Is There Any Other Restriction on Usage of BFF?

Yes, the following names of context types are reserved:

1. BFF_PARENT_CONTEXT
• The name of the context type for upper filter device objects.
2. BFF_DEVICE_CONTEXT
• The name of the context type for bus filter device objects.

You must not name any context type as any of them, since BFF is a static library, i.e., it's in the very same driver context as the upper filter driver; otherwise, the driver would behave unpredictably.