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**IRP（I/O Request Packet）详解** IRP，全称为I/O Request Packet，是Windows操作系统内核中处理I/O请求的核心机制。IRP代表了应用程序、设备驱动程序或者系统服务之间的I/O通信方式，是操作系统与硬件设备交互的重要桥梁。 ### IRP的基本结构 IRP是一个结构体，包含了用于执行I/O操作的所有必要信息。它包括： 1. **MajorFunction**：主要功能代码，定义了I/O操作的类型，如读取、写入、关闭等。 2. **CurrentIrpStackLocation**：指向当前处理该IRP的驱动程序的IrpStack位置，提供了上下文信息。 3. **IoStatus**：包含I/O操作的状态和结果信息。 4. **UserBuffer**：指向用户模式缓冲区的指针，用于数据传输。 5. **AssociatedIrp**：附加的IRP信息，如系统分配的缓冲区。 6. **Flags**：标志字段，指示IRP的特殊属性或状态。 7. **IoCompletionRoutine**：完成例程的地址，用于在I/O操作完成后执行额外的处理。 ### IRP的工作流程 1. **创建IRP**：当用户模式的应用程序发起I/O请求时，系统会创建一个IRP，并填充相关参数。 2. **传递IRP**：IRP通过调用IoCallDriver函数逐级传递给驱动程序链。每个驱动程序处理其部分任务，然后将IRP传递给下一级驱动。 3. **处理IRP**：驱动程序根据IRP中的MajorFunction字段执行相应的操作，如读取、写入等。 4. **完成IRP**：当所有驱动程序都完成了IRP的处理，最后的驱动程序会设置IoStatus字段并调用IoCompleteRequest来通知系统I/O操作已完成。 5. **回调**：如果IRP中指定了完成例程，那么在完成I/O操作后，该例程会被调用。 ### IRP的多层调度在Windows内核中，IRP的处理涉及了多个层次的调度，包括系统调度、设备驱动调度以及中断处理。这种多层次的设计允许系统灵活地处理复杂的I/O请求，同时确保了驱动程序的模块化和可扩展性。 ### IRP的同步和异步 IRP可以是同步的，意味着发起I/O操作的线程会阻塞，直到IRP被完全处理。也可以是异步的，此时线程不会等待，而是立即返回，IRP的完成由系统通知。 ### IRP的扩展性 IRP允许驱动程序添加自定义信息，通过增加IrpStackSize和扩展区域，以适应特定的硬件或驱动需求。 ### 中文资源虽然提供的文件是英文原版，但网上可以找到中文翻译版的IRP手册，这对于中文读者来说是非常有价值的资源。通过阅读这些资料，可以更深入地理解IRP的细节及其在实际编程中的应用。 IRP是Windows操作系统中处理I/O请求的核心机制，理解和掌握IRP的使用对于开发驱动程序或进行系统级编程至关重要。通过深入学习，开发者能够更好地理解系统如何管理设备通信，从而优化应用程序的性能和稳定性。

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Handling IRPs: What Every Driver

Writer Needs to Know

July 31, 2006

Abstract

This paper presents an overview of the I/O request packet (IRP) mechanism that is

used in the Microsoft® Windows® family of operating systems. It is intended to

provide driver writers with a greater understanding of how I/O works in the operating

system and how their drivers should manage and respond to I/O requests.

This information applies for the following operating systems:

Microsoft Windows Vista™

Microsoft Windows Server® 2003

Microsoft Windows XP

Microsoft Windows 2000

The current version of this paper is maintained at:

http://www.microsoft.com/whdc/driver/kernel/IRPs.mspx

Contents

Introduction.................................................................................................................................................3

Definition 1: IRP as a Container for an I/O Request...................................................................................3

Contents of the IRP Header..................................................................................................................4

IRP Parameters ....................................................................................................................................4

Definition 2: IRP as a Thread-Independent Call Stack...............................................................................5

Passing an IRP to the Next Lower Driver...................................................................................................5

Completing an IRP .....................................................................................................................................6

Synchronous I/O Responses......................................................................................................................7

Asynchronous I/O Responses....................................................................................................................8

IoCompletion Routines and Asynchronous I/O Responses ..................................................................9

Summary of Guidelines for Pending IRPs ..........................................................................................12

