FreeBSD操作系统设计与实现(影印版)

.　　FreeBSD is widely used to support the core infrastructure of many companies worldwide. Because it can be built with a small footprint, it is also seeing increased use in embedded applications. The licensing terms of FreeBSD do not require the distribution of changes and enhancements to the system. The licensing terms of Linux require that all changes and enhancements to the kernel be made available in source form at minimal cost. Thus, companies that need to control the distribution of their intellectual property build their products using FreeBSD.
　　This book is of direct use to the professionals who work with FreeBSD systerns. Individuals involved in technical and sales support can learn the capabilities and limitations of the system; applications developers can learn how to effectively and efficiently interface to the system; system administrators without direct experience with the FreeBSD kernel can learn how to maintain, tune, and configure the system; and systems programmers can learn how to extend, enhance, and interface to the system.
　　Readers who will benefit from this book include operating-system implementors, system programmers, UNIX application developers, administrators, and curious users. The book can be read as a companion to the source code of the system, falling as it does between the manual pages and the code in detail of treatment. But this book is neither exclusively a UNIX programming manual nor a user tutorial (for a tutorial, see Libes & Ressler [1988]). Familiarity with the use of some version of the UNIX system (sec, for example, Stevens [1992]) and with the C programming language (see, for example, Kernighan & Ritchie [1989]) would be extremely useful.
　　Use in Courses on Operating Systems
　　This book is suitable for use as a reference text to provide background for a primary textbook in a first-level course on operating systems. It is not intended for use as an introductory operating-system textbook; the reader should have already encountered terminology such as memory management, process scheduling, and I/0 systems [Silberschatz et al., 2002]. Familiarity with the concepts of network protocols [Comer, 2000; Stallings, 2000; Tanenbaum, 2003] will be useful for understanding some of the later chapters.
　　This book can be used in combination with a copy of the FrecBSD system for more advanced operating systems courses. Students' assignments can include changes to, or replacements of, key system components such as the scheduler, the paging daemon, the filesystems, thread signalling, various networking layers, and I/O management. The ability to load, replace, and unload modules from a running kernel allows students to experiment without the need to compile and reboot the system. By working with a real operating system, students can directly measure and experience the effects of their changes. Because of the intense peer review and insistence on well-defined coding standards throughout its 25-year lifetime, the FreeBSD kernel is considerably cleaner, more modular, and thus easier to understand and modify than most software projects of its size and age.
　　Exercises are provided at the end of each chapter. The exercises are graded into three categories indicated by zero, one, or two asterisks. The answers to exercises that carry no asterisks can be found in the text. Exercises with a single asterisk require a step of reasoning or intuition beyond a concept presented in the text. Exercises with two asterisks present major design projects or open research questions. ..
　　Organization
　　This text discusses both philosophical and design issues, as well as details of the actual implementation. Often, the discussion starts at the system-call level and descends into the kernel. Tables and figures are used to clarify data structures and control flow. Pseudocode similar to the C language displays algorithms. Boldface font identifies program names and filesystem pathnames. Italics font introduces terms that appear in the glossary and identifies the names of system calls, variables, routines, and structure names. Routine names (other than system calls) are further identified by the name followed by a pair of parenthesis (e.g., mallocO is the name of a routine, whereas argv is the name of a variable).
　　The book is divided into five parts, organized as follows:
　　Part I, Overview Three introductory chapters provide the context for the complete operating system and for the rest of the book. Chapter 1, History and Goals, sketches the historical development of the system, emphasizing the system's research orientation. Chapter 2, Design Overview of FreeBSD, describes the services offered by the system and outlines the internal organization of the kernel. It also discusses the design decisions that were made as the system was developed. Sections 2.3 through 2.14 in Chapter 2 give an overview of their
　　corresponding chapter. Chapter 3, Kernel Services, explains how system calls are done and describes in detail several of the basic services of the kernel.
　　Part II, Processes The first chapter in this part---Chapter 4, Process Management--lays the foundation for later chapters by describing the structure of a process, the algorithms used for scheduling the execution of the threads that make up a process, and the synchronization mechanisms used by the system to ensure consistent access to kernel-resident data structures. In Chapter 5, Mereor), Management, the virtual-memory-management system is discussed in detail.
　　Part III, ldo System First, Chapter 6, I/0 System Overview, explains the system interface to FO and describes the structure of the facilities that support this interface. Following this introduction are four chapters that give the details of the main parts of the I/O system. Chapter 7, Devices, gives a description of the I/O architecture of the PC and describes how the I/O subsystem is managed and how the kernel initially maps out and later manages the arrival and departure of connected devices. Chapter 8, Local Filesystems, details the data structures and algorithms that implement filesystems as seen by application programs as well as how local filesystems are interfaced with the device interface described in Chapter 7. Chapter 9, The Network Filesystem, explains the network filesystern from both the server and client perspectives. Chapter 10, Terminal Handling, discusses support for character terminals and provides a description of the pseudo-terminal device driver.
