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#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <limits.h>
#include <errno.h>
#include <sys/types.h>
#include <dirent.h>
#define BACKLIGHT_DIR "/sys/class/backlight"
void
die(const char *msg)
{
puts(msg);
exit(1);
}
void
err(const char *msg)
{
perror(msg);
exit(1);
}
void*
ecalloc(size_t nmemb, size_t size)
{
void *ret = calloc(nmemb, size);
if (!ret)
err("ecalloc");
return ret;
}
char*
appendStr(size_t len, const char *a, const char *b)
{
char *buf = ecalloc(len, sizeof(char));
int ret = snprintf(buf, len, "%s%s", a, b);
if (ret == -1 || ret > len)
err("snprintf");
return buf;
}
/* returns errno */
int
maxBrightness(const char *prefix, long *max)
{
int e;
char *buf = appendStr(256, prefix, "/max_brightness");
int fd = open(buf, O_RDONLY);
if (fd == -1) {
e = errno;
free(buf);
return e;
}
memset(buf, '\0', 256);
int b = read(fd, buf, 256);
if (b==-1) {
e = errno;
free(buf);
close(fd);
return e;
}
for (int i=0; i<256 ; i++) {
if (buf[i] == '\n') {
buf[i] = '\0';
break;
}
}
long n = strtol(buf, NULL, 10);
if (n == LONG_MIN || n == LONG_MAX || n == 0)
err("strtol");
free(buf);
buf = NULL;
close(fd);
*max = n;
return 0;
}
int
setBacklight(const char *prefix, int percent)
{
char *fn = appendStr(256, prefix, "/brightness");
int fd = open(fn, O_WRONLY);
if (fd == -1) {
free(fn);
return -1;
}
int n = dprintf(fd, "%d\n", percent);
if (n == -1) {
close(fd);
free(fn);
return -1;
}
close(fd);
free(fn);
fn = NULL;
return 0;
}
int
main(int argc, char **argv)
{
uid_t euid = geteuid();
char **a = argv+1;
if (euid != 0)
die("Program must be run as root/setuid");
if (!*a)
die("Brightness percentage must be supplied");
long percent = strtol(*a, NULL, 10);
if (percent <= LONG_MIN || percent >= LONG_MAX)
err("invalid percent");
if (percent < 0 || percent > 100)
die("percent must be between 0 and 100");
DIR *d = opendir(BACKLIGHT_DIR);
if (!d)
err("opendir");
errno = 0;
for (;;) {
struct dirent *dent = readdir(d);
if(!dent&&errno!=0)
err("readdir");
if (!dent)
break;
if (strcmp("..", dent->d_name)==0 || strcmp(".", dent->d_name)==0)
continue;
char *prefix = appendStr(1024, BACKLIGHT_DIR"/", dent->d_name);
printf("found backlight: %s\n", prefix);
int ret;
long max = 0;
ret = maxBrightness(prefix, &max);
if (ret != 0) {
const char *msg = strerror(ret);
printf("Error getting max brightness for: %s : %s\n",
prefix, msg);
free(prefix);
prefix = NULL;
continue;
}
float p = (double)max*((double)percent/100.0);
ret = setBacklight(prefix, (int)p);
if (ret != 0) {
perror("setBacklight");
}
free(prefix);
prefix = NULL;
}
}
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