virtio networking: fix two minor issues (#13810)

* virtio networking: fix two minor issues

* Update src/windows/common/VirtioNetworking.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/windows/common/NatNetworking.cpp

@@ -506,23 +506,12 @@ CATCH_LOG()
 
 void NatNetworking::UpdateMtu()
 {
-    unique_interface_table interfaceTable{};
+    const auto minMtu = GetMinimumConnectedInterfaceMtu();
-    THROW_IF_WIN32_ERROR(::GetIpInterfaceTable(AF_UNSPEC, &interfaceTable));
-
-    ULONG minMtu = ULONG_MAX;
-    for (ULONG index = 0; index < interfaceTable.get()->NumEntries; index++)
-    {
-        const auto& ipInterface = interfaceTable.get()->Table[index];
-        if (ipInterface.Connected)
-        {
-            minMtu = std::min(ipInterface.NlMtu, minMtu);
-        }
-    }
 
     // Only send the update if the MTU changed.
-    if (minMtu != ULONG_MAX && minMtu != m_networkMtu)
+    if (minMtu && minMtu.value() != m_networkMtu)
     {
-        m_networkMtu = minMtu;
+        m_networkMtu = minMtu.value();
 
         hns::ModifyGuestEndpointSettingRequest<hns::NetworkInterface> notification{};
         notification.ResourceType = hns::GuestEndpointResourceType::Interface;

src/windows/common/VirtioNetworking.cpp

@@ -22,6 +22,14 @@ VirtioNetworking::VirtioNetworking(
 {
 }
 
+VirtioNetworking::~VirtioNetworking()
+{
+    // Unregister the network notification callback to prevent it from using the GNS channel.
+    m_networkNotifyHandle.reset();
+    // Stop the GNS channel to unblock any stuck communications with the guest.
+    m_gnsChannel.Stop();
+}
+
 void VirtioNetworking::Initialize()
 try
 {
@@ -271,32 +279,25 @@ void VirtioNetworking::UpdateDns(hns::DNS&& dnsSettings)
 
 void VirtioNetworking::UpdateMtu()
 {
-    unique_interface_table interfaceTable{};
+    const auto minMtu = GetMinimumConnectedInterfaceMtu();
-    THROW_IF_WIN32_ERROR(::GetIpInterfaceTable(AF_UNSPEC, &interfaceTable));
-
-    ULONG minMtu = ULONG_MAX;
-    for (ULONG index = 0; index < interfaceTable.get()->NumEntries; index++)
-    {
-        const auto& ipInterface = interfaceTable.get()->Table[index];
-        if (ipInterface.Connected)
-        {
-            minMtu = std::min(ipInterface.NlMtu, minMtu);
-        }
-    }
 
     // Only send the update if the MTU changed.
-    if (minMtu != ULONG_MAX && minMtu != m_networkMtu)
+    if (minMtu && minMtu.value() != m_networkMtu)
     {
+        m_networkMtu = minMtu.value();
+
         hns::ModifyGuestEndpointSettingRequest<hns::NetworkInterface> notification{};
         notification.ResourceType = hns::GuestEndpointResourceType::Interface;
         notification.RequestType = hns::ModifyRequestType::Update;
-        notification.Settings.NlMtu = m_networkMtu;
         notification.Settings.Connected = true;
+        notification.Settings.NlMtu = m_networkMtu;
 
-        WSL_LOG("VirtioNetworking::UpdateMtu", TraceLoggingValue(m_networkMtu, "VirtioMtu"));
+        WSL_LOG(
+            "VirtioNetworking::UpdateMtu",
+            TraceLoggingValue(m_adapterId, "endpointId"),
+            TraceLoggingValue(m_networkMtu, "virtioMtu"));
 
-        // TODO: Why was this commented ?
+        m_gnsChannel.SendHnsNotification(ToJsonW(notification).c_str(), m_adapterId);
-        // m_gnsChannel.SendHnsNotification(ToJsonW(notification).c_str(), m_endpointId);
     }
 }
 

src/windows/common/VirtioNetworking.h

@@ -14,7 +14,7 @@ class VirtioNetworking : public INetworkingEngine
 {
 public:
     VirtioNetworking(GnsChannel&& gnsChannel, bool enableLocalhostRelay, std::shared_ptr<GuestDeviceManager> guestDeviceManager, wil::shared_handle userToken);
-    ~VirtioNetworking() = default;
+    ~VirtioNetworking();
 
     // Note: This class cannot be moved because m_networkNotifyHandle captures a 'this' pointer.
     VirtioNetworking(const VirtioNetworking&) = delete;

src/windows/common/WslCoreNetworkingSupport.cpp

@@ -248,3 +248,25 @@ wsl::core::networking::EphemeralHcnEndpoint wsl::core::networking::CreateEphemer
 
     return endpoint;
 }
+
+std::optional<ULONG> wsl::core::networking::GetMinimumConnectedInterfaceMtu() noexcept
+{
+    std::optional<ULONG> minMtu{};
+    try
+    {
+        unique_interface_table interfaceTable{};
+        THROW_IF_WIN32_ERROR(::GetIpInterfaceTable(AF_UNSPEC, &interfaceTable));
+
+        for (ULONG index = 0; index < interfaceTable.get()->NumEntries; index++)
+        {
+            const auto& ipInterface = interfaceTable.get()->Table[index];
+            if (ipInterface.Connected)
+            {
+                minMtu = std::min(minMtu.value_or(ipInterface.NlMtu), ipInterface.NlMtu);
+            }
+        }
+    }
+    CATCH_LOG()
+
+    return minMtu;
+}

src/windows/common/WslCoreNetworkingSupport.h

@@ -456,6 +456,11 @@ std::vector<wsl::core::networking::CurrentInterfaceInformation> EnumerateConnect
 
 bool IsMetered(ABI::Windows::Networking::Connectivity::NetworkCostType cost) noexcept;
 
+/// <summary>
+/// Gets the minimum MTU across all connected network interfaces.
+/// </summary>
+std::optional<ULONG> GetMinimumConnectedInterfaceMtu() noexcept;
+
 /// <summary>
 /// This instance acts as an IP_ADAPTER_ADDRESS pointer.
 /// </summary>