Handling PnP Start in a Storage Filter Driver
A storage filter driver (SFD) performs device-specific initialization and sets up its device extension when the PnP manager calls its DispatchPnP routine with a start request (IRP_MJ_PNP with IRP_MN_START_DEVICE). An SFD handles a start request in much the same way as does a storage class driver.
For information about how a storage class driver handles a start request and sets up its device extension, see Storage Class Drivers. For general information about handling a PnP start request, see Plug and Play.