Kernel: Add an initial implementation of virtio-net driver

It can be exercised by setting
    SERENITY_ETHERNET_DEVICE_TYPE=virtio-net-pci.

Kernel/Net/VirtIO/VirtIONetworkAdapter.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2023, Kirill Nikolaev <cyril7@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/Bus/VirtIO/Device.h>
+#include <Kernel/Memory/RingBuffer.h>
+#include <Kernel/Net/NetworkAdapter.h>
+
+namespace Kernel {
+
+class VirtIONetworkAdapter
+    : public VirtIO::Device
+    , public NetworkAdapter {
+
+public:
+    static ErrorOr<bool> probe(PCI::DeviceIdentifier const&);
+    static ErrorOr<NonnullRefPtr<NetworkAdapter>> create(PCI::DeviceIdentifier const&);
+    virtual ~VirtIONetworkAdapter() override = default;
+
+    // VirtIO::Device
+    virtual ErrorOr<void> initialize_virtio_resources() override;
+    virtual StringView device_name() const override { return class_name(); }
+
+    // NetworkAdapter
+    virtual StringView class_name() const override { return "VirtIONetworkAdapter"sv; }
+    virtual Type adapter_type() const override { return Type::Ethernet; }
+    virtual ErrorOr<void> initialize(Badge<NetworkingManagement>) override;
+
+    virtual bool link_up() override { return m_link_up; }
+    virtual bool link_full_duplex() override { return m_link_duplex; }
+    virtual i32 link_speed() override { return m_link_speed; }
+
+private:
+    explicit VirtIONetworkAdapter(PCI::DeviceIdentifier const&, NonnullOwnPtr<KString> interface_name);
+
+    // VirtIO::Device
+    virtual bool handle_device_config_change() override;
+    virtual void handle_queue_update(u16 queue_index) override;
+
+    // NetworkAdapter
+    virtual void send_raw(ReadonlyBytes) override;
+
+private:
+    VirtIO::Configuration const* m_device_config { nullptr };
+
+    // FIXME: Make atomic as they are read without sync.
+    // Note that VirtIO::NetworkAdapter may also have the same defect.
+    bool m_link_up { false };
+    i32 m_link_speed { LINKSPEED_INVALID };
+    bool m_link_duplex { false };
+
+    OwnPtr<Memory::RingBuffer> m_rx_buffers;
+    OwnPtr<Memory::RingBuffer> m_tx_buffers;
+};
+
+}