Linux appliance design: a hands-on guide to building Linux applications

388 Pages·2007·8.47 MB·English

by  Bob Smith

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Companion CD LLIINNUU XX AA PPPPLLII AA NNCCEE
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includes a prototype
appliance—a home BBUUIILLDDIINNGG LLIINNUUXX
alarm system—that supports DDEESSIIGGNN
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the book’s lessons.
CD
Inside
A H A N D S - O N G U I D E T O B U I L D I N G
L I N U X A P P L I A N C E S
Modern appliances are complex machines with Learn to:
processors, operating systems, and application software.
• Separate your user interfaces from your daemons
While there are books that will tell you how to run Linux LL BOB SMI T H, JOH N H A R DIN, G R A H A M PH IL L IP S, A ND BIL L PIE RCE
on embedded hardware, and books on how to build • Give user interfaces run time access to configuration, II
a Linux application, Linux Appliance Design is the first status, and statistics NN
book to demonstrate how to merge the two and create UU
• Add professional network management capabilities to
a Linux appliance. You’ll see for yourself why Linux is
your application XX
the embedded operating system of choice for low-cost

development and a fast time to market. • Use SNMP and build a MIB AA
Linux Appliance Design shows how to build better • Build a web-based appliance interface PP
appliances—appliances with more types of interfaces, PP
• Build a command line interface (CLI)
more dynamic interfaces, and better debugged inter- LL
faces. You’ll learn how to build backend daemons, • Build a framebuffer interface with an infrared control
II
handle asynchronous events, and connect various user as input AA
interfaces (including web, framebuffers, infrared control, • Manage logs and alarms on an appliance NN
SNMP, and front panels) to these processes for remote
CC
configuration and control. Linux Appliance Design ABOUT THE AUTHORS
also introduces the Run-Time Access library, which EE
Bob Smith, John Hardin, Graham Phillips, and Bill Pierce
provides a uniform mechanism for user interfaces to
have experience in embedded systems, commercial Linux DD
communicate with daemons.
and BSD appliances, network management systems, and EE
designing software solutions for business problems.
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This b o o k u“sIe sL RAeYpK FoLveArT—.”a durable binding that won’t snap shut. G SYSTEMS/LIN: ® ®
UX

