The IRP structure is a partial opaque structure that represents an I/O request packet. Drivers can use the following members of the IRP structure.

typedef struct _IRP {
  .
  .
  PMDL  MdlAddress;
  ULONG  Flags;
  union {
    struct _IRP  *MasterIrp;
    .
    .
    PVOID  SystemBuffer;
  } AssociatedIrp;
  .
  .
  IO_STATUS_BLOCK  IoStatus;
  KPROCESSOR_MODE  RequestorMode;
  BOOLEAN PendingReturned;
  .
  .
  BOOLEAN  Cancel;
  KIRQL  CancelIrql;
  .
  .
  PDRIVER_CANCEL  CancelRoutine;
  PVOID UserBuffer;
  union {
    struct {
    .
    .
    union {
      KDEVICE_QUEUE_ENTRY DeviceQueueEntry;
      struct {
        PVOID  DriverContext[4];
      };
    };
    .
    .
    PETHREAD  Thread;
    .
    .
    LIST_ENTRY  ListEntry;
    .
    .
    } Overlay;
  .
  .
  } Tail;
} IRP, *PIRP;

Members

MdlAddress

Pointer to an MDL describing a user buffer, if the driver is using direct I/O, and the IRP major function code is one of the following:

IRP_MJ_READ

The MDL describes an empty buffer that the device or driver fills in.

IRP_MJ_WRITE

The MDL describes a buffer that contains data for the device or driver.

IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL

If the IOCTL code specifies the METHOD_IN_DIRECT transfer type, the MDL describes a buffer that contains data for the device or driver.

If the IOCTL code specifies the METHOD_OUT_DIRECT transfer type, the MDL describes an empty buffer that the device or driver fills in.

For more information about the buffers that are associated with METHOD_IN_DIRECT and METHOD_OUT_DIRECT transfer types in IOCTL codes, see Buffer Descriptions for I/O Control Codes.

If the driver is not using direct I/O, this pointer is NULL.

Flags

File system drivers use this field, which is read-only for all drivers. Network and, possibly, highest-level device drivers also might read this field, which can be set with one or more of the following system-defined masks:

IRP_NOCACHE

IRP_PAGING_IO

IRP_MOUNT_COMPLETION

IRP_SYNCHRONOUS_API

IRP_ASSOCIATED_IRP

IRP_BUFFERED_IO

IRP_DEALLOCATE_BUFFER

IRP_INPUT_OPERATION

IRP_SYNCHRONOUS_PAGING_IO

IRP_CREATE_OPERATION

IRP_READ_OPERATION

IRP_WRITE_OPERATION

IRP_CLOSE_OPERATION

IRP_DEFER_IO_COMPLETION

AssociatedIrp.MasterIrp

Pointer to the master IRP in an IRP that was created by a highest-level driver's call to IoMakeAssociatedIrp.

AssociatedIrp.SystemBuffer

Pointer to a system-space buffer.

If the driver is using buffered I/O, the buffer's purpose is determined by the IRP major function code, as follows:

IRP_MJ_READ

The buffer receives data from the device or driver. The buffer's length is specified by Parameters.Read.Length in the driver's IO_STACK_LOCATION structure.

IRP_MJ_WRITE

The buffer supplies data for the device or driver. The buffer's length is specified by Parameters.Write.Length in the driver's IO_STACK_LOCATION structure.

IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL

The buffer represents both the input and output buffers that are supplied to DeviceIoControl and IoBuildDeviceIoControlRequest. Output data overwrites input data.

For input, the buffer's length is specified by Parameters.DeviceIoControl.InputBufferLength in the driver's IO_STACK_LOCATION structure.

For output, the buffer's length is specified by Parameters.DeviceIoControl.OutputBufferLength in the driver's IO_STACK_LOCATION structure.

For more information, see Buffer Descriptions for I/O Control Codes.

If the driver is using direct I/O, the buffer's purpose is determined by the IRP major function code, as follows:

IRP_MJ_READ

NULL.

IRP_MJ_WRITE

NULL.

IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL

The buffer represents the input buffer that is supplied to DeviceIoControl and IoBuildDeviceIoControlRequest.

The buffer's length is specified by Parameters.DeviceIoControl.InputBufferLength in the driver's IO_STACK_LOCATION structure.

For more information, see Buffer Descriptions for I/O Control Codes.

IoStatus

Contains the IO_STATUS_BLOCK structure in which a driver stores status and information before calling IoCompleteRequest.

RequestorMode

Indicates the execution mode of the original requester of the operation, one of UserMode or KernelMode.

PendingReturned

If set to TRUE, a driver has marked the IRP pending. Each IoCompletion routine should check the value of this flag. If the flag is TRUE, and if the IoCompletion routine will not return STATUS_MORE_PROCESSING_REQUIRED, the routine should call IoMarkIrpPending to propagate the pending status to drivers above it in the device stack.

Cancel

If set to TRUE, the IRP either is or should be canceled.

CancelIrql

Contains the IRQL at which a driver is running when IoAcquireCancelSpinLock is called.

CancelRoutine

Contains the entry point for a driver-supplied Cancel routine to be called if the IRP is canceled. NULL indicates that the IRP is not currently cancelable.

UserBuffer

Contains the address of an output buffer if the major function code in the I/O stack location is IRP_MJ_DEVICE_CONTROL or IRP_MJ_INTERNAL_DEVICE_CONTROL and the I/O control code was defined with METHOD_NEITHER.

Tail.Overlay.DeviceQueueEntry

If IRPs are queued in the device queue associated with the driver's device object, this field links IRPs in the device queue. These links can be used only while the driver is processing the IRP.

Tail.Overlay.DriverContext

If IRPs are not queued in the device queue associated with the driver's device object, this field can be used by the driver to store up to four pointers. This field can be used only while the driver owns the IRP.

Tail.Overlay.Thread

Is a pointer to the caller's thread control block. Higher-level drivers that allocate IRPs for lower-level removable-media drivers must set this field in the IRPs they allocate. Otherwise, the FSD cannot determine which thread to notify if the underlying device driver indicates that the media requires verification.

Tail.Overlay.ListEntry

If a driver manages its own internal queues of IRPs, it uses this field to link one IRP to the next. These links can be used only while the driver is holding the IRP in its queue or is processing the IRP.

Comments

Undocumented members of the IRP structure are reserved, used only by the I/O manager or, in some cases, by FSDs.

An IRP is the basic I/O manager structure used to communicate with drivers and to allow drivers to communicate with each other. A packet consists of two different parts:

• Header, or fixed part of the packet — This is used by the I/O manager to store information about the original request, such as the caller's device-independent parameters, the address of the device object upon which a file is open, and so on. It is also used by drivers to store information such as the final status of the request.
• I/O stack locations — Following the header is a set of I/O stack locations, one per driver in the chain of layered drivers for which the request is bound. Each stack location contains the parameters, function codes, and context used by the corresponding driver to determine what it is supposed to be doing. For more information, see the IO_STACK_LOCATION structure.

While a higher-level driver might check the value of the Cancel Boolean in an IRP, that driver cannot assume the IRP will be completed with STATUS_CANCELLED by a lower-level driver even if the value is TRUE.

Requirements

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

See Also

IoCreateDevice, IoGetCurrentIrpStackLocation, IoGetNextIrpStackLocation, IoSetCancelRoutine, IoSetNextIrpStackLocation, IO_STACK_LOCATION, IO_STATUS_BLOCK

APIScan Requirements

Header: Wdm.h, Ntddk.h, Ntifs.h
Function: IRP