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Linux kernel design patterns - part 2

Jun 30, 2009, 13:32 (0 Talkback[s])
(Other stories by Neil Brown)

"The idea behind Abstract Data Types is to encapsulate the entire implementation of a data structure, and provide just a well defined interface for manipulating it. The benefit of this approach is that it provides a clean separation. The data type can be implemented with no knowledge of the application which might end up using it, and the application can be implemented with no knowledge of the implementation details of the data type. Both sides simply write code based on the interface which works like a contract to explicitly state what is required and what can be expected.

"On the other hand, one of the costs of this approach is tightly connected with the abstract nature of the interface. The point of abstracting an interface is to remove unnecessary details. This is good for introductory computing students, but is bad for kernel programmers. In kernel programming. performance is very important, coming as a close third after correctness and maintainability, and sometimes taking precedence over maintainability. Not all code paths in the kernel are performance-critical, but many are, and the development process benefits from the same data structures being using in both performance critical and less critical paths. So it is essential that data types are not overly abstracted, but that all details of the implementation are visible so that the programmer can make optimal choices when using them."

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