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.

Kernel/Devices/HID/PS2KeyboardDevice.cpp

@@ -9,6 +9,7 @@
 #include <AK/Singleton.h>
 #include <AK/Types.h>
 #include <Kernel/Debug.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/Devices/HID/HIDManagement.h>
 #include <Kernel/Devices/HID/PS2KeyboardDevice.h>
 #include <Kernel/IO.h>
@@ -83,7 +84,7 @@ bool PS2KeyboardDevice::handle_irq(const RegisterState&)
 
 UNMAP_AFTER_INIT RefPtr<PS2KeyboardDevice> PS2KeyboardDevice::try_to_initialize(const I8042Controller& ps2_controller)
 {
-    auto keyboard_device_or_error = try_create_device<PS2KeyboardDevice>(ps2_controller);
+    auto keyboard_device_or_error = DeviceManagement::try_create_device<PS2KeyboardDevice>(ps2_controller);
     // FIXME: Find a way to propagate errors
     VERIFY(!keyboard_device_or_error.is_error());
     if (keyboard_device_or_error.value()->initialize())

Kernel/Devices/HID/PS2KeyboardDevice.h

@@ -21,6 +21,8 @@ namespace Kernel {
 class PS2KeyboardDevice final : public IRQHandler
     , public KeyboardDevice
     , public I8042Device {
+    friend class DeviceManagement;
+
 public:
     static RefPtr<PS2KeyboardDevice> try_to_initialize(const I8042Controller&);
     virtual ~PS2KeyboardDevice() override;
@@ -35,10 +37,9 @@ public:
         enable_irq();
     }
 
-    // FIXME: We expose this constructor to make try_create_device helper to work
+private:
     explicit PS2KeyboardDevice(const I8042Controller&);
 
-private:
     // ^IRQHandler
     virtual bool handle_irq(const RegisterState&) override;
 

Kernel/Devices/HID/PS2MouseDevice.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/Memory.h>
 #include <Kernel/Debug.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/Devices/HID/PS2MouseDevice.h>
 #include <Kernel/Devices/VMWareBackdoor.h>
 #include <Kernel/IO.h>
@@ -174,7 +175,7 @@ void PS2MouseDevice::set_sample_rate(u8 rate)
 
 UNMAP_AFTER_INIT RefPtr<PS2MouseDevice> PS2MouseDevice::try_to_initialize(const I8042Controller& ps2_controller)
 {
-    auto mouse_device_or_error = try_create_device<PS2MouseDevice>(ps2_controller);
+    auto mouse_device_or_error = DeviceManagement::try_create_device<PS2MouseDevice>(ps2_controller);
     // FIXME: Find a way to propagate errors
     VERIFY(!mouse_device_or_error.is_error());
     if (mouse_device_or_error.value()->initialize())

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;
 

Kernel/Devices/HID/VMWareMouseDevice.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/Devices/HID/VMWareMouseDevice.h>
 #include <Kernel/Devices/VMWareBackdoor.h>
 #include <Kernel/Sections.h>
@@ -16,7 +17,7 @@ UNMAP_AFTER_INIT RefPtr<VMWareMouseDevice> VMWareMouseDevice::try_to_initialize(
         return {};
     if (!VMWareBackdoor::the()->vmmouse_is_absolute())
         return {};
-    auto mouse_device_or_error = try_create_device<VMWareMouseDevice>(ps2_controller);
+    auto mouse_device_or_error = DeviceManagement::try_create_device<VMWareMouseDevice>(ps2_controller);
     // FIXME: Find a way to propagate errors
     VERIFY(!mouse_device_or_error.is_error());
     if (mouse_device_or_error.value()->initialize())

Kernel/Devices/HID/VMWareMouseDevice.h

@@ -17,13 +17,14 @@ namespace Kernel {
 
 class VMWareMouseDevice final : public PS2MouseDevice {
 public:
+    friend class DeviceManagement;
     static RefPtr<VMWareMouseDevice> try_to_initialize(const I8042Controller&);
     virtual ~VMWareMouseDevice() override;
 
     // ^I8042Device
     virtual void irq_handle_byte_read(u8 byte) override;
 
-    // FIXME: We expose this constructor to make try_create_device helper to work
+private:
     explicit VMWareMouseDevice(const I8042Controller&);
 };