Android中用戶管理的一些總結(jié)

用戶管理

  • 如何創(chuàng)建另外一個用戶？如何區(qū)分訪客用戶及其他用戶？各種用戶的區(qū)別是什么？
  • Android是怎么限制最多用戶數(shù)量的？Flyme最多可以創(chuàng)建幾個，在哪里控制了？
  • 切換用戶做了些什么操作？第三方應(yīng)用有什么辦法知道用戶切換了？如何知道自己當(dāng)前處于哪個用戶？
  • 用戶切換后，原來的進(jìn)程怎么處理的？SystemUI是新的進(jìn)程嗎？微信是開了兩個進(jìn)程嗎，進(jìn)程ID是怎么分配的，有什么特點(diǎn)？
  • 不同用戶是如何分別存儲數(shù)據(jù)的？多個用戶之間如何共享數(shù)據(jù)？

UserManagerService創(chuàng)建過程

 mUsersDir = new File(dataDir, USER_INFO_DIR);
 
// Make zeroth user directory, for services to migrate their files to that location
File userZeroDir = new File(mUsersDir, "0");
userZeroDir.mkdirs();
FileUtils.setPermissions(mUsersDir.toString(),
FileUtils.S_IRWXU|FileUtils.S_IRWXG
    |FileUtils.S_IROTH|FileUtils.S_IXOTH,
    -1, -1);

創(chuàng)建0號用戶的路徑并設(shè)置對應(yīng)的路徑權(quán)限,下面貼一段網(wǎng)上找到的標(biāo)志位與權(quán)限之間的關(guān)系(GRP=group, OTH=other)


S_IFMT
    type of file 
S_IFBLK
    block special 
S_IFCHR
    character special 
S_IFIFO
    FIFO special 
S_IFREG
    regular 
S_IFDIR
    directory 
S_IFLNK
    symbolic link 

File mode bits:

S_IRWXU
    read, write, execute/search by owner 
S_IRUSR
    read permission, owner 
S_IWUSR
    write permission, owner 
S_IXUSR
    execute/search permission, owner 
S_IRWXG
    read, write, execute/search by group 
S_IRGRP
    read permission, group 
S_IWGRP
    write permission, group 
S_IXGRP
    execute/search permission, group 
S_IRWXO
    read, write, execute/search by others 
S_IROTH
    read permission, others 
S_IWOTH
    write permission, others 
S_IXOTH
    execute/search permission, others 
S_ISUID
    set-user-ID on execution 
S_ISGID
    set-group-ID on execution 
S_ISVTX
    on directories, restricted deletion flag

存儲用戶信息的文件路徑在: data/system/users/userlist.xml

createUser 用戶創(chuàng)建

用戶創(chuàng)建過程首先會檢查 uid 是否符合要求.

    /**
     * Enforces that only the system UID or root's UID or apps that have the
     * {@link android.Manifest.permission#MANAGE_USERS MANAGE_USERS}
     * permission can make certain calls to the UserManager.
     *
     * @param message used as message if SecurityException is thrown
     * @throws SecurityException if the caller is not system or root
     */
    private static final void checkManageUsersPermission(String message) {
        final int uid = Binder.getCallingUid();
        if (uid != Process.SYSTEM_UID && uid != 0
                && ActivityManager.checkComponentPermission(
                        android.Manifest.permission.MANAGE_USERS,
                        uid, -1, true) != PackageManager.PERMISSION_GRANTED) {
            throw new SecurityException("You need MANAGE_USERS permission to: " + message);
        }
    }

然后會進(jìn)入到 CreateUserInternal() 方法中,在該方法中首先會檢查 用戶是否被賦予了 DISALLOW_ADD_USER 權(quán)限，該權(quán)限禁止用戶添加用戶.

        if (getUserRestrictions(UserHandle.getCallingUserId()).getBoolean(
                UserManager.DISALLOW_ADD_USER, false)) {
            Log.w(LOG_TAG, "Cannot add user. DISALLOW_ADD_USER is enabled.");
            return null;
        }

