XFS changes for 4.21: - Fix CoW remapping of extremely fragmented file areas - Fix a zero-length symlink verifier error - Constify some of the rmap owner structures for per-AG metadata - Precalculate inode geometry for later use - Fix scrub counting problems - Don't crash when rtsummary inode is null - Fix x32 ioctl operation - Fix enum->string mappings for ftrace output - Cache realtime summary information in memory