androidQ sd卡權(quán)限使用詳解

更新時(shí)間：2020年06月23日 11:27:44 作者：十八磚

這篇文章主要介紹了androidQ sd卡權(quán)限使用詳解，文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面隨著小編來(lái)一起學(xué)習(xí)學(xué)習(xí)吧

默認(rèn)情況下，如果應(yīng)用以 Android Q 為目標(biāo)平臺(tái)，則在訪問(wèn)外部存儲(chǔ)設(shè)備中的文件時(shí)會(huì)進(jìn)入過(guò)濾視圖。應(yīng)用可以使用 Context.getExternalFilesDir() 將專用于自己的文件存儲(chǔ)在特定于自己的目錄中。

1. 臨時(shí)停用分區(qū)存儲(chǔ)行為:

以 Android 9（API 級(jí)別 28）或更低版本為目標(biāo)平臺(tái)。
如果您以 Android Q 為目標(biāo)平臺(tái)，請(qǐng)?jiān)趹?yīng)用的清單文件中將 requestLegacyExternalStorage 的值設(shè)為 true。

<manifest ... >
 <!-- This attribute is "false" by default on apps targeting Android Q. -->
 <application android:requestLegacyExternalStorage="true" ... >
 ...
 </application>
</manifest>

2. 如何實(shí)現(xiàn)隔離存儲(chǔ):

2.1 ApplicationInfo新增PRIVATE_FLAG_REQUEST_LEGACY_EXTERNAL_STORAGE標(biāo)記

PackageParser.java:

if (sa.getBoolean(
  R.styleable.AndroidManifestApplication_requestLegacyExternalStorage,
  owner.applicationInfo.targetSdkVersion < Build.VERSION_CODES.Q)) {
 ai.privateFlags |= ApplicationInfo.PRIVATE_FLAG_REQUEST_LEGACY_EXTERNAL_STORAGE;
}

ApplicationInfo.java:

public boolean hasRequestedLegacyExternalStorage() {
 return (privateFlags & PRIVATE_FLAG_REQUEST_LEGACY_EXTERNAL_STORAGE) != 0;
}

2.2 grantRuntimePermission()重新掛載視圖

apk啟動(dòng)時(shí)默認(rèn)掛載runtime/default視圖，grantRuntimePermission()時(shí)如果是READ_EXTERNAL_STORAGE或WRITE_EXTERNAL_STORAGE，則會(huì)獲取掛載模式重新掛載對(duì)應(yīng)視圖。

PermissionManagerService.java:

 private void grantRuntimePermission(String permName, String packageName, boolean overridePolicy,
   int callingUid, final int userId, PermissionCallback callback) {
  ......
  if (READ_EXTERNAL_STORAGE.equals(permName)
    || WRITE_EXTERNAL_STORAGE.equals(permName)) {
   final long token = Binder.clearCallingIdentity();
   try {
    if (mUserManagerInt.isUserInitialized(userId)) {
     StorageManagerInternal storageManagerInternal = LocalServices.getService(
       StorageManagerInternal.class);
     storageManagerInternal.onExternalStoragePolicyChanged(uid, packageName);
    }
   } finally {
    Binder.restoreCallingIdentity(token);
   }
  }

 }

獲取掛載模式這塊android10有修改，沒(méi)有設(shè)置Legacy標(biāo)志的話，總是獲取default掛載模式，沒(méi)有讀寫(xiě)權(quán)限。
android 10會(huì)設(shè)置屬性[persist.sys.isolated_storage]: [true]，因此走到if(ENABLE_ISOLATED_STORAGE)中的getMountMode()。

public static boolean hasIsolatedStorage() {
 //[persist.sys.isolated_storage]: [true]
 //[sys.isolated_storage_snapshot]: [true]
 return SystemProperties.getBoolean("sys.isolated_storage_snapshot",
   SystemProperties.getBoolean("persist.sys.isolated_storage", true));
}

private static final boolean ENABLE_ISOLATED_STORAGE = StorageManager.hasIsolatedStorage();

public int getExternalStorageMountMode(int uid, String packageName) {
+ //android 10新增邏輯
+ if (ENABLE_ISOLATED_STORAGE) {
+  return getMountMode(uid, packageName);
+ }
 ......
 int mountMode = Integer.MAX_VALUE;
 for (ExternalStorageMountPolicy policy : mPolicies) {
  final int policyMode = policy.getMountMode(uid, packageName);
  if (policyMode == Zygote.MOUNT_EXTERNAL_NONE) {
   return Zygote.MOUNT_EXTERNAL_NONE;
  }
  mountMode = Math.min(mountMode, policyMode);
 }
 if (mountMode == Integer.MAX_VALUE) {
  return Zygote.MOUNT_EXTERNAL_NONE;
 }
 return mountMode;
}

