question: @ Override public void onFullBackup ( FullBackupDataOutput output ) throws IOException { if ( mVolumes != null ) { if ( DEBUG ) Slog . i ( TAG , "Backing up " + mVolumes . length + " shared volumes" ) ; HashSet < String > externalFilesDirFilter = new HashSet < String > ( ) ; final File externalAndroidRoot = new File ( Environment . getExternalStorageDirectory ( ) , Environment . DIRECTORY_ANDROID ) ; externalFilesDirFilter . add ( externalAndroidRoot . getCanonicalPath ( ) ) ; for ( int i = 0 ; i < mVolumes . length ; i ++ ) { StorageVolume v = mVolumes [ i ] ; String domain = FullBackup . SHARED_PREFIX + i ; fullBackupFileTree ( null , domain , v . getPath ( ) , externalFilesDirFilter , output ) ; } } }
target:  Full backup of the shared-storage filesystem