LXR linux/tools/leds/led_hw_brightness

   1/*
   2 * led_hw_brightness_mon.c
   3 *
   4 * This program monitors LED brightness level changes having its origin
   5 * in hardware/firmware, i.e. outside of kernel control.
   6 * A timestamp and brightness value is printed each time the brightness changes.
   7 *
   8 * Usage: led_hw_brightness_mon <device-name>
   9 *
  10 * <device-name> is the name of the LED class device to be monitored. Pressing
  11 * CTRL+C will exit.
  12 */
  13
  14#include <errno.h>
  15#include <fcntl.h>
  16#include <poll.h>
  17#include <stdio.h>
  18#include <stdlib.h>
  19#include <string.h>
  20#include <time.h>
  21#include <unistd.h>
  22
  23#include <linux/uleds.h>
  24
  25int main(int argc, char const *argv[])
  26{
  27        int fd, ret;
  28        char brightness_file_path[LED_MAX_NAME_SIZE + 11];
  29        struct pollfd pollfd;
  30        struct timespec ts;
  31        char buf[11];
  32
  33        if (argc != 2) {
  34                fprintf(stderr, "Requires <device-name> argument\n");
  35                return 1;
  36        }
  37
  38        snprintf(brightness_file_path, LED_MAX_NAME_SIZE,
  39                 "/sys/class/leds/%s/brightness_hw_changed", argv[1]);
  40
  41        fd = open(brightness_file_path, O_RDONLY);
  42        if (fd == -1) {
  43                printf("Failed to open %s file\n", brightness_file_path);
  44                return 1;
  45        }
  46
  47        /*
  48         * read may fail if no hw brightness change has occurred so far,
  49         * but it is required to avoid spurious poll notifications in
  50         * the opposite case.
  51         */
  52        read(fd, buf, sizeof(buf));
  53
  54        pollfd.fd = fd;
  55        pollfd.events = POLLPRI;
  56
  57        while (1) {
  58                ret = poll(&pollfd, 1, -1);
  59                if (ret == -1) {
  60                        printf("Failed to poll %s file (%d)\n",
  61                                brightness_file_path, ret);
  62                        ret = 1;
  63                        break;
  64                }
  65
  66                clock_gettime(CLOCK_MONOTONIC, &ts);
  67
  68                ret = read(fd, buf, sizeof(buf));
  69                if (ret < 0)
  70                        break;
  71
  72                ret = lseek(pollfd.fd, 0, SEEK_SET);
  73                if (ret < 0) {
  74                        printf("lseek failed (%d)\n", ret);
  75                        break;
  76                }
  77
  78                printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));
  79        }
  80
  81        close(fd);
  82
  83        return ret;
  84}
  85