###############
## sample code suggested at nixos irc-channel
 #fileSystems."/where/to/mount" = {
 #device = "LABEL=btrfs";
 #fsType = "btrfs;
 #options = [ "subvol=subvolxyz" ];
 #};
##############
#My code - fail :-(
 fileSystems."/home" = {
  device = "LABEL = multisys";
  fsType = "btrfs;
  options = [ "subvol" = "root/sysroot/nixos-mountpoints/users/home" ];
  };
###################