About This Book

This book discusses advanced topics related to writing device drivers for computer systems running the Digital UNIX® operating system. These advanced topics are beyond the scope of the core tutorial.

Audience

This book is intended for systems engineers who:

Use standard library interfaces to develop programs in the C language
Know the Bourne or some other shell based on the UNIX operating system
Understand basic Digital UNIX concepts such as kernel, shell, process, configuration, and autoconfiguration
Understand how to use the Digital UNIX programming tools, compilers, and debuggers
Develop programs in an environment that involves dynamic memory allocation, linked list data structures, and multitasking
Understand the hardware device for which the driver is being written
Understand the basics of the CPU hardware architecture, including interrupts, direct memory access (DMA) operations, and I/O

This book assumes that you have a strong background in operating systems based on the UNIX operating system. It also assumes that you have a strong background in systems and C programming, and that you are familiar with topics presented in Writing Device Drivers: Tutorial. In addition, the book assumes that you have no source code licenses.

New and Changed Features

The following sections summarize the changes and additions made to this version of the book.

Changes to Chapter 5: Using Funnels

This chapter is rewritten to reflect the replacement of the bdevsw and cdevsw structures with the dsent structure and the replacement of the bdevsw_add, cdevsw_add, and dualdevsw_add interfaces with the devsw_add interface.

Changes to Chapter 7: Using Kernel Threads-Related Interfaces

This chapter contains a new section, ``Terminating a Kernel Thread,'' that discusses how to terminate a kernel thread. Terminating a kernel thread involves the use of the current_thread, thread_halt_self, and thread_terminate interfaces.

Chapter 8: Writing a Disk Device Driver

This new chapter describes how to write a disk device driver for Digital UNIX.

Appendix B: Example Disk Device Driver

This new appendix provides a sample disk device driver.

Scope of the Book

This book is for users of the Digital UNIX operating system on computer systems developed by Digital Equipment Corporation.
The book builds on the concepts and topics presented in Writing Device Drivers: Tutorial, the core book for developing device drivers on Digital UNIX.

The book introduces driver writers to topics that are beyond the scope of the core tutorial; it does not emphasize any specific types of device drivers. The book presents examples that show how to use the interfaces associated with symmetric multiprocessing and kernel threads.

The book assumes that you have written at least one Digital UNIX device driver, adhering to the guidelines and using the interfaces described in Writing Device Drivers: Tutorial and Writing Device Drivers: Reference.

Organization

The book contains the following chapters and appendixes.

Part 1 Overview

Part 1 contains one chapter, whose goal is to provide you with a review of general device driver concepts.

Chapter 1 Review of Device Driver Concepts

Reviews general device driver concepts, which are discussed in detail in Writing Device Drivers: Tutorial.

Part 2 Device Drivers and Symmetric Multiprocessing

Part 2 contains four chapters, whose combined goal is to provide the information necessary to write device drivers that can operate in a symmetric multiprocessing (SMP) environment.

Chapter 2 Overview of the Symmetric Multiprocessing Environment

Provides an overview of the symmetric multiprocessing (SMP) environment, including guidelines on which items a device driver must lock. The chapter also compares simple locks, complex locks, and funnels, which are the methods available in Digital UNIX for writing SMP-safe device drivers. Read this chapter to gain an understanding of the differences between the methods and to choose the method most appropriate for your device drivers.

Chapter 3 Using Simple Lock Interfaces

Describes how to use the simple lock interfaces to make device drivers safe in an SMP environment. Read this chapter to learn how to use the simple lock interfaces.

Chapter 4 Using Complex Lock Interfaces

Describes how to use the complex lock interfaces to make device drivers safe in an SMP environment. Read this chapter to learn how to use the complex lock interfaces.

Chapter 5 Using Funnels

Describes how to initialize the dsent table to implement SMP-safe device drivers. Read this chapter to learn how to use the funnel mechanism to implement SMP-safe device drivers.

Part 3 Device Drivers and Kernel Threads

Part 3 contains two chapters, whose combined goal is to provide the information necessary to use kernel threads in device drivers.

Chapter 6 Device Drivers and Multithreaded Programming

Provides an introduction to multithreaded programming in device drivers. Read this chapter to gain an understanding of kernel threads as they relate to device drivers.

