[winswitch] assigning input devices to xpra instance?

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Hello,

I am exploring making a multiseat system (multiple users with multiple
monitors/mice/keyboards on one computer) with only one graphics card
feeding two terminals.  Tutorials on line for doing this all talk about
Xephyr.  (If you had multiple cards, you'd start an new X server for each
user.)  The Xephyr dev hates that xypher is used for multiseat and so it
really isn't the best tool.

Xpra is sort of similar to Xephyr.  One thing Xephyr has is the ability to
have devices from evdev (/dev/input/) assigned to a particular instance of
it, so one mouse and one keyboard only send information to that one Xephyr
session.  Does Xpra have any functionality like that, or could it be hacked
in some way using another program in conjunction with Xpra?

Thanks,
Elliot