Re: [PATCH v4 3/3] untracked cache: fix entry invalidation

> First, the current code in untracked_cache_invalidate_path() is wrong
> because it can only handle paths "a" or "a/b", not "a/b/c" because
> lookup_untracked() only looks for entries directly under the given
> directory. In the last case, it will look for the entry "b/c" in
> directory "a" instead. This means if you delete or add an entry in a
> subdirectory, untracked cache may become out of date because it does not
> invalidate properly. This is noticed by David Turner.
> 
> The second problem is about invalidation inside a fully untracked/excluded
> directory. In this case we may have to invalidate back to root. See the
> comment block for detail.