Optimizations ......................................................................................................................................13

Life Cycle of a File Object ........................................................................................................................13

IRP_MJ_CREATE Requests ..............................................................................................................13

IRP_MJ_CLEANUP Requests ............................................................................................................14

IRP_MJ_CLOSE Requests.................................................................................................................14

Data Transfer Mechanisms ......................................................................................................................15

Buffered I/O.........................................................................................................................................15

Direct I/O.............................................................................................................................................15

Neither Buffered nor Direct I/O ...........................................................................................................15

I/O Control Codes (IOCTLs).....................................................................................................................16

METHOD_BUFFERED IOCTLs..........................................................................................................16

METHOD_OUT_DIRECT IOCTLs ......................................................................................................17

METHOD_IN_DIRECT IOCTLs ..........................................................................................................17

METHOD_NEITHER IOCTLs .............................................................................................................17

Success, Error, and Warning Status for IRP Completion.........................................................................18

Building IRPs............................................................................................................................................19

Threaded IRPs....................................................................................................................................19

Nonthreaded IRPs ..............................................................................................................................19

IRP Cancellation .................................................................................................................................20

Debugging I/O Problems ..........................................................................................................................20

Call to Action and Resources ...................................................................................................................20

Handling IRPs: What Every Driver Writer Needs to Know - 2

The information contained in this document represents the current view of Microsoft Corporation on the

issues discussed as of the date of publication. Because Microsoft must respond to changing market

conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot

guarantee the accuracy of any information presented after the date of publication.

This White Paper is for informational purposes only. MICROSOFT MAKES NO WARRANTIES,

EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS DOCUMENT.

Complying with all applicable copyright laws is the responsibility of the user. Without limiting the rights

under copyright, no part of this document may be reproduced, stored in or introduced into a retrieval

system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording, or

otherwise), or for any purpose, without the express written permission of Microsoft Corporation.

Microsoft may have patents, patent applications, trademarks, copyrights, or other intellectual property

rights covering subject matter in this document. Except as expressly provided in any written license

agreement from Microsoft, the furnishing of this document does not give you any license to these

patents, trademarks, copyrights, or other intellectual property.

Unless otherwise noted, the example companies, organizations, products, domain names, e-mail

addresses, logos, people, places and events depicted herein are fictitious, and no association with any

real company, organization, product, domain name, email address, logo, person, place or event is

intended or should be inferred.

Microsoft, Windows, Windows Server, Windows Vista are either registered trademarks or trademarks of

Microsoft Corporation in the United States and/or other countries.

The names of actual companies and products mentioned herein may be the trademarks of their

respective owners.

Handling IRPs: What Every Driver Writer Needs to Know - 3

Introduction

The Microsoft® Windows® family of operating systems communicates with drivers

by sending I/O request packets (IRPs). The data structure that encapsulates the

IRP not only describes an I/O request but also maintains information about the

status of the request as it passes through the drivers that handle it. Because the

data structure serves two purposes, an IRP can be defined as:

� a container for an I/O request

– or –

� a thread-independent call stack

Considering IRPs from these two perspectives may help driver writers understand

what their drivers must do to respond correctly to I/O requests.

For current documentation on routines and issues discussed in this paper, see the

most recent version of the Microsoft Windows Driver Kit (WDK).

Definition 1: IRP as a Container for an I/O Request

The operating system presents most I/O requests to drivers using IRPs. IRPs are

appropriate for this purpose because:

� IRPs can be processed asynchronously.

� IRPs can be cancelled.

� IRPs are designed for I/O that involves more than one driver.

The IRP data structure packages the information that a driver requires to respond to

an I/O request. The request might be from user mode or from kernel mode;

regardless of the request’s origin, a driver requires the same information.

Every IRP has two parts, shown in Figure 1:

� A header that describes the primary I/O request

� An array of parameters that describe subordinate requests (sometimes called

sub-requests)

Figure 1. Structure of an IRP

The size of the header is fixed and is the same for every IRP. The size of the array

of parameters depends on the number of drivers that will handle the request.

IRP Header

Parameters for sub-request

Handling IRPs: What Every Driver Writer Needs to Know - 4

Contents of the IRP Header

An IRP is usually handled by a stack of drivers. The header of each IRP contains

data that is used by each driver that handles the IRP. While a given driver is

handling an IRP, that driver is considered to be the current owner of the IRP.

