深入浅出Linux设备驱动开发

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"Linux Device Driver Development" 本书《Linux Device Driver Development》由John Madieu撰写，主要讲解如何为嵌入式Linux系统开发定制化的设备驱动。书中深入探讨了内核驱动的经典机制，是驱动开发者的重要参考资料。在第二章"Device Driver Basis"中，作者介绍了用户空间与内核空间的区别，这对于理解驱动程序的工作环境至关重要。这一章还讨论了驱动程序的基本框架，错误处理和消息打印，以及如何构建你的第一个模块，这些都是驱动开发的基础。第三章"Kernel Facilities and Helper Functions"深入探讨了内核提供的各种设施和辅助函数。包括了`container_of`宏的理解，链表操作，内核的睡眠机制，延迟和定时器管理，内核锁机制，工作队列延迟机制，内核中断机制，以及如何从内核空间调用用户空间应用程序。这些内容构成了内核驱动的核心功能。第四章"Character Device Drivers"专注于字符设备驱动的开发，讲解了主次设备号的概念，设备文件操作的引入，如何分配和注册字符设备，以及编写文件操作函数。这对于实现与用户空间的交互至关重要。第五章"Platform Device Drivers"则介绍了平台驱动，包括平台设备的概念，设备、驱动和总线匹配的过程。这部分内容对于理解和开发特定硬件的驱动非常关键。第六章"The Concept of Device Tree"讨论了设备树机制，这是在Linux系统中描述硬件结构和配置的重要方式，包括如何表示和寻址设备，以及设备树在设备驱动程序中的应用。《Linux Device Driver Development》涵盖了从驱动基础到高级内核机制的广泛内容，是Linux驱动开发者深入学习和实践的宝贵资料。通过阅读此书，读者将能够掌握创建高效、可靠的Linux设备驱动所需的知识和技巧。

Chapter 3. Kernel Facilities and Helper Functions

The kernel is a standalone piece of software, as you'll see in this chapter, that does not make use

of any C library. It implements any mechanism you may encounter in modern libraries, and even

more, such as compression, string functions, and so on. We will walk step by step through the

most important aspects of such capabilities.

In this chapter, we will cover the following topic:

Introducing the kernel container data structure

Dealing with the kernel sleeping mechanism

Using timers

Delving into the kernel locking mechanism (mutex, spnlock)

Deferring work using a kernel dedicated API

Using IRQs

[12]

Understanding container_of macro

When it comes to managing several data structures in the code, you'll almost always need to

embed one structure into another and retrieve them at any moment without being asked questions

about memory offset or boundaries. Let's say you have a struct person, as defined here:

struct person {

int age;

char *name;

} p;

By only having a pointer on age or name, one can retrieve the whole structure wrapping

(containing) that pointer. As the name says, container_of macro is used to find the container of

the given field of a structure. The macro is defined in include/linux/kernel.h and looks like:

#define container_of(ptr, type, member) ({ \

const typeof(((type *)0)->member) * __mptr = (ptr); \

(type *)((char *)__mptr - offsetof(type, member)); })

Don't be afraid by the pointers; just see it as:

container_of(pointer, container_type, container_field);

Here are the elements of the preceding code fragment:

pointer: This is the pointer to the field in the structure

container_type: This is the type of structure wrapping (containing) the pointer

container_field: This is the name of the field to which pointer points inside the structure

Let us consider the following container:

struct person {

int age;

char *name;

};

Now let us consider one of its instance, along with a pointer to the name member:

struct person somebody;

[...]

char *the_name_ptr = somebody.name;

Along with a pointer to the name member (the_name_ptr), you can use the container_of macro in

order to get a pointer to the whole structure (container) that wraps this member by using the

following:

struct person *the_person;

the_person = container_of(the_name_ptr, struct person, name);

container_of takes the offset of name at the beginning of the struct into account to get the correct

pointer location. If you subtract the offset of the field name from the pointer the_name_ptr, you will

get the correct location. It is what the macro's last line does:

(type *)( (char *)__mptr - offsetof(type,member) );

[13]

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