Inside the Android OS Building, Customizing, Managing and Operating Android System Services Android Deep Dive Series

The Complete Guide to Customizing Android for New IoT and Embedded Devices

Inside the Android OS is a comprehensive guide and reference for technical professionals who want to customize and integrate Android into embedded devices, and construct or maintain successful Android-based products. Replete with code examples, it encourages you to create your own working code as you read---whether for personal insight or a professional project in the fast-growing marketplace for smart IoT devices.

Expert Android developers G. Blake Meike and Larry Schiefer respond to the real-world needs of embedded and IoT developers moving to Android. After presenting an accessible introduction to the Android environment, they guide you through boot, subsystem startup, hardware interfaces, and application support---offering essential knowledge without ever becoming obscure or overly specialized.

Reflecting Android's continuing evolution, Meike and Schiefer help you take advantage of relevant innovations, from the ART application runtime environment to Project Treble. Throughout, a book-length project covers all you need to start implementing your own custom Android devices, one step at a time.

You will:

• Assess advantages and tradeoffs using Android in smart IoT devices
• Master practical processes for customizing Android
• Set up a build platform, download the AOSP source, and build an Android image
• Explore Android's components, architecture, source code, and development tools
• Understand essential kernel modules that are unique to Android
• Use Android's extensive security infrastructure to protect devices and users
• Walk through Android boot, from power-on through system initialization
• Explore subsystem startup, and use Zygote containers to control application processes
• Interface with hardware through Android's Hardware Abstraction Layer (HAL)
• Provide access to Java programs via Java Native Interface (JNI)
• Gain new flexibility by using binderized HAL (Project Treble)
• Implement native C/C++ or Java client apps without bundling vendor libraries

Preface xiii

Chapter 1 Why Android? 1

Adopting Android 1

Full Stack 2

Broad Acceptance 2

Beautiful UI 2

Linux Based 2

Powerful Development Environment 3

Open Source 3

AOSP and Google 5

Other Choices 6

Micro-Controllers 6

Other RTOSs 7

Summary 8

Chapter 2 Booting Acme 9

Setting Up a Build Machine 10

Downloading the Code 11

Repo 11

Forking the Source 15

Android Version Selection 16

Local Mirror 17

Hosted Git Repositories 18

Tree Snapshot 19

Repository Commit Pinning 19

Example: Local Mirror of Forked Repositories 19

Building an Image 24

Device Tools 27

fastboot 28

adb 29

Flashing the Device 30

Summary 33

Chapter 3 Getting Started 35

Putting Android in Its Place 35

Hardware 36

The Linux Kernel 36

System Libraries 37

Applications 38

The Android Framework 39

The Android Service Model 40

Exploring the Source 43

Other Sources 44

What’s in the Box? 44

Summary 48

Chapter 4 The Kernel 49

The Linux Kernel 49

Kernel Process Management 50

Kernel Memory Management 51

The Android Kernel 53

Android Kernel Features 54

Building a Kernel 62

The Build System 63

Downloading the Source 63

Summary 66

Chapter 5 Platform Security 67

Types of Security 67

Verified Boot 68

Operational Security 69

Android Software Layers 70

The Process Sandbox 70

SE Linux for Android 72

SE Policy Definition 73

Android Permissions 76

File Systems 79

User Protections 82

Customizing Permissions 83

Sample Custom Permission-Protected App 83

Sample Custom Permission Client App 88

Summary 92

Chapter 6 System Startup: Installing and Booting the System 93

The Boot Process 93

Bootloader 95

Fastboot 99

Kernel 100

The File System 102

init 104

Recovery 106

Building a Daemon 107

Creating the Acme Device 107

Repo Again 110

Starting the Daemon 111

Summary 114

Chapter 7 Android Startup: Dalvik and Zygote 115

Dalvik 116

ART 120

ART Basics 120

Hybrid ART 122

Zygote 123

Zygote Memory Management 123

Zygote Startup 127

Runtime Initialization 128

System Service Startup 129

Summary 131

Citations 131

Chapter 8 Getting to Android: The HAL 133

Why a HAL? 133

Is a HAL Necessary? 135

Designing the HAL 136

Building a HAL 137

Code Structure 138

Implementing the HAL 140

Summary 151

Chapter 9 Getting to Java: The JNI 153

Code Structure 154

Using the Device 155

Using the HAL 157

Using the Java Native Interface 159

Executing Native Code 160

JNI: The Java Side 161

JNI: The Native Side 162

A Java Proximity Application 165

JNI: Some Hints 176

Summary 182

Chapter 10 Project Treble: Binderized HAL 183

HIDL Architecture 183

hwservicemanager 185

HIDL Services 185

HIDL Client Applications 186

Hardware Interface Definition Language (HIDL) 186

HIDL Types 191

HIDL Services 194

HIDL Clients 197

Summary 198

Chapter 11 Creating a Custom Binderized HAL 199

Acme Custom HIDL 199

Summary 217

Chapter 12 Clients for a Custom Binderized HAL 219

Native C++ Aproximity Client 219

SE Linux for Android Changes for aproximitycl 224

Build aproximitycl into Acme 225

Java/Kotlin Aproximity Client 226

SE Linux for Android Changes for AproximityClient 229

Build AproximityClient into Acme 229

Summary 231

Index 233

Blake Meike is a passionate engineer, code poet, and veteran of more than 10 years of Android development at organizations including D2, Realm, Twitter, and Cyanogen. As a teacher, he has trained hundreds of new Android developers. He is author of several books on Android development, including O’Reilly’s bestselling Programming Android and Addison-Wesley’s Android Concurrency. He holds a degree in Mathematics and Computer Science from Dartmouth College and lives in the Pacific Northwest.

Larry Schiefer is the CTO and co-founder of HIQES, LLC, a mobile platform and app engineering services company. He has made a career out of creating software solutions for mobile, embedded, and desktop systems. He started his career at Motorola working on large area telecommunications systems then moved to startups in the telecommunications, networking, and embedded spaces. Digging into Android’s internals was a natural progression with his background in telecommunications, embedded systems, and Linux kernel work. He has traveled around the world training engineers at Intel, Qualcomm, Bose, and others about the internal workings of Android. In addition to being an entrepreneur and technical leader, he continues to stay involved with the development of new software and platform solutions.