Build breakage in linux-next

I've been doing linux kernel testing on next, mainline, and LTS for the past couple years as part of my work. Bugs are easier to fix when you find them in linux-next.

Obviously, no one develops new drivers against linux-next. Kernel developers who work upstream just download an -rc kernel and work against that. There are people who don't care about upstream and they use LTS kernels, but I think it's going to be more and more difficult to ignore upstream with laws like the CRA. Products based on Android will need to go through several major kernel upgrades during their ten year life time. The more out of tree code, the more complicated each kernel upgrade becomes.

But I wasn't really talking about development, I was talking about hardware which are already supported by upstream and the vendor want to make sure it keeps working. The best tree to test against is linux-next. If that's not possible then you still want to be as close as reasonable to upstream.

Android has a tree which is updated within a couple weeks of when Linus releases a kernel. This is a good model. People think they are saving time by only upgrading once every other year instead of every eight weeks, but it's actually harder. When you upgrade regularly, then that's a smaller upgrade. You learn to be good at it. Also since everyone else is upgrading there is a built in support system if you have questions. But if you upgrade randomly after two years, no one will remember the old API or how it changed.