[$] Snapshots, inodes, and filesystem identifiers

A longstanding problem with Btrfs subvolumesand duplicate inode numbers was the topic of a late-breaking filesystem sessionat the2022 Linux Storage,Filesystem, Memory-management and BPF Summit (LSFMM). The problem hadcropped up in the bcachefs session butJosef Bacik deferred that discussion to this just-created session, which he led. Theproblem is not limited to Btrfs, though, since filesystem snapshots forother filesystems canhave similar kinds of problems.