The header of each IRP contains pointers to the following:

� Buffers to read the input and write the output of the IRP

� A memory area for the driver that currently owns the IRP

� A routine, supplied by the driver that currently owns the IRP, which the

operating system calls if the IRP is canceled

� The parameters for the current sub-request

In addition to the pointers, the IRP header contains other data that describes the

nature and state of the request.

IRP Parameters

Following the IRP header is an array of sub-requests. An IRP can have more than

one sub-request because IRPs are usually handled by a stack of drivers. Each IRP

is allocated with a fixed number of such sub-requests, usually one for each driver in

the device stack. This number typically matches the StackSize field of the top

device object in the stack, though a driver in the middle of a stack could allocate

fewer. If a driver must forward a request to a different device stack, it must allocate

a new IRP.

Each sub-request is represented as an I/O stack location (a structure of type

IO_STACK_LOCATION), and the IRP typically contains one such I/O stack location

for each driver in the device stack to which the IRP is sent. A field in the IRP header

identifies the I/O stack location that is currently in use. The value of this field is

called the IRP stack pointer or the current stack location.

The IO_STACK_LOCATION structure includes the following:

� The major and minor function codes for the IRP

� Arguments specific to these codes

� A pointer to the device object for the corresponding driver

� A pointer to an IoCompletion routine if the driver has set one

� A pointer to the file object associated with the request

� Various flags and context areas

The IO_STACK_LOCATION does not contain the pointers to the input and output

locations; these pointers are in the IRP itself. All the sub-requests operate on the

same buffers.

Handling IRPs: What Every Driver Writer Needs to Know - 5

Definition 2: IRP as a Thread-Independent Call

Stack

Performing an I/O operation typically requires more than one driver for a device.

Each driver for a device creates a device object, and these device objects are

organized hierarchically into a device stack. IRPs are passed down the device stack

from one driver to the next. For each driver in the stack, the IRP contains a pointer

to an I/O stack location. Because the drivers can handle the requests

asynchronously, an IRP is similar to a thread-independent call stack, as Figure 2

shows.

Figure 2. IRP as Thread-independent Call Stack

On the left side of Figure 2, the thread stack shows how the parameters and return

address for drivers A, B, and C might be organized into a call stack. On the right,

the figure shows how these parameters and return addresses correspond to the I/O

stack locations and IoCompletion routines in an IRP.

The asynchronous nature of IRP handling is critical to the operating system and the

Windows Driver Model (WDM). In a synchronous, single-threaded I/O design, the

application that issues a request and each driver through which the request passes

must wait until all lower components have completed the request. Such a design

uses system resources inefficiently, thus decreasing system performance.

The structure of the IRP provides for an inherently asynchronous design, enabling

applications to queue one or more I/O requests without waiting. While the I/O

request is in progress, the application thread is free to perform calculations or

queue additional I/O requests. Because all the information required to process the

request is encapsulated in the IRP, the requesting thread’s call stack can be

decoupled from the I/O request.

Passing an IRP to the Next Lower Driver

Passing an IRP to the next lower driver (also called forwarding an IRP) is the IRP

equivalent of a subroutine call. When a driver forwards an IRP, it must populate the

next I/O stack location with parameters, advance the IRP stack pointer, and invoke

the next driver’s dispatch routine. In essence, the driver is calling down the IRP

stack.

To pass an IRP, a driver typically takes the following steps:

1. Set up the parameters for the next I/O stack location. The driver can either:

� Call the IoGetNextIrpStackLocation routine to get a pointer to the next I/O

stack location, and then copy the required parameters to that location.

� Call the IoCopyCurrentIrpStackLocationToNext routine (if the driver sets

an IoCompletion routine in step 2), or the IoSkipCurrentIrpStackLocation

Parameter1 for A

IoCompletion routine for

initiator

Parameter2 for A

Parameter1 for B Parameter2 for B

Parameter1 for C Parameter2 for C

IoCompletion routine for A

IoCompletion routine for B

IRP Header

Thread Stack

Parameter1 for A

Parameter2 for A

Return address to initiator

…

Parameter1 for B

Parameter2 for B

Return address to A

…

Parameter1 for C

Parameter2 for C

Return address to B

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