typedef struct _FS_FILTER_CALLBACK_DATA
{
     ULONG SizeOfFsFilterCallbackData;
     UCHAR Operation;
     UCHAR Reserved;
     PDEVICE_OBJECT DeviceObject;
     PFILE_OBJECT FileObject;
     FS_FILTER_PARAMETERS Parameters;
} FS_FILTER_CALLBACK_DATA, *PFS_FILTER_CALLBACK_DATA;

Windows Vista Kernel Structures