Raw keyboard input - keyboard

Question

What I would like to do is to have e.g. a spare raspberry pi with four USB keyboards attached (or four mice).
What I want is to know, not just if a key is pressed, but which keyboard it was pressed on, so that different keyboard's buttons can do different things. (Think macro buttons.)
Likewise if I have four mice plugged in, I want to receive raw data and to be able to distinguish which mouse moved.
Ideally I'd like to know how to do this in C.
The device with the devices plugged into it will be controlled by SSH, so there is no need for keypresses to do what they normally do.

Answer 1

I've made a start. For Linux, and this will suffice for now, there are devices in /dev/input called e.g. /dev/input/event0 from which you can read. Some of these will correspond to actual input devices, and some will be virtual.
Information can be found in /sys/class/input.
For example for my USB keyboard:
$ cat /sys/class/input/input24/name
Logitech K360
Also /sys/class/input/input24/uevent has a lot of useful information.
Now to read raw input from a keyboard, you read from something like /dev/input/event0. To find out what these events are, for example for /dev/input/event0, then /sys/class/input/event0/device points to the corresponding input24 above.
Now to read, in C,
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/input.h>
/*
struct input_event {
struct timeval time;
__u16 type;
__u16 code;
__s32 value;
};
*/
int main() {
int fd = open("/dev/input/event0", O_RDONLY);
struct input_event evt;
while(1) {
read(fd,&evt,sizeof(evt));
printf("Event: type=%hd code=%hd value=%08x=%d\n",evt.type,evt.code,evt.value,evt.value);
}
}
The only remaining issue I have is how to 'disconnect' a keyboard so that its events are ignored (aside from processes reading raw input). I know how to xinput float 34 to float e.g. device 34. That that is for Xorg, not the text console on a device without X, nor f

Answer 2

I have a solution for keyboards. It's also resistent to unplugging/plugging-in the devices.
save_keys.py:
import keyboard
import requests
from threading import Thread
import subprocess
import time
import sys
import os
if not os.path.exists("/tmp/pressed_keys"):
with open("/tmp/pressed_keys", 'a+') as f:
f.write('somedevice:somekey') #this line has no sence, just creating the file
def keyPressed(keyboardEvent: keyboard.KeyboardEvent):
key = keyboardEvent.name
print(key)
device = keyboardEvent.device
print(device)
with open("/tmp/pressed_keys", 'a+') as f:
f.write(f"{device}:{key)
def getDevices():
return subprocess.getoutput('ls /dev/input/by-id/')
def startNewDeviceListener():
while True:
print("checking devices")
newDevices = getDevices()
print("got devices: ",newDevices)
if (devices != newDevices):
print('Device changes detected, exiting')
sys.exit(1)
time.sleep(0.5)
keyboard.on_press(keyPressed, True)
devices = getDevices()
t = Thread(target=startNewDeviceListener)
t.start()
read_keys.py:
import os
pipe_path = "/tmp/pressed_keys"
pipe_fd = os.open(pipe_path, os.O_RDONLY | os.O_NONBLOCK)
with os.fdopen(pipe_fd) as pipe:
pipe.read() #seek to the end of the file
while True: #read new keys
device_key = pipe.read()
device, key = device_key.split(':')
print(f"got {key} key from {device} device")
save_keys.sh:
#!/bin/bash
while :
do
sudo python3 save_keys.py
sleep 1
done
run.sh:
#!/bin/bash
nohup ./save_keys.sh < /dev/null 2>&1 > /dev/null &
python3 read_keys.py
And finally run everything via:
sudo sh run.sh