Logitech TrackMan Marble FX scroll wheel patch for the Linux kernel
This patch alters the usbmouse kernel driver to support a "scroll wheel mode" using the fourth button (the red button) when connected through a "ID 04d9:1400 Holtek Semiconductor, Inc. PS/2 keyboard + mouse controller" usb-to-ps2 adapter. No idea how things work with other adapters.
It seems the fourth button generates events, but the state of the button is not represented in any bits.
However since "no buttons pressed" is only ever reported when releasing a single button being pressed, detecting multiple "no buttons pressed" events can be used to identify usage of the fourth button.