diff --git a/install-zfs.sh b/install-zfs.sh
index b14248f..29bd464 100755
--- a/install-zfs.sh
+++ b/install-zfs.sh
@@ -43,6 +43,8 @@ v_suitable_disks=()          # (/dev/by-id/disk_id, ...); scope: find_suitable_d
 # Note that Linux Mint is "Linuxmint" from v20 onwards. This actually helps, since some operations are
 # specific to it.
 
+c_hotswap_file=$PWD/install-zfs.hotswap.sh # see hotswap() for an explanation.
+
 c_bpool_name=bpool
 c_ppa=ppa:jonathonf/zfs
 c_efi_system_partition_size=512 # megabytes
@@ -107,49 +109,74 @@ c_udevadm_settle_timeout=10 # seconds
 
 # HELPER FUNCTIONS #############################################################
 
-# Chooses a function and invokes it depending on the O/S distribution.
+# Invoke a function, with a primitive dynamic dispatch based on the distribution.
 #
-# Example:
+# Format: `invoke "function" [--optional]`.
+#
+# A target function must exist, otherwise a error is raised, unless `--optional` is specified.
+# `--optional` is useful when a step is specific to a single distribution, e.g. Debian's root password.
+#
+# Examples:
 #
 #   $ function install_jail_zfs_packages { :; }
 #   $ function install_jail_zfs_packages_Debian { :; }
 #   $ distro_dependent_invoke "install_jail_zfs_packages"
 #
-# If the distribution is `Debian`, the second will be invoked, otherwise, the
-# first.
-#
-# If the function is invoked with `--noforce` as second parameter, and there is
-# no matching function:
+#   If the distribution is `Debian`, the second will be invoked, otherwise, the first.
 #
 #   $ function update_zed_cache_Ubuntu { :; }
-#   $ distro_dependent_invoke "install_jail_zfs_packages" --noforce
+#   $ distro_dependent_invoke "update_zed_cache" --optional
 #
-# then nothing happens. Without `--noforce`, this invocation will cause an
-# error.
+#   If the distribution is `Debian`, nothing will happen.
 #
-function distro_dependent_invoke {
-  local distro_specific_fx_name="$1_$v_linux_distribution"
+#   $ function update_zed_cache_Ubuntu { :; }
+#   $ distro_dependent_invoke "update_zed_cache"
+#
+#   If the distribution is `Debian`, an error will be raised.
+#
+function invoke {
+  local base_fx_name=$1
+  local distro_specific_fx_name=$1_$v_linux_distribution
+  local invoke_option=${2:-}
+
+  if [[ ! $invoke_option =~ ^(|--optional)$ ]]; then
+    >&2 echo "Invalid invoke() option: $invoke_option"
+    exit 1
+  fi
+
+  hot_swap_script
+
+  # Invoke it regardless when it's not optional.
 
   if declare -f "$distro_specific_fx_name" > /dev/null; then
+    print_step_info_header "$distro_specific_fx_name"
+
     "$distro_specific_fx_name"
-  else
-    if ! declare -f "$1" > /dev/null && [[ "${2:-}" == "--noforce" ]]; then
-      : # do nothing
-    else
-      "$1"
-    fi
+  elif declare -f "$base_fx_name" > /dev/null || [[ ! $invoke_option == "--optional" ]]; then
+    print_step_info_header "$base_fx_name"
+
+    "$base_fx_name"
+  fi
+}
+
+# Tee-hee-hee!!
+#
+# This is extremely useful for debugging long procedures. Since bash scripts can't be modified while
+# running, this allows the dev to create a snapshot, and if the script fails after that, resume and
+# add the hotswap script, so that the new code will be loaded automatically.
+#
+function hot_swap_script {
+  if [[ -f $c_hotswap_file ]]; then
+    source "$c_hotswap_file"
   fi
 }
 
-# shellcheck disable=SC2120 # allow parameters passing even if no calls pass any
 function print_step_info_header {
+  local function_name=$1
+
   echo -n "
 ###############################################################################
-# ${FUNCNAME[1]}"
-
-  [[ "${1:-}" != "" ]] && echo -n " $1" || true
-
-  echo "
+# $function_name
 ###############################################################################
 "
 }
@@ -231,8 +258,6 @@ Root pool default create options: '"${c_default_rpool_create_options[*]/#-/$'\n'
 }
 
 function activate_debug {
-  print_step_info_header
-
   mkdir -p "$c_log_dir"
 
   exec 5> "$c_install_log"
@@ -251,8 +276,6 @@ function set_distribution_data {
 }
 
 function store_os_distro_information {
-  print_step_info_header
-
   lsb_release --all > "$c_os_information_log"
 
   # Madness, in order not to force the user to invoke "sudo -E".
@@ -276,8 +299,6 @@ function store_running_processes {
 }
 
 function check_prerequisites {
-  print_step_info_header
-
   local distro_version_regex=\\b${v_linux_version//./\\.}\\b
 
   if [[ ! -d /sys/firmware/efi ]]; then
@@ -308,8 +329,6 @@ function check_prerequisites {
 }
 
 function display_intro_banner {
-  print_step_info_header
-
   local dialog_message='Hello!
 
