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The Definitive Guide to the Xen Hypervisor [NOOK Book]

Overview

“The Xen hypervisor has become an incredibly strategic resource for the industry, as the focal point of innovation in cross-platform virtualization technology. David’s book will play a key role in helping the Xen community and ecosystem to grow.”

Simon Crosby, CTO, XenSource

An Under-the-Hood Guide to the Power of Xen Hypervisor Internals

The Definitive Guide to the Xen Hypervisor is a comprehensive handbook on the inner workings of ...

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The Definitive Guide to the Xen Hypervisor

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Overview

“The Xen hypervisor has become an incredibly strategic resource for the industry, as the focal point of innovation in cross-platform virtualization technology. David’s book will play a key role in helping the Xen community and ecosystem to grow.”

Simon Crosby, CTO, XenSource

An Under-the-Hood Guide to the Power of Xen Hypervisor Internals

The Definitive Guide to the Xen Hypervisor is a comprehensive handbook on the inner workings of XenSource’s powerful open source paravirtualization solution. From architecture to kernel internals, author David Chisnall exposes key code components and shows you how the technology works, providing the essential information you need to fully harness and exploit the Xen hypervisor to develop cost-effective, highperformance Linux and Windows virtual environments.

Granted exclusive access to the XenSource team, Chisnall lays down a solid framework with overviews of virtualization and the design philosophy behind the Xen hypervisor. Next, Chisnall takes you on an in-depth exploration of the hypervisor’s architecture, interfaces, device support, management tools, and internals—including key information for developers who want to optimize applications for virtual environments. He reveals the power and pitfalls of Xen in real-world examples and includes hands-on exercises, so you gain valuable experience as you learn.

This insightful resource gives you a detailed picture of how all the pieces of the Xen hypervisor fit and work together, setting you on the path to building and implementing a streamlined, cost-efficient virtual enterprise.

Coverage includes

· Understanding the Xen virtual architecture

· Using shared info pages, grant tables, and the memory management subsystem

· Interpreting Xen’s abstract device interfaces

· Configuring and managing device support, including event channels, monitoring with XenStore, supporting core devices, and adding new device types

· Navigating the inner workings of the Xen API and userspace tools

· Coordinating virtual machines with the Scheduler Interface and API, and adding a new scheduler

· Securing near-native speed on guest machines using HVM

· Planning for future needs, including porting, power management, new devices, and unusual architectures

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Product Details

  • ISBN-13: 9780132703024
  • Publisher: Pearson Education
  • Publication date: 11/23/2007
  • Sold by: Barnes & Noble
  • Format: eBook
  • Edition number: 1
  • Pages: 320
  • File size: 2 MB

Meet the Author

David Chisnall is a regular columnist for InformIT and is nearing completion of a Ph.D. in computer science from the University of Wales. He cofounded and actively contributes to the open source Étoilé desktop environment, participated in a Knowledge Transfer Project, and has jumped enthusiastically into numerous other in-the trenches tech adventures.

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Read an Excerpt

This book aims to serve as a guide to the Xen hypervisor. The interface to paravirtualized guests is described in detail, along with some description of the internals of the hypervisor itself.

Any book about an open source project will, by nature, be less detailed than the code of the project that it attempts to describe. Anyone wishing to fully understand the Xen hypervisor will find no better source of authoritative information than the code itself. This book aims to provide a guided tour, indicating features of interest to help visitors find their way around the code. As with many travel books, it is to be hoped that readers will find it an informative read whether or not they visit the code.

Much of the focus of this book is on the kernel interfaces provided by Xen. Anyone wishing to write code that runs on the Xen hypervisor will find this material relevant, including userspace program developers wanting to take advantage of hypervisor-specific features. Overview and Organization

This book is divided into three parts. The first two describe the hypervisor interfaces, while the last looks inside Xen itself.

