DirectBoot功能介紹

原文鏈接：https://www.jianshu.com/p/c9534e487f15

當手機已經通電開機但是用戶並有解鎖鎖屏的時候，Android N運行於一個安全的模式，也就是Dierect Boot模式。
​ 爲了支持Dierect Boot模式，系統提供了兩個存儲數據的地方：
1.Credential encrypted storage，默認存儲數據的地方，僅在用戶解鎖手機後可用。2.Device encrypted storage，主要對應的就是Direct Boot使用的存儲空間。在Direct Boot模式下和用戶解鎖手機後都可以使用的存儲空間。
​ 系統把部分系統數據和已經註冊了相關權限的Apps的數據保存在device-encrypted store 。其他的數據默認保存到credential-encrypted store。當手機開機，首先進入一個Dierect Boot的模式，在這個模式下只可以訪問device-encrypted store下的數據，無法訪問credential-encrypted store下的數據。當用戶解鎖後就都可以訪問了。
​ 一般情況下，應用是無法在Direct Boot模式下運行的如果需要某個app能夠在Direct Boot模式下運行，需要註冊相關APP的組件。通常需要在這個模式下運行的app：1.計劃通知的應用，例如Clock2.重要的用戶通知的應用，例如sms3.提供無障礙服務的應用，例如Talkback
​ 應用組件申請在Direct Boot模式下運行：在AndroidManinfest.xml中設置 android:directBootAware="true"。
​ 應用訪問device encrypted storage：創建Context.createDeviceEncryptedStorageContext().然後通過這個Context來使用device encrypted storage 的存儲空間。

1. Context directBootContext = Context.createDeviceEncryptedStorageContext();

2. // Access appDataFilename that lives in device encrypted storage

3. FileInputStream inStream = directBootContext.openFileInput(appDataFilename);

4. // Use inStream to read content...

應用獲取解鎖的通知：

監聽廣播ACTION_USER_UNLOCKED 。

或者接收ACTION_BOOT_COMPLETED ，這個廣播的意思是手機開機並且用戶解鎖。

也可調用UserManager.isUserUnlocked()方法來查詢。

應用遷移已經存在的數據：

Context.migrateSharedPreferencesFrom()

Context.migrateDatabaseFrom()

兩種方法在credential encrypted storage 和device encrypted storage存儲空間之間去遷移preference 和database的數據.

實例分析：啓動FallbackHome流程
在分析7.0過程中發現在啓動Launcher之前會先啓動一個FallbackHome，之後纔會啓動Launcher，通過調查發現FallbackHome屬於Settings中的一個activity，Settings的android:directBootAware爲true，並且FallbackHome在category中配置了Home屬性，而Launcher的android:directBootAware爲false，所有隻有FallbackHome可以在direct boot模式下啓動。

1. <application android:label="@string/settings_label"

2. android:icon="@mipmap/ic_launcher_settings"

3. ............

4. android:directBootAware="true">

5.  

6. <!-- Triggered when user-selected home app isn't encryption aware -->

7. <activity android:name=".FallbackHome"

8. android:excludeFromRecents="true"

9. android:theme="@style/FallbackHome">

10. <intent-filter android:priority="-1000">

11. <action android:name="android.intent.action.MAIN" />

12. <category android:name="android.intent.category.HOME" />

13. <category android:name="android.intent.category.DEFAULT" />

14. </intent-filter>

15. </activity>

所以在ActivityManagerService啓動Home界面時，從PackageManagerService中獲取到的Home界面就是FallbackHome

1. Intent getHomeIntent() {

2. Intent intent = new Intent(mTopAction, mTopData != null ? Uri.parse(mTopData) : null);

3. intent.setComponent(mTopComponent);

4. intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);

5. if (mFactoryTest != FactoryTest.FACTORY_TEST_LOW_LEVEL) {

6. intent.addCategory(Intent.CATEGORY_HOME);

7. }

8. return intent;

9. }

10.  

11. boolean startHomeActivityLocked(int userId, String reason) {

12. if (mFactoryTest == FactoryTest.FACTORY_TEST_LOW_LEVEL

13. && mTopAction == null) {

14. // We are running in factory test mode, but unable to find

15. // the factory test app, so just sit around displaying the

16. // error message and don't try to start anything.

17. return false;

18. }

19. Intent intent = getHomeIntent();

20. ActivityInfo aInfo = resolveActivityInfo(intent, STOCK_PM_FLAGS, userId); //獲取Home activity信息

21. if (aInfo != null) {

22. intent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));

23. // Don't do this if the home app is currently being

24. // instrumented.