 This script will prepare the ZFS pools on the system, install Ubuntu, and configure the boot.
@@ -341,8 +360,6 @@ In such cases, the module building may fail abruptly, either without visible err
 }
 
 function save_disks_log {
-  print_step_info_header
-
   # shellcheck disable=SC2012 # `ls` may clean the output, but in this case, it doesn't matter
   ls -l /dev/disk/by-id | tail -n +2 | perl -lane 'print "@F[8..10]"' > "$c_disks_log"
 
@@ -360,8 +377,6 @@ LOG
 }
 
 function find_suitable_disks {
-  print_step_info_header
-
   # In some freaky cases, `/dev/disk/by-id` is not up to date, so we refresh. One case is after
   # starting a VirtualBox VM that is a full clone of a suspended VM with snapshots.
   #
@@ -426,8 +441,6 @@ If you think this is a bug, please open an issue on https://github.com/saveriomi
 # install_host_packages() and install_host_packages_UbuntuServer().
 #
 function set_zfs_ppa_requirement {
-  print_step_info_header
-
   apt update
 
   local zfs_package_version
@@ -450,25 +463,19 @@ function set_zfs_ppa_requirement_Debian {
 # to it being incorrectly setup).
 #
 function set_zfs_ppa_requirement_Linuxmint {
-  print_step_info_header
-
   perl -i -pe 's/^(deb cdrom)/# $1/' /etc/apt/sources.list
 
-  set_zfs_ppa_requirement
+  invoke "set_zfs_ppa_requirement"
 }
 
 # By using a FIFO, we avoid having to hide statements like `echo $v_passphrase | zpoool create ...`
 # from the logs.
 #
 function create_passphrase_named_pipe {
-  print_step_info_header
-
   mkfifo "$c_passphrase_named_pipe"
 }
 
 function register_exit_hook {
-  print_step_info_header
-
   function _exit_hook {
     rm -f "$c_passphrase_named_pipe"
 
@@ -517,8 +524,6 @@ export ZFS_FREE_TAIL_SPACE=12
 }
 
 function select_disks {
-  print_step_info_header
-
   if [[ "${ZFS_SELECTED_DISKS:-}" != "" ]]; then
     mapfile -d, -t v_selected_disks < <(echo -n "$ZFS_SELECTED_DISKS")
   else
@@ -558,8 +563,6 @@ Devices with mounted partitions, cdroms, and removable devices are not displayed
 }
 
 function select_pools_raid_type {
-  print_step_info_header
-
   local raw_pools_raid_type=
 
   if [[ -v ZFS_POOLS_RAID_TYPE ]]; then
@@ -603,8 +606,6 @@ function select_pools_raid_type {
 }
 
 function ask_root_password_Debian {
-  print_step_info_header
-
   set +x
   if [[ ${ZFS_DEBIAN_ROOT_PASSWORD:-} != "" ]]; then
     v_root_password="$ZFS_DEBIAN_ROOT_PASSWORD"
@@ -623,8 +624,6 @@ function ask_root_password_Debian {
 }
 
 function ask_encryption {
-  print_step_info_header
-
   set +x
 
   if [[ -v ZFS_PASSPHRASE ]]; then
@@ -655,8 +654,6 @@ Leave blank to keep encryption disabled.
 }
 
 function ask_boot_partition_size {
-  print_step_info_header
-
   if [[ ${ZFS_BOOT_PARTITION_SIZE:-} != "" ]]; then
     v_boot_partition_size=$ZFS_BOOT_PARTITION_SIZE
   else
@@ -675,8 +672,6 @@ Supported formats: '512M', '3G'" 30 100 ${c_default_boot_partition_size}M 3>&1 1
 }
 
 function ask_swap_size {
-  print_step_info_header
-
   if [[ ${ZFS_SWAP_SIZE:-} != "" ]]; then
     v_swap_size=$ZFS_SWAP_SIZE
   else
@@ -693,8 +688,6 @@ function ask_swap_size {
 }
 
