# GPT disk with a single HFS+ partition named VMIX. macOS mounts it natively by
# name at /Volumes/VMIX (its FAT driver rejects Linux-made FAT volumes as
# "damaged"; HFS+ made by mkfs.hfsplus mounts cleanly). The partition starts at
# 1 MiB. Files are staged with their target names and copied in via libguestfs.
# files: list of { source = <path|drv>; name = "dest name"; } — directories copied recursively.
{ pkgs, lib, ... }:
{ name ? "vmix", files, size ? "64M" }:
pkgs.runCommand "${name}-vmix-volume.img" {
  nativeBuildInputs = with pkgs; [ hfsprogs gptfdisk gnutar libguestfs-with-appliance ];
} ''
  mkdir stage
  ${lib.concatMapStringsSep "\n" (f: ''
    mkdir -p "$(dirname "stage/${f.name}")"
    cp -r --no-preserve=mode ${f.source} "stage/${f.name}"
  '') files}
  tar -C stage -cf stage.tar .

  truncate -s ${size} $out
  sgdisk -n 1:2048:0 -t 1:AF00 -c 1:VMIX $out >/dev/null
  FIRST=$(sgdisk -i 1 $out | sed -n 's/First sector: \([0-9]*\).*/\1/p')
  LAST=$(sgdisk -i 1 $out | sed -n 's/Last sector: \([0-9]*\).*/\1/p')
  truncate -s $(( (LAST - FIRST + 1) * 512 )) hfs.part
  mkfs.hfsplus -v VMIX hfs.part >/dev/null

  # tar-in takes a host-side tarball and unpacks it into the mounted volume
  guestfish -a hfs.part run : mount /dev/sda / : tar-in stage.tar / : ls / : umount /
  dd if=hfs.part of=$out bs=512 seek=$FIRST conv=notrunc status=none
''