How does close() make dup() work in getty??

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2 total messages Started by usenet Fri, 13 Mar 1987 15:11

#24

Author: usenet
Date: Fri, 13 Mar 1987 15:11

46 lines
1816 bytes

I recently wrote a new getty for a RT built around curses.

My question is about why one version works and another not.
The following code out lines the differences in the two versions.
Version 1 does not work while Version 2 does.

Version 1.

		main(tty)
			char *tty;				/* tty to use */
			{
			set_ioctl();			/* put in known mode */
			close(0);
			close(1);
			close(2);
			dup(dup(open(tty,2)));
			write_utmp(tty);		/* do utmp stuff */
			get_logid(logid);			/* prompt for logid */
			execle("/bin/login",logid,NULL);
			}

Version 2.
		main(tty)
			char *tty;				/* tty to use */
			{
			set_ioctl();			/* put in known mode */
			close(0);
			close(1);
			open(tty,2);
			close(2);
			dup(0);
			dup(1);
			write_utmp(tty);		/* do utmp stuff */
			get_logid(logid);			/* prompt for logid */
			execle("/bin/login",logid,NULL);
			}

Does close() cause something to settle that dup() needes from the open()?
The problem with Version one is that /dev/tty does not get attached to
the control group.

Any idea's that might explain this mystery would be greatly appreciated!!
-- 
Larry Baird 					Dept. of Computer Science
uucp: {ihnp4!decvax,peora}!ucf-cs!baird		University of Central Florida
						Orlando, FL  32816

Re: How does close() make dup() work in getty??

#30

Author: usenet
Date: Thu, 26 Mar 1987 23:15

49 lines
2340 bytes

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

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Name:	John F. Wardale
UUCP:	... {seismo | harvard | ihnp4} !uwvax!astroatc!johnw
arpa:   astroatc!johnw@rsch.wisc.edu
snail:	5800 Cottage Gr. Rd. ;;; Madison WI 53716
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