Kernel: Introduce the DeviceManagement singleton

This singleton simplifies many aspects that we struggled with before:
1. There's no need to make derived classes of Device expose the
constructor as public anymore. The singleton is a friend of them, so he
can call the constructor. This solves the issue with try_create_device
helper neatly, hopefully for good.
2. Getting a reference of the NullDevice is now being done from this
singleton, which means that NullDevice no longer needs to use its own
singleton, and we can apply the try_create_device helper on it too :)
3. We can now defer registration completely after the Device constructor
which means the Device constructor is merely assigning the major and
minor numbers of the Device, and the try_create_device helper ensures it
calls the after_inserting method immediately after construction. This
creates a great opportunity to make registration more OOM-safe.

1 files changed, 2 insertions, 3 deletions

diff --git a/Kernel/TTY/VirtualConsole.h b/Kernel/TTY/VirtualConsole.h
index d90e718cbe..fd0047cdcd 100644
--- a/Kernel/TTY/VirtualConsole.h
+++ b/Kernel/TTY/VirtualConsole.h
@@ -50,6 +50,7 @@ class VirtualConsole final : public TTY
     , public VT::TerminalClient {
     AK_MAKE_ETERNAL
     friend class ConsoleManagement;
+    friend class DeviceManagement;
     friend class ConsoleImpl;
     friend class VT::Terminal;
 
@@ -84,11 +85,9 @@ public:
 
     void emit_char(char);
 
-    // FIXME: We expose these constructors to make try_create_device helper to work
+private:
     explicit VirtualConsole(const unsigned index);
     VirtualConsole(const unsigned index, const CircularQueue<char, 16384>&);
-
-private:
     // ^KeyboardClient
     virtual void on_key_pressed(KeyEvent) override;