Linux内核模块编程指南

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“Linux内核模块编程指南” 在深入探讨Linux内核模块编程之前，首先要理解Linux内核本身的角色。Linux内核是操作系统的核心部分，它负责管理系统的硬件资源，如处理器、内存，以及与设备驱动程序的交互。内核模块（Kernel Module）是Linux内核的一部分，可以在需要时动态加载或卸载，这为系统提供了灵活性，允许添加或移除特定功能而不必重启整个系统。《Linux内核模块编程指南》是一本由Peter Jay Salzman、Michael Burian和Ori Pomerantz共同编写的开源书籍，旨在教育读者如何编写和调试Linux内核模块。根据描述，该书涵盖了内核编程的注意事项以及调试技术，这些都是成功进行内核开发的关键要素。在进行Linux内核模块编程时，需要注意以下几点： 1. 内存管理：内核模块需要遵循严格的内存管理规则，如使用kmalloc和kfree来分配和释放内存，避免内存泄漏，并确保在模块卸载时正确清理内存。 2. 异步处理：内核代码可能在任意上下文中运行，包括中断服务例程，因此必须确保所有的操作都是原子的，不会被中断。 3. 锁定机制：为了保证数据一致性，内核编程经常涉及到互斥锁（mutex）、读写锁（rwlock）等同步原语，以防止数据竞争。 4. 性能优化：内核代码执行速度直接影响到系统性能，因此要尽量减少不必要的函数调用，避免循环内的昂贵操作，使用预编译宏和内联函数提高效率。 5. 调试技巧：内核模块的调试通常使用kdb（Kernel Debugging Bridge）或kgdb（Kernel GNU Debugger），它们提供了一种方式来在运行时检查和修改内核状态。此外，日志记录（printk）也是常用的调试手段。 6. 模块加载和卸载：使用insmod、rmmod和modprobe命令来管理内核模块的生命周期，开发者需要确保模块加载和卸载过程的安全性。 7. 符号表和符号解析：内核模块需要能够访问其他内核组件的符号，因此需要处理内核符号表，这通常通过EXPORT_SYMBOL和EXPORT_SYMBOL_GPL宏完成。 8. 内核API：理解并正确使用内核提供的API是至关重要的，这些API包括设备驱动程序接口、进程管理、网络协议栈等。 9. 安全性：由于内核模块运行在特权模式下，任何安全漏洞都可能导致严重的后果。因此，编写安全的代码，避免缓冲区溢出和其他类型的攻击，是内核编程的重要部分。通过学习《Linux内核模块编程指南》，开发者可以掌握编写高效、安全且可靠的内核模块的技能，从而更好地扩展和定制Linux系统。同时，由于该书遵循Open Software License，鼓励广泛传播和改进，为社区贡献新的材料或翻译版本。

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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