[$] A filesystem for namespaces

It is natural, when looking at the kernel development process, to focus on
patches that find their way to acceptance and become a part of future
kernels. But there can be value in looking at work that doesn't clear the
bar; in failing, these patches often reveal things about the kernel and the
community that creates it. Such is the case with the proof-of-concept
namespacefs
patch series recently posted by Yordan Karadzhov. One should not
expect to see namespacefs in a future kernel but, in failing, this work
showed a real use case and why it is hard to satisfy that use case in the
kernel.