How can I notify a program of a hardware event?

Question

I am looking to write a program that waits indefinitely for an event, in this case, for USB/s to be plugged in and to do some after action that.

I intend to write it in C or Python.

The question is, how can the program be notified when the event has happened (a USB device is plugged in)?

Secondly, if it were done in Python, is there a less resource-intensive way of waiting for the event besides looping?

Answer 1

On Linux, you can, thanks to udev.

1. Identify your usb device with udevadm info -a /dev/yourdevice. See Writing udev rules.

2. from your device information, create a udev rule:

   SUBSYSTEM=="zzz", ATTRS{idVendor}=="xxx", ATTRS{idProduct}=="yyy",  RUN+="/usr/bin/my_signaler /dev/%k
   

3. write your signaler program (in my udev rule, it's located at /usr/bin/my_sampler):

   #! /bin/bash
   NEW_DEVICE="$1"
   TARGETS=$(pgrep program_name)
   for proc in $TARGETS
   do
       kill -s SIGUSR1 $proc
   done
   

4. Make your program handle the SIGUSR1

   #include <stdio.h>
   #include <signal.h> 
   #include <unistd.h>
   
   void wakeup(int sig) {
        printf("go check /dev" );
   }
   
   int main(void) {
       signal(SIGUSR1, wakeup);
   
       while (1) { 
           /* if the SIGUSR1 signal is received while sleep is waiting, sleep will return*/
           sleep(20);
       }
       return 0;
   }