Be aware that most distributions of GNU/Linux modify the official kernel to implement new features or to improve its efficiency. In a few cases, the source code provided by your favorite distribution might differ significantly from the one described in this book.
In many cases, we show fragments of the original code rewritten in an easier-to-read but less efficient way. This occurs at time-critical points at which sections of programs are often written in a mixture of hand-optimized C and assembly code. Once again, our aim is to provide some help in studying the original Linux code.While discussing kernel code, we often end up describing the underpinnings of many familiar features that Unix programmers have heard of and about which they may be curious (shared and mapped memory, signals, pipes, symbolic links, and so on).
需要注意的是大多数的GNU/Linux的发行版都部分修改了官方内核来实现新的功能或者提高性能，所以在有些情况下你最喜欢的发行版可能与本书中描述的功能有很大的不同。
在许多情况下，我们以更易读但更低效的方式呈现了那些被重写的原始代码片段。这种情况发生在对时间有严格要求的场景，此时这部分的内容往往是用复杂的C和汇编语言混合写成的。再次说明一下，我们的目的是为帮助那些学习原始的Linux代码的人士；当我们在讨论Linux代码的时候，我们往往以阐述许多熟悉的基础特性而告终，这些特性是Unix程序员听过的、甚至感到非常奇特的地方（比如共享内存、内存映射、信号、管道、连接符等）。