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/*
* led_hw_brightness_mon.c
*
* This program monitors LED brightness level changes having its origin
* in hardware/firmware, i.e. outside of kernel control.
* A timestamp and brightness value is printed each time the brightness changes.
*
* Usage: led_hw_brightness_mon <device-name>
*
* <device-name> is the name of the LED class device to be monitored. Pressing
* CTRL+C will exit.
*/
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <linux/uleds.h>
int main(int argc, char const *argv[])
{
int fd, ret;
char brightness_file_path[LED_MAX_NAME_SIZE + 11];
struct pollfd pollfd;
struct timespec ts;
char buf[11];
if (argc != 2) {
fprintf(stderr, "Requires <device-name> argument\n");
return 1;
}
snprintf(brightness_file_path, LED_MAX_NAME_SIZE,
"/sys/class/leds/%s/brightness_hw_changed", argv[1]);
fd = open(brightness_file_path, O_RDONLY);
if (fd == -1) {
printf("Failed to open %s file\n", brightness_file_path);
return 1;
}
/*
* read may fail if no hw brightness change has occurred so far,
* but it is required to avoid spurious poll notifications in
* the opposite case.
*/
read(fd, buf, sizeof(buf));
pollfd.fd = fd;
pollfd.events = POLLPRI;
while (1) {
ret = poll(&pollfd, 1, -1);
if (ret == -1) {
printf("Failed to poll %s file (%d)\n",
brightness_file_path, ret);
ret = 1;
break;
}
clock_gettime(CLOCK_MONOTONIC, &ts);
ret = read(fd, buf, sizeof(buf));
if (ret < 0)
break;
ret = lseek(pollfd.fd, 0, SEEK_SET);
if (ret < 0) {
printf("lseek failed (%d)\n", ret);
break;
}
printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));
}
close(fd);
return ret;
}
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