創(chuàng)建用戶的過程中會創(chuàng)建 UserInfo 對象, UserInfo 對象中的 partial 屬性表明該 UserInfo 對象并沒有完全創(chuàng)建.接著會創(chuàng)建用戶的目錄,調(diào)用 getUserSystemDirectory 創(chuàng)建某個用戶對應(yīng)的路徑.
這里會判斷系統(tǒng)中 EFS 這一功能是否打開. EFS(文件加密系統(tǒng)) ,如果打開了 EFS 功能，就會創(chuàng)建一個加密路徑 /data/secure/system/, 否則創(chuàng)建的就是普通路徑 /data/system .

    userInfo.partial = true;
    Environment.getUserSystemDirectory(userInfo.id).mkdirs();

    /**
     * Gets the system directory available for secure storage.
     * If Encrypted File system is enabled, it returns an encrypted directory (/data/secure/system).
     * Otherwise, it returns the unencrypted /data/system directory.
     * @return File object representing the secure storage system directory.
     * @hide
     */
    public static File getSystemSecureDirectory() {
        if (isEncryptedFilesystemEnabled()) {
            return new File(SECURE_DATA_DIRECTORY, "system");
        } else {
            return new File(DATA_DIRECTORY, "system");
        }
    }

最后系統(tǒng)會發(fā)出 ACTION_USER_ADDED 這個廣播,只有聲明了 MANAGE_USERS 這個權(quán)限才能接受到這個廣播.

            if (userInfo != null) {
                Intent addedIntent = new Intent(Intent.ACTION_USER_ADDED);
                addedIntent.putExtra(Intent.EXTRA_USER_HANDLE, userInfo.id);
                mContext.sendBroadcastAsUser(addedIntent, UserHandle.ALL,
                        android.Manifest.permission.MANAGE_USERS);
            }

用戶的權(quán)限類別

  • FLAG_PRIMARY : 只有一個用戶能設(shè)置擁有這個標(biāo)志位。意味著這個標(biāo)志位TBD.
  • FLAG_ADMIN : 擁有創(chuàng)建和刪除用戶的權(quán)限.
  • FLAG_GUEST : 訪客用戶的標(biāo)識.
  • FLAG_RESTRICTED : 受限，可能無法安裝應(yīng)用，或認(rèn)證wifi路徑.
  • FLAG_MANAGED_PROFILE : 表明該user是另外一個用戶的 profile.
  • FLAG_DISABLED : 表明該用戶被禁用.

各種用戶擁有不同的權(quán)限組合. 例如 USER_OWNER 是 PRIMARY 和 ADMIN 的組合.

第三方應(yīng)用獲取當(dāng)前用戶

getCurrentUser() 是AMS中的一個接口，用來獲取當(dāng)前用戶,這里會檢查 是否有 INTERACT_ACROSS_USERS 和 INTERACT_ACROSS_USERS_FULL 這兩個權(quán)限.

    @Override
    public UserInfo getCurrentUser() {
        if ((checkCallingPermission(INTERACT_ACROSS_USERS)
                != PackageManager.PERMISSION_GRANTED) && (
                checkCallingPermission(INTERACT_ACROSS_USERS_FULL)
                != PackageManager.PERMISSION_GRANTED)) {
            String msg = "Permission Denial: getCurrentUser() from pid="
                    + Binder.getCallingPid()
                    + ", uid=" + Binder.getCallingUid()
                    + " requires " + INTERACT_ACROSS_USERS;
            Slog.w(TAG, msg);
            throw new SecurityException(msg);
        }
        synchronized (this) {
            int userId = mTargetUserId != UserHandle.USER_NULL ? mTargetUserId : mCurrentUserId;
            return getUserManagerLocked().getUserInfo(userId);
        }
    }

切換用戶

切換用戶用的是 AMS 中的 SwitchUser() 函數(shù).