Part I begins with a description of the history and current state of virtualization, including the conditions that caused Xen to be created, and an overview of the design decisions made by the developers of the hypervisor. The remainder of this part describes the core components of the virtual environment, which must be supported by any non-trivial guest kernel.

The second part focuses on device support for paravirtualized and paravirtualization-aware kernels. Xen provides an abstract interface to devices, built on some core communication systemsprovided by the hypervisor. Virtual equivalents of interrupts and DMA and the mechanism used for device discovery are all described in Part II, along with the interfaces used by specific device categories.

Part III takes a look at how the management tools interact with the hypervisor. It looks inside Xen to see how it handles scheduling of virtual machines, and how it uses CPU-specific features to support unmodified guests.

An appendix provides a quick reference for people wishing to port operating systems to run atop Xen. Book Conventions

This book uses a number of different typefaces and other visual hints to describe different types of material.

Longer listings have line numbers down the left, and a gray background. In all listings, bold is used to indicate keywords, and italicized text represents strings and comments.

Listings that are taken from external files will retain the line numbers of the original file, allowing the referenced section to be found easily by the reader. The captions contain the original source in square brackets. Those beginning with example/ are from the example sources. All others, unless otherwise specified, are from the Xen sources.

Comments from files in the Xen source code have been preserved, complete with errors. Since the Xen source code predominantly uses U.K. English for comments, and variable and function names, this convention has been preserved in examples from this book.

During the course of this book, a simple example kernel is constructed. The source code for this can be downloaded from: http://www.prenhallprofessional.com/title/9780132349710.Use as a Text

In addition to the traditional uses for hypervisors, Xen makes an excellent teaching tool. Early versions of Xen only supported paravirtualized guests, and newer ones continue to support these in addition to unmodified guests. The architecture exposed by the hypervisor to paravirtualized guests is very similar to x86, but differs in a number of ways. Driver support is considerably easier, with a single abstract device being exposed for each device category, for example. In spite of this, a number of things are very similar. A guest operating system must handle interrupts (or their virtual equivalent), manage page tables, schedule running tasks, etc.

This makes Xen an excellent platform for development of new operating systems. Unlike a number of simple emulated systems, a guest running atop Xen can achieve performance within 10% that of the native host. The simple device interfaces make it easy for Xen guests to support devices, without having to worry about the multitude of peripherals available for real machines.

The similarity to real hardware makes Xen an ideal platform for teaching operating systems concepts. Writing a simple kernel that runs atop Xen is a significantly easier task than writing one that runs on real hardware, and significantly more rewarding than writing one that runs in a simplified machine emulator.

An operating systems course should use this text in addition to a text on general operating systems principles to provide the platform-specific knowledge required for students to implement their own kernels.

Xen is also a good example of a successful, modern, microkernel (although it does more in kernelspace than many microkernels), making it a good example for contrasting with popular monolithic systems.

