AlpineLinux netboot initrd missing ext4 module

alpine-netboot-missing-ext4-verify.sh

# download firecracker
latest=$(basename $(curl -fsSLI -o /dev/null -w  %{url_effective} https://github.com/firecracker-microvm/firecracker/releases/latest))
curl -LOJ https://github.com/firecracker-microvm/firecracker/releases/download/${latest}/firecracker-${latest}-$(uname -m)
mv firecracker-${latest}-$(uname -m) firecracker
chmod +x firecracker

# download netbook kernel and initrd
curl --remote-name-all -LC- https://mirrors.aliyun.com/alpine/v3.12/releases/x86_64/netboot/{modloop,vmlinuz,config,initramfs}-virt

# vmlinux
curl -LOC- https://raw.githubusercontent.com/torvalds/linux/master/scripts/extract-vmlinux
chmod +x extract-vmlinux
./extract-vmlinux $PWD/vmlinuz-virt > vmlinux-virt

# rootfs - invalid rootfs to check the initrd modules
fallocate -l 1G alpine.rootfs.ext4

# conf
cat <<CONF > alpine.json
{
  "boot-source": {
    "initrd_path":"initramfs-virt",
    "kernel_image_path": "vmlinux-virt",
    "boot_args": "console=ttyS0 reboot=k panic=1 pci=off modules=virtio_mmio,ext4 rootfstype=ext4"
  },
  "drives": [
    {
      "drive_id": "rootfs",
      "path_on_host": "ubuntu.rootfs.ext4",
      "is_root_device": true,
      "is_read_only": false
    }
  ],
  "machine-config": {
    "vcpu_count": 1,
    "mem_size_mib": 1024,
    "ht_enabled": false
  }
}
CONF

# start
rm /tmp/firecracker.socket;./firecracker --api-sock /tmp/firecracker.socket --config-file alpine.json

# missing ext4
cat /proc/filesystems