From owner-freebsd-current  Fri Mar 15 18:34:33 1996
Return-Path: owner-current
Received: (from root@localhost)
          by freefall.freebsd.org (8.7.3/8.7.3) id SAA21409
          for current-outgoing; Fri, 15 Mar 1996 18:34:33 -0800 (PST)
Received: from phaeton.artisoft.com (phaeton.Artisoft.COM [198.17.250.211])
          by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id SAA21403
          Fri, 15 Mar 1996 18:34:17 -0800 (PST)
Received: (from terry@localhost) by phaeton.artisoft.com (8.6.11/8.6.9) id TAA14695; Fri, 15 Mar 1996 19:28:53 -0700
From: Terry Lambert <terry@lambert.org>
Message-Id: <199603160228.TAA14695@phaeton.artisoft.com>
Subject: Re: -current and accelx
To: dawes@rf900.physics.usyd.edu.au (David Dawes)
Date: Fri, 15 Mar 1996 19:28:53 -0700 (MST)
Cc: toor@dyson.iquest.net, sos@FreeBSD.org, coredump@nervosa.com,
        mmead@Glock.COM, current@FreeBSD.org
In-Reply-To: <199603160127.MAA14131@rf900.physics.usyd.edu.au> from "David Dawes" at Mar 16, 96 12:27:20 pm
X-Mailer: ELM [version 2.4 PL24]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-current@FreeBSD.org
X-Loop: FreeBSD.org
Precedence: bulk

> I'm don't have any ideas about AccelX, but after looking at the changes
> in vm_mmap.c, I tried adding MAP_SHARED to the mmap() flags in my test
> program, and that fixed it when using the 1.38 version of vm_mmap.c.
> I don't understand why the mapping needs to be shared to prevent a
> *parent* losing it after it has forked.  We certainly don't need (or want)
> the child to share the mapping.  I may be mis-understanding the intention
> of MAP_SHARED.

It shouldn't need to be present in that case.

The MAP_SHARED is supposed to mean that pages are not copy-on-write
faulted, nothing more.  Generally used for implementing IPC facilities.

This isn't well documented in the man page, but...

When the parent forks, and there is mapped memory, unless the MAP_INHERIT
flag is present, the child process should lose the mapping to the address
space, in all cases.

Are you sure that whatever it is isn't using "vfork"?  I don't know
if vfork handled this correctly at all.

In any case, you are not misinterpreting MAP_SHARED, IMO.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.