[Expectperl-discuss] controlling terminal problems on FreeBSD

[Guy R. <gu...@cw...>]

Hi,
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I am running into a few problems with Expect-1.15 on perl5.005. =
Specifically, I get "Error: could not connect pty as controlling =
terminal!" from time to time when trying to spawn a telnet to another =
machine.
I'm using FreeBSD 4.3 on i586.
As far as I can tell from digging a little in the Pty/Expect/Tty code as =
well as the kernel code, there's a problem with getting rid of =
controlling terminals on FreeBSD. Actually the sentence "Implement =
TIOCNOTTY or remove it from <sys/ioctl.h>" appears in the todo list in =
/src/sys/kern/tty.c on FreeBSD.
The problem as I can see it is in the following scenario:
1. in Expect->new, a pty is assigned
2. in spawn, Pty->make_slave_controlling_terminal is called
3. there it performs setsid()
4. afterwards it checks for the member {'io_pty_slave'} which was =
generated before, in the context of the previous session, and therefor =
the session struct in the kernel holds data about the previous session's =
controlling terminal
5. the call for TIOCSCTTY has the following code in it (tty.c):
                if (!SESS_LEADER(p) ||
                    ((p->p_session->s_ttyvp || tp->t_session) &&
                    (tp->t_session !=3D p->p_session)))
                        return (EPERM);
    where p is the proc structure, and tp is the tty structure (pointers =
ofcourse)
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Remembering that setsid() creates a new session context for the process =
and that tp might have had a controlling tty associated with it, =
problems may occur.
Btw, as I mentioned earlier TIOCNOTTY has not yet been implemented.
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I'm pretty sure that I haven't reached a full understanding in all of =
this, so any corrections would be very welcome.
=20
    Guy