Chapter 7 Using Kernel Threads-Related Interfaces

Describes how to use the kernel threads-related interfaces. Read this chapter to learn how to use the kernel threads interfaces to implement kernel threads in device drivers.

Part 5 Appendixes

Part 5 contains two appendixes and a glossary.

Appendix A Summary Tables

Presents tables that summarize the header files, kernel interfaces, data structures, and other interfaces that device drivers use.

Appendix B Example Disk Device Driver

Presents the source listing for a sample disk device driver called /dev/xxx_disk.

Glossary Glossary

Provides definitions of terms used in the book.

Related Documentation

The printed version of the Digital UNIX documentation set is color coded to help specific audiences quickly find the books that meet their needs. (You can order the printed documentation from Digital.) This color coding is reinforced with the use of an icon on the spines of books. The following list describes this convention:

Audience Icon Color Code

General users G Blue

System and network administrators S Red

Programmers P Purple

Device driver writers D Orange

Reference page users R Green

Some books in the documentation set help meet the needs of several audiences. For example, the information in some system books is also used by programmers. Keep this in mind when searching for information on specific topics.

The Documentation Overview, Glossary, and Master Index provides information on all of the books in the Digital UNIX documentation set.

Writing device drivers is a complex task; driver writers require knowledge in a variety of areas. One way to acquire this knowledge is to have at least the following categories of documentation available:

Hardware documentation
Bus-specific device driver documentation
Operating system overview documentation
Programming tools documentation
Network programming documentation
System management documentation
Porting documentation
Kernel kits product documentation
Reference pages

The following sections list the documentation associated with each of these categories.

Hardware Documentation

You should have available the hardware manual associated with the device for which you are writing the device driver. You should also have access to the manual that describes the architecture associated with the CPU that the driver operates on, for example, the Alpha Architecture Reference Manual.

Bus-Specific Device Driver Documentation

Writing Device Drivers: Tutorial is the core book for developing device drivers on the Digital UNIX operating system. It contains information needed for developing drivers on any bus that operates on Digital platforms.

Writing Device Drivers: Reference is a companion volume to the tutorial and describes, in reference-page style, the header files, kernel interfaces, data structures, and other interfaces that device drivers use.

Writing Device Drivers: Advanced Topics provides information on topics that are beyond the scope of the core tutorial. Systems engineers can find information on such advanced topics as kernel threads and writing device drivers in a symmetric multiprocessing (SMP) environment.

The following books provide information about writing device drivers for a specific bus that is beyond the scope of the core tutorial and reference:

Writing EISA and ISA Bus Device Drivers
This manual provides information for systems engineers who write device drivers for the EISA/ISA bus. The manual describes EISA/ISA bus-specific topics, including EISA/ISA bus architecture and data structures that EISA/ISA bus device drivers use.
Writing PCI Bus Device Drivers
This manual provides information for systems engineers who write device drivers for the PCI bus. The manual describes PCI bus-specific topics, including PCI bus architecture and data structures that PCI bus device drivers use.
Writing Device Drivers for the SCSI/CAM Architecture Interfaces
This manual provides information for systems engineers who write device drivers for the SCSI/CAM Architecture interfaces.
The manual provides an overview of the Digital UNIX SCSI/CAM Architecture and describes User Agent routines, data structures, common and generic routines and macros, error handling and debugging routines.
The manual includes information on configuration and installation. Examples show how programmers can define SCSI/CAM device drivers and write to the SCSI/CAM special I/O interface supplied by Digital to process special SCSI I/O commands.
Writing TURBOchannel Device Drivers
This manual contains information systems engineers need to write device drivers that operate on the TURBOchannel bus. The manual describes TURBOchannel-specific topics, including TURBOchannel kernel interfaces that TURBOchannel device drivers use.
Writing VMEbus Device Drivers
This manual contains information systems engineers need to write device drivers that operate on the VMEbus. The manual describes VMEbus-specific topics, including VMEbus architecture and kernel interfaces that VMEbus device drivers use. A VMEbus device driver example illustrates the use of these kernel interfaces.

