linux-kernel - Re: [PATCH 0/7] overlay filesystem: request for inclusion

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Date:	Tue, 12 Jul 2011 18:15:03 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Hans-Peter Jansen" <hpj@...la.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, viro@...iv.linux.org.uk,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, apw@...onical.com, nbd@...nwrt.org,
	neilb@...e.de, hramrach@...trum.cz, jordipujolp@...il.com,
	ezk@....cs.sunysb.edu, hooanon05@...oo.co.jp
Subject: Re: [PATCH 0/7] overlay filesystem: request for inclusion

"Hans-Peter Jansen" <hpj@...la.net> writes:

> On Friday 08 July 2011, 14:57:09 Miklos Szeredi wrote:
>> Allow using namspace polluting xattr replacements, such as aufs is
>> doing.
>>
>> But why?  Why is it better to do the overlaying on the client instead
>> of the server?
>
> Exporting layered filesystems via NFS suffered from many problems 
> traditionally, because that permuted NFS export issues of the server FS 
> in use (say xfs) with FS layering issues. Since I'm doing diskless 
> computing for more then two decades now, I always persued for lowering 
> complexity, and/or localize it. Layering on the client is done with the 
> latter in mind. While the basic concept of layered FS is sound, 
> especially, things like mmapping and splicing cause hard to track down 
> and problems, that are even harder to solve properly. 
>
> Do you have experiences with NFS exported overlay FSs already? If that 
> proves stable, does scale, and a client is able to survive a server 
> reboot, layering on the server is a sexy approach of course (I hate to 
> being forced to maintain my own kernel flavors for diskless clients, 
> while I love to track the Linux kernel progress in general..).

Well, you are right, exporting an overlay has its own complexities.

Abstracting the whiteout/opaque flags behind an implementation that can
use xattr or plain files sounds pretty easy to do in comparison.  I'll
look into that.  But this is again a feature that needs to go in a
later.

> Does a openSUSE build service kernel project exist with overlayfs 
> included? If I read the patch correctly, it's not possible to just bake 
> overlayfs as a standalone KMP ATM.

No, it needs small VFS modifications, so a standalone module doesn't
work.

Thanks,
Miklos
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