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Table of Contents

>List of Figures xi

List of Tables xiii

Foreword xv

Preface xvii

Part I: The Xen Virtual Machine 1

Chapter 1: The State of Virtualization 3

1.1 What Is Virtualization? 3

1.2 Why Virtualize? 7

1.3 The First Virtual Machine 8

1.4 The Problem of x86 9

1.5 Some Solutions 9

1.6 The Xen Philosophy 15

1.7 The Xen Architecture 16

Chapter 2: Exploring the Xen Virtual Architecture 27

2.1 Booting as a Paravirtualized Guest 27

2.2 Restricting Operations with Privilege Rings 28

2.3 Replacing Privileged Instructions with Hypercalls 30

2.4 Exploring the Xen Event Model 33

2.5 Communicating with Shared Memory 34

2.6 Split Device Driver Model 35

2.7 The VM Lifecycle 37

2.8 Exercise: The Simplest Xen Kernel 38

Chapter 3: Understanding Shared Info Pages 47

3.1 Retrieving Boot Time Info 47

3.2 The Shared Info Page 51

3.3 Time Keeping in Xen 53

3.4 Exercise: Implementing gettimeofday() 54

Chapter 4: Using Grant Tables 59

4.1 Sharing Memory 59

4.2 Device I/O Rings 65

4.3 Granting and Revoking Permissions 66

4.4 Exercise: Mapping a Granted Page 69

4.5 Exercise: Sharing Memory between VMs 71

Chapter 5: Understanding Xen Memory Management 75

5.1 Managing Memory with x86 75

5.2 Pseudo-Physical Memory Model 78

5.3 Segmenting on 32-bit x86 80

5.4 Using Xen Memory Assists 82

5.5 Controlling Memory Usage with the Balloon Driver 84

5.6 Other Memory Operations 86

5.7 Updating the Page Tables 89

5.8 Exercise: Mapping the Shared Info Page 95

Part II: Device I/O 97

Chapter 6: Understanding Device Drivers 99

6.1 The Split Driver Model 100

6.2 Moving Drivers out of Domain 0 102

6.3 Understanding Shared Memory Ring Buffers 103

6.4 Connecting Devices with XenBus 109

6.5 Handling Notifications from Events 111

6.6 Configuring via the XenStore 112

6.7 Exercise: The Console Device 112

Chapter 7: Using Event Channels 119

7.1 Events and Interrupts 119

7.2 Handling Traps 120

7.3 Event Types 123

7.4 Requesting Events 124

7.5 Binding an Event Channel to a VCPU 127

7.6 Operations on Bound Channels 128

7.7 Getting a Channel’s Status 129

7.8 Masking Events 130

7.9 Events and Scheduling 132

7.10 Exercise: A Full Console Driver 133

Chapter 8: Looking through the XenStore 141

8.1 The XenStore Interface 141

8.2 Navigating the XenStore 142

8.3 The XenStore Device 145

8.4 Reading and Writing a Key 147

8.5 Other Operations 158

Chapter 9: Supporting the Core Devices 161

9.1 The Virtual Block Device Driver 161

9.2 Using Xen Networking 169

Chapter 10: Other Xen Devices 177

10.1 CD Support 177

10.2 Virtual Frame Buffer 178

10.3 The TPM Driver 183

10.4 Native Hardware 184

10.5 Adding a New Device Type 187

Part III: Xen Internals 195

Chapter 11: The Xen API 197

11.1 XML-RPC 198

11.2 Exploring the Xen Interface Hierarchy 200

11.3 The Xen API Classes 201

11.4 The Function of Xend 206

11.5 Xm Command Line 208

11.6 Xen CIM Providers 209

11.7 Exercise: Enumerating Running VMs 210

11.8 Summary 215

Chapter 12: Virtual Machine Scheduling 217

12.1 Overview of the Scheduler Interface 218

12.2 Historical Schedulers 219

12.3 Using the Scheduler API 224

12.4 Exercise: Adding a New Scheduler 229

12.5 Summary 233

Chapter 13: HVM Support 235

13.1 Running Unmodified Operating Systems 235

13.2 Intel VT-x and AMD SVM 237

13.3 HVM Device Support 239

13.4 Hybrid Virtualization 240

13.5 Emulated BIOS 244

13.6 Device Models and Legacy I/O Emulation 245

13.7 Paravirtualized I/O 246

13.8 HVM Support in Xen 248

Chapter 14: Future Directions 253

14.1 Real to Virtual, and Back Again 253

14.2 Emulation and Virtualization 254

14.3 Porting Efforts 255

14.4 The Desktop 257

14.5 Power Management 259

14.6 The Domain 0 Question 261

14.7 Stub Domains 263

14.8 New Devices 264

14.9 Unusual Architectures 265

14.10 The Big Picture 267

Part IV: Appendix 271

Appendix: PV Guest Porting Cheat Sheet 273

A.1 Domain Builder 273

A.2 Boot Environment 274

A.3 Setting Up the Virtual IDT 274

A.4 Page Table Management 275

A.5 Drivers 276

A.6 Domain 0 Responsibilities 276

A.7 Efficiency 277

A.8 Summary 278

Index 279

Read More Show Less

Preface

This book aims to serve as a guide to the Xen hypervisor. The interface to paravirtualized guests is described in detail, along with some description of the internals of the hypervisor itself.

