Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!elroy!spl1!laidbak!obdient!yclept!root
From: root@yclept.UUCP (Root)
Newsgroups: comp.unix.questions
Subject: Re: How do you find the user structure?
Keywords: kernel addressing
Message-ID: <109@yclept.UUCP>
Date: 12 Dec 88 03:54:04 GMT
References: <214@fesk.UUCP> <13232@ncoast.UUCP>
Reply-To: root@yclept.UUCP (PUT YOUR NAME HERE)
Organization: Leptons & Quarks, Winfield, IL 60190-1412
Lines: 28

In article <13232@ncoast.UUCP> allbery@ncoast.UUCP (Brandon S. Allbery) writes:
>As quoted from <214@fesk.UUCP> by sverre@fesk.UUCP (Sverre Froyen):
>+---------------
>| I have tried to get Brandon's sysV version of w to work on my
>| National Semiconductor ICM3216 running SysV.2.2.  This is a
>| demand paged system ....
>+---------------
>I've been trying to find it myself, via trial-and-error; I want to use it on
>a few demand-paged System V-based machines myself.  Anyone know what V.2.2
>and V.3.1 do with the ublock?

I have seen several methods used to address the user block.  One method is to
use a pointer in a fixed location, possibly an area that is particulary easy
to address for the particular processor the system is running on.  If memory
copying is relatively cheap on the particular processor, the user area can be
swapped to a fixed real memory address.  If the kernel itself runs with the
memory mapping unit active, another method is possible -- the active user area
is remapped to a fixed virtual area.  The most likely places to look for the
code that handles to user switch is in the interrupt handlers and in the
sleep() routine which dispatches a waiting process onto the processor.  That
is determined by the implementation and not by any description of the interface
between the kernel and the application programs.

	Randy Herber,
	@ home: {att|amdahl|mcdchg|obdient|wheaton}!yclept!rjh,
		rjh@yclept.chi.il.us,

Disclaimer: These are my personal views.  Nothing may be construed about my
employer's or customers' views or plans from this information.