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Date: Thu, 21 Jun 2001 18:06:39 -0400
From: Pete Zaitcev <zaitcev@redhat.com>
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To: root@chaos.analogic.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: Is it useful to support user level drivers
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> There is no such thing as a "user mode" interrupt service routine.
> There never was one, and there will never be one on any machine
> that fetches instructions from memory for execution. [...]

If memory does not deceive me, SunLab Spring processed interrupts
in user space. I do not remember for sure, but I think QNX did, too.
User mode interrupt handlers are perfectly doable, provided that the
hardware allows to mask interrupts selectively.

Large part of the post that I quoted was spent on spitting
in the general direction of clueless programmers; indeed,
I observe that perhaps 90% of requests for user mode interrupt
processing come from the same people who would like to write
Linux kernel mode code in C++ (total retards, in other words).

It does not mean, however, that there are not justified cases
for user-mode interrupt handlers, especially outside of Linux.
Some OSes are even written in C++ and Java, and run just fine
on a machine that fetches instructions from memory.

-- Pete