On Mon, 10 Sep 2012 03:47:04 +0200 (CEST) Jan Engelhardt <jengelh@inai.de>
wrote:

> 
> On Wednesday 2012-08-15 17:48, Miklos Szeredi wrote:
> >[...]
> >+This is most obvious from the 'st_dev' field returned by stat(2).
> >+
> >+While directories will report an st_dev from the overlay-filesystem,
> >+all non-directory objects will report an st_dev from the lower or
> >+upper filesystem that is providing the object.
> 
> That would seem to render `rsync --one-filesystem` unusable?
> (or similar options in other tools)
> 

Would it?  Have you tested? or examine source code? or just guessed?

I quick look at rsync and du suggest that you only consider --one-file-system
when looking at a directory - they assume files are in the same filesystem as
their parent.
I cannot promise that everything would work exactly as expected, but I
suspect most things will..... though that might  depend on your expectations.

NeilBrown