WdfFdoInitQueryProperty function (wdffdo.h)

[Applies to KMDF and UMDF]

The WdfFdoInitQueryProperty method retrieves a specified device property.

Syntax

NTSTATUS WdfFdoInitQueryProperty(
  [in]  PWDFDEVICE_INIT          DeviceInit,
  [in]  DEVICE_REGISTRY_PROPERTY DeviceProperty,
  [in]  ULONG                    BufferLength,
  [out] PVOID                    PropertyBuffer,
  [out] PULONG                   ResultLength
);

Parameters

[in] DeviceInit

A pointer to a WDFDEVICE_INIT structure that the driver obtained from its EvtDriverDeviceAdd callback function.

[in] DeviceProperty

A DEVICE_REGISTRY_PROPERTY-typed enumerator value that identifies the device property to be retrieved.

[in] BufferLength

The size, in bytes, of the buffer that is pointed to by PropertyBuffer.

[out] PropertyBuffer

A caller-supplied pointer to a caller-allocated buffer that receives the requested device property. This pointer can be NULL if the BufferLength parameter is zero.

[out] ResultLength

A caller-supplied location that, on return, contains the size, in bytes, of the information that WdfFdoInitQueryProperty stored in PropertyBuffer. If this method's return value is STATUS_BUFFER_TOO_SMALL, ResultLength receives the required buffer size.

Return value

If the operation succeeds, the method returns STATUS_SUCCESS. Additional return values include:

The method might also return other NTSTATUS values.

Remarks

Before receiving device property data, drivers typically must make an initial call to WdfFdoInitQueryProperty to obtain the required buffer size. For some properties, the data size can change between the time that the required size is returned and the time that the driver calls this routine again. Therefore, drivers should call WdfFdoInitQueryProperty inside a loop that executes until the return status is not STATUS_BUFFER_TOO_SMALL.

It is best to use WdfFdoInitQueryProperty only if the required buffer size is known and unchanging, because in that case the driver has to call WdfFdoInitQueryProperty only once. If the required buffer size is unknown or varies, the driver should call WdfFdoInitAllocAndQueryProperty.

The driver can call WdfFdoInitQueryProperty only before calling WdfDeviceCreate. For more information about calling WdfDeviceCreate, see Creating a Framework Device Object.

After calling WdfDeviceCreate, a driver can obtain device property information by calling WdfDeviceQueryProperty.

For more information about the WdfFdoInitQueryProperty method, see Creating Device Objects in a Function Driver.

Alternatively, you can use WdfFdoInitQueryPropertyEx to access device properties that are exposed through the Unified Property Model.

Examples

The following code example obtains a Unicode string that represents the name of a device's enumerator and returns TRUE if the string is "PCI".

NTSTATUS  status = STATUS_SUCCESS;
WCHAR  enumeratorName[64] = {0};
ULONG  returnSize;
UNICODE_STRING  unicodeEnumName, temp;

status = WdfFdoInitQueryProperty(
                                 DeviceInit,
                                 DevicePropertyEnumeratorName,
                                 sizeof(enumeratorName),
                                 enumeratorName,
                                 &returnSize
                                 );
if(!NT_SUCCESS(status)){
    return status;
}

RtlInitUnicodeString(
                     &unicodeEnumName,
                     enumeratorName
                     );
RtlInitUnicodeString(
                     &temp,
                     L"PCI"
                     );
if(RtlCompareUnicodeString(
                           &unicodeEnumName,
                           &temp,
                           TRUE
                           ) == 0) {
    //
    // This device is a PCI device.
    //
    return TRUE;
}

Requirements

See also

WdfDeviceQueryProperty

WdfFdoInitAllocAndQueryProperty