Operating System Overview Documentation

Refer to the Technical Overview for a technical introduction to the Digital UNIX operating system. This manual provides a technical overview of the Digital UNIX system, focusing on the networking subsystem, the file system, virtual memory, and the development environment. In addition, the manual lists all system limits.

This manual does not supersede the Software Product Description (SPD), which is the definitive description of the Digital UNIX system.

Programming Tools Documentation

To create your device drivers, you use a number of programming development tools and should have on hand the manuals that describe how to use these tools. The following manuals provide information related to programming tools used in the Digital UNIX operating system environment:

Kernel Debugging
This manual provides information about debugging kernels. The manual describes using the dbx, kdbx, and kdebug debuggers to find problems in kernel code. It also describes how to write a kdbx utility extension and how to create and analyze a crash dump file.
This manual is for system administrators responsible for modifying, rebuilding, and debugging the kernel configuration. It is also for system programmers who need to debug their kernel space programs.
Programming Support Tools
This manual describes several commands and utilities in the Digital UNIX system, including facilities for text manipulation, macro and program generation, and source file management.
The commands and utilities described in this manual are primarily for programmers, but some of them (such as grep, awk, sed, and the Source Code Control System (SCCS)) are useful for other users. This manual assumes that you are a moderately experienced user of UNIX systems.
Programmer's Guide
This manual describes the programming environment of the Digital UNIX operating system, with an emphasis on the C programming language.
This manual is for all programmers who use the Digital UNIX operating system to create or maintain programs in any supported language.

System Management Documentation

Refer to the System Administration manual for information about building a kernel and for general information on system administration. This manual describes how to configure, use, and maintain the Digital UNIX operating system. It includes information on general day-to-day activities and tasks, changing your system configuration, and locating and eliminating sources of trouble.

This manual is for the system administrators responsible for managing the operating system. It assumes a knowledge of operating system concepts, commands, and configurations.

Porting Documentation

Refer to the Digital UNIX Migration Guide for a discussion of the differences between the Digital UNIX and ULTRIX operating systems. This manual compares the Digital UNIX operating system to the ULTRIX operating system by describing the differences between the two systems.

This manual has three audiences, as follows:

General users can read this manual to determine the differences between using an ULTRIX system and using the Digital UNIX system.
System and network administrators can read this manual to determine the differences between ULTRIX and Digital UNIX system administration.
Programmers can read this manual to determine the differences between the ULTRIX programming environment and the Digital UNIX programming environment.

This manual assumes you are familiar with the ULTRIX operating system.

Reference Pages

The following reference pages are of interest to device driver writers:

Reference Pages Section 2
This section defines system calls (entries into the Digital UNIX kernel) that programmers use. The introduction to Section 2, intro(2), lists error numbers with brief descriptions of their meanings. The introduction also defines many of the terms used in this section. This section is for programmers.
Reference Pages Section 3
This section describes the routines available in Digital UNIX programming libraries, including the C library, Motif library, and X library. This section is for programmers. In printed format, this section is divided into six volumes.
Reference Pages Section 4
Section 4 describes the format of system files and how the files are used. The files described include assembler and link editor output, system accounting, and file system formats. This section is for programmers and system administrators. In printed format, this section is divided into two volumes.
Reference Pages Section 5
Section 5 contains miscellaneous information, including ASCII character codes, mail-addressing formats, text-formatting macros, and a description of the root file system. This section is for programmers and system administrators.
Reference Pages Section 7
Section 7 describes special files, related device driver functions, databases, and network support. This section is for programmers and system administrators.
Reference Pages Section 8 and 1m
This section describes commands for system operation and maintenance. It is for system administrators. In printed format, this section is divided into two volumes.

Reader's Comments

Digital welcomes any comments and suggestions you have on this and other Digital UNIX manuals.

You can send your comments in the following ways:

Fax: 603-881-0120 Attn: UEG Publications, ZK03-3/Y32
Internet electronic mail: readers_comment@zk3.dec.com
A Reader's Comment form is located on your system in the following location:
```
/usr/doc/readers_comment.txt
```
Mail:
Digital Equipment Corporation
UEG Publications Manager
ZK03-3/Y32
110 Spit Brook Road
Nashua, NH 03062-9987
A Reader's Comment form is located in the back of each printed manual. The form is postage paid if you mail it in the United States.

