HW_BUILDIO callback function (storport.h)

The HwStorBuildIo routine processes the SRB with unsynchronized access to shared system data structures before passing it to HwStorStartIo.



BOOLEAN HwBuildio(
  PVOID DeviceExtension,



A pointer to the miniport driver's per HBA storage area.


A pointer to the SCSI request block (SRB) to be processed.

Return value

HwStorBuildIo returns TRUE to inform the caller that StorPort should call the HwStorStartIo routine if StorPort considers the LUN ready to receive I/O. HwStorBuildIo returns FALSE to inform the caller that the SRB should not be passed to HwStorStartIo. In such cases, the miniport driver must complete the SRB by calling StorPortNotification with a notification type of RequestComplete. This can be done in HwStorBuildIo or elsewhere in the miniport driver, as long as the SRB is completed before the timeout that is specified in the TimeOutValue field of the SRB structure.


The name HwStorBuildIo is just a placeholder for the miniport function that is pointed to by the HwBuildIo member in the HW_INITIALIZATION_DATA structure. The actual prototype of this routine is defined in Storport.h as follows:

  _In_ PVOID DeviceExtension,

The port driver calls the HwStorBuildIo routine at DISPATCH IRQL without holding any spin locks. Because of this, memory allocation using StorPortAllocatePool and mutual exclusion via StorPortAcquireSpinLock are allowed in HwStorBuildIo. In a multiprocessor environment, more than one HwStorBuildIo can be active at a time, so the miniport driver is required to synchronize access to system resources, which may be in contention if more than one instance of HwStorBuildIo is active at any given time.

By completed time-consuming I/O setup activities in HwStorBuildIo instead of in HwStorStartIo, the miniport driver enables greater I/O concurrency and therefore improves I/O throughput. For highest performance, miniport drivers are expected to do as much preprocessing as possible in HwStorBuildIo so that it can send requests to the HBA via HwStorStartIo in as short amount of time as possible. Preprocessed data and state can be stored in either the DeviceExtension or SrbExtension structures. Only modifications to unique portions of the DeviceExtension must occur since no locks are held. HwStorBuildIo and HwStorStartIo receive the following Srb function types:

  • SRB_FUNCTION_EXECUTE_SCSI: Sends a CDB to the specified bus/target/lun.

    • Srb->DataTransferLength is valid for all Cdbs.
    • Srb->DataBuffer is NULL for read and write requests. To access the associated data, either use StorPortGetScatterGatherList (for Dma transfers) or StorPortGetSystemAddress (for program controlled I/O ) to get the Scatter Gather list or the virtual address of the buffer. For other requests, Srb->Databuffer points to the data that is associated with the Srb.
    • Srb->PathId is valid and represents the pathid given to Storport in StorPortNotification (BusChange). Writers of miniport drivers need to use pathid as an index into a table of busses within the miniport.
    • Srb->TargetId and Srb->Lun are valid.
  • SRB_FUNCTION_IO_CONTROL: Miniport defined.

    • Srb->DataTransferLength and Srb->DataBuffer are valid if set by the requester.
    • Srb->PathId, Srb->TargetId, and Srb->Lun are all valid.
  • SRB_FUNCTION_RESET_LOGICAL_UNIT: Reset the specified logical unit (if the device is capable).

    • Srb->DataTransferLength and Srb->DataBuffer are invalid.
    • Srb->PathId, Srb->TargetId, and Srb->Lun are all valid.
  • SRB_FUNCTION_RESET_DEVICE: Reset the specified Scsi Target.

    • Srb->DataTransferLength and Srb->DataBuffer, Srb->Lun are invalid.
    • Srb->PathId and Srb->TargetId are valid.
  • SRB_FUNCTION_RESET_BUS: Reset all of the targets on the specified SCSI bus.

    • Only Srb->PathId is valid.
  • SRB_FUNCTION_FLUSH: Instructs the miniport driver to flush all cached data.

    • Only performed by the miniport driver if it sets CachesData == TRUE in the PORT_CONFIGURATION_INFORMATION structure.
    • Srb->PathId, Srb->TargetId, and Srb->Lun are all valid.
  • SRB_FUNCTION_SHUTDOWN: Instructs the miniport driver to flush all cached data preparatory to shut down.

    • Only performed by the miniport driver if it sets CachesData == TRUE in the PORT_CONFIGURATION_INFORMATION structure.
    • Srb->PathId, Srb->TargetId, and Srb->Lun are all valid.
  • SRB_FUNCTION_DUMP_POINTERS: Supplies information needed for the miniport driver to support crash dump and hibernation.

    • This request is sent to a Storport virtual miniport driver that is used to control the disk that holds the crash dump data. Starting with Windows 8, non-virtual miniport drivers can optionally receive this request.
    • Srb->PathId, Srb->TargetId, and Srb->Lun are all valid.
  • SRB_FUNCTION_FREE_DUMP_POINTERS: Starting with Windows 8, this request is sent to the miniport to free resources allocated during the SRB_FUNCTION_DUMP_POINTERS request.

    • Srb->PathId, Srb->TargetId, and Srb->Lun are all valid.

Starting in Windows 8, the Srb parameter may point to either SCSI_REQUEST_BLOCK or STORAGE_REQUEST_BLOCK. If the function identifier in the Function field of Srb is SRB_FUNCTION_STORAGE_REQUEST_BLOCK, the SRB is a STORAGE_REQUEST_BLOCK request structure.

For more information about what you can and cannot do safely in this miniport driver routine, see Unsynchronized HwStorBuildIo Routine.


To define an HwStorBuildIo callback function, you must first provide a function declaration that identifies the type of callback function you’re defining. Windows provides a set of callback function types for drivers. Declaring a function using the callback function types helps Code Analysis for Drivers, Static Driver Verifier (SDV), and other verification tools find errors, and it’s a requirement for writing drivers for the Windows operating system.

For example, to define a HwStorBuildIo callback routine that is named MyHwBuildIo, use the HW_BUILDIO type as shown in this code example:


Then, implement your callback routine as follows:

MyHwBuildIo (
  _In_ PVOID  DeviceExtension,

The HW_BUILDIO function type is defined in the Storport.h header file. To more accurately identify errors when you run the code analysis tools, be sure to add the Use_decl_annotations annotation to your function definition. The Use_decl_annotations annotation ensures that the annotations that are applied to the HW_BUILDIO function type in the header file are used. For more information about the requirements for function declarations, see Declaring Functions Using Function Role Types for Storport Drivers. For information about Use_decl_annotations, see Annotating Function Behavior.


Requirement Value
Target Platform Universal
Header storport.h (include Storport.h)
IRQL DISPATCH_LEVEL (See Remarks section.)

See also