Linux内核3.0详解：第1-6章概览与关键概念

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《理解Linux内核3rd版》是一本深入探讨Linux系统核心的教材，涵盖了从第一章基础介绍到第五章关键概念的深入剖析。本书主要关注Linux内核的架构、内存管理、进程处理以及中断与同步机制。在第一章"Introduction"中，作者首先区分了Linux与其他类Unix内核的区别，强调了Linux对硬件的依赖性和版本演进。接着，读者会学习基本的操作系统概念，如文件系统的概述和Unix内核的架构。这一部分有助于理解Linux作为操作系统的核心组件如何协同工作。第二章"Memory Addressing"深入解析内存地址的组织方式，包括硬件层面的分段和Linux中的页式管理。章节详细介绍了内存地址的表示、硬件级的分段机制，以及Linux如何利用虚拟内存来提高效率。此外，还涵盖了硬件和Linux中的页面调度机制。第三章"Processes"着重于进程及其子类别，如轻量级进程和线程。这里介绍了进程描述符、进程切换的过程，以及创建和销毁进程的步骤。中断信号的作用、异常处理和中断/异常处理的层次结构也被详细讨论，还包括初始化中断描述符表和软中断任务队列等内容。第四章"Interrupts and Exceptions"围绕中断和异常处理展开，包括它们在系统中的作用、处理流程，以及如何在中断和异常中实现嵌套执行。此外，还有初始化中断处理程序、异常处理机制、软中断和任务队列，以及从中断或异常返回的方法。最后一章"Kernel Synchronization"探讨了内核同步技术，这是确保并发安全的关键。这部分讲解了内核如何响应服务请求，以及如何通过锁、信号量等机制来协调多个线程或进程之间的数据访问和执行。《Understanding the Linux Kernel 3rd》是Linux内核入门和进阶学习者的理想资源，它不仅提供了理论知识，还深入展示了内核运作的实际细节，帮助读者建立起对Linux内核全面而深入的理解。

1.5. An Overview of the Unix Filesystem

The Unix operating system design is centered on its filesystem, which has several interesting

characteristics. We'll review the most significant ones, since they will be mentioned quite

often in forthcoming chapters.

1.5.1. Files

A Unix file is an information container structured as a sequence of bytes; the kernel does not

interpret the contents of a file. Many programming libraries implement higher-level

abstractions, such as records structured into fields and record addressing based on keys.

However, the programs in these libraries must rely on system calls offered by the kernel.

From the user's point of view, files are organized in a tree-structured namespace, as shown

in Figure 1-1.

Figure 1-1. An example of a directory tree

All the nodes of the tree, except the leaves, denote directory names. A directory node

contains information about the files and directories just beneath it. A file or directory name

consists of a sequence of arbitrary ASCII characters,

[*]

with the exception of / and of the null

character \0. Most filesystems place a limit on the length of a filename, typically no more than

255 characters. The directory corresponding to the root of the tree is called the root directory.

By convention, its name is a slash (/). Names must be different within the same directory, but

the same name may be used in different directories.

[*]

Some operating systems allow filenames to be expressed in many different alphabets, based on 16-bit extended coding of graphical characters

such as Unicode.

Unix associates a current working directory with each process (see the section "The

Process/Kernel Model" later in this chapter); it belongs to the process execution context, and

it identifies the directory currently used by the process. To identify a specific file, the process

uses a pathname, which consists of slashes alternating with a sequence of directory names

that lead to the file. If the first item in the pathname is a slash, the pathname is said to be

absolute, because its starting point is the root directory. Otherwise, if the first item is a

directory name or filename, the pathname is said to be relative, because its starting point is

the process's current directory.

While specifying filenames, the notations "." and ".." are also used. They denote the current

working directory and its parent directory, respectively. If the current working directory is the

root directory, "." and ".." coincide.

1.5.2. Hard and Soft Links

A filename included in a directory is called a file hard link, or more simply, a link. The same

file may have several links included in the same directory or in different ones, so it may have

several filenames.

The Unix command:

$ ln p1 p2

is used to create a new hard link that has the pathname p2 for a file identified by the

pathname p1.

Hard links have two limitations:

 It is not possible to create hard links for directories. Doing so might transform the

directory tree into a graph with cycles, thus making it impossible to locate a file

according to its name.

 Links can be created only among files included in the same filesystem. This is a

serious limitation, because modern Unix systems may include several filesystems

located on different disks and/or partitions, and users may be unaware of the

physical divisions between them.

To overcome these limitations, soft links (also called symbolic links) were introduced a long

time ago. Symbolic links are short files that contain an arbitrary pathname of another file. The

pathname may refer to any file or directory located in any filesystem; it may even refer to a

nonexistent file.

The Unix command:

$ ln -s p1 p2

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Linux内核3.0详解：第1-6章概览与关键概念

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