[PATCH] ubifs: Fix a potential space leak problem while linking tmpfile

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Perhaps I misunderstood what commit 32fe905c17f001 ("ubifs: Fix
> O_TMPFILE corner case in ubifs_link()") wanted to fix.
> I think orphan area is used to remind filesystem don't forget to delete
> inodes (whose nlink is 0) in next unclean rebooting. Generally, the file
> system is not corrupted caused by replaying orphan nodes.
> Ralph reported a filesystem corruption in combination with overlayfs.
> Can you tell me the details about that problem? Thanks.

On my test bed I didn't see a fs corruption, what I saw was a failing orphan
self test while playing with O_TMPFILE and linkat().

When you create a tmpfile it has a link count of 0 and an orphan is
installed. Such that the tmpfile is gone after a reboot but you can
still use it prior to that.
By using linkat() you can raise the link counter to 1 again.
Thus, the orphan needs to be removed.
This is pattern overlayfs uses a lot.

Since UBIFS never supported raising the link counter from 0 to 1
we have many corner cases and fixing all these turned out into a nightmare.
...as you can see from the amount broken patches from me :-(.

Thanks,
//richard