Kernel: Get RefPtr<Device> from the DeviceManagement::get_device method

Instead of returning a raw pointer, which could be technically invalid
when using it in the caller function, we return a valid RefPtr of such
device.

This ensures that the code in DevPtsFS is now safe from a rare race
condition in which the SlavePTY device is gone but we still have a
pointer to it.

Kernel/Devices/DeviceManagement.cpp

@@ -42,13 +42,13 @@ DeviceManagement& DeviceManagement::the()
     return *s_the;
 }
 
-Device* DeviceManagement::get_device(MajorNumber major, MinorNumber minor)
+RefPtr<Device> DeviceManagement::get_device(MajorNumber major, MinorNumber minor)
 {
-    return m_devices.with([&](auto& map) -> Device* {
+    return m_devices.with([&](auto& map) -> RefPtr<Device> {
         auto it = map.find(encoded_device(major.value(), minor.value()));
         if (it == map.end())
             return nullptr;
-        return it->value;
+        return *it->value;
     });
 }
 

Kernel/Devices/DeviceManagement.h

@@ -41,7 +41,7 @@ public:
 
     void for_each(Function<void(Device&)>);
     ErrorOr<void> try_for_each(Function<ErrorOr<void>(Device&)>);
-    Device* get_device(MajorNumber major, MinorNumber minor);
+    RefPtr<Device> get_device(MajorNumber major, MinorNumber minor);
 
     NullDevice const& null_device() const;
     NullDevice& null_device();

Kernel/Devices/Storage/StorageManagement.cpp

@@ -353,9 +353,9 @@ UNMAP_AFTER_INIT void StorageManagement::determine_block_boot_device()
     // Note: We simply fetch the corresponding BlockDevice with the major and minor parameters.
     // We don't try to accept and resolve a partition number as it will make this code much more
     // complicated. This rule is also explained in the boot_device_addressing(7) manual page.
-    LockRefPtr<Device> device = DeviceManagement::the().get_device(parameters_view[0], parameters_view[1]);
+    auto device = DeviceManagement::the().get_device(parameters_view[0], parameters_view[1]);
     if (device && device->is_block_device())
-        m_boot_block_device = static_ptr_cast<BlockDevice>(device);
+        m_boot_block_device = *static_ptr_cast<BlockDevice>(device);
 }
 
 UNMAP_AFTER_INIT void StorageManagement::determine_boot_device_with_logical_unit_number()

Kernel/FileSystem/DevPtsFS/FileSystem.cpp

@@ -23,7 +23,7 @@ DevPtsFS::~DevPtsFS() = default;
 
 ErrorOr<void> DevPtsFS::initialize()
 {
-    m_root_inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) DevPtsFSInode(*this, 1, nullptr)));
+    m_root_inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) DevPtsFSInode(*this)));
     m_root_inode->m_metadata.inode = { fsid(), 1 };
     m_root_inode->m_metadata.mode = 0040555;
     m_root_inode->m_metadata.uid = 0;
@@ -55,15 +55,15 @@ ErrorOr<NonnullRefPtr<Inode>> DevPtsFS::get_inode(InodeIdentifier inode_id) cons
         return *m_root_inode;
 
     unsigned pty_index = inode_index_to_pty_index(inode_id.index());
-    auto* device = DeviceManagement::the().get_device(201, pty_index);
+    auto device = DeviceManagement::the().get_device(201, pty_index);
     VERIFY(device);
 
-    auto* pts_device = static_cast<SlavePTY*>(device);
+    auto& pts_device = static_cast<SlavePTY&>(*device);
     auto inode = TRY(adopt_nonnull_ref_or_enomem(new (nothrow) DevPtsFSInode(const_cast<DevPtsFS&>(*this), inode_id.index(), pts_device)));
     inode->m_metadata.inode = inode_id;
     inode->m_metadata.size = 0;
-    inode->m_metadata.uid = pts_device->uid();
-    inode->m_metadata.gid = pts_device->gid();
+    inode->m_metadata.uid = pts_device.uid();
+    inode->m_metadata.gid = pts_device.gid();
     inode->m_metadata.mode = 0020600;
     inode->m_metadata.major_device = device->major();
     inode->m_metadata.minor_device = device->minor();

Kernel/FileSystem/DevPtsFS/Inode.cpp

@@ -16,11 +16,16 @@ static InodeIndex pty_index_to_inode_index(unsigned pty_index)
     return pty_index + 2;
 }
 
-DevPtsFSInode::DevPtsFSInode(DevPtsFS& fs, InodeIndex index, SlavePTY* pty)
-    : Inode(fs, index)
+// NOTE: This constructor is used for the root inode only.
+DevPtsFSInode::DevPtsFSInode(DevPtsFS& fs)
+    : Inode(fs, 1)
+{
+}
+
+DevPtsFSInode::DevPtsFSInode(DevPtsFS& fs, InodeIndex index, SlavePTY& pty)
+    : Inode(fs, index)
+    , m_pty(pty)
 {
-    if (pty)
-        m_pty = *pty;
 }
 
 DevPtsFSInode::~DevPtsFSInode() = default;

Kernel/FileSystem/DevPtsFS/Inode.h

@@ -23,7 +23,10 @@ public:
     DevPtsFS const& fs() const { return static_cast<DevPtsFS const&>(Inode::fs()); }
 
 private:
-    DevPtsFSInode(DevPtsFS&, InodeIndex, SlavePTY*);
+    DevPtsFSInode(DevPtsFS&, InodeIndex, SlavePTY&);
+
+    // NOTE: This constructor is used for the root inode only.
+    DevPtsFSInode(DevPtsFS&);
 
     // ^Inode
     virtual ErrorOr<size_t> read_bytes_locked(off_t, size_t, UserOrKernelBuffer& buffer, OpenFileDescription*) const override;