[libvirt-users] Create and revert to snapshot fails silently after device update on running domain

[Jasper Spit]

Hi list,

I'm having an issue with snapshot creation. Scenario:

qemu 1.1
libvirt 0.9.12

I create a domain, and start it. The domain has 1 IDE cdrom device 
defined (see below).
When started, I want to mount an ISO file to it. So I do 
updateDeviceFlags in libvirt-python or update-device in virsh (both have 
the same problem).
This works fine, the ISO image becomes available to the domain. Now I 
create a snapshot on the still running domain using snapshotCreateXML in 
libvirt-python or snapshot-create in virsh. The command returns 
immediately without error (a normal snapshot takes several seconds to 
complete). If I revert to this snapshot this command also returns 
immediately without error, but the snapshot is not actually reverted to, 
the domain remains running in the same state as if nothing had happened 
(I test this by verifying console output and checking if a testfile is 
present on the domain). If I do not use the update device commands prior 
to creating a snapshot, all is well. If I remove the source from the 
cdrom device using update device, the snapshots work properly again.

Any idea what causes this?

Steps to reproduce using virsh:

virsh # start 4d5d722b-864c-657e-0f39-55d1bafc760e
Domain 4d5d722b-864c-657e-0f39-55d1bafc760e started

virsh # snapshot-create 4d5d722b-864c-657e-0f39-55d1bafc760e
Domain snapshot 1348653920 created

virsh # snapshot-revert 4d5d722b-864c-657e-0f39-55d1bafc760e 1348653920

All is good, the snapshot is reverted to properly. Now I update the 
cdrom device:

virsh # update-device 4d5d722b-864c-657e-0f39-55d1bafc760e deb.xml
Device updated successfully

virsh # snapshot-create 4d5d722b-864c-657e-0f39-55d1bafc760e
Domain snapshot 1348654116 created

Command returns instantly.

virsh # snapshot-revert 4d5d722b-864c-657e-0f39-55d1bafc760e 1348654116

No errors, but the snapshot is not reverted to. Now I remove the 
<source .../> again and do an update-device.

virsh # update-device 4d5d722b-864c-657e-0f39-55d1bafc760e deb-off.xml
Device updated successfully

virsh # snapshot-create 4d5d722b-864c-657e-0f39-55d1bafc760e
Domain snapshot 1348654540 created

virsh # snapshot-revert 4d5d722b-864c-657e-0f39-55d1bafc760e 1348654540

Snapshot is created and reverted to properly.

virsh # dumpxml 4d5d722b-864c-657e-0f39-55d1bafc760e
<domain type='kvm' id='135'>
   <name>4d5d722b-864c-657e-0f39-55d1bafc760e</name>
   <uuid>4d5d722b-864c-657e-0f39-55d1bafc760e</uuid>
   <memory unit='KiB'>786432</memory>
   <currentMemory unit='KiB'>786432</currentMemory>
   <vcpu placement='static'>1</vcpu>
   <os>
     <type arch='x86_64' machine='pc-1.1'>hvm</type>
     <boot dev='hd'/>
     <boot dev='cdrom'/>
   </os>
   <features>
     <acpi/>
     <apic/>
     <pae/>
   </features>
   <clock offset='utc'/>
   <on_poweroff>destroy</on_poweroff>
   <on_reboot>restart</on_reboot>
   <on_crash>destroy</on_crash>
   <devices>
     <emulator>/usr/bin/kvm</emulator>
     <disk type='file' device='cdrom'>
       <driver name='qemu' type='raw'/>
       <source 
file='/data/images/debian-live-6.0.4-amd64-standard.iso'/>
       <target dev='hdc' bus='ide'/>
       <readonly/>
       <alias name='ide0-1-0'/>
       <address type='drive' controller='0' bus='1' target='0' 
unit='0'/>
     </disk>
     <disk type='file' device='disk'>
       <driver name='qemu' type='qcow2'/>
       <source 
file='/data/domains/2f8baacd-563c-b747-b621-c0ddb4aa84bd'/>
       <target dev='vda' bus='virtio'/>
       <alias name='virtio-disk0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x05' 
function='0x0'/>
     </disk>
     <controller type='usb' index='0'>
       <alias name='usb0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x2'/>
     </controller>
     <controller type='ide' index='0'>
       <alias name='ide0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x1'/>
     </controller>
     <interface type='bridge'>
       <mac address='52:54:00:39:86:29'/>
       <source bridge='br0'/>
       <target dev='vnet2'/>
       <model type='virtio'/>
       <alias name='net0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x03' 
function='0x0'/>
     </interface>
     <input type='tablet' bus='usb'>
       <alias name='input0'/>
     </input>
     <input type='mouse' bus='ps2'/>
     <graphics type='vnc' port='5902' autoport='yes'/>
     <video>
       <model type='vga' vram='9216' heads='1'/>
       <alias name='video0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x02' 
function='0x0'/>
     </video>
     <memballoon model='virtio'>
       <alias name='balloon0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x04' 
function='0x0'/>
     </memballoon>
   </devices>
   <seclabel type='none'/>
</domain>

deb.xml:

<disk type='file' device='cdrom'>
   <driver name='qemu' type='raw'/>
   <source file='/data/images/debian-live-6.0.4-amd64-standard.iso'/>
   <target dev='hdc' bus='ide'/>
</disk>

deb-off.xml:

<disk type='file' device='cdrom'>
   <driver name='qemu' type='raw'/>
   <target dev='hdc' bus='ide'/>
</disk>

Thanks much,

- Jasper