[$] Policies for merging new filesystems

In a filesystem-track session at the 2026 Linux Storage,Filesystem, Memory Management, and BPF Summit, Amir Goldstein wanted todiscuss his proposeddocumentation on adding new filesystems to the kernel. There are anumber of unmaintained and untestable filesystems already in the kernel,which are a burden to VFS-layer developers who are trying to make sweepingchanges, such as switching to folios and the "new" mount API. Goldstein'sdocument is an attempt to head off the addition of filesystems that mayincrease that burden down the road.