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Registering for Synchronous Driver Notification

To use synchronous driver notification, a device driver implements a callback function that the operating system calls when you dynamically add a new processor to the hardware partition. The following code example is a prototype for such a callback function:


// Prototype for the synchronous
// notification callback function
VOID
  SyncProcessorCallback(
    IN PVOID CallbackContext,
    IN PKE_PROCESSOR_CHANGE_NOTIFY_CONTEXT ChangeContext,
    IN PNTSTATUS OperationStatus
    );

A device driver registers for synchronous driver notification by calling the KeRegisterProcessorChangeCallback function. A device driver typically calls the KeRegisterProcessorChangeCallback function from within its DriverEntry function. If the device driver specifies the KE_PROCESSOR_CHANGE_ADD_EXISTING flag, the callback function is immediately called for each active processor that currently exists in the hardware partition, in addition to being called when a new processor is added to the hardware partition. The following code example shows how to register for the synchronous driver notifications:


PVOID CallbackRegistrationHandle;
NTSTATUS CallbackStatus = STATUS_SUCCESS;

// The driver's DriverEntry routine
NTSTATUS  DriverEntry(
    PDRIVER_OBJECT DriverObject,
    PUNICODE_STRING RegistryPath
    )
{
  ...

  // Register the callback function
  CallbackRegistrationHandle =
    KeRegisterProcessorChangeCallback(
      SyncProcessorCallback,
      &CallbackStatus,
      KE_PROCESSOR_CHANGE_ADD_EXISTING
      );

  // Check the result
  if (CallbackRegistrationHandle == NULL)
  {
    // Perform any necessary cleanup
    ...

    // Check the callback status
    if (CallbackStatus != STATUS_SUCCESS)
    {
      // Return the error status from the callback function
      return CallbackStatus;
    }
    else
    {
      // Return a generic error status
      return STATUS_UNSUCCESSFUL;
    }
  }

  ...

  return STATUS_SUCCESS;
}

When a device driver must stop receiving synchronous driver notifications, such as when it is being unloaded, it must unregister the callback function by calling the KeDeregisterProcessorChangeCallback function. A device driver typically calls the KeDeregisterProcessorChangeCallback function from within its Unload function. The following code example shows how to unregister the callback function:


// The driver's Unload routine
VOID
  Unload(
    IN PDRIVER_OBJECT DriverObject
    );
{
  ...

  // Unregister the callback function
  KeDeregisterProcessorChangeCallback(
    CallbackRegistrationHandle
    );

  ...
}

 

 

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