Detect CAPSLOCK

kb.c

// I find the excellent code at http://stackoverflow.com/a/20946151
// Put it here for further work on the CAPSLOCK detection prog

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

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

int main() {
    const char *dev = "/dev/input/by-path/platform-i8042-serio-0-event-kbd";
    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 && ev.code == 58)
                printf("%s CPASLOCK\n", evval[ev.value]);
           }
    }
    fflush(stdout);
    fprintf(stderr, "%s.\n", strerror(errno));
    return EXIT_FAILURE;
}