androidQ sd卡許可權使用詳解
預設情況下，如果應用以 Android Q 為目標平臺，則在訪問外部儲存裝置中的檔案時會進入過濾檢視。應用可以使用 Context.getExternalFilesDir() 將專用於自己的檔案儲存在特定於自己的目錄中。
1. 臨時停用分割槽儲存行為:
以 Android 9（API 級別 28）或更低版本為目標平臺。
如果您以 Android Q 為目標平臺，請在應用的清單檔案中將 requestLegacyExternalStorage 的值設為 true。
<manifest ... > <!-- This attribute is "false" by default on apps targeting Android Q. --> <application android:requestLegacyExternalStorage="true" ... > ... </application> </manifest>
2. 如何實現隔離儲存:
2.1 ApplicationInfo新增PRIVATE_FLAG_REQUEST_LEGACY_EXTERNAL_STORAGE標記
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()重新掛載檢視
apk啟動時預設掛載runtime/default檢視，grantRuntimePermission()時如果是READ_EXTERNAL_STORAGE或WRITE_EXTERNAL_STORAGE，則會獲取掛載模式重新掛載對應檢視。
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，沒有設定Legacy標誌的話，總是獲取default掛載模式，沒有讀寫許可權。
android 10會設定屬性[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許可權就走到WRITE模式分支。
private int getMountModeInternal(int uid,String packageName) {
try {
......
final boolean hasRead = StorageManager.checkPermissionAndCheckOp(mContext,false,uid,packageName,READ_EXTERNAL_STORAGE,OP_READ_EXTERNAL_STORAGE);
final boolean hasWrite = StorageManager.checkPermissionAndCheckOp(mContext,WRITE_EXTERNAL_STORAGE,OP_WRITE_EXTERNAL_STORAGE);
......
final boolean hasLegacy = mIAppOpsService.checkOperation(OP_LEGACY_STORAGE,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屬性對許可權的影響
安裝apk時，就會根據requestLegacyExternalStorage屬性來對ops state進行設定，修改OP_LEGACY_STORAGE的預設狀態。
<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啟動時首先進行許可權變化監聽：
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,changedUserId));
}
......
}
}
}
APK安裝時，會根據requestLegacyExternalStorage屬性來通知storage許可權變化，呼叫關係如下：
//呼叫關係：
1.PackageManagerService.java:
installPackagesLI()
commitPackagesLocked()
updateSettingsLI()
updateSettingsInternalLI()
2.PermissionManagerService.java:
mPermissionManager.updatePermissions()
restorePermissionState()
//關鍵程式碼：
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);
}
}
最終呼叫到PermissionPolicyService的監聽函式synchronizePackagePermissionsAndAppOpsForUser()，進行預設許可權獲取和設定。
當apk安裝時，聲明瞭requestLegacyExternalStorage="true"屬性，並且聲明瞭READ_EXTERNAL_STORAGE、WRITE_EXTERNAL_STORAGE，那麼addOpIfRestricted()就會將LEGACY_STORAGE設定為allow模式。
//呼叫關係：
synchronizePackagePermissionsAndAppOpsForUser()：
synchroniser.addPackage()
addOpIfRestricted()//LEGACY_STORAGE加入到mOpsToAllow
synchroniser.syncPackages()
setUidModeAllowed()
setUidMode()//設定LEGACY_STORAGE為allow
//關鍵程式碼：
private void addOpIfRestricted(@NonNull PermissionInfo permissionInfo,@NonNull PackageInfo pkg) {
......
//forPermission()會根據requestLegacyExternalStorage的值進行返回
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:
//在宣告READ_EXTERNAL_STORAGE許可權下，會將LEGACY_STORAGE加入到mOpsToAllow
if (policy.shouldSetAppOpIfNotDefault()) {
mOpsToAllow.add(new OpToChange(uid,op));
} else {
mOpsToAllowIfDefault.add(
new OpToChange(uid,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) {
//聲明瞭requestLegacyExternalStorage就返回allow
return MODE_ALLOWED;
} else {
return MODE_IGNORED;
}
}
@Override
public boolean shouldSetAppOpIfNotDefault() {
return getDesiredOpMode() != MODE_IGNORED;
}
};
}
3. sdcard路徑許可權說明:
- rwx:421，umask預設為八進位制022(----w--w-)
- /mnt/runtime/default的gid為1015，也就是sdcard_rw；mask 為6，八進位制006，group sdcard_rw可讀寫，也就是other沒有rw許可權
- /mnt/runtime/read的gid為9997，也就是everybody；mask 為23，八進位制027，group everybody可讀、不可寫，other沒有讀寫執行許可權
- /mnt/runtime/write的gid為9997，也就是everybody；mask 為7，八進位制007，group everybody可讀寫，other沒有讀寫可執行許可權
- /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,gid=9997,mask=23,default_normal)
/data/media on /mnt/runtime/write/emulated type sdcardfs (rw,mask=7,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檔案儲存示例:
4.1 getExternalFilesDir()隨解除安裝而刪除
///storage/emulated/0/Android/data/com.xx.xx/files File file = File(context.getExternalFilesDir(null),"test.txt");
4.2 媒體檔案
媒體檔案使用MediaStore操作，解除安裝後不會刪除。
訪問其他應用生成的照片、視訊、音訊，需要READ_EXTERNAL_STORAGE許可權。
4.3 儲存訪問框架(SAF)
訪問其他應用建立的檔案，例如"Download"目錄，必須使用儲存訪問框架，使用者通過框架選擇特定檔案。
4.4 照片中的位置資訊
需要ACCESS_MEDIA_LOCATION許可權，才能獲取元資料中的位置資訊。
<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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