Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uwm.edu!ux1.cso.uiuc.edu!phil
From: phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN)
Newsgroups: comp.os.msdos.programmer
Subject: Re: How can a TSR detect if it has been installed?
Message-ID: <1991Jun26.173756.19925@ux1.cso.uiuc.edu>
Date: 26 Jun 91 17:37:56 GMT
References: <0094A83A.9AE8E1A0@MAPLE.CIRCA.UFL.EDU> <1991Jun23.145337.20537@netcom.COM>
Organization: University of Illinois at Urbana
Lines: 23

resnicks@netcom.COM (Steve Resnick) writes:

>>I have written a  TSR that takes over the command line input for INT21H, in
>>other words an INT21H replacement.
>>
>>How can it prevent itself from being re-installed?  I know programs such as
>>NORTON SI will show you who "owns" an interrupt, and my program comes up 
>>as the owner.  If there was a way to see if the owner was NOT DOS (i.e. anothe
>>program, such as a TSR, owned it) and to not install itself in that case, I
>>would like to know.
>The way I have handled this, when using an interrupt vector which may
>already be used by some other utility/tsr/system function is to
>grab a few bytes in the CS of the ISR as a "signature", then when installing
>my TSR, look at that segment address and the specific offset. If my signature
>is there, I know my TSR has been installed, otherwise it's not and I can
>install it....

How can you differentiate between some other TSR owning it and DOS owning it?
-- 
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/ Phil Howard -- KA9WGN -- phil@ux1.cso.uiuc.edu   |  Guns don't aim guns at  \
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