evdev

evdev (short for 'event device') is a generic input event interface in the Linux kernel and FreeBSD.^[1] It generalizes raw input events from device drivers and makes them available through character devices in the /dev/input/ directory.

The user-space library for the kernel component evdev is called libevdev. Libevdev abstracts the evdev ioctls through type-safe interfaces and provides functions to change the appearance of the device. Libevdev shares similarities with the read system call.^[2]

It sits below the process that handles input events, in between the kernel and that process.

kernel → libevdev → xf86-input-evdev → X server → X client

For Weston/Wayland compositor, the stack would look like this:

kernel → libevdev → libinput → Wayland compositor → Wayland client

Since version 1.16 the xorg-xserver obtained support for libinput:

kernel → libevdev → libinput → xf86-input-libinput → X server → X client

evdev is primarily used by display servers like X.org (via xf86-input-evdev driver and libevdev) and Weston, as well as by games and console emulators making use of USB and Bluetooth controllers.