Re: Reparenting processes?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> It actually occurs to me that this is a potential problem even
>> today: what happens if all the processes in a session close the
>> descriptors they have on the ctty, and there are no others lying
>> around in other [...]
> or similarly, if they TIOCNOTTY it (although tty(4) tells me it's
> obsolete)

That would be testing something else.  The case where a process has no
ctty is comparatively well understood.  I'm wondering about the case
where a process has a ctty but the real ctty device is not open.

> I think sys/kern/tty_tty.c is the implementation of /dev/tty, and it
> seems you get ENXIO.

That's what I see for open on /dev/tty if there is no ctty.  (I/O on
/dev/tty when there's no ctty returns EIO in the code I have at hand.)
The case I'm wondering about is:

	- open real tty
	- make it the control tty
	- open /dev/tty
	- close the real tty
	- read/write the /dev/tty fd

It looks to me as though this could lead to the underlying tty driver
getting a read/write call when, according to its open/close calls, it's
not open.  I suspect it's a case that has never been tested; indeed,
until this discussion, the possibility had never occurred to me.

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