On Tue, Jul 13, 2010 at 12:05:56PM +0800, Ian Kent wrote:
> On Tue, Jun 15, 2010 at 11:39:37AM -0700, Valerie Aurora wrote:
> > From: Jan Blunck <jblunck@suse.de>
> > 
> > In case of an union directory we don't want that the directories on lower
> > layers of the union "show through". So to prevent that the contents of
> > underlying directories magically shows up after a mkdir() we set the S_OPAQUE
> > flag if directories are created where a whiteout existed before.
> 
> I found this hard to understand.
> 
> Do you mean:
> 
> For directories within a union that are whiteouts we don't want the entries of
> lower layer file system to "show through". To achieve this we set the S_OPAQUE
> flag after a mkdir() on directories that are whiteouts.

That is much clearer.  I ended up with this version, what do you think?

whiteout: Set opaque flag if new directory was previously a whiteout

If we mkdir() a directory on the top layer of a union, we don't want
entries from a matching directory on the lower layer to "show through"
suddenly.  To prevent this, we set the opaque flag on a directory if
there was previously a white-out with the same name. (If there is no
white-out and the directory exists in a lower layer, then mkdir() will
fail with EEXIST.)

-VAL