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Date:      Sun, 17 Dec 2000 12:30:54 -0500 (EST)
From:      Robert Watson <rwatson@FreeBSD.ORG>
To:        Andrew Reilly <areilly@bigpond.net.au>
Cc:        Jordan Hubbard <jkh@winston.osd.bsdi.com>, Patryk Zadarnowski <pat@jantar.org>, Tony Finch <dot@dotat.at>, SteveB <admin@bsdfan.cncdsl.com>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: kernel type
Message-ID:  <Pine.NEB.3.96L.1001217122839.48123C-100000@fledge.watson.org>
In-Reply-To: <20001217203917.A42764@gurney.reilly.home>

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On Sun, 17 Dec 2000, Andrew Reilly wrote:

> Yeah, but in what sense is that use of Mach a serious microkernel, if
> it's only got one server: BSD?  I've never understood the point of that
> sort of use.  It makes sense for a QNX or GNU/Hurd or minix or Amoeba
> style of architecture, but how does Mach help Apple, instead of using
> the bottom half of BSD as well as the top half? 

What I'd really like to know, and haven't had a chance to investigate
much, is to what extent the Mach primitives are used by their userland
environment.  I.e., does their software really just use the BSD ABI/API,
or does it rely on the Mach IPC primitives for performance in their
graphics subsystem.  If it relies only on the BSD interface, that gives
them a path towards migrating more in the direction of a pure FreeBSD
kernel, if they desire, or swapping it out with whatever they choose, as
well as leveraging a lot of other work (in particular, security work) 
based on UNIX-like ABI/API's.  If they do rely on the Mach primitives,
then that may be less easy.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Project
robert@fledge.watson.org      NAI Labs, Safeport Network Services



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