Enabling a FirewallHook Function

An IPv6 firewall-hook driver enables its FirewallHookfunction by calling the IPv6EnableFirewallHookfunction. An IPv6 firewall-hook driver typically calls the IPv6EnableFirewallHookfunction from within its DriverEntryfunction. For example:

// Prototype for the FirewallHook callback function
IPv6Action
  FirewallHook(
    const IPv6Addr  *SourceAddress,
    const IPv6Addr  *DestinationAddress,
    uint  PayloadLength,
    uchar  HeaderType,
    const uchar  *HeaderData,
    const void  *PacketContext,
    uint  DataLength,
    uint  InterfaceIndex,
    IPv6Direction  Direction,
    BOOLEAN  IsLoopBack
    );

// Prototype for the driver's Unload function
VOID
  Unload(
    IN PDRIVER_OBJECT DriverObject
    );

// Driver's DriverEntry function
NTSTATUS
  DriverEntry(
    IN PDRIVER_OBJECT DriverObject,
    IN PUNICODE_STRING RegistryPath
    )
{
  NTSTATUS Status;

  // Specify the callout driver's Unload function
  DriverObject->DriverUnload = Unload;

  // Enable the FirewallHook callback function
  Status =
    IPv6EnableFirewallHook(
      FirewallHook
      );

  // Return status from call to IPv6EnableFirewallHook
  return Status;
}

An IPv6 firewall-hook driver is not required to enable its FirewallHookfunction from within its DriverEntryfunction. For example, if the IPv6 firewall-hook functionality is only a subcomponent of a more complex driver, the call to the IPv6EnableFirewallHookfunction might occur when the IPv6 firewall-hook subcomponent is activated.

Only one FirewallHookfunction can be enabled at any given time. If an IPv6 firewall-hook driver calls the IPv6EnableFirewallHookfunction when another FirewallHookfunction is currently enabled, the IPv6EnableFirewallHookfunction returns STATUS_INVALID_DEVICE_REQUEST. To replace a currently enabled FirewallHookfunction with a different FirewallHookfunction, the currently enabled FirewallHookfunction must first be disabled before the replacement FirewallHookfunction can be enabled. For more information about how to disable a FirewallHookfunction, see Disabling a FirewallHook Function.

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