linux-kernel - Re: [PATCH 07/38] whiteout: Set S_OPAQUE inode flag when creating directories

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Date:	Sat, 17 Jul 2010 12:14:36 +0800
From:	Ian Kent <raven@...maw.net>
To:	Valerie Aurora <vaurora@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Miklos Szeredi <miklos@...redi.hu>,
	Jan Blunck <jblunck@...e.de>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 07/38] whiteout: Set S_OPAQUE inode flag when creating
 directories

On Fri, 2010-07-16 at 16:12 -0400, Valerie Aurora wrote:
> 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@...e.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.)

That's much clearer IMHO.

> 
> -VAL


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