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Date: Sat, 25 May 2002 11:08:30 +0200
From: Robert Schwebel <robert@schwebel.de>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: patent on O_ATOMICLOOKUP [Re: [PATCH] loopable tmpfs (2.4.17)]
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On Fri, May 24, 2002 at 08:25:38PM -0700, Linus Torvalds wrote:
> With RTLinux, you have to split the app up into the "hard realtime" part
> (which ends up being in kernel space) and the "rest".
> 
> Which is, in my opinion, the only sane way to handle hard realtime. No
> confusion about priority inversions, no crap. Clear borders between what
> is "has to happen _now_" and "this can do with the regular soft realtime".

... which in turn results in the situation that applications must be
implemented as kernel modules. 

> Your claim was that RTLinux made realtime hard to do with licensing
> concerns. MY claim is that if you actually were to use RTLinux, you
> wouldn't _have_ any licensing concerns: the kernel module would have to
> be GPL (both because the kernel wants it that way _and_ because you get
> the liences to the patent that way), and the user-level code that uses
> whatever data the RT module produces is no longer hard realtime at all.

This is only correct for open-loop applications. Most real life apps are
closed-loop. 

Robert
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