    @Override
    public boolean switchUser(final int userId) {
        enforceShellRestriction(UserManager.DISALLOW_DEBUGGING_FEATURES, userId);
        String userName;
        synchronized (this) {
            UserInfo userInfo = getUserManagerLocked().getUserInfo(userId);
            if (userInfo == null) {
                Slog.w(TAG, "No user info for user #" + userId);
                return false;
            }
            if (userInfo.isManagedProfile()) {
                Slog.w(TAG, "Cannot switch to User #" + userId + ": not a full user");
                return false;
            }
            userName = userInfo.name;
            mTargetUserId = userId;
        }
        mHandler.removeMessages(START_USER_SWITCH_MSG);
        mHandler.sendMessage(mHandler.obtainMessage(START_USER_SWITCH_MSG, userId, 0, userName));
        return true;
    }

這里首先會調(diào)用 enforceShellRestriction() 函數(shù)檢查是否是 通過 shell終端來調(diào)用這個方法來切換用戶.

如果 userHandle 小于0或者該用戶受到限制，就會拋出 SecurityException 這個異常.

    enforceShellRestriction(UserManager.DISALLOW_DEBUGGING_FEATURES, userId);



    void enforceShellRestriction(String restriction, int userHandle) {
        if (Binder.getCallingUid() == Process.SHELL_UID) {
            if (userHandle < 0
                    || mUserManager.hasUserRestriction(restriction, userHandle)) {
                throw new SecurityException("Shell does not have permission to access user "
                        + userHandle);
            }
        }
    }

最后會發(fā)送 START_USER_SWITCH_MSG 這個廣播,AMS本身接收這個廣播后會調(diào)用 startUser() 方法來調(diào)起新用戶.

startUser() 函數(shù)很長.

首先會檢查 用戶是否有 INTERACT_ACROSS_USERS_FULL 這個權(quán)限，如果沒有就會直接拋出異常.

       if (checkCallingPermission(INTERACT_ACROSS_USERS_FULL)
                != PackageManager.PERMISSION_GRANTED) {
            String msg = "Permission Denial: switchUser() from pid="
                    + Binder.getCallingPid()
                    + ", uid=" + Binder.getCallingUid()
                    + " requires " + INTERACT_ACROSS_USERS_FULL;
            Slog.w(TAG, msg);
            throw new SecurityException(msg);
        }

接著這里有一行代碼，作用暫時未知.

                mStackSupervisor.setLockTaskModeLocked(null, false, "startUser");

這里會判斷是否處于前臺狀態(tài)，如果處于前臺狀態(tài)，會進(jìn)行一個動畫的切換.

            if (foreground) {
                mWindowManager.startFreezingScreen(R.anim.screen_user_exit,
                       R.anim.screen_user_enter);
            }

這里判斷如果處于前臺狀態(tài)，就要隱藏掉切換后用戶不可見的 display , 這里 mWindowManager.lockNow(null) 的邏輯被屏蔽掉了.如果不處于前臺狀態(tài)，這里就沒有屏蔽圖層，只是切換了用戶的profile，然后會在 mUserLru 中記錄最近使用的user.

                if (foreground) {
                    mCurrentUserId = userId;
                    mTargetUserId = UserHandle.USER_NULL; // reset, mCurrentUserId has caught up
                    updateCurrentProfileIdsLocked();
                    mWindowManager.setCurrentUser(userId, mCurrentProfileIds);
                    //FLYME:huangxiaotao@SHELL.Feature modify for the guest mode {@
                    if (mzIsFalse()) {
                     // Once the internal notion of the active user has switched, we lock the device
                        // with the option to show the user switcher on the keyguard.
                        mWindowManager.lockNow(null);
                    }
                    //@}
                } else {
                    final Integer currentUserIdInt = Integer.valueOf(mCurrentUserId);
                    updateCurrentProfileIdsLocked();
                    mWindowManager.setCurrentProfileIds(mCurrentProfileIds);
                    mUserLru.remove(currentUserIdInt);
                    mUserLru.add(currentUserIdInt);
                }

這里會更新一波 UserState , 這里的 UserState 有些類似操作系統(tǒng)里的進(jìn)程切換概念，
分為 STATE_BOOTING , STATE_RUNNING , STATE_STOPPING , STATE_SHUTDOWN 這幾個狀態(tài).

                final UserState uss = mStartedUsers.get(userId);