Please include the following information along with your comments:

The full title of the book and the order number. (The order number is printed on the title page of this book and on its back cover.)
The section numbers and page numbers of the information on which you are commenting.
The version of Digital UNIX that you are using.
If known, the type of processor that is running the Digital UNIX software.

The Digital UNIX Publications group cannot respond to system problems or technical support inquiries. Please address technical questions to your local system vendor or to the appropriate Digital technical support office. Information provided with the software media explains how to send problem reports to Digital.

Conventions

The following conventions are used in this book:

.
.
.
A vertical ellipsis indicates that a portion of an example that would normally be present is not shown.

. . . In syntax definitions, a horizontal ellipsis indicates that the preceding item can be repeated one or more times.

filename In examples, syntax descriptions, and function definitions, this typeface indicates variable values.

buf In function definitions and syntax definitions used in driver configuration, this typeface is used to indicate names that you must type exactly as shown.

[ ] In formal parameter declarations in function definitions and in structure declarations, brackets indicate arrays. Brackets are also used to specify ranges for device minor numbers and device special files in stanza.loadable file fragments. However, for the syntax definitions used in driver configuration, these brackets indicate items that are optional.

| Vertical bars separating items that appear in the syntax definitions used in driver configuration indicate that you choose one item from among those listed.

This book uses the word kernel ``interface'' instead of kernel ``routine'' or kernel ``macro.''

Chapter 1	Review of Device Driver Concepts
	Reviews general device driver concepts, which are discussed in detail in Writing Device Drivers: Tutorial.

Chapter 2	Overview of the Symmetric Multiprocessing Environment
	Provides an overview of the symmetric multiprocessing (SMP) environment, including guidelines on which items a device driver must lock. The chapter also compares simple locks, complex locks, and funnels, which are the methods available in Digital UNIX for writing SMP-safe device drivers. Read this chapter to gain an understanding of the differences between the methods and to choose the method most appropriate for your device drivers.
Chapter 3	Using Simple Lock Interfaces
	Describes how to use the simple lock interfaces to make device drivers safe in an SMP environment. Read this chapter to learn how to use the simple lock interfaces.
Chapter 4	Using Complex Lock Interfaces
	Describes how to use the complex lock interfaces to make device drivers safe in an SMP environment. Read this chapter to learn how to use the complex lock interfaces.
Chapter 5	Using Funnels
	Describes how to initialize the `dsent` table to implement SMP-safe device drivers. Read this chapter to learn how to use the funnel mechanism to implement SMP-safe device drivers.

Chapter 6	Device Drivers and Multithreaded Programming
	Provides an introduction to multithreaded programming in device drivers. Read this chapter to gain an understanding of kernel threads as they relate to device drivers.
Chapter 7	Using Kernel Threads-Related Interfaces
	Describes how to use the kernel threads-related interfaces. Read this chapter to learn how to use the kernel threads interfaces to implement kernel threads in device drivers.

Appendix A	Summary Tables
	Presents tables that summarize the header files, kernel interfaces, data structures, and other interfaces that device drivers use.
Appendix B	Example Disk Device Driver
	Presents the source listing for a sample disk device driver called `/dev/xxx_disk`.
Glossary	Glossary
	Provides definitions of terms used in the book.

Audience	Icon	Color Code
General users	G	Blue
System and network administrators	S	Red
Programmers	P	Purple
Device driver writers	D	Orange
Reference page users	R	Green

. . .	A vertical ellipsis indicates that a portion of an example that would normally be present is not shown.
. . .	In syntax definitions, a horizontal ellipsis indicates that the preceding item can be repeated one or more times.
`filename`	In examples, syntax descriptions, and function definitions, this typeface indicates variable values.
`buf`	In function definitions and syntax definitions used in driver configuration, this typeface is used to indicate names that you must type exactly as shown.
`[ ]`	In formal parameter declarations in function definitions and in structure declarations, brackets indicate arrays. Brackets are also used to specify ranges for device minor numbers and device special files in `stanza.loadable` file fragments. However, for the syntax definitions used in driver configuration, these brackets indicate items that are optional.
\|	Vertical bars separating items that appear in the syntax definitions used in driver configuration indicate that you choose one item from among those listed.