Stage the Windows ISO files with rsync before copying them into the image

Copy the ISO without install.wim to a staging directory, split install.wim
into it, and fill the image with one recursive mcopy instead of a mmd and
mcopy per directory. rsync --chmod keeps the staged directories writable so
that cleanup can remove them.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

build-windows-install-disk.sh

@@ -15,7 +15,7 @@
 #
 # Dependencies
 #   macOS (Homebrew)  wimlib dosfstools gptfdisk mtools
-#   Debian            wimtools dosfstools gdisk mtools udisks2
+#   Debian            wimtools dosfstools gdisk mtools rsync udisks2
 #
 # Usage: build-windows-install-disk.sh [--force] ISO [OUTPUT.img]
 # OUTPUT defaults to the ISO path with ".img" in place of ".iso".
@@ -46,8 +46,8 @@ die() {
   exit 1
 }
 
-# The build has four steps; step prints a numbered heading for each of them.
-total_steps=4
+# The build has five steps; step prints a numbered heading for each of them.
+total_steps=5
 step_number=0
 step() {
   step_number=$((step_number + 1))
@@ -88,7 +88,7 @@ for dir in ${brew_prefix:+"$brew_prefix/sbin"} /opt/homebrew/sbin /usr/local/sbi
   [[ -d "$dir" ]] && PATH="$PATH:$dir"
 done
 
-tools=(wimlib-imagex mkfs.fat sgdisk mcopy mmd)
+tools=(wimlib-imagex mkfs.fat sgdisk mcopy rsync)
 [[ "$os" == Darwin ]] && tools+=(hdiutil)
 missing=()
 for tool in "${tools[@]}"; do
@@ -98,7 +98,7 @@ if ((${#missing[@]} > 0)); then
   if [[ "$os" == Darwin ]]; then
     hint="brew install wimlib dosfstools gptfdisk mtools"
   else
-    hint="apt install wimtools dosfstools gdisk mtools"
+    hint="apt install wimtools dosfstools gdisk mtools rsync"
   fi
   die "missing tools: ${missing[*]} ($hint)"
 fi
@@ -128,6 +128,8 @@ cleanup() {
       udisksctl unmount -b "$loop_device" >/dev/null 2>&1 || true
       udisksctl loop-delete -b "$loop_device" >/dev/null 2>&1 || true ;;
   esac
+  # Staged directories may be read-only when the run was cancelled early.
+  chmod -R u+rwX "$work_dir" >/dev/null 2>&1 || true
   rm -rf "$work_dir"
 }
 trap cleanup EXIT
@@ -202,20 +204,27 @@ install_wim="$mount_dir/sources/install.wim"
 [[ -d "$mount_dir/efi/boot" ]] || die "efi/boot was not found in the ISO; is it a UEFI Windows ISO?"
 note "install.wim: $(stat "${size_args[@]}" "$install_wim") bytes"
 
+# The staging directory holds everything that goes into the image: the ISO files
+# without install.wim, and the install.swm parts in sources/.
+stage_dir="$work_dir/stage"
+mkdir "$stage_dir"
+step "Staging the ISO files without install.wim"
+# The UDF mount is read-only, so its directories are too; --chmod keeps the copies
+# writable, otherwise cleanup cannot remove them.
+run rsync -rt --chmod=u+rwX --exclude=/sources/install.wim "$mount_dir/" "$stage_dir/"
+run mkdir -p "$stage_dir/sources"
+
 # Parts must stay below the 4 GiB FAT32 file limit; wimlib takes MiB.
 step "Splitting install.wim into install.swm parts (FAT32 files must stay below 4 GiB)"
-split_dir="$work_dir/split"
-mkdir "$split_dir"
-run wimlib-imagex split "$install_wim" "$split_dir/install.swm" 3800 >/dev/null
-for part in "$split_dir"/install*.swm; do
+run wimlib-imagex split "$install_wim" "$stage_dir/sources/install.swm" 3800 >/dev/null
+for part in "$stage_dir"/sources/install*.swm; do
   note "$(basename "$part"): $(stat "${size_args[@]}" "$part") bytes"
 done
 
-# Size the image: everything but install.wim, the split parts, and 5% plus 64 MiB
-# of room for FAT32 metadata and partition alignment.
+# Size the image: the staged files, and 5% plus 64 MiB of room for FAT32
+# metadata and partition alignment.
 content_bytes=$(
-  { find "$mount_dir" -type f ! -path "$install_wim" -exec stat "${size_args[@]}" {} +
-    find "$split_dir" -type f -exec stat "${size_args[@]}" {} +; } |
+  find "$stage_dir" -type f -exec stat "${size_args[@]}" {} + |
     awk '{ total += $1 } END { printf "%d", total }'
 )
 mib=$((1024 * 1024))
@@ -240,29 +249,13 @@ mtools_image="$image@@$((2048 * 512))"
 note "partition: $sectors sectors, formatted as FAT32 (label WINPE)"
 export MTOOLS_SKIP_CHECK=1
 
-copy_dir() { # copy_dir SOURCE_DIR TARGET_DIR_IN_IMAGE
-  local source="$1" target="$2" files=() entry
-  while IFS= read -r -d '' entry; do
-    files+=("$entry")
-  done < <(find "$source" -maxdepth 1 -type f ! -path "$install_wim" -print0)
-  if ((${#files[@]} > 0)); then
-    note "\$ mcopy -Q -m -i $mtools_image <${#files[@]} files from ${source#"$mount_dir"} > ::$target/"
-    mcopy -Q -m -i "$mtools_image" "${files[@]}" "::$target/"
-  fi
-}
-
 step "Copying the installation files into the image"
-copy_dir "$mount_dir" ""
-dir_count=0
-while IFS= read -r -d '' dir; do
-  relative="${dir#"$mount_dir"/}"
-  dir_count=$((dir_count + 1))
-  run mmd -i "$mtools_image" "::$relative"
-  copy_dir "$dir" "$relative"
-done < <(find "$mount_dir" -mindepth 1 -type d -print0 | sort -z)
-note "copied $dir_count directories"
-note "copying the install*.swm parts to sources/"
-run mcopy -Q -m -i "$mtools_image" "$split_dir"/install*.swm "::sources/"
+entries=()
+while IFS= read -r -d '' entry; do
+  entries+=("$entry")
+done < <(find "$stage_dir" -mindepth 1 -maxdepth 1 -print0)
+note "\$ mcopy -s -Q -m -i $mtools_image <${#entries[@]} entries from the staging directory> ::/"
+mcopy -s -Q -m -i "$mtools_image" "${entries[@]}" "::/"
 
 partial_output=""
 printf 'Built Windows 11 installation disk: %s\n' "$output"