BACKLIGHT wrapper functions for Linux userspace sysfs backlights.
#include <periphery/backlight.h>
/* Primary Functions */
backlight_t *backlight_new(void);
int backlight_open(backlight_t *bl, const char *name);
int backlight_read(backlight_t *bl, bool *value);
int backlight_write(backlight_t *bl, bool value);
int backlight_close(backlight_t *bl);
void backlight_free(backlight_t *bl);
/* Getters */
int backlight_get_brightness(backlight_t *bl, unsigned int *brightness);
int backlight_get_max_brightness(backlight_t *bl, unsigned int *max_brightness);
/* Setters */
int backlight_set_brightness(backlight_t *bl, unsigned int brightness);
/* Miscellaneous */
int backlight_name(backlight_t *bl, char *str, size_t len);
int backlight_tostring(backlight_t *bl, char *str, size_t len);
/* Error Handling */
int backlight_errno(backlight_t *bl);
const char *backlight_errmsg(backlight_t *bl);backlight_t *backlight_new(void);Allocate an BACKLIGHT handle.
Returns a valid handle on success, or NULL on failure.
int backlight_open(backlight_t *bl, const char *name);Open the sysfs BACKLIGHT with the specified name.
backlight should be a valid pointer to an allocated BACKLIGHT handle structure.
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_read(backlight_t *bl, bool *value);Read the state of the BACKLIGHT into value, where true is non-zero brightness, and false is zero brightness.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open(). value should be a pointer to an allocated bool.
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_write(backlight_t *bl, bool value);Write the state of the BACKLIGHT to value, where true is max brightness, and false is zero brightness.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_close(backlight_t *bl);Close the BACKLIGHT.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
Returns 0 on success, or a negative BACKLIGHT error code on failure.
void backlight_free(backlight_t *bl);Free an BACKLIGHT handle.
int backlight_get_brightness(backlight_t *bl, unsigned int *brightness);Get the brightness of the BACKLIGHT.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_get_max_brightness(backlight_t *bl, unsigned int *max_brightness);Get the max brightness of the BACKLIGHT.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_set_brightness(backlight_t *bl, unsigned int brightness);Set the brightness of the BACKLIGHT.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_name(backlight_t *bl, char *str, size_t len);Return the name of the sysfs BACKLIGHT.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
Returns 0 on success, or a negative BACKLIGHT error code on failure.
int backlight_tostring(backlight_t *bl, char *str, size_t len);Return a string representation of the BACKLIGHT handle.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
This function behaves and returns like snprintf().
int backlight_errno(backlight_t *bl);Return the libc errno of the last failure that occurred.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
const char *backlight_errmsg(backlight_t *bl);Return a human readable error message of the last failure that occurred.
backlight should be a valid pointer to an BACKLIGHT handle opened with backlight_open().
The periphery BACKLIGHT functions return 0 on success or one of the negative error codes below on failure.
The libc errno of the failure in an underlying libc library call can be obtained with the backlight_errno() helper function. A human readable error message can be obtained with the backlight_errmsg() helper function.
| Error Code | Description |
|---|---|
BL_ERROR_ARG |
Invalid arguments |
BL_ERROR_OPEN |
Opening BACKLIGHT |
BL_ERROR_QUERY |
Querying BACKLIGHT attributes |
BL_ERROR_IO |
Reading/writing BACKLIGHT brightness |
BL_ERROR_CLOSE |
Closing BACKLIGHT |
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include "backlight.h"
int main(void) {
backlight_t *bl;
unsigned int max_brightness;
unsigned int bl_val;
backlight = backlight_new();
/* Open sgm3735-backlight backlight device on /sys/class/backlight */
if (backlight_open(backlight, "sgm3735-backlight") < 0) {
fprintf(stderr, "backlight_open(): %s\n", backlight_errmsg(backlight));
exit(1);
}
/* Turn on BACKLIGHT (set max brightness) */
if (backlight_write(backlight, true) < 0) {
fprintf(stderr, "backlight_write(): %s\n", backlight_errmsg(backlight));
exit(1);
}
/* Get max brightness */
if (backlight_get_max_brightness(backlight, &max_brightness) < 0) {
fprintf(stderr, "backlight_get_max_brightness(): %s\n", backlight_errmsg(backlight));
exit(1);
}
/* Set half brightness */
if (backlight_set_brightness(backlight, max_brightness / 2) < 0) {
fprintf(stderr, "backlight_set_brightness(): %s\n", backlight_errmsg(backlight));
exit(1);
}
/* Set 10 % brightness */
bl_val = max_brightness * 10 / 100;
if (backlight_set_brightness(backlight, bl_val) < 0) {
fprintf(stderr, "backlight_set_brightness(): %s\n", backlight_errmsg(backlight));
exit(1);
}
backlight_close(backlight);
backlight_free(backlight);
return 0;
}