Joonwoo Park:
> Sorry for confusion.
> # mount -t ubifs -o rw /dev/brabra /mnt
> # ls -al /mnt
> (error occurs here, .wh.dir doesn't appear)

It seems that is the problem of ubifs.


> No, I'm not using aufs2-util at all.

aufs2-util is necessary.
But I don't know that is the root cause of the problem.


> I don't think I fully understand what .wh..wh.plnk is for.
> But I was under the impression somehow .wh..wh.plnk keep changes.
> That's why I was curious that how it's synced.
>
> But it sounds like it's changes only when filesystem is
> remount/umount.  is it true?

When you handle a hardllinked file, an internal hidden hardlink is
created under .wh..wh.plnk. And it is restored to the RW branch when you
remount/umount. This is doen by aufs2-util.
For instance,
- /u = /rw + /ro
- /ro/fileA and /ro/fileB are hardlinked.
- when you modify /u/fileA, aufs copies-up to /rw/fileA and create a
  hardlink /rw/.wh..wh.plnk/XX.YY.
- when you remount/unmount /u, aufs2-util is invoked. aufs2-util creates
  /rw/fileB and removes /rw/.wh..wh.plnk/XX.YY.


J. R. Okajima

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