免费Linux内核模块编程指南

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《Linux内核模块编程指南》(LKMPG)是由Peter Jay Salzman、Michael Burian和Ori Pomerantz合著的一本开源书籍，版权于2001年首次发布，最新更新日期为2007年5月18日，对应Linux内核版本2.6.4。这本书的目标是提供免费的学习资源，读者可以根据Open Software License (OSL) 1.1版条款进行复制和修改。该指南的核心内容涵盖了Linux内核模块的开发，它旨在帮助开发者理解如何创建自定义模块以扩展或增强Linux内核的功能。作者鼓励个人或商业用户广泛传播此书，只要保留原始版权信息并遵循OSL的规定即可。这意味着，无论是打印版还是电子版，用户都可以自由地复制和分发此书，无论是出于个人学习还是商业目的，无需事先获得作者的特别许可。 OSL要求任何基于本书的衍生作品或翻译也必须采用同样的开放许可，并保持原版权声明完整。如果读者对本书有所贡献，无论是新内容还是代码修改，都必须确保这些修改和源代码可供获取，并通过文档维护者Peter Jay Salzman的邮件地址<p@dirac.org>进行分享，以便与其他更新合并，为Linux社区提供一致和持续的改进。《Linux Kernel Module Programming Guide》是一份极具价值的参考资料，它详细讲解了模块化编程的原理、内核接口的使用、模块编译、加载与卸载、错误处理以及内存管理和资源管理等核心主题。对于希望深入Linux内核开发领域的工程师来说，这是一本不可或缺的工具书。

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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