                // Make sure user is in the started state.  If it is currently
                // stopping, we need to knock that off.
                if (uss.mState == UserState.STATE_STOPPING) {
                    // If we are stopping, we haven't sent ACTION_SHUTDOWN,
                    // so we can just fairly silently bring the user back from
                    // the almost-dead.
                    uss.mState = UserState.STATE_RUNNING;
                    updateStartedUserArrayLocked();
                    needStart = true;
                } else if (uss.mState == UserState.STATE_SHUTDOWN) {
                    // This means ACTION_SHUTDOWN has been sent, so we will
                    // need to treat this as a new boot of the user.
                    uss.mState = UserState.STATE_BOOTING;
                    updateStartedUserArrayLocked();
                    needStart = true;
                }

                if (uss.mState == UserState.STATE_BOOTING) {
                    // Booting up a new user, need to tell system services about it.
                    // Note that this is on the same handler as scheduling of broadcasts,
                    // which is important because it needs to go first.
                    mHandler.sendMessage(mHandler.obtainMessage(SYSTEM_USER_START_MSG, userId, 0));
                }

接著發(fā)送用戶切換的MSG,這個message有兩秒的延遲，兩秒后會停止當(dāng)前屏幕上用戶切換的活動.

                if (foreground) {
                    mHandler.sendMessage(mHandler.obtainMessage(SYSTEM_USER_CURRENT_MSG, userId,
                            oldUserId));
                    mHandler.removeMessages(REPORT_USER_SWITCH_MSG);
                    mHandler.removeMessages(USER_SWITCH_TIMEOUT_MSG);
                    mHandler.sendMessage(mHandler.obtainMessage(REPORT_USER_SWITCH_MSG,
                            oldUserId, userId, uss));
                    mHandler.sendMessageDelayed(mHandler.obtainMessage(USER_SWITCH_TIMEOUT_MSG,
                            oldUserId, userId, uss), USER_SWITCH_TIMEOUT);
                }

會調(diào)用到 mWindowManager.stopFreezingScreen() 這個接口.

            if (!uss.switching && !uss.initializing) {
                mWindowManager.stopFreezingScreen();
                unfrozen = true;
            }

然后會把后臺的訪客模式用戶停掉.

        stopGuestUserIfBackground();

接著會發(fā)送調(diào)起用戶的廣播

  if (needStart) {
                    /// M: Mobile Management @{
                    mAmPlus.monitorBootReceiver(true, "User(" + userId + ") Bootup Start");
                    /// @}
                    // Send USER_STARTED broadcast
                    Intent intent = new Intent(Intent.ACTION_USER_STARTED);
                    intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY
                            | Intent.FLAG_RECEIVER_FOREGROUND);
                    intent.putExtra(Intent.EXTRA_USER_HANDLE, userId);
                    broadcastIntentLocked(null, null, intent,
                            null, null, 0, null, null, null, AppOpsManager.OP_NONE,
                            null, false, false, MY_PID, Process.SYSTEM_UID, userId);
                }

切換用戶的操作就到這里結(jié)束了.

用戶數(shù)量的控制

關(guān)于用戶數(shù)量的控制，原生代碼并沒有對用戶數(shù)量加以限制，F(xiàn)lyme中對用戶的限制數(shù)量為1.

可創(chuàng)建的最大用戶數(shù)量由 UserManager 中的 getMaxSupportedUsers() 方法控制.可以在 framework/base 工程下的 config.xml 文件中進(jìn)行配置.


    /**
     * Returns the maximum number of users that can be created on this device. A return value
     * of 1 means that it is a single user device.
     * @hide
     * @return a value greater than or equal to 1
     */
    public static int getMaxSupportedUsers() {
        // Don't allow multiple users on certain builds
        if (android.os.Build.ID.startsWith("JVP")) return 1;
        // Svelte devices don't get multi-user.
        if (ActivityManager.isLowRamDeviceStatic()) return 1;
        return SystemProperties.getInt("fw.max_users",
                Resources.getSystem().getInteger(R.integer.config_multiuserMaximumUsers));
    }

配置選項(xiàng)如下.

1598    <!--  Maximum number of supported users -->
1599    <integer name="config_multiuserMaximumUsers">1</integer>
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