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From: rmgtkro@cs.vu.nl (Rob ten Kroode)
Newsgroups: comp.os.minix
Subject: Re: Process group initialization (was: SIGNAL Handling Problems)
Message-ID: <1019@ark.cs.vu.nl>
Date: Mon, 18-May-87 13:24:28 EDT
Article-I.D.: ark.1019
Posted: Mon May 18 13:24:28 1987
Date-Received: Tue, 19-May-87 04:18:45 EDT
References: <3882@cae780.TEK.COM> <2508@ncoast.UUCP>
Organization: V.U. Informatica, Amsterdam, the Netherlands
Lines: 43

In article <2508@ncoast.UUCP> allbery@ncoast.UUCP (Brandon Allbery) writes:
>As quoted from <3882@cae780.TEK.COM> by hubble@cae780.TEK.COM (Larry Hubble):
>+---------------
>| Third and last, the process group is never set to anything.  Which means
>| it is always zero now.  I'm not sure what I did is the best answer, but
>| it works.  In mm/forkexit.c when a fork is done, do_fork() now looks to
>| see if the parent doing the fork is INIT.  If it is INIT, a new PRIVATE
>| variable (process_group) is incremented and put in the process table. 
>| If the parent is not INIT, the child inherits the parents process group.
>+---------------
>
>The process group should be the same as the parent process's pid.  The correct
>fix would not be in the kernel, it should be in init.  After init forks a
>child but before the child execs getty (login?), the child should setpgrp().
>(Okay, I lied; this requires MM to have a setpgrp() system call.  Probably it
>should be added to do_getset().  The action of setpgrp() is to set the caller's
>pgrp to its pid, and any process should be allowed to do this, so very little
>if any checking should need to be done.)
>
>++Brando

I don't agree. A process should inherit it's parent's process group (unless
you put the child in a specified process group). This means I don't check
in do_fork() if the parent is INIT. During initiliation I put INIT in a 
"special" process-group. In the INIT-program all the children are put in a 
process group which differs from it's parent. 

The action of setpgrp() is NOT to set the caller's process group to it's pid.
Setpgrp() has two arguments: a pid, and a process group. Setpgrp() puts the 
process whith the specified pid in the specified process group (which is
most of the time the pid).
I made setpgrp() and getpgrp(), which returns the process group of the
specified pid. 

I made these system calls while I was busy imlementing job-control for
MINIX. I had to change a lot before it worked properly, but now everything
seems to work perfect (I only need a new shell, but I don't have time to
write a new one myself).

If someone wants the sources of setpgrp(), getpgrp() and/or job-control
please let me know (the sources of job-control are a LOT of diff's !).

Rob ten Kroode (rmgtkro@cs.vu.nl).