Linux Device Drivers

Chapter 10. Judicious Use of Data Types

Before we go on to more advanced topics, we need to stop for a quick note on portability issues. The difference between versions 1.2 and 2.0 of Linux lies in the addition of multiplatform capabilities; as a result, most source-level portability problems have been eliminated. This means that a serious Linux driver should be multiplatform as well.

But a core issue with kernel code is being able to both access data items of known length (for example, filesystem data structures or registers on device boards) and to exploit the capabilities of different processors (32-bit and 64-bit architectures, and possibly 16-bit as well).

Several problems encountered by kernel developers while porting x86 code to new architectures have been related to incorrect data typing. Adherence to strict data typing and compiling with the -Wall -Wstrict-prototypes flags can prevent most bugs.

Data types used by kernel data are divided into three main classes: standard C types like int, explicitly sized types like u32, and interface-specific types, like pid_t. We are going to see when and how each of the three typing classes should be used. The final sections of the chapter talk about some other typical problems you might run into when porting driver code from the x86 to other platforms.

If you follow the guidelines I provide, your driver will compile and run even on platforms where you are unable to test it.

Use of Standard C Types

While most programmers are accustomed ...