25. aInfo = new ActivityInfo(aInfo);

26. aInfo.applicationInfo = getAppInfoForUser(aInfo.applicationInfo, userId);

27. ProcessRecord app = getProcessRecordLocked(aInfo.processName,

28. aInfo.applicationInfo.uid, true);

29. if (app == null || app.instrumentationClass == null) {

30. intent.setFlags(intent.getFlags() | Intent.FLAG_ACTIVITY_NEW_TASK);

31. mActivityStarter.startHomeActivityLocked(intent, aInfo, reason); //啓動FallbackHome

32. }

33. } else {

34. Slog.wtf(TAG, "No home screen found for " + intent, new Throwable());

35. }

36. return true;

37. }

接着就會將FallbackHome啓動起來，其實這個activity的代碼非常簡單不到100行，是個透明的activity，創建FallbackHome時註冊ACTION_USER_UNLOCKED廣播，然後進行判斷用戶是否都已經解鎖，如果沒有就結束執行。之後就會等待接收ACTION_USER_UNLOCKED廣播，繼續判斷用戶是否已經解鎖，如果此時已經解鎖，就找Home界面，如果沒有找到就發延遲消息500ms再找一次，如果找到Launcher就會將FallbackHome finish掉。
​ 下面就要看具體什麼時候發送ACTION_USER_UNLOCKED廣播了。
​ 代碼位置packages/apps/Settings/src/com/android/settings/FallbackHome.Java

1. * Copyright (C) 2015 The Android Open Source Project

2.  

3. package com.android.settings;

4.  

5. import android.app.Activity;

6.  

7. public class FallbackHome extends Activity {

8. private static final String TAG = "FallbackHome";

9.  

10. @Override

11. protected void onCreate(Bundle savedInstanceState) {

12. super.onCreate(savedInstanceState);

13.  

14. // Set ourselves totally black before the device is provisioned so that

15. // we don't flash the wallpaper before SUW

16. if (Settings.Global.getInt(getContentResolver(),

17. Settings.Global.DEVICE_PROVISIONED, 0) == 0) {

18. setTheme(android.R.style.Theme_Black_NoTitleBar_Fullscreen);

19. }

20. registerReceiver(mReceiver, new IntentFilter(Intent.ACTION_USER_UNLOCKED));

21. maybeFinish();

22. }

23.  

24. @Override

25. protected void onDestroy() {

26. super.onDestroy();

27. unregisterReceiver(mReceiver);

28. }

29.  

30. private BroadcastReceiver mReceiver = new BroadcastReceiver() {

31. @Override

32. public void onReceive(Context context, Intent intent) {

33. maybeFinish();

34. }

35. };

36.  

37. private void maybeFinish() {

38. if (getSystemService(UserManager.class).isUserUnlocked()) {

39. final Intent homeIntent = new Intent(Intent.ACTION_MAIN)

40. .addCategory(Intent.CATEGORY_HOME);

41. final ResolveInfo homeInfo = getPackageManager().resolveActivity(homeIntent, 0);

42. if (Objects.equals(getPackageName(), homeInfo.activityInfo.packageName)) {

43. Log.d(TAG, "User unlocked but no home; let's hope someone enables one soon?");

44. mHandler.sendEmptyMessageDelayed(0, 500);

45. } else {

46. Log.d(TAG, "User unlocked and real home found; let's go!");

47. finish();

48. }

49. }

50. }

51.  

52. private Handler mHandler = new Handler() {

53. @Override

54. public void handleMessage(Message msg) {

55. maybeFinish();

56. }

57. };

58. }

發送ACTION_USER_UNLOCKED廣播

在開機將近尾聲時WindowManagerService會調用enableScreenIfNeededLocked函數來判斷是否將Screen enable。通過Handler發送ENABLE_SCREEN消息到主線程

1. void enableScreenIfNeededLocked() {

2.  

3. if (mDisplayEnabled) {

4. return;

5. }

6. if (!mSystemBooted && !mShowingBootMessages) {

7. return;

8. }

9.  

10. mH.sendEmptyMessage(H.ENABLE_SCREEN);

11. }

在mH的handleMessage中處理消息ENABLE_SCREEN，調用函數performEnableScreen來處理。

1. final class H extends Handler {

2. ........

3. public static final int ENABLE_SCREEN = 16;

4. ........

5. @Override

6. public void handleMessage(Message msg) {

7.  

8. case ENABLE_SCREEN: {

9. performEnableScreen();

10. break;

11. }

12. ........

13.  
14.  
15.  

16. public void performEnableScreen() {

17. synchronized(mWindowMap) {

18. if (mDisplayEnabled) { //如果設備已經enabled，返回

19. return;

20. }

21. if (!mSystemBooted && !mShowingBootMessages) { //如果不是系統啓動，並且沒有啓動信息，返回

22. return;

23. }

24.  

25. // Don't enable the screen until all existing windows have been drawn.

