[$] When and why to deprecate filesystems

It is a good bet that a significant amount of code in the kernel isentirely unused. Even so, that code must still be maintained and shipped,posing an ongoing cost to the development community. What should be donewith code that is unmaintained and, possibly, unused? Answering thatquestion requires understanding which users still exist, if any, and takinga hard look at what the future support requirements for that code will be.The kernel community has recently discussed this problem in the context offilesystems, and the Reiserfs filesystem in particular, with a focus on the approaching 2038 deadline.