Using Request Object Context
Every framework request object, whether created by the framework or by a driver, can contain driver-defined context space. When a framework-based driver initializes a framework device object, the driver can call WdfDeviceInitSetRequestAttributes to specify a WDF_OBJECT_ATTRIBUTES structure that describes context space for the device's request objects.
The framework allocates context space for request objects as follows:
When the framework creates request objects for your driver, it allocates context space with the size that your driver specified when it called WdfDeviceInitSetRequestAttributes.
If your driver creates additional request objects by calling WdfRequestCreate, you can specify a context size by providing a WDF_OBJECT_ATTRIBUTES structure.
For more information about allocating and accessing context space for framework objects, see Framework Object Context Space.