src/kernel/linux/v4.14/tools/leds/uledmon.c

// SPDX-License-Identifier: GPL-2.0
/*
 * uledmon.c
 *
 * This program creates a new userspace LED class device and monitors it. A
 * timestamp and brightness value is printed each time the brightness changes.
 *
 * Usage: uledmon <device-name>
 *
 * <device-name> is the name of the LED class device to be created. Pressing
 * CTRL+C will exit.
 */

#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <linux/uleds.h>

int main(int argc, char const *argv[])
{
	struct uleds_user_dev uleds_dev;
	int fd, ret;
	int brightness;
	struct timespec ts;

	if (argc != 2) {
		fprintf(stderr, "Requires <device-name> argument\n");
		return 1;
	}

	strncpy(uleds_dev.name, argv[1], LED_MAX_NAME_SIZE);
	uleds_dev.max_brightness = 100;

	fd = open("/dev/uleds", O_RDWR);
	if (fd == -1) {
		perror("Failed to open /dev/uleds");
		return 1;
	}

	ret = write(fd, &uleds_dev, sizeof(uleds_dev));
	if (ret == -1) {
		perror("Failed to write to /dev/uleds");
		close(fd);
		return 1;
	}

	while (1) {
		ret = read(fd, &brightness, sizeof(brightness));
		if (ret == -1) {
			perror("Failed to read from /dev/uleds");
			close(fd);
			return 1;
		}
		clock_gettime(CLOCK_MONOTONIC, &ts);
		printf("[%ld.%09ld] %u\n", ts.tv_sec, ts.tv_nsec, brightness);
	}

	close(fd);

	return 0;
}