 function ask_free_tail_space {
-  print_step_info_header
-
   if [[ ${ZFS_FREE_TAIL_SPACE:-} != "" ]]; then
     v_free_tail_space=$ZFS_FREE_TAIL_SPACE
   else
@@ -719,8 +712,6 @@ For detailed informations, see the wiki page: https://github.com/saveriomiroddi/
 }
 
 function ask_rpool_name {
-  print_step_info_header
-
   if [[ ${ZFS_RPOOL_NAME:-} != "" ]]; then
     v_rpool_name=$ZFS_RPOOL_NAME
   else
@@ -737,8 +728,6 @@ function ask_rpool_name {
 }
 
 function ask_pool_create_options {
-  print_step_info_header
-
   local bpool_create_options_message='Insert the create options for the boot pool
 
 The mount-related options are automatically added, and must not be specified.'
@@ -759,8 +748,6 @@ The encryption/mount-related options are automatically added, and must not be sp
 }
 
 function install_host_packages {
-  print_step_info_header
-
   if [[ $v_use_ppa == "1" ]]; then
     if [[ ${ZFS_SKIP_LIVE_ZFS_MODULE_INSTALL:-} != "1" ]]; then
       add-apt-repository --yes "$c_ppa"
@@ -785,8 +772,6 @@ function install_host_packages {
 }
 
 function install_host_packages_Debian {
-  print_step_info_header
-
   if [[ ${ZFS_SKIP_LIVE_ZFS_MODULE_INSTALL:-} != "1" ]]; then
     echo "zfs-dkms zfs-dkms/note-incompatible-licenses note true" | debconf-set-selections
 
@@ -807,27 +792,21 @@ function install_host_packages_Debian {
 # Differently from Ubuntu, Mint doesn't have the package installed in the live version.
 #
 function install_host_packages_Linuxmint {
-  print_step_info_header
-
   apt install --yes zfsutils-linux
 
-  install_host_packages
+  invoke "install_host_packages"
 }
 
 function install_host_packages_elementary {
-  print_step_info_header
-
   if [[ ${ZFS_SKIP_LIVE_ZFS_MODULE_INSTALL:-} != "1" ]]; then
     apt update
     apt install --yes software-properties-common
   fi
 
-  install_host_packages
+  invoke "install_host_packages"
 }
 
 function install_host_packages_UbuntuServer {
-  print_step_info_header
-
   if [[ $v_use_ppa != "1" ]]; then
     apt install --yes zfsutils-linux efibootmgr
 
@@ -859,8 +838,6 @@ function install_host_packages_UbuntuServer {
 }
 
 function setup_partitions {
-  print_step_info_header
-
   local required_tail_space=$((v_free_tail_space > c_temporary_volume_size ? v_free_tail_space : c_temporary_volume_size))
 
   for selected_disk in "${v_selected_disks[@]}"; do
@@ -916,8 +893,6 @@ function setup_partitions {
 }
 
 function install_operating_system {
-  print_step_info_header
-
   local dialog_message='The Ubuntu GUI installer will now be launched.
 
 Proceed with the configuration as usual, then, at the partitioning stage:
@@ -959,8 +934,6 @@ Proceed with the configuration as usual, then, at the partitioning stage:
 }
 
 function install_operating_system_Debian {
-  print_step_info_header
-
   # The temporary volume size displayed is an approximation of the format used by the installer,
   # but it's acceptable - the complexity required is not worth (eg. converting hypothetical units,
   # etc.).
@@ -1013,8 +986,6 @@ CONF
 }
 
 function install_operating_system_UbuntuServer {
-  print_step_info_header
-
   # O/S Installation
   #
   # Subiquity is designed to prevent the user from opening a terminal, which is (to say the least)
@@ -1056,8 +1027,6 @@ You can switch anytime to this terminal, and back, in order to read the instruct
 }
 
 function custom_install_operating_system {
-  print_step_info_header
-
   sudo "$ZFS_OS_INSTALLATION_SCRIPT"
 }
 
