linux-kernel - Re: [PATCH] Allow userspace block device implementation

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Date:	Fri, 7 Aug 2009 20:08:42 +0200
From:	Pavel Machek <pavel@....cz>
To:	Zachary Amsden <zamsden@...hat.com>
Cc:	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	axboe@...nel.dk, hch@...radead.org, akpm@...ux-foundation.org,
	Paul.Clements@...eleye.com, tytso@....edu
Subject: Re: [PATCH] Allow userspace block device implementation

Hi!

> Well, it may be a good, bad, idiotic or brilliant idea depending on your
> personal philosophy.  I went down this route out of pragmatism.
> Hopefully I have not fully re-invented the wheel.

I did, long ago. I called it nbd... aha and you know about it (from
following mails in thread).

> accidental deadlock.  There may of course be some hidden deep deadlock
> potential in such a device, especially if one decided to use it as a
> swap device, but again, this is a philosophical issue.

What's philosophical about 'it does not work for swap or dirty mmap'?

(last time I checked, dirty mmap data behaved very much like swap).

(And yes, nbd has same problem. It should be safe for r/o access to
localhost, but may deadlock when it is mounted locally...)

And yes, I believe that's show stopper. OTOH if you _can_ solve
that... then you have some rather significant advantage over nbd.

(But guaranteeing progress for dirty writeout will be tricky even with
mlocked userland, AFAICT...)

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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