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, 3 insertions, 2 deletions

diff --git a/Kernel/Devices/HID/PS2MouseDevice.h b/Kernel/Devices/HID/PS2MouseDevice.h
index fc3b84cd00..b232bf2d1f 100644
--- a/Kernel/Devices/HID/PS2MouseDevice.h
+++ b/Kernel/Devices/HID/PS2MouseDevice.h
@@ -17,6 +17,8 @@ namespace Kernel {
 class PS2MouseDevice : public IRQHandler
     , public MouseDevice
     , public I8042Device {
+    friend class DeviceManagement;
+
 public:
     static RefPtr<PS2MouseDevice> try_to_initialize(const I8042Controller&);
     bool initialize();
@@ -32,10 +34,9 @@ public:
         enable_irq();
     }
 
-    // FIXME: We expose this constructor to make try_create_device helper to work
+protected:
     explicit PS2MouseDevice(const I8042Controller&);
 
-protected:
     // ^IRQHandler
     virtual bool handle_irq(const RegisterState&) override;