XML validation of <filesystem type='mount'> with reordered sub-elements fails

Software environment

• Operating system: Arch Linux
• Architecture: x86_64
• kernel version: 5.19.13
• libvirt version: 8.8.0
• Hypervisor and version: QEMU 7.1.0

Description of problem

This is a only a minor issue. Please see https://github.com/virt-manager/virt-manager/issues/437 for background.

Steps to reproduce

1. virt-install --osinfo linux2022 --disk none --filesystem "/tmp,host,driver.type=virtiofs" --memorybacking "source.type=memfd,access.mode=shared" --print-xml > /tmp/foo.xml
2. virsh define /tmp/foo.xml --validate FAILS
3. virsh define /tmp/foo.xml WORKS
4. virt-xml-validate /tmp/foo.xml FAILS

Additional information

• It seems odd that libvirt won't validate the domain XML but will accept it otherwise
• The order of the XML nodes matters. This fails:

<filesystem type="mount">
  <source dir="/tmp"/>
  <target dir="host"/>
  <driver type="virtiofs"/>
</filesystem>

• This works:

<filesystem type="mount">
  <driver type="virtiofs"/>
  <source dir="/tmp"/>
  <target dir="host"/>
</filesystem>