1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * uledmon.c
4  *
5  * This program creates a new userspace LED class device and monitors it. A
6  * timestamp and brightness value is printed each time the brightness changes.
7  *
8  * Usage: uledmon <device-name>
9  *
10  * <device-name> is the name of the LED class device to be created. Pressing
11  * CTRL+C will exit.
12  */
13 
14 #include <fcntl.h>
15 #include <stdio.h>
16 #include <string.h>
17 #include <time.h>
18 #include <unistd.h>
19 
20 #include <linux/uleds.h>
21 
main(int argc,char const * argv[])22 int main(int argc, char const *argv[])
23 {
24 	struct uleds_user_dev uleds_dev;
25 	int fd, ret;
26 	int brightness;
27 	struct timespec ts;
28 
29 	if (argc != 2) {
30 		fprintf(stderr, "Requires <device-name> argument\n");
31 		return 1;
32 	}
33 
34 	strncpy(uleds_dev.name, argv[1], LED_MAX_NAME_SIZE);
35 	uleds_dev.max_brightness = 100;
36 
37 	fd = open("/dev/uleds", O_RDWR);
38 	if (fd == -1) {
39 		perror("Failed to open /dev/uleds");
40 		return 1;
41 	}
42 
43 	ret = write(fd, &uleds_dev, sizeof(uleds_dev));
44 	if (ret == -1) {
45 		perror("Failed to write to /dev/uleds");
46 		close(fd);
47 		return 1;
48 	}
49 
50 	while (1) {
51 		ret = read(fd, &brightness, sizeof(brightness));
52 		if (ret == -1) {
53 			perror("Failed to read from /dev/uleds");
54 			close(fd);
55 			return 1;
56 		}
57 		clock_gettime(CLOCK_MONOTONIC, &ts);
58 		printf("[%ld.%09ld] %u\n", ts.tv_sec, ts.tv_nsec, brightness);
59 	}
60 
61 	close(fd);
62 
63 	return 0;
64 }
65