Multihead support

[Sean D'Epagnier <sean@depagnier.com>]

I think multihead support is slightly broken with fbdev.

I have multihead working with nvidiafb and matroxfb. I had to patch the
kernel to get console text to update on the non-active vt.

In userspace programs, I know how to  register signal handlers to notify
a program when it gains or loses the active vt, but I don't think there is
a way to correctly detect when a framebuffer device becomes visible or
hidden.   The FBIOGET_CON2FBMAP ioctl provides a means to find which 
fbdev devices is mapped to a given console, but as far as I know to do
the reverse lookup (find the vt attached to a given fbdev) can't be done.
There are really 3 states a vt can be in:
1. active/visible
2. inactive/visible   (only applies to multihead)
3. inactive/invisible

If it were possible to register a signal handler for visible changes the
same way as active changes, this would fix the problem.

Xorg for example won't run on /dev/fb0 and allow me to run something else
on /dev/fb1  I have in my own programs written hacks to poll con2fb, at
a timed interval.  This is a terrible solution, and it has a high probability
of corrupting the screen output (until refresh)

I think in the future this will be come a bigger concern as x11 is slowly
being separated from the hardware, and it will become useful to run
multiple sessions of x11.  I would like to discuss all possible solutions,
and hopefully implement a simple working solution.


Thanks,
Sean D'Epagnier

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