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From: Terry Lambert <terry@lambert.org>
Message-Id: <199603161939.MAA17753@phaeton.artisoft.com>
Subject: Re: Try this vm_mmap.c -- please
To: davidg@Root.COM
Date: Sat, 16 Mar 1996 12:39:53 -0700 (MST)
Cc: jkh@time.cdrom.com, dawes@rf900.physics.usyd.edu.au, sos@FreeBSD.org,
        dyson@FreeBSD.org, current@FreeBSD.org, mmead@Glock.COM
In-Reply-To: <199603161406.GAA07890@Root.COM> from "David Greenman" at Mar 16, 96 06:06:26 am
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> >Which turns MAP_PRIVATE *off* for device objects.  My Xaccel 1.2 now
> >works perfectly!  Yay!
> 
>    Yes, as John and I have discussed, it really doesn't make any sense to
> allow COW (MAP_PRIVATE) mappings of devices. I think forcing them shared
> is reasonable.

Say I mmap'ed a video card, but I wanted to virtualize the card for
multiple console instances.  Wouldn't I want COW for that?

I'm not saying that it isn't right to disallow non-shared mappings
of devices, only that we should try to think of instances of devices
where it might be a mistake.

And maybe add a flag on the device driver as to what mappings are
allowable, assuming there's an example of needing MAP_PRIVATE.


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