[$] A FUSE implementation for famfs

The famfs
filesystem is meant to provide a shared-memory filesystem for large data
sets that are accessed for computations by multiple systems. It was
developed by John Groves, who led a combined filesystem and
memory-management session at
the 2025 Linux Storage, Filesystem, Memory
Management, and BPF Summit (LSFMM+BPF) to discuss it. The session was a
follow-up to the famfs session at last year's
summit, but it was also meant to discuss whether the kernel's direct-access (DAX)
mechanism, which is used by famfs, could be replaced in the filesystem
by using other kernel features.