Linux设备驱动开发指南：深度探索与2.6内核兼容

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《Linux设备驱动》是一本深度探讨在Linux系统中编写设备驱动的关键书籍。它不仅关注于如何为Linux开发新硬件产品的驱动程序，更深层次地揭示了Linux内核的工作原理及其适应性。作为第三版，作者紧跟时代的步伐，针对2.6.10内核进行了全面更新，尽管舍弃了对旧版本兼容性的讨论，因为2.4接口在第二版中已有详尽文档。新版本新增了大量与2.6内核相关的内容，如扩展的锁定和并发处理章节，详细介绍了Linux设备模型，以及关于USB总线、串行驱动子系统和PCI章节的增强。尽管整体框架保留了前几版的结构，但每个章节都进行了彻底的更新，以反映当前内核技术的最新进展。该书强调了Linux开源的本质，使得开发者群体能够更好地理解和参与。作为入门指南，书中解释了设备驱动在Linux中的核心作用，它们是特殊的“黑盒”，负责将特定硬件功能映射到内核的统一编程接口上，隐藏了硬件工作的复杂细节。用户通过一套标准化的独立于特定驱动的API来执行操作，这为潜在的内核开发者提供了一个易于入手的切入点。《Linux设备驱动》不仅是一本实用的技术手册，也是理解Linux内核架构和扩展的最佳教材，它鼓励开发者积极参与开源社区，共同推动Linux生态的发展。无论是对于现有驱动开发者还是希望进入这一领域的学习者，这本书都是不可或缺的参考资料。

This is the Title of the Book, eMatter Edition

The Role of the Device Driver

array of data blocks. Higher levels of the system provide policies, such as who may

access the floppy drive, whether the drive is accessed directly or via a filesystem, and

whether users may mount filesystems on the drive. Since different environments usu-

ally need to use hardware in different ways, it’s important to be as policy free as

possible.

When writing drivers, a programmer should pay particular attention to this funda-

mental concept: write kernel code to access the hardware, but don’t force particular

policies on the user, since different users have different needs. The driver should deal

with making the hardware available, leaving all the issues about how to use the hard-

ware to the applications. A driver, then, is flexible if it offers access to the hardware

capabilities without adding constraints. Sometimes, however, some policy decisions

must be made. For example, a digital I/O driver may only offer byte-wide access to

the hardware in order to avoid the extra code needed to handle individual bits.

You can also look at your driver from a different perspective: it is a software layer

that lies between the applications and the actual device. This privileged role of the

driver allows the driver programmer to choose exactly how the device should appear:

different drivers can offer different capabilities, even for the same device. The actual

driver design should be a balance between many different considerations. For

instance, a single device may be used concurrently by different programs, and the

driver programmer has complete freedom to determine how to handle concurrency.

You could implement memory mapping on the device independently of its hardware

capabilities, or you could provide a user library to help application programmers

implement new policies on top of the available primitives, and so forth. One major

consideration is the trade-off between the desire to present the user with as many

options as possible and the time you have to write the driver, as well as the need to

keep things simple so that errors don’t creep in.

Policy-free drivers have a number of typical characteristics. These include support for

both synchronous and asynchronous operation, the ability to be opened multiple

times, the ability to exploit the full capabilities of the hardware, and the lack of soft-

ware layers to “simplify things” or provide policy-related operations. Drivers of this

sort not only work better for their end users, but also turn out to be easier to write

and maintain as well. Being policy-free is actually a common target for software

designers.

Many device drivers, indeed, are released together with user programs to help with

configuration and access to the target device. Those programs can range from simple

utilities to complete graphical applications. Examples include the tunelp program,

which adjusts how the parallel port printer driver operates, and the graphical cardctl

utility that is part of the PCMCIA driver package. Often a client library is provided as

well, which provides capabilities that do not need to be implemented as part of the

driver itself.

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Linux设备驱动开发指南：深度探索与2.6内核兼容

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