This fd has nothing to do with cleanup, that's just the name of the field in zfs_cmd_t that was used to pass it to the kernel. Call it what it is, an fd for a user namespace. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Allan Jude <allan@klarasystems.com> Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org> Closes #13554