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/Storage/PATADiskDevice.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <AK/StringView.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/OpenFileDescription.h>
 #include <Kernel/Sections.h>
 #include <Kernel/Storage/IDEChannel.h>
@@ -15,7 +16,7 @@ namespace Kernel {
 
 UNMAP_AFTER_INIT NonnullRefPtr<PATADiskDevice> PATADiskDevice::create(const IDEController& controller, IDEChannel& channel, DriveType type, InterfaceType interface_type, u16 capabilities, u64 max_addressable_block)
 {
-    auto device_or_error = try_create_device<PATADiskDevice>(controller, channel, type, interface_type, capabilities, max_addressable_block);
+    auto device_or_error = DeviceManagement::try_create_device<PATADiskDevice>(controller, channel, type, interface_type, capabilities, max_addressable_block);
     // FIXME: Find a way to propagate errors
     VERIFY(!device_or_error.is_error());
     return device_or_error.release_value();

Kernel/Storage/PATADiskDevice.h

@@ -20,6 +20,7 @@ class IDEController;
 class IDEChannel;
 class PATADiskDevice final : public StorageDevice {
     friend class IDEController;
+    friend class DeviceManagement;
     AK_MAKE_ETERNAL
 public:
     // Type of drive this IDEDiskDevice is on the ATA channel.
@@ -44,10 +45,9 @@ public:
     virtual void start_request(AsyncBlockDeviceRequest&) override;
     virtual String storage_name() const override;
 
-    // FIXME: We expose this constructor to make try_create_device helper to work
+private:
     PATADiskDevice(const IDEController&, IDEChannel&, DriveType, InterfaceType, u16, u64);
 
-private:
     // ^DiskDevice
     virtual StringView class_name() const override;
 

Kernel/Storage/Partition/DiskPartition.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <Kernel/Debug.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/OpenFileDescription.h>
 #include <Kernel/Storage/Partition/DiskPartition.h>
 
@@ -12,7 +13,7 @@ namespace Kernel {
 
 NonnullRefPtr<DiskPartition> DiskPartition::create(BlockDevice& device, unsigned minor_number, DiskPartitionMetadata metadata)
 {
-    auto partition_or_error = try_create_device<DiskPartition>(device, minor_number, metadata);
+    auto partition_or_error = DeviceManagement::try_create_device<DiskPartition>(device, minor_number, metadata);
     // FIXME: Find a way to propagate errors
     VERIFY(!partition_or_error.is_error());
     return partition_or_error.release_value();

Kernel/Storage/Partition/DiskPartition.h

@@ -14,6 +14,8 @@
 namespace Kernel {
 
 class DiskPartition final : public BlockDevice {
+    friend class DeviceManagement;
+
 public:
     static NonnullRefPtr<DiskPartition> create(BlockDevice&, unsigned, DiskPartitionMetadata);
     virtual ~DiskPartition();
@@ -28,10 +30,8 @@ public:
 
     const DiskPartitionMetadata& metadata() const;
 
-    // FIXME: We expose this constructor to make try_create_device helper to work
-    DiskPartition(BlockDevice&, unsigned, DiskPartitionMetadata);
-
 private:
+    DiskPartition(BlockDevice&, unsigned, DiskPartitionMetadata);
     virtual StringView class_name() const override;
 
     WeakPtr<BlockDevice> m_device;

Kernel/Storage/RamdiskDevice.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/Memory.h>
 #include <AK/StringView.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/OpenFileDescription.h>
 #include <Kernel/Storage/RamdiskController.h>
 #include <Kernel/Storage/RamdiskDevice.h>
@@ -14,7 +15,7 @@ namespace Kernel {
 
 NonnullRefPtr<RamdiskDevice> RamdiskDevice::create(const RamdiskController& controller, NonnullOwnPtr<Memory::Region>&& region, int major, int minor)
 {
-    auto device_or_error = try_create_device<RamdiskDevice>(controller, move(region), major, minor);
+    auto device_or_error = DeviceManagement::try_create_device<RamdiskDevice>(controller, move(region), major, minor);
     // FIXME: Find a way to propagate errors
     VERIFY(!device_or_error.is_error());
     return device_or_error.release_value();

Kernel/Storage/RamdiskDevice.h

@@ -15,6 +15,7 @@ class RamdiskController;
 
 class RamdiskDevice final : public StorageDevice {
     friend class RamdiskController;
+    friend class DeviceManagement;
     AK_MAKE_ETERNAL
 public:
     static NonnullRefPtr<RamdiskDevice> create(const RamdiskController&, NonnullOwnPtr<Memory::Region>&& region, int major, int minor);

Kernel/Storage/SATADiskDevice.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <AK/StringView.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/OpenFileDescription.h>
 #include <Kernel/Storage/AHCIController.h>
 #include <Kernel/Storage/IDEChannel.h>
@@ -14,7 +15,7 @@ namespace Kernel {
 
 NonnullRefPtr<SATADiskDevice> SATADiskDevice::create(const AHCIController& controller, const AHCIPort& port, size_t sector_size, u64 max_addressable_block)
 {
-    auto device_or_error = try_create_device<SATADiskDevice>(controller, port, sector_size, max_addressable_block);
+    auto device_or_error = DeviceManagement::try_create_device<SATADiskDevice>(controller, port, sector_size, max_addressable_block);
     // FIXME: Find a way to propagate errors
     VERIFY(!device_or_error.is_error());
     return device_or_error.release_value();

Kernel/Storage/SATADiskDevice.h

@@ -16,6 +16,7 @@ namespace Kernel {
 class AHCIController;
 class SATADiskDevice final : public StorageDevice {
     friend class AHCIController;
+    friend class DeviceManagement;
 
 public:
     enum class InterfaceType : u8 {
@@ -32,10 +33,9 @@ public:
     virtual void start_request(AsyncBlockDeviceRequest&) override;
     virtual String storage_name() const override;
 
-    // FIXME: We expose this constructor to make try_create_device helper to work
+private:
     SATADiskDevice(const AHCIController&, const AHCIPort&, size_t sector_size, u64 max_addressable_block);
 
-private:
     // ^DiskDevice
     virtual StringView class_name() const override;
     WeakPtr<AHCIPort> m_port;