Add percentage backlight

src/backlight.c

@@ -2,17 +2,24 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <stdbool.h>
 
 static char *argv0 = "./backlight";
 static char *backlight_file = "/sys/devices/platform/backlight/backlight/backlight/brightness";
+static char *max_backlight_file = "/sys/devices/platform/backlight/backlight/backlight/max_brightness";
+
+int max_brightness = 10;
 
 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");
+    printf("    get         ... prints current raw backlight level\n");
+    printf("    get_percent ... prints current percentage backlight level\n");
+    printf("    set         ... sets backlight level to raw VALUE_RAW\n");
+    printf("    set_percent ... sets backlight level to percentage VALUE_PCT\n");
+    printf("  VALUE_RAW = [0..%d]\n", max_brightness);
+    printf("  VALUE_PCT = [0..100]\n");
 }
 
 void print_usage_and_fail()
@@ -21,7 +28,19 @@ void print_usage_and_fail()
     exit(EXIT_FAILURE);
 }
 
-void command_get()
+void read_max_brightness()
+{
+    FILE *fp = fopen(max_backlight_file, "r");
+    if (fp == NULL) {
+        fprintf(stderr, "Cannot open file '%s' for reading. Using the default max brightness '%d'.\n",
+		max_backlight_file, max_brightness);
+	return;
+    }
+    fscanf(fp, "%d", &max_brightness);
+    fclose(fp);
+}
+
+void command_get(bool percent)
 {
     FILE *fp = fopen(backlight_file, "r");
     if (fp == NULL) {
@@ -30,13 +49,17 @@ void command_get()
     }
     int buffer_length = 255;
     char buffer[buffer_length];
-    while (fgets(buffer, buffer_length, fp)) {
+    fgets(buffer, buffer_length, fp);
+    if (percent) {
+        int value = atoi(buffer);
+        printf("%d\n", value * 100 / max_brightness);
+    } else {
         printf("%s", buffer);
     }
     fclose(fp);
 }
 
-void command_set(int value)
+void command_set(int value, bool percent)
 {
     if (setuid(0)) {
         fprintf(stderr, "Cannot set root permissions via setuid(0).\n");
@@ -48,12 +71,14 @@ void command_set(int value)
         fprintf(stderr, "Cannot open file '%s' for writing.\n", backlight_file);
         exit(EXIT_FAILURE);
     }
-    fprintf(fp, "%d\n", value);
+    int raw = percent ? (value * max_brightness / 100) : value;
+    fprintf(fp, "%d\n", raw);
     fclose(fp);
 }
 
 int main(int argc, char *argv[])
 {
+    read_max_brightness();
     if (argc < 1) {
         print_usage_and_fail();
     }
@@ -63,15 +88,24 @@ int main(int argc, char *argv[])
     }
     char *command = argv[1];
     if ((strcmp(command, "get") == 0) && (argc == 2)) {
-        command_get();
+        command_get(false);
+    } else if ((strcmp(command, "get_percent") == 0) && (argc == 2)) {
+        command_get(true);
     } else if ((strcmp(command, "set") == 0) && (argc == 3)) {
         int value = atoi(argv[2]);
-        if (value < 0 || value > 10) {
+        if (value < 0 || value > max_brightness) {
+            print_usage_and_fail();
+        }
+        command_set(value, false);
+    } else if ((strcmp(command, "set_percent") == 0) && (argc == 3)) {
+        int value = atoi(argv[2]);
+        if (value < 0 || value > 100) {
             print_usage_and_fail();
         }
-        command_set(value);
+        command_set(value, true);
     } else {
         print_usage_and_fail();
     }
     exit(EXIT_SUCCESS);
 }
+