Official explaination about IRP_MJ_FAST_IO_CHECK_IF_POSSIBLE

The WDK document or MSDN pages do not provide any information about this
pseudo IRP valid return values.
I guess the pre-operation routine returns FLT_PREOP_DISALLOW_FASTIO to
disallow FastIO or FLT_PREOP_SUCCESS_NO_CALLBACK to allow fastIO.

Please let me know if this is not right.

Thanks,

Shangwu