Module input 

Keyboard and pointing-device detection.

Linux reads /proc/bus/input/devices, a single file listing every evdev node with its handlers and capability bitmaps. Classification is deliberately exclusive: a device is reported as a keyboard or a mouse or neither, never both.

Why a device can be unclassifiable

A peripheral paired through a Logitech Unifying/Bolt receiver is presented by the kernel with a merged capability set — the receiver synthesizes one descriptor covering every device class it can carry. Measured on a Bolt receiver carrying an MX Keys keyboard and an MX Master 3 mouse, every kernel-visible signal is identical for the two:

source	MX Keys (keyboard)	MX Master 3 (mouse)
/proc/bus/input/devices handlers	sysrq kbd leds mouse6 event26	sysrq kbd leds mouse5 event25
capabilities/rel	0x1943	0x1943
capabilities/key (alphabet block)	present	present
udev ID_INPUT_*	POINTINGSTICK	POINTINGSTICK
USB HID bInterfaceProtocol	00	00
HID report descriptor prologue	05 01 09 06 a1 01	05 01 09 06 a1 01

So capability inspection alone cannot separate them, and a classifier that guesses gets it wrong in both directions (fastfetch 2.66 reports the MX Master 3 as a keyboard and the MX Keys as a mouse on this hardware). The one place the truth survives is the HID++ driver’s battery model_name ("MX Keys Wireless Keyboard" / "Wireless Mouse MX Master 3"), so that is consulted as a tiebreak — and when it is absent too, the device is reported in neither field rather than asserted into the wrong one.

Structs

InputDevice

One record from /proc/bus/input/devices.

Enums

DeviceKind

What a device was classified as.

Functions

classify_device

Classifies one device, consulting model_name only when the capabilities are ambiguous.

classify_input_devices_with

Classifies a whole device list into (keyboards, mice), de-duplicated by name.

detect_input_devices

Detects connected keyboards and pointing devices as (keyboards, mice).

has_alpha_block

Returns whether a key bitmap covers the whole alphabetic block ([ALPHA_KEYS]).

parse_bitmap

Parses a B: …= capability bitmap into 64-bit words, least-significant word first.

parse_input_devices

Parses the whole of /proc/bus/input/devices into records.