I'm trying to abstract away some /dev/input files so that user-level systems can know when the touchscreen is being used vs. when the touchpad is being used (without having access to raw mouse data).To do this, I want to create a root system service which watches the /dev/input files for changes, and publishes currently using touchpad or currently using touchscreen messages which non-root session services can pick up (e.g., so a service under /etc/systemd/user/ can leverage the information)Potential Methods I've thought of:Have the root service manage a file which non-root services can watch for updates onPublish over some sort of bus, like dbus (I haven't worked with dbus before, but it seems like the system bus vs. session bus is isolated)What are some recommended patterns here? I haven't worked much at all with process -> process communication on linux, but I figure there must be a clean way to do something like this. 
system service to user service information flow
root;not root user;d bus;ipc