B.17.3. Logic and Configuration Errors

A well-formatted XML document can contain errors that are correct in syntax but libvirt cannot parse. Many of these errors exist, with two of the most common cases outlined below.

B.17.3.1. Vanishing parts

Symptom
Parts of the change you have made do not show up and have no effect after editing or defining the domain. The define or edit command works, but when dumping the XML once again, the change disappears.
Investigation
This error likely results from a broken construct or syntax that libvirt does not parse. The libvirt tool will generally only look for constructs it knows but ignore everything else, resulting in some of the XML changes vanishing after libvirt parses the input.
Solution
Validate the XML input before passing it to the edit or define commands. The libvirt developers maintain a set of XML schemas bundled with libvirt which define the majority of the constructs allowed in XML documents used by libvirt.
Validate libvirt XML files using the following command: 
# virt-xml-validate libvirt.xml
If this command passes, libvirt will likely understand all constructs from your XML, except if the schemas cannot detect options which are valid only for a given hypervisor. For example, any XML generated by libvirt as a result of a virsh dump command should validate without error.