Brightness: add support for Linux

CMakeLists.txt

@@ -310,7 +310,7 @@ if(LINUX)
         src/detection/battery/battery_linux.c
         src/detection/bios/bios_linux.c
         src/detection/board/board_linux.c
-        src/detection/brightness/brightness_nosupport.c
+        src/detection/brightness/brightness_linux.c
         src/detection/chassis/chassis_linux.c
         src/detection/cpu/cpu_linux.c
         src/detection/cpuUsage/cpuUsage_linux.c

src/detection/brightness/brightness_linux.c

@@ -0,0 +1,55 @@
+#include "brightness.h"
+#include "common/io.h"
+
+#include <dirent.h>
+
+const char* ffDetectBrightness(FF_UNUSED_PARAM FFlist* result)
+{
+    //https://www.kernel.org/doc/Documentation/ABI/stable/sysfs-class-backlight
+    const char* backlightDirPath = "/sys/class/backlight/";
+
+    DIR* dirp = opendir(backlightDirPath);
+    if(dirp == NULL)
+        return "Failed to open `/sys/class/backlight/`";
+
+    FFstrbuf backlightDir;
+    ffStrbufInitA(&backlightDir, 64);
+    ffStrbufAppendS(&backlightDir, backlightDirPath);
+
+    uint32_t backlightDirLength = backlightDir.length;
+
+    FFstrbuf buffer;
+    ffStrbufInit(&buffer);
+
+    struct dirent* entry;
+    while((entry = readdir(dirp)) != NULL)
+    {
+        if(strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
+            continue;
+
+        ffStrbufAppendS(&backlightDir, entry->d_name);
+        ffStrbufAppendS(&backlightDir, "/actual_brightness");
+        if(ffReadFileBuffer(backlightDir.chars, &buffer))
+        {
+            double actualBrightness = ffStrbufToDouble(&buffer);
+            ffStrbufSubstrBefore(&backlightDir, backlightDirLength);
+            ffStrbufAppendS(&backlightDir, entry->d_name);
+            ffStrbufAppendS(&backlightDir, "/max_brightness");
+            if(ffReadFileBuffer(backlightDir.chars, &buffer))
+            {
+                FFBrightnessResult* display = (FFBrightnessResult*) ffListAdd(result);
+                ffStrbufInitS(&display->name, entry->d_name);
+                double maxBrightness = ffStrbufToDouble(&buffer);
+                display->value = (float) (actualBrightness * 100 / maxBrightness);
+            }
+
+            break;
+        }
+    }
+
+    closedir(dirp);
+    ffStrbufDestroy(&backlightDir);
+    ffStrbufDestroy(&buffer);
+
+    return NULL;
+}