A parent driver desiring to access a service of a child driver in a driver stack
creates a virtual device object. The virtual device object is inserted into the
driver stack below the child driver. When a query to dynamically remove the driver
stack arrives at the virtual device object, the virtual device object notifies
the parent driver. The parent driver stops accessing the child driver before directly
receiving and processing the remove query, allowing the driver stack to be removed
after all drivers in the driver stack process the remove query.