUserRestriction(ComponentName, String)
     * @see #getUserRestrictions()
     */
    public static final String DISALLOW_SAFE_BOOT = "no_safe_boot";

开机初始化UserManagerService时会生成并写入限制功能到这两个xml文件中：

private UserManagerService(Context context, PackageManagerService pm,
            Object packagesLock, File dataDir) {
        mContext = context;
        mPm = pm;
        mPackagesLock = packagesLock;
        mHandler = new MainHandler();
        synchronized (mPackagesLock) {
            mUsersDir = new File(dataDir, USER_INFO_DIR);
            mUsersDir.mkdirs();
            // Make zeroth user directory, for services to migrate their files to that location
            File userZeroDir = new File(mUsersDir, String.valueOf(UserHandle.USER_SYSTEM));
            userZeroDir.mkdirs();
            FileUtils.setPermissions(mUsersDir.toString(),
                    FileUtils.S_IRWXU | FileUtils.S_IRWXG | FileUtils.S_IROTH | FileUtils.S_IXOTH,
                    -1, -1);
            mUserListFile = new File(mUsersDir, USER_LIST_FILENAME);
            initDefaultGuestRestrictions(); // 初始化游客权限
            readUserListLP(); // 初始化管理员权限
            sInstance = this;
        }
        mLocalService = new LocalService();
        LocalServices.addService(UserManagerInternal.class, mLocalService);
        mLockPatternUtils = new LockPatternUtils(mContext);
        mUserStates.put(UserHandle.USER_SYSTEM, UserState.STATE_BOOTING);
    }

initDefaultGuestRestrictions()很简单明了，不多说：

/**
     * If default guest restrictions haven't been initialized yet, add the basic
     * restrictions.
     */
    private void initDefaultGuestRestrictions() {
        synchronized (mGuestRestrictions) {
            if (mGuestRestrictions.isEmpty()) {
                mGuestRestrictions.putBoolean(UserManager.DISALLOW_CONFIG_WIFI, true);
                mGuestRestrictions.putBoolean(UserManager.DISALLOW_INSTALL_UNKNOWN_SOURCES, true);
                mGuestRestrictions.putBoolean(UserManager.DISALLOW_OUTGOING_CALLS, true);
                mGuestRestrictions.putBoolean(UserManager.DISALLOW_SMS, true);
            }
        }
    }

readUserListLP首先会查看是否存在该文件，如果存在就不初始化了，所以之前调试抓log的时候，里面的log永远打不出来，需要恢复出厂设置才会打。

if (!mUserListFile.exists()) {
            fallbackToSingleUserLP();
            return;
        }

之后关键的代码在fallbackToSingleUserLP

Bundle restrictions = new Bundle();
        try {
            final String[] defaultFirstUserRestrictions = mContext.getResources().getStringArray(
                    com.android.internal.R.array.config_defaultFirstUserRestrictions);
            for (String userRestriction : defaultFirstUserRestrictions) {
                if (UserRestrictionsUtils.isValidRestriction(userRestriction)) {
                    restrictions.putBoolean(userRestriction, true);
                }
            }
        } catch (Resources.NotFoundException e) {
            Log.e(LOG_TAG, "Couldn't find resource: config_defaultFirstUserRestrictions", e);
        }

config_defaultFirstUserRestrictions文件配置需要限制的功能，然后初始化的时候一一设置为true。
想要限制安全模式功能，按如下修改即可：

    
    	no_safe_boot
    

注意overlay