26. if (!mForceDisplayEnabled && checkWaitingForWindowsLocked()) { //如果不是強制設備enable，並且Windows還沒有繪製完成，返回

27. return;

28. }

29.  

30. ...........

31.  

32. if (!mForceDisplayEnabled && !checkBootAnimationCompleteLocked()) { //如果不是強制設備enable，並且開機動畫還沒有結束，返回

33. return;

34. }

35.  

36. EventLog.writeEvent(EventLogTags.WM_BOOT_ANIMATION_DONE, SystemClock.uptimeMillis());

37. mDisplayEnabled = true;

38. if (DEBUG_SCREEN_ON || DEBUG_BOOT) Slog.i(TAG_WM, "**** ENABLING SCREEN!");

39.  

40. // Enable input dispatch.

41. mInputMonitor.setEventDispatchingLw(mEventDispatchingEnabled);

42. }

43.  

44. try {

45. mActivityManager.bootAnimationComplete(); //通知ActivityManagerService開機動畫完成

46. } catch (RemoteException e) {

47. }

48.  

49. mPolicy.enableScreenAfterBoot(); //通知ActivityManagerService Screen可以enable

50.  

51. // Make sure the last requested orientation has been applied.

52. updateRotationUnchecked(false, false);

53. }

54.  

55. private boolean checkWaitingForWindowsLocked() {

56.  

57. boolean haveBootMsg = false; //是否有啓動message

58. boolean haveApp = false; //是否有APP

59. // if the wallpaper service is disabled on the device, we're never going to have

60. // wallpaper, don't bother waiting for it

61. boolean haveWallpaper = false; //是否有Wallpaper

62. boolean wallpaperEnabled = mContext.getResources().getBoolean(

63. com.android.internal.R.bool.config_enableWallpaperService)

64. && !mOnlyCore; //Wallpaper是否可用

65. boolean haveKeyguard = true; //是否有Keyguard

66. // TODO(multidisplay): Expand to all displays?

67. final WindowList windows = getDefaultWindowListLocked(); //獲取所有的Windows

68. final int N = windows.size();

69. for (int i=0; i<N; i++) {

70. WindowState w = windows.get(i);

71. if (w.isVisibleLw() && !w.mObscured && !w.isDrawnLw()) {

72. return true;

73. }

74. if (w.isDrawnLw()) { 判斷Window的屬性

75. if (w.mAttrs.type == TYPE_BOOT_PROGRESS) {

76. haveBootMsg = true;

77. } else if (w.mAttrs.type == TYPE_APPLICATION) {

78. haveApp = true;

79. } else if (w.mAttrs.type == TYPE_WALLPAPER) {

80. haveWallpaper = true;

81. } else if (w.mAttrs.type == TYPE_STATUS_BAR) {

82. haveKeyguard = mPolicy.isKeyguardDrawnLw();

83. }

84. }

85. }

86.  

87. // If we are turning on the screen to show the boot message,

88. // don't do it until the boot message is actually displayed.

89. if (!mSystemBooted && !haveBootMsg) {

90. return true;

91. }

92.  

93. // If we are turning on the screen after the boot is completed

94. // normally, don't do so until we have the application and

95. // wallpaper.

96. if (mSystemBooted && ((!haveApp && !haveKeyguard) ||

97. (wallpaperEnabled && !haveWallpaper))) {

98. return true;

99. }

100.  

101. return false;

102. }

103.  

104. private boolean checkBootAnimationCompleteLocked() {

105. if (SystemService.isRunning(BOOT_ANIMATION_SERVICE)) {

106. mH.removeMessages(H.CHECK_IF_BOOT_ANIMATION_FINISHED);

107. mH.sendEmptyMessageDelayed(H.CHECK_IF_BOOT_ANIMATION_FINISHED,

108. BOOT_ANIMATION_POLL_INTERVAL);

109. if (DEBUG_BOOT) Slog.i(TAG_WM, "checkBootAnimationComplete: Waiting for anim complete");

110. return false;

111. }

112. if (DEBUG_BOOT) Slog.i(TAG_WM, "checkBootAnimationComplete: Animation complete!");

113. return true;

114. }

115.  

116. case CHECK_IF_BOOT_ANIMATION_FINISHED: {

117. final boolean bootAnimationComplete;

118. synchronized (mWindowMap) {

119. if (DEBUG_BOOT) Slog.i(TAG_WM, "CHECK_IF_BOOT_ANIMATION_FINISHED:");

120. bootAnimationComplete = checkBootAnimationCompleteLocked();

121. }

122. if (bootAnimationComplete) {

123. performEnableScreen();

124. }

125. }

126.  

127. @Override

128. public void bootAnimationComplete() {

129. final boolean callFinishBooting;

130. synchronized (this) {

131. callFinishBooting = mCallFinishBooting;

132. mBootAnimationComplete = true; //設置mBootAnimationComplete爲true

133. }

134. if (callFinishBooting) {

135. Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "FinishBooting");

136. finishBooting(); //調用finishBooting

137. Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

138. }

139. }

140.  

