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Path: utzoo!mnetor!seismo!lll-lcc!ames!ucbcad!ucbvax!sdcsvax!mod-os
From: mod-os@sdcsvax.uucp
Newsgroups: mod.os
Subject: kernel servers vs. user servers.
Message-ID: <2450@sdcsvax.UCSD.EDU>
Date: Mon, 12-Jan-87 12:22:06 EST
Article-I.D.: sdcsvax.2450
Posted: Mon Jan 12 12:22:06 1987
Date-Received: Mon, 12-Jan-87 22:42:41 EST
Sender: darrell@sdcsvax.UCSD.EDU
Reply-To: jack@mcvax.cwi.nl (Jack Jansen)
Organization: AMOEBA project, CWI, Amsterdam
Lines: 35
Approved: mod-os@sdcsvax.uucp

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In article <2438@sdcsvax.UCSD.EDU> henry@utzoo.uucp writes:
>
>Alternatively, does it matter?  It's all very well to say that your file
>system is in a user-state server rather than in your kernel, but your users
>are probably just as dependent on every little detail being right.  To make
>user-state servers more than an irrelevant implementation detail, the user
>must be offered a choice of servers AND IT MUST BE EASY TO WRITE A SERVER!
>Or at least, not impossibly hard.  If writing a server is as touchy a job
>as writing the equivalent inside the kernel, the wonderful flexibility will
>get little use. 
>
I think that user-state servers have a lot of advantages over
kernel-state servers. Of course, it shouldn't matter to the user
directly, but some of the advantages of user-state servers
I see are:

- Testing and debugging a new, improved, better and faster (and,
therefore, completely unreliable:-) server can be done during
normal production time, and all normal debugging tools are available.

- Backward compatability or emulation of a different OS is much
easier.

- By splitting a service into smaller services these services become
much easier to understand (and, hopefully, robust).

Of course, performance is still better for kernel-state servers,
but the gap seems to be closing quite fast.
-- 
	Jack Jansen, jack@cwi.nl (or jack@mcvax.uucp)
	The shell is my oyster.

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