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From: mbr@THEORY.LCS.MIT.EDU
Newsgroups: comp.unix.wizards
Subject: How do NFS implementations fit into 4.[23]BSD and derived systems?
Message-ID: <7044@brl-adm.ARPA>
Date: Wed, 22-Apr-87 15:56:07 EST
Article-I.D.: brl-adm.7044
Posted: Wed Apr 22 15:56:07 1987
Date-Received: Fri, 24-Apr-87 03:11:44 EST
Sender: news@brl-adm.ARPA
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I can see two totally different ways of implementing NFS in BSD.  The "clean"
way is to have *all* filesystem abstractions (including directories) be fully
supported by the kernel (this was never the case in older Unixes).  Library
routines for things like opendir() and scandir() will use system calls instead
of reading directory files, but no other library routines will change.  The
interface to NFS will be entirely in the kernel, and you will only have to
relink everything once.  Of course, you won't be able to take a binary to a
vanilla BSD system and expect it to work, since it will use nonexistent system
calls.  But you'll be able to take it to any other system that supports the
same system calls, even if it uses a different NFS implementation (or doesn't
support NFS at all).

The "dirty" way is to put all of the NFS code into library routines.  System
calls like open() will no longer be stub procedures that do the appropriate
chmk; they will now contain code to trap and handle remote file operations.
This method requires no kernel changes, but binaries will get a lot bigger,
will become dependent on the particular NFS implementation in use, and will not
be portable between machines that use different NFS implementations.

A quick examination of the sources for Sun Unix 3.2 indicates that Sun has
integrated NFS into BSD the "clean" way (correct me if I'm wrong).  I've heard
rumors that other NFS implementations are done the "dirty" way; does anyone
have information about specific implementations?  (I'm particularly interested
in Mt. Xinu 4.3+NFS and Ultrix 2.0.)  Finally, are the new system calls
supported in Sun Unix becoming standard for BSD and derived sytems, even for
those that don't have NFS?

Thanks,
Mark Reinhold
Theory of Computation Group                mbr@theory.lcs.mit.edu
MIT Laboratory for Computer Science        (617)-253-3037