2 * led_hw_brightness_mon.c
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.
8 * Usage: led_hw_brightness_mon <device-name>
10 * <device-name> is the name of the LED class device to be monitored. Pressing
23 #include <linux/uleds.h>
25 int main(int argc, char const *argv[])
28 char brightness_file_path[LED_MAX_NAME_SIZE + 11];
34 fprintf(stderr, "Requires <device-name> argument\n");
38 snprintf(brightness_file_path, LED_MAX_NAME_SIZE,
39 "/sys/class/leds/%s/brightness_hw_changed", argv[1]);
41 fd = open(brightness_file_path, O_RDONLY);
43 printf("Failed to open %s file\n", brightness_file_path);
48 * read may fail if no hw brightness change has occurred so far,
49 * but it is required to avoid spurious poll notifications in
52 read(fd, buf, sizeof(buf));
55 pollfd.events = POLLPRI;
58 ret = poll(&pollfd, 1, -1);
60 printf("Failed to poll %s file (%d)\n",
61 brightness_file_path, ret);
66 clock_gettime(CLOCK_MONOTONIC, &ts);
68 ret = read(fd, buf, sizeof(buf));
72 ret = lseek(pollfd.fd, 0, SEEK_SET);
74 printf("lseek failed (%d)\n", ret);
78 printf("[%ld.%09ld] %d\n", ts.tv_sec, ts.tv_nsec, atoi(buf));