深入理解Linux内核工作原理

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《Linux内核详解》是一本专门为Linux爱好者编写的书籍，它深入探讨了Linux内核的工作原理和机制，而非纯粹的技术手册。作者David Rusling以其在Linux领域的专业知识，基于当时最新、稳定的Linux 2.4.0版本源码进行讲解，确保读者能够了解实际应用中的内核运作方式。这本书适合那些希望理解Linux核心结构和功能特性的读者，特别强调Linux作为一个动态目标，其内容反映了业界广泛采用的开源代码。作者大卫·拉斯林将复杂的内核知识以易于理解的方式呈现，让读者不仅知道“怎么做”，更能理解“为什么这样做”。值得注意的是，Linux内核是一个活跃的项目，本书会随着技术的发展而更新。书中包含了版权和分发声明，明确指出可以自由地在特定条件下复制和重新分发，但必须遵守相关规定。此外，书中还提到了法律声明，指出Linux是Linus Torvalds的商标，并且与Unix和Univention等公司没有关系。《Linux内核》一书的写作地点设在了英国沃金，它不仅提供了一门技术课程，也体现了开源社区的共享精神。通过阅读这本书，读者不仅能掌握Linux内核的基础知识，还能培养对操作系统底层运作的理解，有助于提升编程和系统管理能力。这是一本值得所有Linux专业人士和爱好者收藏的宝贵参考资料。

List of Figures

1.1 Atypical PC motherb oard. . . . . . . . . . . . . . . . . . . . . . . . . 2

3.1 Abstract model of Virtual to Physical address mapping . . . . . . . . 16

3.2 Alpha AXP Page Table Entry . . . . . . . . . . . . . . . . . . . . . . . 20

3.3 Three Level Page Tables . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.4 The

free area

data structure . . . . . . . . . . . . . . . . . . . . . . . 24

3.5 Areas of Virtual Memory . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.6 The Linux Page Cache . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.1 A Process's Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4.2 A Process's Virtual Memory . . . . . . . . . . . . . . . . . . . . . . . . 44

4.3 Registered Binary Formats . . . . . . . . . . . . . . . . . . . . . . . . 47

4.4 ELF Executable File Format . . . . . . . . . . . . . . . . . . . . . . . 48

5.1 Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

5.2 System V IPC Message Queues . . . . . . . . . . . . . . . . . . . . . . 56

5.3 System V IPC Semaphores . . . . . . . . . . . . . . . . . . . . . . . . 57

5.4 System V IPC Shared Memory . . . . . . . . . . . . . . . . . . . . . . 59

6.1 Example PCI Based System . . . . . . . . . . . . . . . . . . . . . . . . 62

6.2 The PCI Conguration Header . . . . . . . . . . . . . . . . . . . . . . 63

6.3 Type 0 PCI Conguration Cycle . . . . . . . . . . . . . . . . . . . . . 65

6.4 Type 1 PCI Conguration Cycle . . . . . . . . . . . . . . . . . . . . . 65

6.5 Linux Kernel PCI Data Structures . . . . . . . . . . . . . . . . . . . . 67

6.6 Conguring a PCI System: Part 1 . . . . . . . . . . . . . . . . . . . . 69

6.7 Conguring a PCI System: Part 2 . . . . . . . . . . . . . . . . . . . . 70

6.8 Conguring a PCI System: Part 3 . . . . . . . . . . . . . . . . . . . . 71

6.9 Conguring a PCI System: Part 4 . . . . . . . . . . . . . . . . . . . . 71

6.10 PCI Conguration Header: Base Address Registers . . . . . . . . . . . 72

7.1 A Logical Diagram of Interrupt Routing . . . . . . . . . . . . . . . . . 76

7.2 Linux Interrupt Handling Data Structures . . . . . . . . . . . . . . . . 78

8.1 Character Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Chapter 1

Hardware Basics

An op erating system has to work closely with the hardware system that

acts as its foundations. The op erating system needs certain services that

can only be provided by the hardware. In order to fully understand

the Linux op erating system, you need to understand the basics of the

underlying hardware. This chapter gives a brief introduction to that

hardware: the mo dern PC.

When the \Popular Electronics" magazine for January 1975 was printed with an

illustration of the Altair 8080 on its front cover, a revolution started. The Altair

8080, named after the destination of an early Star Trek episode, could b e assembled

by home electronics enthusiasts for a mere $397. With its Intel 8080 pro cessor and

256 bytes of memory but no screen or keyboard it was punybytoday's standards.

Its inventor, Ed Rob erts, coined the term \p ersonal computer" to describ e his new

invention, but the term PC is now used to refer to almost any computer that you

can pick up without needing help. By this denition, even some of the very p owerful

Alpha AXP systems are PCs.

