INFO: IoMarkIrpPending(Irp) vs. IoStatus.Status=STATUS_PENDING

ID: Q180589

The information in this article applies to:

Microsoft Win32 Device Driver Kit (DDK) for Windows NT, version 4.0

SUMMARY

This article explains the difference between IoMarkIrpPending(Irp), IoStatus.Status=STATUS_PENDING, and return STATUS_PENDING.

MORE INFORMATION

To see exactly what IoMarkIrpPending does, look at the following definition in NTDDK.H:


   // VOID
   // IoMarkIrpPending(
   //     IN OUT PIRP Irp
   //     )
   // 
   // Routine Description:
   // 
   // This routine marks the specified I/O Request Packet (IRP) to indicate
   // that an initial status of STATUS_PENDING was returned to the caller.
   // This is used so that I/O completion can determine whether or not to
   // fully complete the I/O operation requested by the packet.
   // 
   // Arguments:
   // 
   //     Irp - Pointer to the I/O Request Packet to be marked pending.
   // 
   // Return Value:
   // 
   //     None.
   // 
   //--

   #define IoMarkIrpPending( Irp ) ( \ 
       IoGetCurrentIrpStackLocation( (Irp) )->Control |=
       SL_PENDING_RETURNED )

There is never any reason to store STATUS_PENDING in Irp->IoStatus.Status because Irp->IoStatus.Status is filled in with the "final" status of the IRP just before calling IoCompleteRequest. None of the code paths look at Irp->IoStatus.Status until IoCompleteRequest is called. Therefore, there is no reason to set Irp->IoStatus.Status to any value before IoCompleteRequest is called. Conversely, STATUS_PENDING is never an appropriate value for Irp- >IoStatus.Status when IoCompleteRequest is called.

STATUS_PENDING is the proper return value from any dispatch routine that has not called IoCompleteRequest on the IRP or not passed the IRP to a lower-layer driver. This type of routine must also call IoMarkIrpPending for the IRP.

Keywords : NTDDKKMode
Version : WINNT:4.0
Platform : winnt
Issue type : kbinfo