Re: [PATCH 00/13] cross rename v4

[David Howells <dhowells@redhat.com>]

Miklos Szeredi <miklos@szeredi.hu> wrote:

> Regarding whiteouts, I raised a couple of questions that nobody answered
> yet, so let me ask again.
> 
> - If a filesystem containing whiteouts (fallthroughs, etc...) is mounted as
>   not part of a union, how are these special entities represented to
>   userspace?

I would suggest that whiteouts appear as otherwise negative dentries and that
they don't appear in getdents().

Fallthroughs are far more 'interesting'.  Maybe they should appear in
getdents() with a dentry type saying what they are, but give you EREMOTE or
something if you try to follow them.

Note that there is space in d_flags & DCACHE_ENTRY_TYPE for a whiteout type.
I would, however, mark fallthroughs by a separate flag.  So that the union
dentry will mirror the source dentry's type.

> - Can the user remove them?

Overwriting whiteouts and fallthroughs and unlinking fallthroughs I don't see
as a problem where they can be treated as normal negative dentries and normal
files in this regard.

However, what do you do about non-opaque directories that may or may not have
been unioned if you try and follow a dirent that would be a subdirectory that
hasn't been copied up?

David