141. final void finishBooting() {

142. synchronized (this) {

143. if (!mBootAnimationComplete) {

144. mCallFinishBooting = true;

145. return;

146. }

147. mCallFinishBooting = false;

148. }

149. ................

150. // Let system services know.

151. mSystemServiceManager.startBootPhase(SystemService.PHASE_BOOT_COMPLETED);

152. ...............

153. mUserController.sendBootCompletedLocked(

154. new IIntentReceiver.Stub() {

155. @Override

156. public void performReceive(Intent intent, int resultCode,

157. String data, Bundle extras, boolean ordered,

158. boolean sticky, int sendingUser) {

159. synchronized (ActivityManagerService.this) {

160. requestPssAllProcsLocked(SystemClock.uptimeMillis(),

161. true, false);

162. }

163. }

164. });

經過一系列的代碼跳轉，最終調用UserController的finishUserUnlocked函數來發送ACTION_USER_UNLOCKED廣播。

1. void finishUserUnlocked(final UserState uss) {

2. .................

3. final Intent unlockedIntent = new Intent(Intent.ACTION_USER_UNLOCKED);

4. unlockedIntent.putExtra(Intent.EXTRA_USER_HANDLE, userId);

5. unlockedIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY | Intent.FLAG_RECEIVER_FOREGROUND);

6. mService.broadcastIntentLocked(null, null, unlockedIntent, null, null, 0, null, null, null, AppOpsManager.OP_NONE, null, false, false, MY_PID, SYSTEM_UID, userId);

7. .................

8. }

問題分析
就是因爲現在啓動Launcher時多了一個流程，導致啓動launcher比原來6.0要慢。通過查看開機log可以看到從啓動FallbackHome到啓動google桌面花費了4s

1. 18:10:50.653 769 1910 I ActivityManager: START u0 {act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000100 cmp=com.android.settings/.FallbackHome} from uid 0 on display 0

2.  

3. 18:10:54.586 2029 2029 D FallbackHome: User unlocked and real home found; let's go!

4.  

5. 18:10:54.615 769 2207 I ActivityManager: START u0 {act=android.intent.action.MAIN cat=[android.intent.category.HOME] flg=0x10000100 cmp=com.google.android.setupwizard/.SetupWizardActivity} from uid 0 on display 0

如果啓動FallbackHome到啓動launcher之間相隔的時間再長一點就可能發生開機過程中顯示launcher時發生幾秒的黑屏

小結

Android 7.0新增了DirectBoot功能，AOSP中爲實現該功能修改了開機代碼流程，並且這部分流程並未根據設備是否支持DirectBoot做區分，只是流程上做了兼容，確保不支持DirectBoot的設備在這套流程下也能正常開機。

在這套流程下，用戶解鎖後纔可進入非directBootAware應用，包括Launcher。

com.android.settings/.FallbackHome中判斷用戶解鎖狀態，已解鎖纔會Finish掉去啓動Launcher，未解鎖就

等待ACTION_USER_UNLOCKED廣播後再去啓動Launcher。非DirectBoot模式下耗時4s就是在等待
finishBooting後的系統廣播ACTION_USER_UNLOCKED。

目前已從APP和PackageManagerService的角度嘗試修改，在開機流程中繞過FallbackHome，但驗證失敗：

1）去除FallbackHome的android.intent.category.Home屬性會導致停留在開機動畫之後的界面。因爲此時仍舊處於未解鎖狀態，且Launcher非directBootAware應用，PMS中的限制導致此時無法啓動Launcher；

2）修改FallbackHome和Launcher的優先級仍舊先啓動FallbackHome；

3）將Launcher標記爲directBootAware應用會導致開機後Launcher crash。因爲Launcher中的widget仍舊是非directBootAware的，此時仍舊無法啓動，除非將widget相關的APP都標記爲directBootAware；

4）PMS依賴手機當前的狀態，需要user解鎖才能正常查詢。如果強制修改，不考慮DirectBoot和當前啓動狀態，即使當前user未解鎖，依然

可以查詢符合條件的component，修改後會有無法開機的現象。因爲Launcher不是directBootAware的，當前手機user尚未解鎖，涉及存儲相關的解鎖也未進行。
開機繞過FallbackHome涉及的修改面很多，並非通過修改APP或PMS可以實現，還涉及存儲區域解鎖以及用戶狀態和ACTION_USER_UNLOCKED廣播的修改，對AOSP開機流程改動較大，暫時尚未有較好的優化方案。

作者：mrLiangshuang
鏈接：https://www.jianshu.com/p/c9534e487f15
來源：簡書