How to make a tty un'open(2)'able after another process opens it

[charles spell]

Is there a way (besides lock files) that I can set a /dev/tty* to be
unopenable by other processes once it is opened by a process? The optimal
way would be for open() to return -1 if the tty is already being used.


It seems like there would be an easy way via ioctl(). I would like to
know how to do this on a pyramid 9815 even if it is not portable.
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