Dear Maintainer,

During the partition disks phase it is possible to specify a
filesystem type of btrfs.  It is very useful to use the "autodefrag"
option with btrfs filesystems, but it is not a listed option among the
available mount options in the installer, and you can't add your own
options.  As a consequence I went into a shell and remounted /target
to include this option before going further.  I also needed to go into
a shell to hand edit the target's /etc/fstab prior to finishing the
installation.  It would be nice to either allow your own options, or
present autodefrag as an option for btrfs.