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1// SPDX-License-Identifier: GPL-2.02/*3 * led_hw_brightness_mon.c4 *5 * This program monitors LED brightness level changes having its origin6 * in hardware/firmware, i.e. outside of kernel control.7 * A timestamp and brightness value is printed each time the brightness changes.8 *9 * Usage: led_hw_brightness_mon <device-name>10 *11 * <device-name> is the name of the LED class device to be monitored. Pressing12 * CTRL+C will exit.13 */14 15#include <errno.h>16#include <fcntl.h>17#include <poll.h>18#include <stdio.h>19#include <stdlib.h>20#include <string.h>21#include <time.h>22#include <unistd.h>23 24#include <linux/uleds.h>25 26int main(int argc, char const *argv[])27{28 int fd, ret;29 char brightness_file_path[LED_MAX_NAME_SIZE + 11];30 struct pollfd pollfd;31 struct timespec ts;32 char buf[11];33 34 if (argc != 2) {35 fprintf(stderr, "Requires <device-name> argument\n");36 return 1;37 }38 39 snprintf(brightness_file_path, LED_MAX_NAME_SIZE,40 "/sys/class/leds/%s/brightness_hw_changed", argv[1]);41 42 fd = open(brightness_file_path, O_RDONLY);43 if (fd == -1) {44 printf("Failed to open %s file\n", brightness_file_path);45 return 1;46 }47 48 /*49 * read may fail if no hw brightness change has occurred so far,50 * but it is required to avoid spurious poll notifications in51 * the opposite case.52 */53 read(fd, buf, sizeof(buf));54 55 pollfd.fd = fd;56 pollfd.events = POLLPRI;57 58 while (1) {59 ret = poll(&pollfd, 1, -1);60 if (ret == -1) {61 printf("Failed to poll %s file (%d)\n",62 brightness_file_path, ret);63 ret = 1;64 break;65 }66 67 clock_gettime(CLOCK_MONOTONIC, &ts);68 69 ret = read(fd, buf, sizeof(buf));70 if (ret < 0)71 break;72 73 ret = lseek(pollfd.fd, 0, SEEK_SET);74 if (ret < 0) {75 printf("lseek failed (%d)\n", ret);76 break;77 }78 79 printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));80 }81 82 close(fd);83 84 return ret;85}86