Date: Wed, 28 Aug 1996 14:12:07 +0200 (MET DST)
From: Mark Habersack <grendel AT ananke DOT amu DOT edu DOT pl>
Reply-To: grendel AT ananke DOT amu DOT edu DOT pl
To: Charles Sandmann <sandmann AT clio DOT rice DOT edu>
cc: djgpp AT delorie DOT com
Subject: Re: Memory mapped files using djgpp on DOS
In-Reply-To: <3219030c.sandmann@clio.rice.edu>
Message-ID: <Pine.NEB.3.95.960828140933.13496A-100000@ananke.amu.edu.pl>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Mon, 19 Aug 1996, Charles Sandmann wrote:

>> So my question is: is there a way to implement mmaped files using PF scheme?
>
>Only under a full DPMI 1.0 provider.  Since only 386MAX advertises to be
>a DPMI 1.0 provider, you are pretty much out of luck.  You could modify
>CWSDPMI to provide the augmented exception handler frame described in 
>DPMI 1.0 which would provide you the CR2 and PTE values.
Always a way... But still, it would be provider-dependent...

>
>> How client can make the server reflect PF faults? 
>
>This is a DPMI 1.0 feature, and only supported for uncommitted/readonly
>pages.
>
>> Should it be done by directly modifying IDT?
>
>If you have access to the IDT you can do this (like with CWSDPMI for
>example) but you will need to plan to run at the appropriate ring and
>chain to the previous handler, and will need to find the page tables also.
>At one time I planned to write a demo hook showing how to provide the
>old GRX type driver page fault graphics, but my interest in DOS hacking
>is gone.
>
After giving it a thought I think it is not worthwhile implementing this. If
one needs mmapped files, s/he will also need other advanced features... There
are so many operating systems providing these services... ;-)))

Mark

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