　　Part IV, Intel'process Communication Chapter 11, lnterprocess Communication, describes the mechanism for providing communication between relatd or unrelated processes. Chapters 12 and 13, Network Communication and Network Protocols, are closely related because the facilities explained in the former are implemented by specific protocols, such as the TCP/IP protocol suite, explained in the latter.
　　Part V, System Operation Chapter 14, Startup and Shutdown, discusses system startup and shutdown and explains system initialization at the process level from kernel initialization to user login.
　　The book is intended to be read in the order that the chapters are presented, but the parts other than Part I are independent of one another and can be read separately. Chapter 14 should be read after all the others, but knowledgeable readers may find it useful independently.
　　At the end of the book are a Glossary with brief definitions of major terms and an Index. Each chapter contains a Reference section with citations of related material.
　　Getting BSD
　　All the BSD distributions are available either for downloading from the net or on removable media such as CD-ROM or DVD. Information on obtaining source and binaries for FreeBSD can be obtained from http://www. FreeBSD.org. The NetBSD distribution is compiled and ready to run on most workstation architectures. For
　　more information, contact the NetBSD Project at http://www. NetBSD.orgL The OpenBSD distribution is compiled and ready to mn on a wide variety of workstation architectures and has been extensively vetted for security and reliability. For more information, visit the OpenBSD project's Web site at http://www. OpenBSD.org/.
　　For you diehards who actually read to the end of the preface, your reward is finding out that you can get T-shirts that are a reproduction of the original artwork drawn by John Lasseter for the cover of this book (yes, he is the John Lasseter of Pixar fame who masterminded the production of Toy Story). For further information on purchasing a shirt, visit the "History of BSD T-shirts" Web page at http:/Iwww. McKusick.com/beasrle/. Other items available for sale on the site include a 32-hour introductory video course based on this book, a 40-hour advanced video course based on the FreeBSD 5.2 source code, a 2.5-hour video lecture on the history of BSD, and a 4-CD set containing all the releases and the source-control history of BSD from Berkeley. These items are described in the advertisements that follow the Index.
　　Acknowledgments
　　We extend special thanks to Nate Lawson, who provided invaluable insight on the workings of the PC architecture and FreeBSD's interface to it.
　　We also thank the following people who read and commented on nearly the entire book: Michael Schuster (Sun Microsystems, Inc.) and our Addison-Wesley reviewers Chris Cooper (Hewlett-Packard) and Robert Kitzberger (IBM).
　　We thank the following people, all of whom read and commented on early drafts of various chapters of the book: Samy Al Bahra (Kerneled.com), Dorr H. Clark (Santa Clara University), Matthew Dillon (The DragonFly BSD Project), John Dyson, Andreas Gustafsson, Poul-Henning Kamp (The FreeBSD Project), David G. Lawrence (The FreeBSD Project), Samuel Leffier, M. Warner Losh (Timing Solutions), Andre Oppermann (Intemet Business Solutions AG), David I. Parfitt (independent hacker), Doug Rabson (Qube Software Ltd.), Jeffrey Roberson (The FreeBSD Project), Soren Schmidt (FreeBSD senior developer), Ken Smith (University at Buffalo CSE Department), Gregory Sutter (Daemon News), Charles P. Wright (SUNY Stony Brook), and Erez Zadok (Stony Brook University).
　　We are grateful to our editor, Peter Gordon, who had faith in our ability to get the book written despite several years of delays on our part and who accelerated the production when we finally had a completed manuscript. We thank all the professional people at Addison-Wesley who helped us bring the book to completion: managing editor John Fuller, editorial assistant Bernie Gaffney, production supervisor Elizabeth Ryan, and cover designer Churl Prasertsith. We also thank the people at Stratford Publishing Services: manager of editorial services Kathy Glidden, copy editor Debbie Prato, and proofreader Hilary Farquhar. Finally we acknowledge the contributions of Jaap Akkerhuis, who designed the troff macros for the BSD books, and John Lasseter, who drew the original BSD daemon art used on the cover.
　　This book was produced using James Clark's implementations of pic, tbl, eqn, and groff. The index was generated by awk scripts derived from indexing programs written by Jori Bentley and Brian Kernighan [Bentley & Kernighan, 1986]. Most of the art was created with xfig. Figure placement and widow elimination were handled by the groff macros, but orphan elimination and production of even page bottoms had to be done by hand.
　　We encourage readers to send us suggested improvements or comments about typographical or other errors found in the book; please send electronic mail to FreeBSDbook-bugs @ McKusick. COM. ...