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

PIRP
  IoBuildSynchronousFsdRequest(
    IN ULONG  MajorFunction,
    IN PDEVICE_OBJECT  DeviceObject,
    IN OUT PVOID  Buffer  OPTIONAL,
    IN ULONG  Length  OPTIONAL,
    IN PLARGE_INTEGER  StartingOffset  OPTIONAL,
    IN PKEVENT  Event,
    OUT PIO_STATUS_BLOCK  IoStatusBlock
    );

Parameters

MajorFunction

Supplies a major function code. This code can be IRP_MJ_PNP, IRP_MJ_READ, IRP_MJ_WRITE, IRP_MJ_FLUSH_BUFFERS, or IRP_MJ_SHUTDOWN.

DeviceObject

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

Buffer

Supplies a pointer to a 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.

Length

Supplies the length, in bytes, of Buffer. For devices such as disks, this value must be an integral of 512. This parameter is required for read and write requests, but must be zero for flush and shutdown requests.

StartingOffset

Supplies 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.

Event

Supplies 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.

IoStatusBlock

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.

Comments

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 integrals 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.

Requirements

IRQL: <=APC_LEVEL

Headers: Declared in Wdm.h. Include Wdm.h, Ntddk.h, or Ntifs.h.

See Also

IO_STACK_LOCATION, IoAllocateIrp, IoBuildAsynchronousFsdRequest, IoBuildDeviceIoControlRequest, IoCompleteRequest, IRP, KeInitializeEvent, KeWaitForSingleObject