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From: usenet@mcdchg.UUCP
Newsgroups: mod.os.unix
Subject: Re: How does close() make dup() work in getty??
Message-ID: <284@mcdchg.UUCP>
Date: Thu, 26-Mar-87 18:15:25 EST
Article-I.D.: mcdchg.284
Posted: Thu Mar 26 18:15:25 1987
Date-Received: Sat, 28-Mar-87 06:11:22 EST
References: <233@mcdchg.UUCP>
Sender: usenet@mcdchg.UUCP
Organization: Astronautics Technology Cntr, Madison, WI
Lines: 49
Approved: usenet@mcdchg.UUCP

in /usr/src/sys/sys/tty.c  fuction "ttyopen"
there is the following code:
    pp = u.u_procp;			-- proc table entry
    if (pp->p_pgrp == 0) {		-- no proc-group ??
        u.u_ttyp = tp;			-- set /dev/tty pointer
        if (tp->t_pgrp == 0) 		-- no tty-proc-group ??
            tp->t_pgrp = pp->p_pid;	-- effectivly create new group-leader
        pp->p_pgrp = tp->t_pgrp;	-- alwasy set proc-group
    }

in ttyclose(), which is only called for the *FINAL* close, we have:
    tp->t_pgrp = 0;

tp is always a pointer to the tty struct.
t_prgp is the process group used for keyboard signals, and
p_pgrp is the process group shown by ps l
(t_* are fields in the tty struct; p_* are fields in the proc struct.)


As far as I know, u_ttyp can only be cleared by 
doing an ioctl (TIOCNOTTY) on /dev/tty
    (see the ioctl routine in .../tty_tty.c)

Your process group can be controlled by ioctls too (see tty(4) for
details on those.)

Check your login program carefully, and make *SURE* that t_pgrp is
set *BEFORE* login becomes csh!!!  (If not, and you're useing
version #2, then I think that the users csh will be in the p-group
of init (or whoever you have starting getty!!!!!   It would not be
nice for a user to send a keyboard-quit-signal to init, would it??

Whenever in doubt, read the source!!!!!  (We'll make a hacker out
of you yet!!)

Hope this is of some help

-- 

			John W

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
Name:	John F. Wardale
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