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Re: Research using L4Hurd

From: Marcus Brinkmann
Subject: Re: Research using L4Hurd
Date: Thu, 4 Jul 2002 14:34:43 +0200
User-agent: Mutt/1.4i

On Thu, Jul 04, 2002 at 11:59:47AM +1000, address@hidden wrote:
>         There is an effort to port the Hurd by removing its dependency on
>         the Mach mega-microkernel, and to run it on top of L4. The Hurd
>         is designed as a set of modular components, but there is a big
>         dependency on Mach. Lots of discussion at present, no code yet.

Many people claim that the Hurd has a big dependency on Mach.  When asked
back what specific thing they want to have changed, there is usually no
response :)

If you just glimpse at the current code, it is obvious that the code is
written to run on Mach.  Eg you have a lot of #include <mach.h> statements,
and many RPCs to the Mach kernel.  The Hurd is using the Mach port system
and the external pager interface.  In the most obvious sense, it is very
dependent on Mach.

OTOH, you wrote above "The Hurd is designed as a set of modular components",
and as this design the Hurd is not much dependent on Mach at all.  What the
Hurd depends on is the port abstraction as specified by libports, a VM that
allows for external pagers, etc.

When the Hurd was designed, it was taken into account that at some time it
would be ported to another microkernel, and so the design reflects that.

Of course, no recent microkernel provides such high level abstractions as
Mach does anymore.  And it is worth it to reconsider for example the ports
abstraction, esp in light of L4.  But the grand design of the Hurd will
survive unchanged, and most of the porting will be mostly automatic, as soon
as the gap between L4 and whatever remains of Mach as we use it has been

(It is an interesting task to find the few places in the Hurd where it
really is specific to some Mach idisoyncrasies.  We will cerrtainly find
them all when actually doing the port.)


`Rhubarb is no Egyptian god.' Debian http://www.debian.org address@hidden
Marcus Brinkmann              GNU    http://www.gnu.org    address@hidden

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