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From: dupont@inria.UUCP (Francis Dupont)
Newsgroups: comp.unix.wizards
Subject: Re: multiple-machine executables ?
Message-ID: <502@inria.UUCP>
Date: Wed, 5-Aug-87 06:03:45 EDT
Article-I.D.: inria.502
Posted: Wed Aug  5 06:03:45 1987
Date-Received: Sat, 8-Aug-87 08:52:36 EDT
References: <1853@megaron.arizona.edu> <24830@sun.uucp>
Organization: INRIA, Rocquencourt. France
Lines: 30
Summary: Conditional symbolic links


  LOCUS provides a good solution for multiple-machine executables :
conditional symbolic links. For example : /bin/cat is a conditional link to
a binary for Vaxen and to an other binary for 680x0.
If you are in the vax universe, you follow the Vax branch,
and in the 68k universe, the 68k branch. This feature is named
hidden directory in LOCUS, and is used in dual port Unix
(Pyramid, Sequent, ...) implementations.
  You need a new field (universe) in the proc structure, some system calls
(csymlink (makes a conditional symbolic link), setuniverse (sets the universe
of the current process), ...). You can use conditional symbolic links
for multiple-machine executables, libraries, binary data files, ... or
for environments (for example, Pyramids have two universes : att (SVR2V2)
and ucb (BSD 4.2/4.3)).
  Conditional symbolic links are very simple to implement, and are
a better solution for multiple-machine executable than a new object
format. But they can't save disk space ...

  Good references on conditional symbolic links are :

The LOCUS Distributed System Architecture,
by Gerald J. Popek & Bruce J. Walker.
MIT Press 1985 (Chapter 6.4 : Hidden directories)

OSx 3.x Release Overview, Pyramid Technology Corporation

Balance Technical Summary, Dynix System V User's Guide,
Sequent Computer Systems Inc.

[Francis Dupont] dupont@inria.inria.fr or ..!seismo!mcvax!inria!dupont