[$] Topics from the virtual filesystem layer

In the first filesystem-track session at the 2025 Linux Storage,Filesystem, Memory Management, and BPF Summit (LSFMM+BPF), virtualfilesystem (VFS) layer co-maintainer Christian Brauner had a few differenttopics he wanted to talk about. Issues on the agendaincluded iterating through anonymous mount namespaces, a needed featurefor ID-mapped mounts, the perennial unprivileged mounts topic, potentiallyusing hazard pointers for file reference counting, and Rust bindings. Hedid not expect to get through all of them in the 30 minutes allotted, butthe session did move along pretty quickly to at leastintroduce them to the assembled filesystem developers.