linux-kernel - Re: [PATCH 00/22][RFC] Unionfs: Stackable Namespace Unification Filesystem

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Date:	Tue, 5 Sep 2006 09:01:10 +0200
From:	Jörn Engel <joern@...nheim.fh-wedel.de>
To:	Al Boldi <a1426z@...ab.com>
Cc:	Josef Sipek <jsipek@...sunysb.edu>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org, akpm@...l.org,
	viro@....linux.org.uk, Pavel Machek <pavel@...e.cz>
Subject: Re: [PATCH 00/22][RFC] Unionfs: Stackable Namespace Unification Filesystem

On Tue, 5 September 2006 07:46:44 +0300, Al Boldi wrote:
> Jörn Engel wrote:
> >
> > Direct modification of branches is similar to direct modification of
> > block devices underneith a mounted filesystem.  While I agree that
> > such a thing _should_ not oops the kernel, I'd bet that you can easily
> > run a stresstest on a filesystem while randomly flipping bits in the
> > block device and get just that.
> 
> Not really a fair comparison.  The block level is conceptionally totally 
> different than the fs level, while a stackable fs is within the realms of 
> the fs level.

Well, I didn't realize that unionfs required its backing filesystems
to be mounted.  That's more like having the block device open in a
text editor while mounting ext3.  In the presence of such a design, an
oops clearly is not acceptable.  And this sort of design is just what
I was talking about when I said:

> > There are bigger problems in unionfs to worry about.

Jörn

-- 
You can't tell where a program is going to spend its time. Bottlenecks
occur in surprising places, so don't try to second guess and put in a
speed hack until you've proven that's where the bottleneck is.
-- Rob Pike
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