@@ -1108,8 +1077,6 @@ function create_pools {
 }
 
 function create_swap_volume {
-  print_step_info_header
-
   if [[ $v_swap_size -gt 0 ]]; then
     zfs create \
       -V "${v_swap_size}G" -b "$(getconf PAGESIZE)" \
@@ -1121,15 +1088,11 @@ function create_swap_volume {
 }
 
 function copy_zpool_cache {
-  print_step_info_header
-
   mkdir -p "$c_zfs_mount_dir/etc/zfs"
   cp /etc/zfs/zpool.cache "$c_zfs_mount_dir/etc/zfs/"
 }
 
 function sync_os_temp_installation_dir_to_rpool {
-  print_step_info_header
-
   # On Ubuntu Server, `/boot/efi` and `/cdrom` (!!!) are mounted, but they're not needed.
   #
   local mount_dir_submounts
@@ -1162,8 +1125,6 @@ function sync_os_temp_installation_dir_to_rpool {
 }
 
 function remove_temp_partition_and_expand_rpool {
-  print_step_info_header
-
   if (( v_free_tail_space < c_temporary_volume_size )); then
     if [[ $v_free_tail_space -eq 0 ]]; then
       local resize_reference=100%
@@ -1198,8 +1159,6 @@ function remove_temp_partition_and_expand_rpool {
 }
 
 function prepare_jail {
-  print_step_info_header
-
   for virtual_fs_dir in proc sys dev; do
     mount --rbind "/$virtual_fs_dir" "$c_zfs_mount_dir/$virtual_fs_dir"
   done
@@ -1210,8 +1169,6 @@ function prepare_jail {
 # See install_host_packages() for some comments.
 #
 function install_jail_zfs_packages {
-  print_step_info_header
-
   if [[ $v_use_ppa == "1" ]]; then
     chroot_execute "add-apt-repository --yes $c_ppa"
 
@@ -1236,8 +1193,6 @@ function install_jail_zfs_packages {
 }
 
 function install_jail_zfs_packages_Debian {
-  print_step_info_header
-
   chroot_execute 'echo "deb http://deb.debian.org/debian buster main contrib"     >> /etc/apt/sources.list'
   chroot_execute 'echo "deb-src http://deb.debian.org/debian buster main contrib" >> /etc/apt/sources.list'
 
@@ -1257,26 +1212,20 @@ APT'
 }
 
 function install_jail_zfs_packages_elementary {
-  print_step_info_header
-
   chroot_execute "apt install --yes software-properties-common"
 
-  install_jail_zfs_packages
+  invoke "install_jail_zfs_packages"
 }
 
 function install_jail_zfs_packages_UbuntuServer {
-  print_step_info_header
-
   if [[ $v_use_ppa != "1" ]]; then
     chroot_execute "apt install --yes zfsutils-linux zfs-initramfs grub-efi-amd64-signed shim-signed"
   else
-    install_jail_zfs_packages
+    invoke "install_jail_zfs_packages"
   fi
 }
 
 function prepare_efi_partition {
-  print_step_info_header
-
   # The other mounts are configured/synced in the EFI partitions sync stage.
   #
   chroot_execute "echo /dev/disk/by-uuid/$(blkid -s UUID -o value "${v_selected_disks[0]}"-part1) /boot/efi vfat defaults 0 0 > /etc/fstab"
@@ -1288,8 +1237,6 @@ function prepare_efi_partition {
 }
 
 function configure_and_update_grub {
-  print_step_info_header
-
   chroot_execute "perl -i -pe 's/GRUB_CMDLINE_LINUX_DEFAULT=\"\K/init_on_alloc=0 /'        /etc/default/grub"
 
   # Silence warning during the grub probe (source: https://git.io/JenXF).
@@ -1316,8 +1263,6 @@ function configure_and_update_grub {
 }
 
 function sync_efi_partitions {
-  print_step_info_header
-
   for ((i = 1; i < ${#v_selected_disks[@]}; i++)); do
     local synced_efi_partition_path="/boot/efi$((i + 1))"
 
@@ -1340,14 +1285,10 @@ function sync_efi_partitions {
 # See issue https://github.com/saveriomiroddi/zfs-installer/issues/110.
 #
 function update_initramfs {
-  print_step_info_header
-
   chroot_execute "update-initramfs -u"
 }
 
 function fix_filesystem_mount_ordering {
-  print_step_info_header
-
   chroot_execute "mkdir /etc/zfs/zfs-list.cache"
   chroot_execute "touch /etc/zfs/zfs-list.cache/$c_bpool_name /etc/zfs/zfs-list.cache/$v_rpool_name"
 