Any book about an open source project will, by nature, be less detailed than the code of the project that it attempts to describe. Anyone wishing to fully understand the Xen hypervisor will find no better source of authoritative information than the code itself. This book aims to provide a guided tour, indicating features of interest to help visitors find their way around the code. As with many travel books, it is to be hoped that readers will find it an informative read whether or not they visit the code.

Much of the focus of this book is on the kernel interfaces provided by Xen. Anyone wishing to write code that runs on the Xen hypervisor will find this material relevant, including userspace program developers wanting to take advantage of hypervisor-specific features.

Overview and Organization

This book is divided into three parts. The first two describe the hypervisor interfaces, while the last looks inside Xen itself.

Part I begins with a description of the history and current state of virtualization, including the conditions that caused Xen to be created, and an overview of the design decisions made by the developers of the hypervisor. The remainder of this part describes the core components of the virtual environment, which must be supported by any non-trivial guest kernel.

The second part focuses on device support for paravirtualized and paravirtualization-aware kernels. Xen provides an abstract interface to devices, built on some core communication systems provided by the hypervisor. Virtual equivalents of interrupts and DMA and the mechanism used for device discovery are all described in Part II, along with the interfaces used by specific device categories.

Part III takes a look at how the management tools interact with the hypervisor. It looks inside Xen to see how it handles scheduling of virtual machines, and how it uses CPU-specific features to support unmodified guests.

An appendix provides a quick reference for people wishing to port operating systems to run atop Xen.

Book Conventions

This book uses a number of different typefaces and other visual hints to describe different types of material.

Longer listings have line numbers down the left, and a gray background. In all listings, bold is used to indicate keywords, and italicized text represents strings and comments.

Listings that are taken from external files will retain the line numbers of the original file, allowing the referenced section to be found easily by the reader. The captions contain the original source in square brackets. Those beginning with example/ are from the example sources. All others, unless otherwise specified, are from the Xen sources.

Comments from files in the Xen source code have been preserved, complete with errors. Since the Xen source code predominantly uses U.K. English for comments, and variable and function names, this convention has been preserved in examples from this book.

During the course of this book, a simple example kernel is constructed. The source code for this can be downloaded from: http://www.prenhallprofessional.com/title/9780132349710.

Use as a Text

In addition to the traditional uses for hypervisors, Xen makes an excellent teaching tool. Early versions of Xen only supported paravirtualized guests, and newer ones continue to support these in addition to unmodified guests. The architecture exposed by the hypervisor to paravirtualized guests is very similar to x86, but differs in a number of ways. Driver support is considerably easier, with a single abstract device being exposed for each device category, for example. In spite of this, a number of things are very similar. A guest operating system must handle interrupts (or their virtual equivalent), manage page tables, schedule running tasks, etc.

This makes Xen an excellent platform for development of new operating systems. Unlike a number of simple emulated systems, a guest running atop Xen can achieve performance within 10% that of the native host. The simple device interfaces make it easy for Xen guests to support devices, without having to worry about the multitude of peripherals available for real machines.

The similarity to real hardware makes Xen an ideal platform for teaching operating systems concepts. Writing a simple kernel that runs atop Xen is a significantly easier task than writing one that runs on real hardware, and significantly more rewarding than writing one that runs in a simplified machine emulator.

An operating systems course should use this text in addition to a text on general operating systems principles to provide the platform-specific knowledge required for students to implement their own kernels.

Xen is also a good example of a successful, modern, microkernel (although it does more in kernelspace than many microkernels), making it a good example for contrasting with popular monolithic systems.

Read More Show Less

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