Read Linux Key Events

linux-key-events.c

#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/input.h>
#include <string.h>
#include <stdio.h>

/*
 * Mostly a copy from https://stackoverflow.com/a/20946151
 * Demo of reading from /dev/input/event* devices
 * Compile for ARM: arm-linux-gnueabihf-gcc -static -march=armv7 main.c -o keyevents-arm
 */

static const char *const evval[3] = {
        "RELEASED",
        "PRESSED ",
        "REPEATED"
};

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "please specify only the input event path to listen on (e.g. /dev/input/event0).\n");
        return EXIT_FAILURE;
    }

    fprintf(stdout, "listening to %s\n", argv[1]);
    fflush(stdout);

    char *dev = argv[1];
    struct input_event ev;
    ssize_t n;
    int fd;

    fd = open(dev, O_RDONLY);
    if (fd == -1) {
        fprintf(stderr, "Cannot open %s: %s.\n", dev, strerror(errno));
        return EXIT_FAILURE;
    }
    while (1) {
        n = read(fd, &ev, sizeof ev);
        if (n == (ssize_t) -1) {
            if (errno == EINTR)
                continue;
            else
                break;
        } else if (n != sizeof ev) {
            errno = EIO;
            break;
        }
        if (ev.type == EV_KEY && ev.value >= 0 && ev.value <= 2) {
            fprintf(stdout, "%s 0x%04x (%d)\n", evval[ev.value], (int) ev.code, (int) ev.code);
            fflush(stdout);
        }
    }
    fflush(stdout);
    fprintf(stderr, "%s.\n", strerror(errno));
    return EXIT_FAILURE;
}