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On the management of the Video4Linux subsystem tree

Mar 06, 2009, 07:34 (0 Talkback[s])
(Other stories by Jonathan Corbet)

"The discussion started with this RFC from Hans Verkuil. Hans points out that the size of the V4L subsystem (as found under drivers/media in the kernel source) has grown significantly in recent years - it is 2.5 times larger now than it was in the 2.6.16 kernel. This growth is a sign of success: V4L has added features and support for a vast array of new hardware in this time. But it has its costs as well - that is a lot of code to maintain.

"As it happens, the V4L developers make that maintenance even harder by incorporating backward compatibility into their tree. The tree run by V4L maintainer Mauro Carvalho Chehab does not support just the current mainline kernel; instead, it can be built on any kernel from 2.6.16 forward. This is not a small trick, considering that the majority of that code did not exist when 2.6.16 was released. There have been some major internal kernel API changes over that time; supporting all those kernels requires a complicated array of #ifdefs, compatibility headers, and more. It takes a lot of work to keep this compatibility structure in place. Additionally, this kind of compatibility code is not welcome in the mainline kernel, so it must all be stripped out prior to sending code upstream."

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