Sorry, the WAITEVENT stuff interface you created is unusably broken:

a) it's a sleeping ioctl which makes it unusable in anything but the most trivial applications, because most programs need to respond to more than once wakeup event. Of course, you can then introduce threads but that's horrible.

b) It loses events, because events that happen after you woke up and before you go back into WAITEVENT are completely lost. And those events might actually be relevant, since they might be the most recent events that happened. And those tend to be ones that matter.

Kay's interface also drops events, but only historic events that happened but aren't current anymore. And that's a good thing, because when you track which VT is in the foreground for presentation, or for permission management purposes then you care little of who else should have had access in the past but didn't get it. You are only interested in the most recent update, which is what Kay's interface gives you.

Kay's interface is not intended to be useful for logging purposes. It is useful to track VT changes for service activation, for permission management.

Well, the suff it provides is purely informational. You cannot actually influence the TTY in anyway, you can just watch which VT is currently active.

I am sorry, but WAITEVENT doesn't work for *any* case. It is completely broken. Have you actually ever tried to use it yourself? Do it. Write me a race-free program with it that tracks VT switches and i'd be amazed!

events. And voila, you'll have created Kay's interface.