IoBuildSynchronousFsdRequest function (wdm.h)

The IoBuildSynchronousFsdRequest routine allocates and sets up an IRP for a synchronously processed I/O request.


__drv_aliasesMem PIRP IoBuildSynchronousFsdRequest(
  [in]           ULONG            MajorFunction,
  [in]           PDEVICE_OBJECT   DeviceObject,
  [in, out]      PVOID            Buffer,
  [in, optional] ULONG            Length,
  [in, optional] PLARGE_INTEGER   StartingOffset,
  [in]           PKEVENT          Event,
  [out]          PIO_STATUS_BLOCK IoStatusBlock


[in] MajorFunction

The major function code for the IRP. This code can be IRP_MJ_PNP, IRP_MJ_READ, IRP_MJ_WRITE, IRP_MJ_FLUSH_BUFFERS, or IRP_MJ_SHUTDOWN.

[in] DeviceObject

A pointer to the DEVICE_OBJECT structure for the next-lower driver's device object, which represents the target device.

[in, out] Buffer

A pointer to a data buffer. If MajorFunction is IRP_MJ_WRITE, the buffer contains data to be written. If MajorFunction is IRP_MJ_READ, the buffer receives data. If MajorFunction is IRP_MJ_FLUSH_BUFFERS or IRP_MJ_SHUTDOWN, this parameter must be NULL.

[in, optional] Length

The length, in bytes, of the buffer pointed to by Buffer. For devices such as disks, this value must be an integer multiple of the sector size. Starting with Windows 8, the sector size can be 4,096 or 512 bytes. In earlier versions of Windows, the sector size is always 512 bytes. This parameter is required for read and write requests, but must be zero for flush and shutdown requests.

[in, optional] StartingOffset

A pointer to the offset on the disk, for read and write requests. The units and meaning of this value are driver-specific. This parameter is required for read and write requests, but must be zero for flush and shutdown requests.

[in] Event

A pointer to a caller-allocated and initialized event object. The I/O manager sets the event to the Signaled state when a lower-level driver completes the requested operation. After calling IoCallDriver, the driver can wait for the event object.

[out] IoStatusBlock

A pointer to a location that receives the I/O status block that is set when the IRP is completed by a lower-level driver.

Return value

If the operation succeeds, IoBuildSynchronousFsdRequest returns a pointer to an initialized IRP structure, with the next-lower driver's I/O stack location set up from the supplied parameters. Otherwise, the routine returns NULL.


A file system driver (FSD) or other higher-level driver can call IoBuildSynchronousFsdRequest to set up IRPs that it synchronously sends to lower-level drivers.

IoBuildSynchronousFsdRequest allocates and sets up an IRP that requests lower-level drivers to perform a synchronous read, write, flush, or shutdown operation. The IRP contains enough information to start the operation.

Lower-level drivers might impose restrictions on parameters supplied to this routine. For example, disk drivers might require that values supplied for Length and StartingOffset be integer multiples of the device's sector size.

After calling IoBuildSynchronousFsdRequest to create a request, the driver must call IoCallDriver to send the request to the next-lower driver. If IoCallDriver returns STATUS_PENDING, the driver must wait for the completion of the IRP by calling KeWaitForSingleObject on the given Event. Most drivers do not need to set an IoCompletion routine for the IRP.

IRPs that are created by IoBuildSynchronousFsdRequest must be completed by a driver's call to IoCompleteRequest. A driver that calls IoBuildSynchronousFsdRequest must not call IoFreeIrp, because the I/O manager frees these synchronous IRPs after IoCompleteRequest has been called.

IoBuildSynchronousFsdRequest queues the IRPs that it creates to an IRP queue that is specific to the current thread. If the thread exits, the I/O manager cancels the IRP.


Minimum supported client Available starting with Windows 2000.
Target Platform Universal
Header wdm.h (include Wdm.h, Ntddk.h, Ntifs.h)
Library NtosKrnl.lib
DLL NtosKrnl.exe
DDI compliance rules ForwardedAtBadIrqlFsdSync(wdm), HwStorPortProhibitedDDIs(storport), IoBuildSynchronousFsdRequestNoFree(wdm), IoBuildSynchronousFsdRequestWait(wdm), IoBuildSynchronousFsdRequestWaitTimeout(wdm), PowerIrpDDis(wdm), SignalEventInCompletion(wdm)

See also