// SPDX-License-Identifier: GPL-2.0 /* * 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; }