Overview

In the Windows kernel, an I/O Request Packet (IRP) is the primary data structure used to communicate I/O requests between drivers. Completing an IRP signals that the I/O operation is finished and returns control (and status) to the caller.

This page describes the recommended patterns for completing IRPs, the IoCompleteRequest routine, and best‑practice error handling.

Syntax

VOID IoCompleteRequest(
    _In_ PIRP Irp,
    _In_ CCHAR PriorityBoost
);

Remarks

• The driver that owns the IRP must set Irp->IoStatus.Status and Irp->IoStatus.Information before calling IoCompleteRequest.
• Only the driver that last processed the IRP should complete it. Premature completion can cause memory corruption or deadlocks.
• If the IRP has a completion routine set via IoSetCompletionRoutine, that routine is called after IoCompleteRequest returns.
• For IRPs that are pending, the driver should return STATUS_PENDING after queuing any asynchronous work, and later call IoCompleteRequest when the work finishes.

Example

The following snippet shows a typical driver dispatch routine that processes a read request and completes the IRP.

#include <ntddk.h>

NTSTATUS
MyDriverRead(
    _In_ PDEVICE_OBJECT DeviceObject,
    _Inout_ PIRP Irp
    )
{
    UNREFERENCED_PARAMETER(DeviceObject);

    // Validate buffer length
    ULONG length = IoGetCurrentIrpStackLocation(Irp)->Parameters.Read.Length;
    if (length == 0) {
        Irp->IoStatus.Status = STATUS_INVALID_PARAMETER;
        Irp->IoStatus.Information = 0;
        IoCompleteRequest(Irp, IO_NO_INCREMENT);
        return STATUS_INVALID_PARAMETER;
    }

    // Perform read (synchronously for demo)
    // In a real driver you would copy data to the user buffer here.
    RtlZeroMemory(Irp->AssociatedIrp.SystemBuffer, length);

    Irp->IoStatus.Status = STATUS_SUCCESS;
    Irp->IoStatus.Information = length; // bytes transferred
    IoCompleteRequest(Irp, IO_NO_INCREMENT);
    return STATUS_SUCCESS;
}

See Also

• I/O Completion
• IoSetCompletionRoutine
• IRP Structure
• IoGetCurrentIrpStackLocation