正常模式下hasLegacy=false，走到if判斷的DEFAULT分支；legacy模式hasLegacy=true，與之前保持一致，有write權(quán)限就走到WRITE模式分支。

private int getMountModeInternal(int uid, String packageName) {
 try {
  ......
  final boolean hasRead = StorageManager.checkPermissionAndCheckOp(mContext, false, 0,
    uid, packageName, READ_EXTERNAL_STORAGE, OP_READ_EXTERNAL_STORAGE);
  final boolean hasWrite = StorageManager.checkPermissionAndCheckOp(mContext, false, 0,
    uid, packageName, WRITE_EXTERNAL_STORAGE, OP_WRITE_EXTERNAL_STORAGE);
  ......
  final boolean hasLegacy = mIAppOpsService.checkOperation(OP_LEGACY_STORAGE,
    uid, packageName) == MODE_ALLOWED;
  if (hasLegacy && hasWrite) {
   return Zygote.MOUNT_EXTERNAL_WRITE;
  } else if (hasLegacy && hasRead) {
   return Zygote.MOUNT_EXTERNAL_READ;
  } else {
   return Zygote.MOUNT_EXTERNAL_DEFAULT;
  }
 } catch (RemoteException e) {
  // Should not happen
 }
 return Zygote.MOUNT_EXTERNAL_NONE;
}

2.3 Legacy Storage屬性對(duì)權(quán)限的影響

安裝apk時(shí)，就會(huì)根據(jù)requestLegacyExternalStorage屬性來(lái)對(duì)ops state進(jìn)行設(shè)置，修改OP_LEGACY_STORAGE的默認(rèn)狀態(tài)。

<manifest ... >
 <application android:requestLegacyExternalStorage="true" ... >
 </application>
</manifest>

 
//Q 正常模式
LEGACY_STORAGE: mode=ignore
//Q legacy模式
LEGACY_STORAGE: mode=allow

PermissionPolicyService啟動(dòng)時(shí)首先進(jìn)行權(quán)限變化監(jiān)聽(tīng)：

public void onStart() {
 permManagerInternal.addOnRuntimePermissionStateChangedListener(
 this::synchronizePackagePermissionsAndAppOpsAsyncForUser);
}

private void synchronizePackagePermissionsAndAppOpsAsyncForUser(@NonNull String packageName,
  @UserIdInt int changedUserId) {
 if (isStarted(changedUserId)) {
  synchronized (mLock) {
   if (mIsPackageSyncsScheduled.add(new Pair<>(packageName, changedUserId))) {
    FgThread.getHandler().sendMessage(PooledLambda.obtainMessage(
      PermissionPolicyService
        ::synchronizePackagePermissionsAndAppOpsForUser,
      this, packageName, changedUserId));
   }
   ......
  }
 }
}

APK安裝時(shí)，會(huì)根據(jù)requestLegacyExternalStorage屬性來(lái)通知storage權(quán)限變化，調(diào)用關(guān)系如下：

//調(diào)用關(guān)系：
1.PackageManagerService.java:
 installPackagesLI()
  commitPackagesLocked()
   updateSettingsLI()
    updateSettingsInternalLI()
     2.PermissionManagerService.java:
      mPermissionManager.updatePermissions()
       restorePermissionState()

//關(guān)鍵代碼：
private void restorePermissionState(@NonNull PackageParser.Package pkg, boolean replace,
  @Nullable String packageOfInterest, @Nullable PermissionCallback callback) {
......
  //判斷requestLegacyExternalStorage屬性
  updatedUserIds = checkIfLegacyStorageOpsNeedToBeUpdated(pkg, replace, updatedUserIds);
......
 for (int userId : updatedUserIds) {
  notifyRuntimePermissionStateChanged(pkg.packageName, userId);
 }
}

最終調(diào)用到PermissionPolicyService的監(jiān)聽(tīng)函數(shù)synchronizePackagePermissionsAndAppOpsForUser()，進(jìn)行默認(rèn)權(quán)限獲取和設(shè)置。

當(dāng)apk安裝時(shí)，聲明了requestLegacyExternalStorage="true"屬性，并且聲明了READ_EXTERNAL_STORAGE、WRITE_EXTERNAL_STORAGE，那么addOpIfRestricted()就會(huì)將LEGACY_STORAGE設(shè)置為allow模式。

//調(diào)用關(guān)系：
synchronizePackagePermissionsAndAppOpsForUser()：
 synchroniser.addPackage()
  addOpIfRestricted()//LEGACY_STORAGE加入到mOpsToAllow
 synchroniser.syncPackages()
  setUidModeAllowed()
   setUidMode()//設(shè)置LEGACY_STORAGE為allow

