Enable scroll for the Logitech Trackman Marble mouse on Ubuntu 17.04

40-libinput.conf

# The lines below go into: /usr/share/X11/xorg.conf.d/40-libinput.conf
# Last tested on Ubuntu 18.04 on 13.08.2018
#
# Enable scroll wheel emulation for the Logitech Trackman Marble mouse. Holding
# the small right button will allow you to scroll both vertically and
# horizontally using the ball; for using the left small button use 8 for
# ScrollButton.
# Source: https://wiki.archlinux.org/index.php/Logitech_Marble_Mouse#Using_libinput
# This config also disables the browser back/forward functionality of the small buttons
# and is intended for left-hand users.
Section "InputClass"
        Identifier                 "Marble Mouse"
        MatchProduct               "Logitech USB Trackball"
        Driver                     "libinput"
        Option                     "ScrollMethod" "button"
        Option                     "ScrollButton" "9"
        Option                     "MiddleEmulation" "on"
        Option "ButtonMapping"     "3 9 1 4 5 6 7 2 2"
EndSection