brendangregg / bpf-typewriter

BPF noisy typewriter (bpftrace)

BPF Typewriter

This is a bpftrace program to run locally that turns your keyboard into a noisy typewriter. Keystrokes make a "click" and the enter key makes a "ting".

This works by tracing the Linux tty driver using kprobes. I first wrote tracing-typewriter tools in 2005.

Dependencies

• bpftrace
• alsa-utils for the aplay command. You can edit the source to use a different audio player.

Source

Just the code:

#!/usr/local/bin/bpftrace --unsafe
#include <uapi/linux/input-event-codes.h>

kprobe:kbd_event
/arg1 == EV_KEY && arg3 == 1/
{
	if (arg2 == KEY_ENTER) {
		system("aplay -q clink.au >/dev/null 2>&1 &");
	} else {
		system("aplay -q click.au >/dev/null 2>&1 &");
	}
}

I would have traced kbd_rawcode(), but it appears inlined and unavailable to kprobes. The --unsafe option is necessary because this tool is launching commands via system().