Linux Device Drivers

Chapter 17. Recent Developments

The Linux kernel is subject to relentless development, and the developers feel an urge to improve kernel internals without worrying too much about backward compatibility. This kind of free development shows up in a number of incompatibilities between the device driver interface offered by different versions of the kernel. Nonetheless, no incompatibility is introduced at the application level, with the exception of those few applications whose task requires low-level interaction with kernel features (like ps).

The device driver, on the other hand, is directly linked to the kernel image and must therefore comply with any change in the data structures, global variables, and functions exported by the core system. During development, the internals are modified as new features are added or new implementations replace the old ones because they prove faster or cleaner. Although the incompatibilities require programmers to put in some extra work when writing a module, I see continuous development as a winning point of the Linux community: strict backward-compatibility eventually proves harmful.

This chapter describes the differences between 2.0.x and 2.1.43, which you can expect to be similar to the upcoming 2.2 release. Linus introduced the most relevant changes in the first few 2.1 versions, so that the kernel could go through several more 2.1 versions, giving driver writers time to stabilize things before the development is frozen to release a stable 2.2 ...