Returning Status
Note
For optimal reliability and performance, use file system minifilter drivers with Filter Manager support instead of legacy file system filter drivers. To port your legacy driver to a minifilter driver, see Guidelines for Porting Legacy Filter Drivers.
A legacy file system filter driver's DriverEntry routine normally returns STATUS_SUCCESS. However, if driver initialization fails, the DriverEntry routine should return an appropriate error status value.
If the DriverEntry routine returns a status value that isn't a success status value, the system responds by unloading the driver. For this reason, the DriverEntry routine must always free any memory that was allocated for system resources, such as device objects, before returning a status value that isn't a success status value.