Containerfile

@@ -65,6 +65,7 @@ COPY --from=cpio . /
 COPY --from=mtools . /
 COPY --from=xz . /
 COPY --from=grub . /
+COPY --from=util-linux . /
 
 FROM base as dev
 COPY --from=gcc . /
@@ -197,8 +198,6 @@ FROM build AS install
 ENV SOURCE_DATE_EPOCH=1
 RUN <<-EOF
     set -eux
-    dd if=/dev/zero bs=1M count=10 >> user.img
-    mformat -v user -i user.img -N 0 ::
     find iso -exec touch -hcd "@0" "{}" +
     xorrisofs \
         -output airgap.iso \
@@ -218,8 +217,24 @@ RUN <<-EOF
         -no-emul-boot \
         -isohybrid-gpt-basdat \
         -follow-links \
-        -append_partition 3 0xb user.img \
         iso/
+
+    # Increase ISO size by 512 MB to create space for the third partition
+    dd if=/dev/zero bs=1M count=512 >> airgap.iso
+
+    # Append a new partition that uses the additional space
+    echo ", +" | sfdisk --append airgap.iso
+
+    # Set the newly added third partition to FAT32
+    sfdisk --part-type airgap.iso 3 b
+
+    # Calculate the byte offset of the third partition
+    # This is done by finding the end of the first partition using fdisk,
+    # adding 1 sector, and multiplying by 512 (since each sector is 512 bytes).
+    OFFSET=$(fdisk -l airgap.iso | awk '/^airgap.iso1/ {print ($4 + 1) * 512}')
+
+    # Format the third partition as FAT32 and label it 'USER'
+    mformat -v USER -i airgap.iso@@$OFFSET ::
 EOF
 
 ## Minimal Autorun SD card image