What were you trying to do that didn't work?

Live update per-virtqueue iothread setting of vm disk, it returned success but nothing changed. I expect it to return failure with clear error message.

Please provide the package NVR for which bug is seen:

libvirt-10.0.0-1.el9.x86_64

How reproducible:

100%

Steps to reproduce

1. Start guest with per-virtqueue iothread setting

   # virsh dumpxml uefi --xpath //disk
   <disk type="file" device="disk">
     <driver name="qemu" type="qcow2" queues="3">
       <iothreads>
         <iothread id="1">
           <queue id="0"/>
           <queue id="1"/>
         </iothread>
         <iothread id="3">
           <queue id="2"/>
         </iothread>
       </iothreads>
     </driver>
     <source file="/var/lib/libvirt/images/c.qcow2" index="1"/>
     <backingStore/>
     <target dev="vdb" bus="virtio"/>
     <alias name="virtio-disk1"/>
     <address type="pci" domain="0x0000" bus="0x07" slot="0x00" function="0x0"/>
   </disk>
   

1. Update per-virtqueue iothread setting

# cat vdb.xml
<disk type="file" device="disk">
  <driver name="qemu" type="qcow2" queues="3">
    <iothreads>
      <iothread id="1"/>
      <iothread id="2"/>
      <iothread id="3"/>
      <iothread id="4"/>
    </iothreads>
  </driver>
  <source file="/var/lib/libvirt/images/c.qcow2" index="3"/>
  <backingStore/>
  <target dev="vdb" bus="virtio"/>
  <alias name="virtio-disk1"/>
  <address type="pci" domain="0x0000" bus="0x07" slot="0x00" function="0x0"/>
</disk>

# virsh update-device uefi vdb.xml 
Device updated successfully

1. Check vm xml

# virsh dumpxml uefi --xpath //disk
<disk type="file" device="disk">
  <driver name="qemu" type="qcow2" queues="3">
    <iothreads>
      <iothread id="1">
        <queue id="0"/>
        <queue id="1"/>
      </iothread>
      <iothread id="3">
        <queue id="2"/>
      </iothread>
    </iothreads>
  </driver>
  <source file="/var/lib/libvirt/images/c.qcow2" index="1"/>
  <backingStore/>
  <target dev="vdb" bus="virtio"/>
  <alias name="virtio-disk1"/>
  <address type="pci" domain="0x0000" bus="0x07" slot="0x00" function="0x0"/>
</disk>

Expected results

Update-device returns failure with clear error message

Actual results

Update-device returned success, but no change happened