[$] An overlayfs update

In a shortened session in the filesystem track at the 2026 Linux Storage, Filesystem, Memory Management, and BPF Summit, Amir Goldstein gave an update on theoverlayfs union filesystem. There are some new features over the last few years that he wanted to mention, along with looking at the status of nesting overlayfs layers. Thecomposefs use case that wasdiscussed at the summit in 2023 has led to some interesting changes to overlayfs.