Kernel: add NullDevice to /dev/null

kernel/CMakeLists.txt

@@ -15,6 +15,7 @@ set(KERNEL_SOURCES
 	kernel/CPUID.cpp
 	kernel/Debug.cpp
 	kernel/Device/Device.cpp
+	kernel/Device/NullDevice.cpp
 	kernel/Errors.cpp
 	kernel/Font.cpp
 	kernel/FS/DevFS/FileSystem.cpp

kernel/include/kernel/Device/NullDevice.h

@@ -0,0 +1,27 @@
+#include <BAN/UniqPtr.h>
+#include <kernel/Device/Device.h>
+
+namespace Kernel
+{
+
+	class NullDevice : public CharacterDevice
+	{
+	public:
+		static BAN::ErrorOr<BAN::RefPtr<NullDevice>> create(mode_t, uid_t, gid_t);
+
+		virtual dev_t rdev() const override { return m_rdev; }
+
+		virtual BAN::ErrorOr<size_t> read(size_t, void*, size_t) override { return 0; }
+		virtual BAN::ErrorOr<size_t> write(size_t, const void*, size_t size) override { return size; };
+
+	protected:
+		NullDevice(mode_t mode, uid_t uid, gid_t gid, dev_t rdev)
+			: CharacterDevice(mode, uid, gid)
+			, m_rdev(rdev)
+		{ }
+	
+	private:
+		const dev_t m_rdev;
+	};
+
+}

kernel/kernel/Device/NullDevice.cpp

@@ -0,0 +1,15 @@
+#include <kernel/Device/NullDevice.h>
+#include <kernel/FS/DevFS/FileSystem.h>
+
+namespace Kernel
+{
+
+	BAN::ErrorOr<BAN::RefPtr<NullDevice>> NullDevice::create(mode_t mode, uid_t uid, gid_t gid)
+	{
+		auto* result = new NullDevice(mode, uid, gid, DevFileSystem::get().get_next_rdev());
+		if (result == nullptr)
+			return BAN::Error::from_errno(ENOMEM);
+		return BAN::RefPtr<NullDevice>::adopt(result);
+	}
+
+}

kernel/kernel/FS/DevFS/FileSystem.cpp

@@ -1,4 +1,5 @@
 #include <BAN/ScopeGuard.h>
+#include <kernel/Device/NullDevice.h>
 #include <kernel/FS/DevFS/FileSystem.h>
 #include <kernel/FS/RamFS/Inode.h>
 #include <kernel/LockGuard.h>
@@ -17,6 +18,8 @@ namespace Kernel
 
 		auto root_inode = MUST(RamDirectoryInode::create(*s_instance, 0, Inode::Mode::IFDIR | 0755, 0, 0));
 		MUST(s_instance->set_root_inode(root_inode));
+
+		s_instance->add_device("null", MUST(NullDevice::create(0666, 0, 0)));
 	}
 
 	DevFileSystem& DevFileSystem::get()