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DriverEntry for WDF Drivers routine

[Applies to KMDF and UMDF]

DriverEntry is the first driver-supplied routine that is called after a driver is loaded. It is responsible for initializing the driver.

Syntax


NTSTATUS DriverEntry(
  _In_  PDRIVER_OBJECT DriverObject,
  _In_  PUNICODE_STRING RegistryPath
);

Parameters

DriverObject [in]

A pointer to a DRIVER_OBJECT structure that represents the driver's WDM driver object.

RegistryPath [in]

A pointer to a UNICODE_STRING structure that specifies the path to the driver's Parameters key in the registry.

Return value

If the routine succeeds, it must return STATUS_SUCCESS. Otherwise, it must return one of the error status values that are defined in ntstatus.h.

Remarks

Like all WDM drivers, framework-based drivers must have a DriverEntry routine, which is called after the driver is loaded. A framework-based driver's DriverEntry routine must:

  • Activate WPP software tracing.

    DriverEntry should include a WPP_INIT_TRACING macro to activate software tracing.

  • Call WdfDriverCreate.

    The call to WdfDriverCreate enables the driver to use Windows Driver Framework interfaces. (The driver cannot call other framework routines before calling WdfDriverCreate.)

  • Allocate any non-device-specific system resources and global variables that it might need.

    Typically, drivers associate system resources with individual devices. Therefore, framework-based drivers allocate most resources in an EvtDriverDeviceAdd callback, which is called when individual devices are detected.

    Because multiple instances of a UMDF driver might be hosted by separate instances of Wudfhost, a global variable might not be available across all instances of a UMDF driver.

  • Obtain driver-specific parameters from the registry.

    Some drivers obtain parameters from the registry. These drivers can call WdfDriverOpenParametersRegistryKey to open the registry key that contains these parameters.

  • Provide a DriverEntry return value.

Note  A UMDF driver runs in a user-mode host process, while a KMDF driver runs in kernel mode in a system process. The framework might load multiple instances of a UMDF driver into separate instances of the host process. As a result:

  • The framework might call a UMDF driver’s DriverEntry routine multiple times if it loads instances of the driver in different host processes. In contrast, the framework calls a KMDF driver's DriverEntry routine only once.
  • If a UMDF driver creates a global variable in its DriverEntry routine, the variable might may not be available to all instances of the driver. However, a global variable that a KMDF driver creates in its DriverEntry routine is available to all instances of the driver.

For more information about when a framework-based driver's DriverEntry routine is called, see Building and Loading a WDF Driver.

The DriverEntry routine is not declared in WDK headers. Static Driver Verifier (SDV) and other verification tools may require a declaration such as the following:

DRIVER_INITIALIZE MyDriverEntry;

NTSTATUS
DriverEntry(
    IN PDRIVER_OBJECT  DriverObject,
    IN PUNICODE_STRING  RegistryPath
    )
{
// Function body
}

Examples

The following code example shows the Serial (KMDF) sample driver's DriverEntry routine.


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

    //
    // Initialize WPP tracing.
    //
    WPP_INIT_TRACING(
                     DriverObject,
                     RegistryPath
                     );

    SerialDbgPrintEx(
                     TRACE_LEVEL_INFORMATION,
                     DBG_INIT,
                     "Serial Sample (WDF Version) - Built %s %s\n",
                     __DATE__, __TIME__
                     );
    //
    // Register a cleanup callback function (which calls WPP_CLEANUP)
    // for the framework driver object. The framework will call
    // the cleanup callback function when it deletes the driver object,
    // before the driver is unloaded.
    //
    WDF_OBJECT_ATTRIBUTES_INIT(&attributes);
    attributes.EvtCleanupCallback = SerialEvtDriverContextCleanup;

    WDF_DRIVER_CONFIG_INIT(
                           &config,
                           SerialEvtDeviceAdd
                           );

    status = WdfDriverCreate(
                             DriverObject,
                             RegistryPath,
                             &attributes,
                             &config,
                             &hDriver
                             );
    if (!NT_SUCCESS(status)) {
        SerialDbgPrintEx(
                         TRACE_LEVEL_ERROR,
                         DBG_INIT,
                         "WdfDriverCreate failed with status 0x%x\n",
                         status
                         );
        //
        // Clean up tracing here because WdfDriverCreate failed.
        //
        WPP_CLEANUP(DriverObject);
        return status;
    }

    //
    // Call an internal routine to obtain registry values
    // to use for all the devices that the driver 
    // controls, including whether or not to break on entry.
    //
    SerialGetConfigDefaults(
                            &driverDefaults,
                            hDriver
                            );

    //
    // Break on entry if requested bt registry value.
    //
    if (driverDefaults.ShouldBreakOnEntry) {
        DbgBreakPoint();
    }

    return status;
}

See also

WdfDriverCreate
EvtDriverDeviceAdd

 

 

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