The wayland-system-compositor is the top-level compositor. X sessions
or nested Wayland sessions will run as clients of the system compositor.
The system compositor is licensed under the GPL.
Instead of having the input driver push the events into the core server,
only to have the server call back out to the compositor hooks, the driver now
just calls the compositor directly. The input drivers are always dependent on
the type of compositor anyway so there was no point in passing the events
through the server. Now the server is only involved when it's time to actually
send the events to the clients.
Kristian Høgsberg