From 0f80dba4787e23bdc964799d786e82b434d8a436 Mon Sep 17 00:00:00 2001
From: Jakob Haufe <sur5r@sur5r.net>
Date: Sat, 21 Oct 2017 16:48:07 +0200
Subject: [PATCH] Initial commit

---
 Makefile       |  14 +++++
 sysbacklight.c | 155 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 169 insertions(+)
 create mode 100644 Makefile
 create mode 100644 sysbacklight.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..0916454
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,14 @@
+CFLAGS?=$(shell pkg-config --cflags libsysfs) -Wall -std=c99
+LDFLAGS?=$(shell pkg-config --libs libsysfs)
+
+all: sysbacklight
+
+sysbacklight: sysbacklight.o
+	$(CC) -o $@ $(LDFLAGS) $<
+
+%.o: %.c
+	$(CC) -c -o $@ $(CFLAGS) $<
+
+clean:
+	rm -f sysbacklight sysbacklight.o
+
diff --git a/sysbacklight.c b/sysbacklight.c
new file mode 100644
index 0000000..87a89f9
--- /dev/null
+++ b/sysbacklight.c
@@ -0,0 +1,155 @@
+#include <math.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <libsysfs.h>
+
+enum OP {
+    SET,
+    INC,
+    DEC
+};
+
+struct sysfs_class_device *find_brightness_device(void)
+{
+    struct sysfs_class *cls;
+    struct dlist *backlights;
+
+    cls = sysfs_open_class("backlight");
+    if(!cls)
+    {
+        perror("Could not open backlight class");
+        return NULL;
+    }
+
+    backlights = sysfs_get_class_devices(cls);
+    if(!backlights)
+    {
+        perror("Could not enumerate backlight devices");
+        return NULL;
+    }
+
+    struct sysfs_class_device *iter;
+    struct sysfs_attribute *attr;
+
+    dlist_for_each_data(backlights, iter, struct sysfs_class_device)
+    {
+        if((attr=sysfs_get_classdev_attr(iter, "type")))
+        {
+            if(!strncmp(attr->value, "raw", 3))
+                return iter;
+        }
+    }
+
+    return NULL;
+}
+
+bool set_brightness(struct sysfs_class_device *dev, enum OP op, double value)
+{
+    struct sysfs_attribute *attr;
+    double brightness=0;
+    double max_brightness=0;
+
+    if((attr=sysfs_get_classdev_attr(dev, "max_brightness")))
+    {
+        max_brightness = strtod(attr->value, NULL);
+    }
+
+    if((attr=sysfs_get_classdev_attr(dev, "brightness")))
+    {
+        brightness = strtod(attr->value, NULL);
+    }
+
+    if(max_brightness < 1 || isnan(max_brightness))
+    {
+        fprintf(stderr, "Failed to acquire maximum brightness.");
+        return false;
+    }
+
+    switch(op)
+    {
+        case SET:
+            brightness = (max_brightness / 100) * value;
+            break;
+
+        case INC:
+            brightness += (max_brightness / 100) * value;
+            break;
+
+        case DEC:
+            brightness -= (max_brightness / 100) * value;
+            break;
+    }
+
+    if(brightness > max_brightness)
+        return true;
+    if(brightness < 0)
+        return true;
+
+    int len;
+    char valbuf[32];
+    len=snprintf(valbuf, 32, "%.0f", brightness);
+    if(sysfs_write_attribute(attr, valbuf, len) != 0)
+    {
+        perror("Failed to write brightness attribute");
+        return false;
+    }
+
+    return true;
+}
+
+int main(int argc, char **argv)
+{
+    struct sysfs_class_device *dev;
+
+    enum OP op;
+    double value;
+
+    dev = find_brightness_device();
+    if(!dev)
+    {
+        fprintf(stderr, "Could not find backlight device of type raw!\n");
+        return 1;
+    }
+
+    if(argc >= 3)
+    {
+        switch(argv[1][0])
+        {
+            case '=':
+                op = SET;
+                break;
+
+            case '+':
+                op = INC;
+                break;
+
+            case '-':
+                op = DEC;
+                break;
+
+            default:
+                fprintf(stderr, "Unknown operation '%c'!\n", argv[1][0]);
+                return 2;
+        }
+
+        value = strtod(argv[2], NULL);
+        if(value < 0 || isnan(value))
+        {
+            fprintf(stderr, "Invalid brightness value\n");
+            return 3;
+        }
+    }
+
+
+    if(!set_brightness(dev, op, value))
+    {
+        fprintf(stderr, "Could not set brightness!\n");
+        return 4;
+    }
+
+    return 0;
+}
+
-- 
2.39.5