Evfilter library documentation

F.A.Q.

What is evfilter library?

Evfilter library aims to be userspace library for input event filtering. Input event layer is linux kernel layer for all HID and other human interface devices connected to the computer.
Evfilter library is transparent layer between you and kernel that can modify these events.

How are events filtered/modified?

Evfilter library implements filter api. Filter is something similar to kernel module. When filter is loaded, it's initalized and added into linked list of filters. Filter gets some events and sends some events to the next filter (or back to the application, when end of the list is reached). Linked list of filters can be created per device and devices can be merged together by barrier filter.

What is implemented so far?

The code is mostly finished. Hotplug support is in progress.
System-wide and app-defined profiles are finished and working.
However the code is in alpha state, so testing is needed.

What is profile?

Profile is evfilter configuration. There are two types of profiles, system-wide profile located in /etc/evfilter/profile/ and application defined profiles.
Profile consist of files. Profilerc file, that defines matching rules and files to load, when rules are fulfilled. The rest of files defines lists of modules along with their parameters.
For more see detailed profile description.

What is this good for?

Well, that is good question. This library was created in order to standardized inteface for:

• Touchscreen callibration and filters. (as tslib is old hack that doesn't play nice with event layer)
• Console applications as gpm. (as gpm is even older hack that doesn't work either)
  And is not easy to rewrite gpm without such library.

So far I have two plans with evfilter library. Rewrite gmp so that it's able to work with touchscreens and more. That goal is close to be finished, stay tuned ;). Second goal is to hack X-server input driver to use evfilter library so we can do much more magic with input devices in X-server.