Kernel/VirtIO: Use proper error propagation from the get_config method

This allows us to drop null-checks at call-sites, thus simplifying the
code and reducing the chance of nullptr-dereference errors.

Kernel/Bus/VirtIO/Console.cpp

@@ -22,9 +22,7 @@ UNMAP_AFTER_INIT NonnullLockRefPtr<Console> Console::must_create(PCI::DeviceIden
 UNMAP_AFTER_INIT ErrorOr<void> Console::initialize_virtio_resources()
 {
     TRY(Device::initialize_virtio_resources());
-    auto const* cfg = get_config(VirtIO::ConfigurationType::Device);
-    if (!cfg)
-        return Error::from_errno(ENODEV);
+    auto const* cfg = TRY(get_config(VirtIO::ConfigurationType::Device));
     bool success = negotiate_features([&](u64 supported_features) {
         u64 negotiated = 0;
         if (is_feature_set(supported_features, VIRTIO_CONSOLE_F_SIZE))

Kernel/Bus/VirtIO/Device.cpp

@@ -151,9 +151,9 @@ UNMAP_AFTER_INIT ErrorOr<void> Device::initialize_virtio_resources()
             auto mapping_io_window = TRY(IOWindow::create_for_pci_device_bar(device_identifier(), static_cast<PCI::HeaderType0BaseRegister>(cfg.bar)));
             m_register_bases[cfg.bar] = move(mapping_io_window);
         }
-        m_common_cfg = get_config(ConfigurationType::Common, 0);
-        m_notify_cfg = get_config(ConfigurationType::Notify, 0);
-        m_isr_cfg = get_config(ConfigurationType::ISR, 0);
+        m_common_cfg = TRY(get_config(ConfigurationType::Common, 0));
+        m_notify_cfg = TRY(get_config(ConfigurationType::Notify, 0));
+        m_isr_cfg = TRY(get_config(ConfigurationType::ISR, 0));
     } else {
         auto mapping_io_window = TRY(IOWindow::create_for_pci_device_bar(device_identifier(), PCI::HeaderType0BaseRegister::BAR0));
         m_register_bases[0] = move(mapping_io_window);

Kernel/Bus/VirtIO/Device.h

@@ -30,7 +30,7 @@ protected:
     virtual StringView class_name() const { return "VirtIO::Device"sv; }
     explicit Device(PCI::DeviceIdentifier const&);
 
-    Configuration const* get_config(ConfigurationType cfg_type, u32 index = 0) const
+    ErrorOr<Configuration const*> get_config(ConfigurationType cfg_type, u32 index = 0) const
     {
         for (auto const& cfg : m_configs) {
             if (cfg.cfg_type != cfg_type)
@@ -41,7 +41,7 @@ protected:
             }
             return &cfg;
         }
-        return nullptr;
+        return Error::from_errno(ENXIO);
     }
 
     template<typename F>

Kernel/Graphics/VirtIOGPU/GraphicsAdapter.cpp

@@ -146,9 +146,7 @@ VirtIOGraphicsAdapter::VirtIOGraphicsAdapter(PCI::DeviceIdentifier const& device
 ErrorOr<void> VirtIOGraphicsAdapter::initialize_virtio_resources()
 {
     TRY(VirtIO::Device::initialize_virtio_resources());
-    auto* config = get_config(VirtIO::ConfigurationType::Device);
-    if (!config)
-        return Error::from_errno(ENODEV);
+    auto* config = TRY(get_config(VirtIO::ConfigurationType::Device));
     m_device_configuration = config;
     bool success = negotiate_features([&](u64 supported_features) {
         u64 negotiated = 0;