The design of BFF focuses on processing PnP IRPs; a BFF-based driver may register its own handlers for all minor functions of PnP, except for IRP_MN_REMOVE_DEVICE; non-PnP IRPs or PnP IRPs without registered handlers are simply passed down to the next lower driver, typically the bus driver. Therefore, a BFF-based driver may entirely replace a lower filter driver, if only PnP IRPs are concerned; otherwise, a lower filter driver is still required.
Although no handler can be registered for IRP_MN_REMOVE_DEVICE, a callback function, DeviceRemove, may be specified during BFF initialization, and it will be invoked during the processing of IRP_MN_REMOVE_DEVICE.
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