kernel+init: Add a framebuffer special device file

apps/init.cpp

@@ -20,6 +20,7 @@ static void populate_devfs()
     xmknod("/dev/console", 0666, 1, 0);
     xmknod("/dev/null", 0666, 2, 0);
     xmknod("/dev/zero", 0666, 2, 1);
+    xmknod("/dev/fb0", 0222, 3, 0);
 }
 
 int main()

kernel/CMakeLists.txt

@@ -43,6 +43,7 @@ set(SOURCES
     src/fs/devices/NullDevice.cpp
     src/fs/devices/ZeroDevice.cpp
     src/fs/devices/ConsoleDevice.cpp
+    src/fs/devices/FramebufferDevice.cpp
     src/InitRD.cpp
     src/ELF.cpp
 )

kernel/src/fs/devices/Device.h

@@ -13,6 +13,11 @@ class Device
         return err(ENOTTY);
     }
 
+    virtual usize size() const
+    {
+        return 0;
+    }
+
     virtual bool blocking() const = 0;
 
     virtual ~Device() = default;

kernel/src/fs/devices/DeviceRegistry.cpp

@@ -1,6 +1,7 @@
 #include "fs/devices/DeviceRegistry.h"
 #include "Log.h"
 #include "fs/devices/ConsoleDevice.h"
+#include "fs/devices/FramebufferDevice.h"
 #include "fs/devices/NullDevice.h"
 #include "fs/devices/ZeroDevice.h"
 #include <luna/Vector.h>
@@ -45,6 +46,7 @@ namespace DeviceRegistry
         TRY(register_special_device(DeviceMajorTypes::Memory, 0, NullDevice::create));
         TRY(register_special_device(DeviceMajorTypes::Memory, 1, ZeroDevice::create));
         TRY(register_special_device(DeviceMajorTypes::Console, 0, ConsoleDevice::create));
+        TRY(register_special_device(DeviceMajorTypes::Framebuffer, 0, FramebufferDevice::create));
 
         return {};
     }

kernel/src/fs/devices/DeviceRegistry.h

@@ -11,7 +11,8 @@ namespace DeviceRegistry
     {
         Null = 0,
         Console = 1,
-        Memory = 2
+        Memory = 2,
+        Framebuffer = 3,
     };
 
     Result<SharedPtr<Device>> create_special_device(u32 major, u32 minor);

kernel/src/fs/devices/FramebufferDevice.cpp

@@ -0,0 +1,37 @@
+#include "fs/devices/FramebufferDevice.h"
+#include "video/Framebuffer.h"
+#include <luna/CString.h>
+
+Result<SharedPtr<Device>> FramebufferDevice::create()
+{
+    return (SharedPtr<Device>)TRY(make_shared<FramebufferDevice>());
+}
+
+Result<usize> FramebufferDevice::read(u8*, usize, usize) const
+{
+    return 0;
+}
+
+Result<usize> FramebufferDevice::write(const u8* buf, usize offset, usize length)
+{
+    if ((offset + length) > size()) length = size() - offset;
+
+    memcpy(Framebuffer::ptr() + offset, buf, length);
+
+    return length;
+}
+
+usize FramebufferDevice::size() const
+{
+    return Framebuffer::size();
+}
+
+bool FramebufferDevice::blocking() const
+{
+    return false;
+}
+
+Result<u64> FramebufferDevice::ioctl(int, void*)
+{
+    return err(EINVAL);
+}

kernel/src/fs/devices/FramebufferDevice.h

@@ -0,0 +1,21 @@
+#pragma once
+#include "fs/devices/DeviceRegistry.h"
+
+class FramebufferDevice : public Device
+{
+  public:
+    // Initializer for DeviceRegistry.
+    static Result<SharedPtr<Device>> create();
+
+    Result<usize> read(u8*, usize, usize) const override;
+
+    Result<usize> write(const u8*, usize, usize) override;
+
+    bool blocking() const override;
+
+    Result<u64> ioctl(int request, void* arg) override;
+
+    usize size() const override;
+
+    virtual ~FramebufferDevice() = default;
+};

kernel/src/fs/tmpfs/FileSystem.h

@@ -176,7 +176,7 @@ namespace TmpFS
 
         usize size() const override
         {
-            return 0;
+            return m_device->size();
         }
 
         mode_t mode() const override