+
+mount -o subvolid=0 $crypt /mnt
+# systemd creates subvolumes we want to delete.
+s=($(btrfs subvolume list --sort=-path /mnt |
+ sed -rn "s#^.*path\s*(root_$DISTRO/\S+)\s*\$#\1#p"))
+for subvol in ${s[@]}; do btrfs subvolume delete /mnt/$subvol; done
+btrfs subvolume set-default 0 /mnt
+[[ ! -e /mnt/root_$DISTRO ]] || btrfs subvolume delete /mnt/root_$DISTRO