Specifying an Unload Function
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Specifying an Unload Function

A callout driver must provide an unload function. The operating system calls this function when the callout driver is unloaded from the system. A callout driver's unload function must guarantee that the callout driver's callouts are unregistered from the filter engine before the callout driver is unloaded from system memory. A callout driver cannot be unloaded from the system if it does not provide an unload function.

How a callout driver specifies an unload function depends on whether the callout driver is based on the Windows Driver Model (WDM) or the Windows Driver Frameworks (WDF).

WDM-Based Callout Drivers

If a callout driver is based on WDM, it specifies an Unload function in its DriverEntry function. For example:


VOID
 Unload(
    IN PDRIVER_OBJECT DriverObject
    );

NTSTATUS
 DriverEntry(
    IN PDRIVER_OBJECT DriverObject,
    IN PUNICODE_STRING RegistryPath
    )
{
  ...

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

  ...
}

WDF-Based Callout Drivers

If a callout driver is based on WDF, it specifies an EvtDriverUnload function in its DriverEntry function. For example:


VOID
 Unload(
    IN WDFDRIVER Driver
    );

NTSTATUS
 DriverEntry(
    IN PDRIVER_OBJECT DriverObject,
    IN PUNICODE_STRING RegistryPath
    )
{
  NTSTATUS status;
  WDF_DRIVER_CONFIG config;
  WDFDRIVER driver;

  ...

  // Initialize the driver config structure
  WDF_DRIVER_CONFIG_INIT(&config, NULL);

  // Indicate that this is a non-PNP driver
 config.DriverInitFlags = WdfDriverInitNonPnpDriver;

  // Specify the callout driver's Unload function
 config.EvtDriverUnload = Unload;

  // Create a WDFDRIVER object
 status =
 WdfDriverCreate(
 DriverObject,
 RegistryPath,
      NULL,
      &config,
      &driver
      );

  ...

 return status;
}

For information about how to implement a callout driver's unload function, see Unloading a Callout Driver.

 

 

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