Linux内核模块编程实战教程：从零开始

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《Linux内核模块编程指南》是一本针对Linux操作系统的免费教材，由Peter Jay Salzman、Michael Burian和Ori Pomerantz共同编写，最初出版于2001年，随着Linux内核版本的更新，该书在2007年五月修订至2.6.4。该指南旨在为零基础的学习者提供详细的实践教程，讲解如何开发和管理Linux内核模块，包括模块的添加、编译、装载和卸载过程。书中提供的代码示例可以直接复制并应用于实际操作。作者鼓励本书的广泛传播，无论是个人学习还是商业用途，只要保持原版权信息完整，并遵循Open Software License（OSL）1.1版的条款。OSL允许用户自由复制、修改和分发这本书，无论是纸质版还是电子版，无需事先获得作者的明确许可。这意味着读者可以无障碍地获取并学习内核模块编程技术，但必须确保遵守开放源代码的精神，即作品必须在同样的许可证下分享。对于衍生作品或翻译版本，同样需要在OSL框架下发布，且原始版权声明不能被篡改。如果你在书中加入了新的内容，你也需要确保这些贡献符合OSL的条款，以维护知识共享的开放性。通过这本书，读者将学到内核模块的基础概念，如内核模块的作用、结构、接口设计，以及如何编写、编译和调试模块，甚至如何处理模块加载失败的情况。此外，书中还会涉及模块的安全性和性能优化等关键主题，使学习者能够在实践中深入理解Linux内核的工作原理，并具备独立开发实用内核模块的能力。《Linux内核模块编程指南》是一本极具实用价值的资源，适合想要进入Linux系统底层开发的工程师和开发者使用，是提升Linux技能库的重要参考资料。

2.6. Passing Command Line Arguments

to a Module

Modules can take command line arguments, but not with the argc/argv you might be

used to.

To allow arguments to be passed to your module, declare the variables that will take

the values of the command line arguments as global and then use the

module_param() macro, (defined in linux/moduleparam.h) to set the mechanism

up. At runtime, insmod will fill the variables with any command line arguments that

are given, like ./insmod mymodule.ko myvariable=5. The variable declarations and

macros should be placed at the beginning of the module for clarity. The example code

should clear up my admittedly lousy explanation.

The module_param() macro takes 3 arguments: the name of the variable, its type and

permissions for the corresponding file in sysfs. Integer types can be signed as usual or

unsigned. If you'd like to use arrays of integers or strings see module_param_array()

and module_param_string().

int myint = 3;

module_param(myint, int, 0);

Arrays are supported too, but things are a bit different now than they were in the 2.4.

days. To keep track of the number of parameters you need to pass a pointer to a count

variable as third parameter. At your option, you could also ignore the count and pass

NULL instead. We show both possibilities here:

int myintarray[2];

module_param_array(myintarray, int, NULL, 0); /* not interested in

count */

int myshortarray[4];

int count;

module_parm_array(myshortarray, short, , 0); /* put count into

"count" variable */

A good use for this is to have the module variable's default values set, like an port or

IO address. If the variables contain the default values, then perform autodetection

(explained elsewhere). Otherwise, keep the current value. This will be made clear

later on.

Lastly, there's a macro function, MODULE_PARM_DESC(), that is used to document

arguments that the module can take. It takes two parameters: a variable name and a

free form string describing that variable.

2.8. Building modules for a precompiled

kernel

Obviously, we strongly suggest you to recompile your kernel, so that you can enable a

number of useful debugging features, such as forced module unloading

(MODULE_FORCE_UNLOAD): when this option is enabled, you can force the kernel to

unload a module even when it believes it is unsafe, via a rmmod -f module

command. This option can save you a lot of time and a number of reboots during the

development of a module.

Nevertheless, there is a number of cases in which you may want to load your module

into a precompiled running kernel, such as the ones shipped with common Linux

distributions, or a kernel you have compiled in the past. In certain circumstances you

could require to compile and insert a module into a running kernel which you are not

allowed to recompile, or on a machine that you prefer not to reboot. If you can't think

of a case that will force you to use modules for a precompiled kernel you might want

to skip this and treat the rest of this chapter as a big footnote.

Now, if you just install a kernel source tree, use it to compile your kernel module and

you try to insert your module into the kernel, in most cases you would obtain an error

as follows:

insmod: error inserting 'poet_atkm.ko': -1 Invalid module format

Less cryptical information are logged to /var/log/messages:

Jun 4 22:07:54 localhost kernel: poet_atkm: version magic '2.6.5-

1.358custom 686

REGPARM 4KSTACKS gcc-3.3' should be '2.6.5-1.358 686 REGPARM

4KSTACKS gcc-3.3'

In other words, your kernel refuses to accept your module because version strings

(more precisely, version magics) do not match. Incidentally, version magics are stored

in the module object in the form of a static string, starting with vermagic:. Version

data are inserted in your module when it is linked against the init/vermagic.o file.

To inspect version magics and other strings stored in a given module, issue the

modinfo module.ko command:

[root@pcsenonsrv 02-HelloWorld]# modinfo hello-4.ko

license: GPL

author: Peter Jay Salzman <p@dirac.org>

description: A sample driver

vermagic: 2.6.5-1.358 686 REGPARM 4KSTACKS gcc-3.3

depends:

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