@@ -1406,8 +1347,6 @@ function fix_filesystem_mount_ordering {
 # The code is a straight copy of the `fstrim` service.
 #
 function configure_pools_trimming {
-  print_step_info_header
-
   chroot_execute "cat > /lib/systemd/system/zfs-trim.service << UNIT
 [Unit]
 Description=Discard unused ZFS blocks
@@ -1438,15 +1377,11 @@ TIMER"
 }
 
 function configure_remaining_settings {
-  print_step_info_header
-
   [[ $v_swap_size -gt 0 ]] && chroot_execute "echo /dev/zvol/$v_rpool_name/swap none swap discard 0 0 >> /etc/fstab" || true
   chroot_execute "echo RESUME=none > /etc/initramfs-tools/conf.d/resume"
 }
 
 function prepare_for_system_exit {
-  print_step_info_header
-
   for virtual_fs_dir in dev sys proc; do
     umount --recursive --force --lazy "$c_zfs_mount_dir/$virtual_fs_dir"
   done
@@ -1479,8 +1414,6 @@ function prepare_for_system_exit {
 }
 
 function display_exit_banner {
-  print_step_info_header
-
   local dialog_message="The system has been successfully prepared and installed.
 
 You now need to perform a hard reset, then enjoy your ZFS system :-)"
@@ -1496,59 +1429,59 @@ if [[ $# -ne 0 ]]; then
   display_help_and_exit
 fi
 
-activate_debug
-set_distribution_data
-distro_dependent_invoke "store_os_distro_information"
-store_running_processes
-check_prerequisites
-display_intro_banner
-check_system_memory
-save_disks_log
-find_suitable_disks
-distro_dependent_invoke "set_zfs_ppa_requirement"
-register_exit_hook
-create_passphrase_named_pipe
+invoke "activate_debug"
+invoke "set_distribution_data"
+invoke "store_os_distro_information"
+invoke "store_running_processes"
+invoke "check_prerequisites"
+invoke "display_intro_banner"
+invoke "check_system_memory"
+invoke "save_disks_log"
+invoke "find_suitable_disks"
+invoke "set_zfs_ppa_requirement"
+invoke "register_exit_hook"
+invoke "create_passphrase_named_pipe"
 
-select_disks
-select_pools_raid_type
-distro_dependent_invoke "ask_root_password" --noforce
-ask_encryption
-ask_boot_partition_size
-ask_swap_size
-ask_free_tail_space
-ask_rpool_name
-ask_pool_create_options
+invoke "select_disks"
+invoke "select_pools_raid_type"
+invoke "ask_root_password" --optional
+invoke "ask_encryption"
+invoke "ask_boot_partition_size"
+invoke "ask_swap_size"
+invoke "ask_free_tail_space"
+invoke "ask_rpool_name"
+invoke "ask_pool_create_options"
 
-distro_dependent_invoke "install_host_packages"
-setup_partitions
+invoke "install_host_packages"
+invoke "setup_partitions"
 
 if [[ "${ZFS_OS_INSTALLATION_SCRIPT:-}" == "" ]]; then
   # Includes the O/S extra configuration, if necessary (network, root pwd, etc.)
-  distro_dependent_invoke "install_operating_system"
+  invoke "install_operating_system"
 
-  create_pools
-  create_swap_volume
-  copy_zpool_cache
-  sync_os_temp_installation_dir_to_rpool
-  remove_temp_partition_and_expand_rpool
+  invoke "create_pools"
+  invoke "create_swap_volume"
+  invoke "copy_zpool_cache"
+  invoke "sync_os_temp_installation_dir_to_rpool"
+  invoke "remove_temp_partition_and_expand_rpool"
 else
-  create_pools
-  create_swap_volume
-  copy_zpool_cache
-  remove_temp_partition_and_expand_rpool
+  invoke "create_pools"
+  invoke "create_swap_volume"
+  invoke "copy_zpool_cache"
+  invoke "remove_temp_partition_and_expand_rpool"
 
-  custom_install_operating_system
+  invoke "custom_install_operating_system"
 fi
 
-prepare_jail
-distro_dependent_invoke "install_jail_zfs_packages"
-prepare_efi_partition
-configure_and_update_grub
-sync_efi_partitions
-update_initramfs
-fix_filesystem_mount_ordering
-configure_pools_trimming
-configure_remaining_settings
+invoke "prepare_jail"
+invoke "install_jail_zfs_packages"
+invoke "prepare_efi_partition"
+invoke "configure_and_update_grub"
+invoke "sync_efi_partitions"
+invoke "update_initramfs"
+invoke "fix_filesystem_mount_ordering"
+invoke "configure_pools_trimming"
+invoke "configure_remaining_settings"
 
-prepare_for_system_exit
-display_exit_banner
+invoke "prepare_for_system_exit"
+invoke "display_exit_banner"