Instead of requiring the graphics driver to create a fixed set of VTs in
advance. This fixes the graphical interface when there is a graphics
driver but no boot framebuffer. Previously in that case vesad would exit
before it creates any VT and thus no consumer could show anything as
their VT was missing. In the future creating new VTs on the fly could
also allow a display manager to use a separate VT for each user session.
With this virtio-gpud no longer has to support getting deactivated at
any time to hand back control to vesad. This makes it much easier to add
many new features that a proper graphics driver is supposed to support.
Be aware that virtio-gpud waits for the vsync on every flush request.
Fbcond and orbital are not really happy about this right now and when
something changes multiple times within a single frame, flush requests
queue up, causing the ui to hang until all flush requests are finished.
It is still possible to switch to another VT though which won't hang.
Previously inputd would directly push vt activation events to the
graphics driver, which required being quite lazy to prevent deadlocks as
well as the graphics driver having a location where events can be pushed
to. By having graphics drivers pull the vt activation events instead,
the effective control flow becomes simpler and it becomes easier to
correctly handle multiple graphics drivers on the system. For example it
becomes possible for multiple graphics drivers to present displays for a
single VT as well as making it easier to provide a handoff from the
early framebuffer to a real graphics driver.
ControlHandle is used to switch the active vt, while DisplayHandle is
used by display drivers to register new vt's. There are entirely
unrelated tasks and the fact that they had been merged together has been
confusing me for a while.
Also changed activating a VT to no longer create a new vt when none
existed previously. The target graphics driver may not be able to handle
the new VT. inputd -A already didn't allow activating non-existent VT's
as it first tried to open a consumer handle for the target VT.
bjorn3