Enthusiastic hackers saw the Altair's p otential and started to write software and

build hardware for it. To these early pioneers it represented freedom; the freedom

from huge batch processing mainframe systems run and guarded by an elite priest-

hood. Overnight fortunes were made by college drop outs fascinated by this new

phenomenon, a computer that you could have at home on your kitchen table. A lot

of hardware app eared, all dierent to some degree and software hackers were happy

to write software for these new machines. Paradoxically it was IBM who rmly cast

the mould of the modern PC by announcing the IBM PC in 1981 and shipping it to

customers early in 1982. With its Intel 8088 processor, 64K of memory (expandable

to 256K), two oppy disks and an 80 character by 25 lines Colour Graphics Adapter

(CGA) it was not very p owerful by to day's standards but it sold well. It was fol-

lowed, in 1983, by the IBM PC-XT which had the luxury of a 10Mbyte hard drive.

It was not long b efore IBM PC clones were being produced by a host of companies

such as Compaq and the architecture of the PC became a de-facto standard. This

de-facto standard helped a multitude of hardware companies to comp ete together in

a growing market which, happily for consumers, kept prices low. Many of the system

architectural features of these early PCs have carried over into the modern PC. For

example, even the most p owerful Intel Pentium Pro based system starts running in

the Intel 8086's addressing mo de. When Linus Torvalds started writing what was

to become Linux, he picked the most plentiful and reasonably priced hardware, an

These ones and zeros corresp ond to electrical switches b eing either on or o. Just

as 42 is a decimal numb er meaning \4 10s and 2 units", a binary number is a series

of binary digits each one representing a p ower of 2. In this context, a p ower means

the number of times that a numberismultiplied by itself. 10 to the p ower 1 ( 10

)

is 10, 10 to the power2(10

) is 10x10, 10

is 10x10x10 and so on. Binary 0001 is

decimal 1, binary 0010 is decimal 2, binary 0011 is 3, binary 0100 is 4 and so on. So,

42 decimal is 101010 binary or (2+8+32 or 2

). Rather than using binary

to representnumb ers in computer programs, another base, hexadecimal is usually

used. In this base, each digital representsapower of 16. As decimal numbers only

go from 0 to 9 the numbers 10 to 15 are represented as a single digit by the letters

A, B, C, D, E and F. For example, hexadecimal E is decimal 14 and hexadecimal 2A

is decimal 42 (two 16s) + 10). Using the C programming language notation (as I do

throughout this bo ok) hexadecimal numbers are prefaced by\

"; hexadecimal 2A

is written as

0x2A

Microprocessors can perform arithmetic operations such as add, multiply and divide

and logical op erations such as \is X greater than Y?".

The processor's execution is governed by an external clo ck. This clo ck, the system

clock, generates regular clo ck pulses to the pro cessor and, at each clo ck pulse, the

processor does some work. For example, a pro cessor could execute an instruction

every clock pulse. A processor's speed is described in terms of the rate of the system

clock ticks. A 100Mhz processor will receive 100,000,000 clo ck ticks every second. It

is misleading to describe the power of a CPU by its clo ck rate as dierent processors

perform dierent amounts of work per clock tick. However, all things b eing equal, a

faster clo ck sp eed means a more powerful pro cessor. The instructions executed by the

processor are very simple; for example \read the contents of memory at location X

into register Y". Registers are the micropro cessor's internal storage, used for storing

data and p erforming operations on it. The op erations p erformed may cause the

processor to stop what it is doing and jump to another instruction somewhere else in

memory. These tiny building blo cks give the mo dern micropro cessor almost limitless

power as it can execute millions or even billions of instructions a second.

The instructions have to be fetched from memory as they are executed. Instructions

may themselves reference data within memory and that data must b e fetched from

memory and saved there when appropriate.

The size, number and type of register within a microprocessor is entirely dependent

on its typ e. An Intel 4086 pro cessor has a dierent register set to an Alpha AXP

processor; for a start, the Intel's are 32 bits wide and the Alpha AXP's are 64 bits

wide. In general, though, any given pro cessor will haveanumber of general purpose

registers and a smaller number of dedicated registers. Most pro cessors have the

following special purp ose, dedicated, registers:

Program Counter (PC)

This register contains the address of the next instruction

to be executed. The contents of the PC are automatically incremented each

time an instruction is fetched,

Stack Pointer (SP)

Processors haveto have access to large amounts of external

read/write random access memory (RAM) which facilitates temporary storage

of data. The stackisaway of easily saving and restoring temp orary values in

external memory. Usually, pro cessors have sp ecial instructions which allowyou

to push values onto the stack and to pop them o again later. The stackworks

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