kmap

A Linux kernel module for remapping keyboard scan codes.

Overview

kmap allows you to customize your keyboard layout by remapping scan codes directly in the Linux kernel. This works at a low level, providing an effective solution for:

• Swapping keys (e.g., CapsLock and Ctrl)
• Fixing broken keyboard keys
• Creating custom keyboard layouts

Installation

Prerequisites

• Linux kernel headers
• Build tools (make, gcc)

Building and Loading

make
sudo insmod kmap.ko

To load with default mappings:

sudo insmod kmap.ko default_map="capslock:leftctrl,leftctrl:capslock,zenhan:esc"

Usage

List current mappings:

cat /sys/kernel/debug/kmap/control

Set mappings (format is scancode_src:scancode_dest,...):

Swap CapsLock (58) and Left Ctrl (29)

echo "capslock:leftctrl,leftctrl:capslock" > /sys/kernel/debug/kmap/control

Reset keys to default:

echo "capslock:capslock,leftctrl:leftctrl" > /sys/kernel/debug/kmap/control

For available keynames, please look at key_table in kmap.c.

How It Works

kmap uses a kprobe to intercept keyboard scan codes at the atkbd_receive_byte function. The module maintains a mapping table and provides a debugfs interface at /sys/kernel/debug/kmap/control.

You can customize the hook point by modifying the SYMBOL_NAME define in the source code. This allows you to adapt kmap to different keyboard drivers or input subsystems, such as serio_interrupt() for broader device support, as long as the position of the argument is preserved.