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Date:      Thu, 4 Sep 2003 18:56:27 -0700
From:      David Schultz <das@FreeBSD.ORG>
To:        Alexandr Kovalenko <never@nevermind.kiev.ua>
Cc:        freebsd-stable@FreeBSD.ORG
Subject:   Re: unionfs related patch
Message-ID:  <20030905015627.GB14776@HAL9000.homeunix.com>
In-Reply-To: <20030901160043.GB78655@nevermind.kiev.ua>
References:  <20030612154312.J80219@hub.org> <20030623081927.GC27017@nevermind.kiev.ua> <20030901160043.GB78655@nevermind.kiev.ua>

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On Mon, Sep 01, 2003, Alexandr Kovalenko wrote:
> Hello, Alexandr Kovalenko!
> 
> On Mon, Jun 23, 2003 at 11:19:27AM +0300, you wrote:
> 
> > >   David Schultz, in his spare time, has been working through some of the
> > > issues I've been able to 'tweak' in the unionfs code ... as he is
> > > currently working on forward-patching it to -CURRENT right now, he can't
> > > commit the code to the -STABLE tree ... in order to allow others using
> > > unionfs to test the patch (I've been running it a few weeks now on a very
> > > heavily loaded system), with his permission, I've posted the patch for
> > > download at:
> > > 
> > > 	http://www.hub.org/~scrappy/unionfs
> > 
> > Looks like it pretty stable. I'm running ~10 days with this patch - no
> > even single panic. Thank you!
> 
> I was too optimistic. It panics on high loads after 3-10 days.
> Is there any progress in work on this patch?

The only thing I know to be wrong with the patch is that it looks
like I forgot to MFC it.  Oops.  Unfortunately, there's plenty
wrong with unionfs, even with the patch.

Fundamentally, there are some design problems with VFS in FreeBSD
that make a clean implementation of unionfs impossible; 90% of the
brokenness in unionfs is due to unionfs having to create an
illusion of layering that doesn't really exist.  Fixing some of
the underlying problems is one of the goals for FreeBSD 6.X.

For now, my free time is very limited, so it's hard for me to
justify spending it on fixing a hack on top of a hack.  But if I
get a chance, I'll see what I can do.  I have a list of all the
interesting PRs on the topic, including some that were closed
because ``unionfs is broken''.



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