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.

3 files changed, 7 insertions, 4 deletions

diff --git a/Kernel/FileSystem/DevPtsFS.cpp b/Kernel/FileSystem/DevPtsFS.cpp
index 9543c26ff2..4c64ef1958 100644
--- a/Kernel/FileSystem/DevPtsFS.cpp
+++ b/Kernel/FileSystem/DevPtsFS.cpp
@@ -5,6 +5,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/DevPtsFS.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
 #include <Kernel/TTY/SlavePTY.h>
@@ -58,7 +59,7 @@ KResultOr<NonnullRefPtr<Inode>> DevPtsFS::get_inode(InodeIdentifier inode_id) co
         return *m_root_inode;
 
     unsigned pty_index = inode_index_to_pty_index(inode_id.index());
-    auto* device = Device::get_device(201, pty_index);
+    auto* device = DeviceManagement::the().get_device(201, pty_index);
     VERIFY(device);
 
     auto inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) DevPtsFSInode(const_cast<DevPtsFS&>(*this), inode_id.index(), static_cast<SlavePTY*>(device))));
diff --git a/Kernel/FileSystem/DevTmpFS.cpp b/Kernel/FileSystem/DevTmpFS.cpp
index 5921b8209b..93df86d516 100644
--- a/Kernel/FileSystem/DevTmpFS.cpp
+++ b/Kernel/FileSystem/DevTmpFS.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <AK/StringView.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/DevTmpFS.h>
 #include <Kernel/FileSystem/VirtualFileSystem.h>
 
@@ -321,7 +322,7 @@ KResultOr<size_t> DevTmpFSDeviceInode::read_bytes(off_t offset, size_t count, Us
 {
     MutexLocker locker(m_inode_lock);
     VERIFY(!!description);
-    RefPtr<Device> device = Device::get_device(m_major_number, m_minor_number);
+    RefPtr<Device> device = DeviceManagement::the().get_device(m_major_number, m_minor_number);
     if (!device)
         return KResult(ENODEV);
     if (!device->can_read(*description, offset))
@@ -336,7 +337,7 @@ KResultOr<size_t> DevTmpFSDeviceInode::write_bytes(off_t offset, size_t count, c
 {
     MutexLocker locker(m_inode_lock);
     VERIFY(!!description);
-    RefPtr<Device> device = Device::get_device(m_major_number, m_minor_number);
+    RefPtr<Device> device = DeviceManagement::the().get_device(m_major_number, m_minor_number);
     if (!device)
         return KResult(ENODEV);
     if (!device->can_write(*description, offset))
diff --git a/Kernel/FileSystem/VirtualFileSystem.cpp b/Kernel/FileSystem/VirtualFileSystem.cpp
index 5378a58a2d..886c4cf7d3 100644
--- a/Kernel/FileSystem/VirtualFileSystem.cpp
+++ b/Kernel/FileSystem/VirtualFileSystem.cpp
@@ -9,6 +9,7 @@
 #include <AK/StringBuilder.h>
 #include <Kernel/Debug.h>
 #include <Kernel/Devices/BlockDevice.h>
+#include <Kernel/Devices/DeviceManagement.h>
 #include <Kernel/FileSystem/Custody.h>
 #include <Kernel/FileSystem/FileBackedFileSystem.h>
 #include <Kernel/FileSystem/FileSystem.h>
@@ -270,7 +271,7 @@ KResultOr<NonnullRefPtr<OpenFileDescription>> VirtualFileSystem::open(StringView
     if (metadata.is_device()) {
         if (custody.mount_flags() & MS_NODEV)
             return EACCES;
-        auto device = Device::get_device(metadata.major_device, metadata.minor_device);
+        auto device = DeviceManagement::the().get_device(metadata.major_device, metadata.minor_device);
         if (device == nullptr) {
             return ENODEV;
         }