[$] The Btrfs inode-number epic (part 2: solutions)

The first installment in this two-partseries looked at the difficulties that arise when Btrfs filesystemscontaining subvolumes are exported via NFS. Btrfs has a couple of quirksthat complicate life in this situation: the use of separate device numbersfor subvolumes and the lack of unique inode numbers across the filesystemas a whole. Recently, Neil Brown set off on an effort to tryto solve these problems, only to discover that the situation was evenmore difficult than expected and that many attempts would be required.