Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!mcsun!hp4nl!star.cs.vu.nl!philip
From: philip@cs.vu.nl (Philip Homburg)
Newsgroups: comp.os.minix
Subject: Re: User Process Message-Passing in Minix
Message-ID: <10043@star.cs.vu.nl>
Date: 23 May 91 14:00:19 GMT
References: <1991May22.235824.6939@IDA.ORG>
Sender: news@cs.vu.nl
Organization: Fac. Wiskunde & Informatica, Vrije Universiteit, Amsterdam
Lines: 39

In article <1991May22.235824.6939@IDA.ORG> wheeler@IDA.ORG (David Wheeler) writes:
%
%The original version of Minix did not allow _User Processes_
%to pass messages to OTHER user processes.
%
%
%Two questions for the net:
%
%1. Does the current version (or some modified version everyone uses)
%allow this? (From all I can tell it doesn't).
%
%2. If not, would someone who has the current version of Minix mind
%trying out the following modification to allow it?  Please?
%Or tell me a better way to do it?


Please DON'T DO THIS. May be this is too loud and I should whisper "please,
don't do this" but you are looking for trouble.

I have a kernel which allows user processes to send to and receive from
anyone and it is part of minix 1.6.15 but it is for debugging purposes only.

There are a few problems:
- What to do with signals. You didn't get a message but you got a signal.
- What if somebody is sending to you and you die. The kernel doesn't check.
- How does a server find out his process number.
- How do you send messages larger than about 32 bytes.
- How do you know who sent the request, no userids can be checked.

And, last but not least, you can do it with fifos.

Of course the best way to find out about your idea is to implement it, but 
I think that for IPC you need a dedicated server like FS or in the kernel
that has access to userids, etc.




					Philip