LINUX APPLIANCE DESIGN

LINUX APPLIANCE
DESIGN
A Hands-On Guide to
Building Linux Appliances
by Bob Smith, John Hardin,
Graham Phillips, and Bill Pierce
®
San Francisco
lad_TITLE_COPY.fm Page iv Thursday, March 15, 2007 2:38 PM
LINUX APPLIANCE DESIGN. Copyright © 2007 by Bob Smith, John Hardin, Graham Phillips, and Bill Pierce.
All “Tux’s Workshop” illustrations © 2006 by Jon Colton.
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means, electronic or
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Printed on recycled paper in the United States of America
11 10 09 08 07 1 2 3 4 5 6 7 8 9
ISBN-10: 1-59327-140-9
ISBN-13: 978-1-59327-140-4
Publisher: William Pollock
Production Editor: Elizabeth Campbell
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Library of Congress Cataloging-in-Publication Data
Linux appliance design : a hands-on guide to building linux appliances / Bob Smith ... [et al.].
p. cm.
Includes index.
ISBN-13: 978-1-59327-140-4
ISBN-10: 1-59327-140-9
1. Linux. 2. Application software--Development. 3. Electric apparatus and appliances--Design and
construction. I. Smith, Robert W. (Robert William), 1952-
QA76.76.O63L545115 2007
005.3--dc22
2006020778
No Starch Press and the No Starch Press logo are registered trademarks of No Starch Press, Inc. Other product and
company names mentioned herein may be the trademarks of their respective owners. Rather than use a trademark
symbol with every occurrence of a trademarked name, we are using the names only in an editorial fashion and to the
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The information in this book is distributed on an “As Is” basis, without warranty. While every precaution has been
taken in the preparation of this work, neither the author nor No Starch Press, Inc. shall have any liability to any
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information contained in it.
B R I E F C O N T E N T S
Acknowledgments..........................................................................................................xv
Introduction.................................................................................................................xvii
Chapter 1: Appliance Architecture....................................................................................1
Chapter 2: Managing Daemons........................................................................................7
Chapter 3: Using Run-Time Access..................................................................................19
Chapter 4: Building and Securing Daemons.....................................................................43
Chapter 5: The Laddie Alarm System: A Sample Appliance................................................61
Chapter 6: Logging.......................................................................................................77
Chapter 7: Laddie Event Handling...................................................................................91
Chapter 8: Designing a Web Interface..........................................................................105
Chapter 9: Designing a Command Line Interface............................................................135
Chapter 10: Building a Front Panel Interface..................................................................147
Chapter 11: Designing a Framebuffer Interface...............................................................169
Chapter 12: Infrared Remote Control.............................................................................197
Chapter 13: Hands-on Introduction to SNMP..................................................................223
Chapter 14: Designing an SNMP MIB...........................................................................243
Chapter 15: Implementing Your SNMP MIB....................................................................261
Appendix A: RTA Reference.........................................................................................289
Appendix B: Review of SNMP......................................................................................309
Appendix C: Installing a Framebuffer Device Driver.........................................................325
Appendix D: A DB-to-File Utility.....................................................................................331
Appendix E: The Laddie Appliance Bootable CD............................................................337
Index.........................................................................................................................345
vi Brief Contents
C O N T E N T S I N D E T A I L
ACKNOWLEDGMENTS xv
INTRODUCTION xvii
What This Book Is About ........................................................................................xviii
What This Book Is Not About..................................................................................xviii
Who Should Read This Book ...................................................................................xix
Why Use Linux? .....................................................................................................xix
Availability of Source Code ........................................................................xix
Range of Hardware Supported ..................................................................xix
Availability of Linux Developers ..................................................................xix
Reliability ..................................................................................................xx
Quality Compilers ......................................................................................xx
Good Documentation .................................................................................xx
Existing Software Packages .........................................................................xx
Low Development Cost ................................................................................xx
No Licensing Fees for Deployment ................................................................xx
Security ....................................................................................................xxi
Linux Appliance Design...........................................................................................xxi
1
APPLIANCE ARCHITECTURE 1
UIs and Daemons .....................................................................................................2
Daemons....................................................................................................2
User Interfaces ............................................................................................3
Interprocess Communication .........................................................................4
The Architecture of the Laddie Appliance ....................................................................5
Summary .................................................................................................................5
2
MANAGING DAEMONS 7
Common Approaches to Managing Daemons..............................................................8
File-Based Management ...............................................................................8
A Daemon-Based Web Interface ...................................................................9
An All-in-One Approach .............................................................................10
Control and Status Protocols ....................................................................................11
Requirements for a Control and Status Protocol .............................................12
Common Control and Status Protocols .........................................................13
Summary ...............................................................................................................18
3
USING RUN-TIME ACCESS 19
RTA Appliance Architecture .....................................................................................19
RTA Daemon Architecture ........................................................................................20
Telling RTA About Your Columns and Tables..............................................................21
Columns...................................................................................................22
Tables ......................................................................................................24
Building Your First RTA Program ...............................................................................26
Defining the Problem .................................................................................26
Reviewing the Code ..................................................................................26
Installing RTA ............................................................................................31
Building and Linking ..................................................................................32
Testing .....................................................................................................32
A Little SQL ...........................................................................................................34
SELECT ....................................................................................................35
UPDATE ...................................................................................................35
WHERE....................................................................................................36
LIMIT .......................................................................................................36
Introduction to RTA’s Built-in Tables ...........................................................................37
rta_dbg ....................................................................................................37
rta_stat.....................................................................................................37
rta_tables .................................................................................................38
rta_columns ..............................................................................................38
The RTA Table Editor ..............................................................................................38
Summary ...............................................................................................................41
4
BUILDING AND SECURING DAEMONS 43
How to Build a Daemon ..........................................................................................44
Load the Daemon’s Configuration ...............................................................44
Go into the Background .............................................................................45
Become the Process and Session Leader .......................................................46
Set the Working Directory ..........................................................................47
Redirect stdin, stdout, and stderr .................................................................47
Set Up Logging .........................................................................................48
Set Group and User IDs .............................................................................49
Check for a pidfile ....................................................................................50
Set the umask ...........................................................................................52
Set Up Signal Handlers ..............................................................................52
How to Secure a Daemon .......................................................................................53
Designing a Secure Daemon ......................................................................54
Write a Secure Daemon.............................................................................55
Limit Damage in Case of a Breach ..............................................................57
A Prototype Daemon ..............................................................................................59
Summary ...............................................................................................................60
Further Reading .....................................................................................................60
5
THE LADDIE ALARM SYSTEM: A SAMPLE APPLIANCE 61
Introduction to Alarm Systems ..................................................................................62
Sensors ....................................................................................................62
Enabling a Zone .......................................................................................64
viii Contents in Detail