cregit-Linux how code gets into the kernel

Release 4.10 tools/leds/uledmon.c

Directory: tools/leds
 * uledmon.c
 * This program creates a new userspace LED class device and monitors it. A
 * timestamp and brightness value is printed each time the brightness changes.
 * Usage: uledmon <device-name>
 * <device-name> is the name of the LED class device to be created. Pressing
 * CTRL+C will exit.

#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <linux/uleds.h>

int main(int argc, char const *argv[]) { struct uleds_user_dev uleds_dev; int fd, ret; int brightness; struct timespec ts; if (argc != 2) { fprintf(stderr, "Requires <device-name> argument\n"); return 1; } strncpy(, argv[1], LED_MAX_NAME_SIZE); uleds_dev.max_brightness = 100; fd = open("/dev/uleds", O_RDWR); if (fd == -1) { perror("Failed to open /dev/uleds"); return 1; } ret = write(fd, &uleds_dev, sizeof(uleds_dev)); if (ret == -1) { perror("Failed to write to /dev/uleds"); close(fd); return 1; } while (1) { ret = read(fd, &brightness, sizeof(brightness)); if (ret == -1) { perror("Failed to read from /dev/uleds"); close(fd); return 1; } clock_gettime(CLOCK_MONOTONIC, &ts); printf("[%ld.%09ld] %u\n", ts.tv_sec, ts.tv_nsec, brightness); } close(fd); return 0; }


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Directory: tools/leds
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