Linux内核模块开发详解：免费指南

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《Linux内核模块编程指南》是一本由Peter Jay Salzman、Michael Burian和Ori Pomerantz编写的免费开源书籍，版权日期为2001年，随着Linux内核版本的更新至2.6.4。该书遵循开放源代码许可协议（Open Software License, version 1.1），允许用户在尊重版权和协议条款的前提下复制和修改。本书的主要内容涵盖了Linux内核模块开发的基础知识和实践技巧，包括但不限于模块加载与卸载、系统调用接口、内存管理、信号处理、驱动程序设计、模块间的通信以及错误处理等内容。它旨在帮助读者理解如何编写能够在Linux操作系统内核中运行的可插拔组件，以扩展或定制系统的功能。作者鼓励这本书的广泛传播，无论是个人学习还是商业用途，只要确保保留原始版权声明，并遵循开放软件许可证的规定。这意味着你可以无须额外许可，无论是打印版还是电子版，都可以自由复制和分发。然而，对于基于此书创作的衍生作品或翻译，必须同样遵循Open Software License，保持原版权信息完整，并要求作者贡献的新内容也遵循同样的授权规则。《Linux内核模块编程指南》是一本实用的参考资源，为那些想要深入理解并实践Linux内核模块开发的人提供了宝贵的指导，无论你是初学者还是有经验的开发者，都能从中获益匪浅。通过阅读和实践本书中的内容，读者可以掌握关键技能，构建高效且稳定的内核扩展，为Linux系统增添新的功能特性。

printk(KERN_INFO "Hello, world 4\n");

return 0;

}

static void __exit cleanup_hello_4(void)

{

printk(KERN_INFO "Goodbye, world 4\n");

}

module_init(init_hello_4);

module_exit(cleanup_hello_4);

* You can use strings, like this:

* Get rid of taint message by declaring code as GPL.

MODULE_LICENSE("GPL");

* Or with defines, like this:

MODULE_AUTHOR(DRIVER_AUTHOR); /* Who wrote this module? */

MODULE_DESCRIPTION(DRIVER_DESC); /* What does this module do */

* This module uses /dev/testdevice. The MODULE_SUPPORTED_DEVICE macro might

* be used in the future to help automatic configuration of modules, but is

* currently unused other than for documentation purposes.

MODULE_SUPPORTED_DEVICE("testdevice");

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:

The Linux Kernel Module Programming Guide

Chapter 2. Hello World 11

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.

Example 2−7. hello−5.c

* hello−5.c − Demonstrates command line argument passing to a module.

#include <linux/module.h>

#include <linux/moduleparam.h>

#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/stat.h>

MODULE_LICENSE("GPL");

MODULE_AUTHOR("Peter Jay Salzman");

static short int myshort = 1;

static int myint = 420;

static long int mylong = 9999;

static char *mystring = "blah";

static int myintArray[2] = { −1, −1 };

static int arr_argc = 0;

* module_param(foo, int, 0000)

* The first param is the parameters name

* The second param is it's data type

* The final argument is the permissions bits,

* for exposing parameters in sysfs (if non−zero) at a later stage.

module_param(myshort, short, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);

MODULE_PARM_DESC(myshort, "A short integer");

module_param(myint, int, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);

MODULE_PARM_DESC(myint, "An integer");

module_param(mylong, long, S_IRUSR);

MODULE_PARM_DESC(mylong, "A long integer");

module_param(mystring, charp, 0000);

MODULE_PARM_DESC(mystring, "A character string");

* module_param_array(name, type, num, perm);

* The first param is the parameter's (in this case the array's) name

* The second param is the data type of the elements of the array

* The third argument is a pointer to the variable that will store the number

* of elements of the array initialized by the user at module loading time

* The fourth argument is the permission bits

The Linux Kernel Module Programming Guide

Chapter 2. Hello World 12

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