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- #include <stdio.h>
- #include <stdlib.h>
- #include <string.h>
- #include <unistd.h>
-
- static char *argv0 = "./backlight";
- static char *backlight_file = "/sys/devices/platform/backlight/backlight/backlight/brightness";
-
- void print_usage()
- {
- printf("usage: %s COMMAND [VALUE]\n", argv0);
- printf(" COMMAND = {get, set}\n");
- printf(" get ... prints current backlight level\n");
- printf(" set ... sets backlight level to VALUE\n");
- printf(" VALUE = [0..10] ... backlight amount\n");
- }
-
- void print_usage_and_fail()
- {
- print_usage();
- exit(EXIT_FAILURE);
- }
-
- void command_get()
- {
- FILE *fp = fopen(backlight_file, "r");
- if (fp == NULL) {
- fprintf(stderr, "Cannot open file '%s' for reading.\n", backlight_file);
- exit(EXIT_FAILURE);
- }
- int buffer_length = 255;
- char buffer[buffer_length];
- while (fgets(buffer, buffer_length, fp)) {
- printf("%s", buffer);
- }
- fclose(fp);
- }
-
- void command_set(int value)
- {
- if (setuid(0)) {
- fprintf(stderr, "Cannot set root permissions via setuid(0).\n");
- exit(EXIT_FAILURE);
- }
-
- FILE *fp = fopen(backlight_file, "w+");
- if (fp == NULL) {
- fprintf(stderr, "Cannot open file '%s' for writing.\n", backlight_file);
- exit(EXIT_FAILURE);
- }
- fprintf(fp, "%d\n", value);
- fclose(fp);
- }
-
- int main(int argc, char *argv[])
- {
- if (argc < 1) {
- print_usage_and_fail();
- }
- argv0 = argv[0];
- if (argc < 2) {
- print_usage_and_fail();
- }
- char *command = argv[1];
- if ((strcmp(command, "get") == 0) && (argc == 2)) {
- command_get();
- } else if ((strcmp(command, "set") == 0) && (argc == 3)) {
- int value = atoi(argv[2]);
- if (value < 0 || value > 10) {
- print_usage_and_fail();
- }
- command_set(value);
- } else {
- print_usage_and_fail();
- }
- exit(EXIT_SUCCESS);
- }
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