tools/leds/led_hw_brightness_mon.c

   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
  25 int 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 }