Check for given key event on the hardware level

kbcheck.c

/*
 * kbcheck.c - Check for given key event on the hardware level
 * Copyright (c) 2014 Arkadiusz Bokowy
 *
 * This projected is licensed under the terms of the MIT license.
 *
 * Compilation:
 * gcc -Wall -Wextra -o kbcheck kbcheck.c
 *
 * Exemplary usage:
 * kbcheck -t 500 /dev/input/event4 0x7d  # check for Win key
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <poll.h>
#include <time.h>
#include <linux/input.h>


/* Get time in microseconds (maximal time delta is 255 seconds). */
long timeu(const struct timespec *ts) {

	struct timespec _ts;
	if (ts == NULL) {
		clock_gettime(CLOCK_BOOTTIME, &_ts);
		ts = &_ts;
	}

	return (ts->tv_sec & 0xFF) * 1000000 + ts->tv_nsec / 1000;
}

int main(int argc, char *argv[]) {

	int opt;
	int timeout = 50;

	while ((opt = getopt(argc, argv, "ht:")) != -1)
		switch (opt) {
		case 'h':
return_usage:
			printf("usage: %s [options] <kbdev> <keycode>\n"
					"  -t NUM\ttimeout value in ms (default: %d)\n",
					argv[0], timeout);
			return EXIT_SUCCESS;
		case 't':
			timeout = atoi(optarg);
			break;
		default:
			printf("Try `%s -h` for more informations.\n", argv[0]);
			return EXIT_FAILURE;
		}

	/* it should be two arguments */
	if (optind + 2 != argc)
		goto return_usage;

	char *kbdevice = argv[optind];
	int keycode = strtol(argv[optind + 1], NULL, 0);

	struct pollfd fds;
	struct input_event ev;

	if ((fds.fd = open(kbdevice, O_RDONLY)) == -1) {
		perror("error: unable to open event device");
		return EXIT_FAILURE;
	}

	fds.events = POLLIN;

	/* get our staring time to correctly handling timeout */
	long start = timeu(NULL);
	int _timeout;

	while ((_timeout = timeout - (timeu(NULL) - start) / 1000) > 0) {

		if (poll(&fds, 1, _timeout) <= 0)
			/* timeout or error, we don't care */
			break;

		ev.type = 0;
		read(fds.fd, &ev, sizeof(ev));

		if (ev.type == 1 && ev.code == keycode)
			/* we've got our key press/release event */
			return EXIT_SUCCESS;

	}

	return EXIT_FAILURE;
}