linux-kernel - Re: Heads up on VFS based union mount

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Message-ID: <20070331110935.GA5831@in.ibm.com>
Date:	Sat, 31 Mar 2007 16:39:35 +0530
From:	Bharata B Rao <bharata@...ux.vnet.ibm.com>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	linux-kernel@...r.kernel.org, jblunck@...e.de
Subject: Re: Heads up on VFS based union mount

On Fri, Mar 30, 2007 at 09:04:16PM +0200, Jan Engelhardt wrote:
> 
> On Mar 30 2007 15:38, Bharata B Rao wrote:
> >
> >In union mount approach we maintain this stacking information in the 
> >dentry structure. When a filesytem is union mounted on a mountpoint, 
> >the dentry of the mount root would hold a reference to the mountpoint 
> >dentry as an overlaid dentry and these two dentries together form a 
> >union stack. Any subsequent readdir operation on this union mounted 
> >dentry would work on the overlaid dentry also thereby providing the 
> >merged view of the two filesystems.
> 
> What about whiteouts? (I cannot remember whether Jan Blunk's paper 
> mentioned it at all.)

We do have whiteout support. And as I mentioned earlier, the underlying
filesystem needs to support the new 'whiteout' filetype. As of now it is
supported for ext2, ext3 and ramfs.

Regards,
Bharata.
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