//關(guān)鍵代碼：
private void addOpIfRestricted(@NonNull PermissionInfo permissionInfo,
  @NonNull PackageInfo pkg) {
......
  //forPermission()會(huì)根據(jù)requestLegacyExternalStorage的值進(jìn)行返回
  final SoftRestrictedPermissionPolicy policy =
    SoftRestrictedPermissionPolicy.forPermission(mContext, pkg.applicationInfo,
      mContext.getUser(), permission);

  final int op = policy.resolveAppOp();
  if (op != OP_NONE) {
   switch (policy.getDesiredOpMode()) {
    case MODE_DEFAULT:
     mOpsToDefault.add(new OpToChange(uid, pkg.packageName, op));
     break;
    case MODE_ALLOWED:
     //在聲明READ_EXTERNAL_STORAGE權(quán)限下，會(huì)將LEGACY_STORAGE加入到mOpsToAllow
     if (policy.shouldSetAppOpIfNotDefault()) {
      mOpsToAllow.add(new OpToChange(uid, pkg.packageName, op));
     } else {
      mOpsToAllowIfDefault.add(
        new OpToChange(uid, pkg.packageName, op));
     }
     break;
......
}

public static @NonNull SoftRestrictedPermissionPolicy forPermission(@NonNull Context context,
  @Nullable ApplicationInfo appInfo, @Nullable UserHandle user,
  @NonNull String permission) {
 switch (permission) {
  case READ_EXTERNAL_STORAGE: {
   if (appInfo != null) {
    boolean hasAnyRequestedLegacyExternalStorage =
      appInfo.hasRequestedLegacyExternalStorage();

    hasRequestedLegacyExternalStorage = hasAnyRequestedLegacyExternalStorage;
   }

   return new SoftRestrictedPermissionPolicy() {
    @Override
    public int getDesiredOpMode() {
     if (applyRestriction) {
      return MODE_DEFAULT;
     } else if (hasRequestedLegacyExternalStorage) {
      //聲明了requestLegacyExternalStorage就返回allow
      return MODE_ALLOWED;
     } else {
      return MODE_IGNORED;
     }
    }

    @Override
    public boolean shouldSetAppOpIfNotDefault() {
     return getDesiredOpMode() != MODE_IGNORED;
    }
   };
  }

3. sdcard路徑權(quán)限說(shuō)明:

rwx:421，umask默認(rèn)為八進(jìn)制022(----w--w-)
/mnt/runtime/default的gid為1015，也就是sdcard_rw；mask 為6，八進(jìn)制006，group sdcard_rw可讀寫(xiě)，也就是other沒(méi)有rw權(quán)限
/mnt/runtime/read的gid為9997，也就是everybody；mask 為23，八進(jìn)制027，group everybody可讀、不可寫(xiě)，other沒(méi)有讀寫(xiě)執(zhí)行權(quán)限
/mnt/runtime/write的gid為9997，也就是everybody；mask 為7，八進(jìn)制007，group everybody可讀寫(xiě)，other沒(méi)有讀寫(xiě)可執(zhí)行權(quán)限
/data/media on /mnt/runtime/default/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=1015,multiuser,mask=6,derive_gid,default_normal)

/data/media on /mnt/runtime/read/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=9997,multiuser,mask=23,derive_gid,default_normal)
/data/media on /mnt/runtime/write/emulated type sdcardfs (rw,nosuid,nodev,noexec,noatime,fsuid=1023,fsgid=1023,gid=9997,multiuser,mask=7,derive_gid,default_normal)

/mnt/runtime/default:

drwxrwx--x 3 root sdcard_rw 4096 2018-12-18 03:41 Android
drwxrwx--x 3 root sdcard_rw 4096 2018-12-18 06:11 DCIM

/mnt/runtime/read:

drwxr-x--- 3 root everybody 4096 2018-12-18 03:41 Android
drwxr-x--- 3 root everybody 4096 2018-12-18 06:11 DCIM

/mnt/runtime/write:

drwxrwx--- 3 root everybody 4096 2018-12-18 03:41 Android
drwxrwx--- 3 root everybody 4096 2018-12-18 06:11 DCIM

/sdcard/Android/data:

drwxrwx--- 4 u0_a64 everybody 4096 2018-12-18 06:11 com.android.camera2
drwxrwx--- 3 u0_a15 everybody 4096 2018-12-18 03:41 com.google.android.gms
drwxrwx--- 4 u0_a84 everybody 4096 2018-12-18 03:41 com.google.android.youtube

4. sdcard文件存儲(chǔ)示例:

4.1 getExternalFilesDir()隨卸載而刪除

///storage/emulated/0/Android/data/com.xx.xx/files
File file = File(context.getExternalFilesDir(null), "test.txt");

4.2 媒體文件
媒體文件使用MediaStore操作，卸載后不會(huì)刪除。
訪問(wèn)其他應(yīng)用生成的照片、視頻、音頻，需要READ_EXTERNAL_STORAGE權(quán)限。

4.3 存儲(chǔ)訪問(wèn)框架(SAF)
訪問(wèn)其他應(yīng)用創(chuàng)建的文件，例如"Download"目錄，必須使用存儲(chǔ)訪問(wèn)框架，用戶通過(guò)框架選擇特定文件。

4.4 照片中的位置信息
需要ACCESS_MEDIA_LOCATION權(quán)限，才能獲取元數(shù)據(jù)中的位置信息。

<permission android:name="android.permission.ACCESS_MEDIA_LOCATION"
 android:permissionGroup="android.permission-group.UNDEFINED"
 android:label="@string/permlab_mediaLocation"
 android:description="@string/permdesc_mediaLocation"
 android:protectionLevel="dangerous" />

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