frameworks/base/data/etc/platform.xml中新增如下修改

    <permission name="android.permission.READ_EXTERNAL_STORAGE" >
        <group gid="media_rw" />
    </permission>

    <permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
        <group gid="media_rw" />
        <group gid="sdcard_rw" />
    </permission>

system/vold/PublicVolume.cpp修改如下程式碼

     if (vfat::Mount(mDevPath, mRawPath, false, false, false,
-            AID_MEDIA_RW, AID_MEDIA_RW, 0007, true)) {
+            AID_MEDIA_RW, AID_MEDIA_RW, 0001, true)) {
         PLOG(ERROR) << getId() << " failed to mount " << mDevPath;
         return -EIO;
     }

0007是許可權的掩碼，意思是把r w x的許可權都遮蔽了，001是隻遮蔽x許可權。