[libvirt-users] surprising <backingStore type='file'> setting in domain.xml

Thomas Stein hello at himbee.re
Thu May 16 16:02:00 UTC 2019

Hello all.

My currently used versions: libvirt-5.2.0 and qemu-4.0.0.

Here is my problem. I'm struggeling since a few weeks with a strange 
behaviour by either qemu or libvirt. After a reboot of
the hardware node the $domain.xml contains suddenly a backingStore 
setting which was not there before reboot.
Something like that:

     <disk type='file' device='disk'>
       <driver name='qemu' type='qcow2'/>
       <backingStore type='file'>
         <format type='qcow2'/>
         <source file='/var/lib/libvirt/images/shinymail.qcow2'/>
       <target dev='vda' bus='virtio'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x07' 

This obviousely happens after a backup has been running. The Backup 
Script looks like this:

virsh snapshot-create-as --domain shinymail weekly --diskspec 
+%Y-%m-%d) --disk-only --atomic --no-metadata

cp ...

virsh blockcommit shinymail vda --active --verbose --pivot

So after that "dmblklist shinymail" does show the right source file but 
after a reboot it tries to use the weekly snapshot
again which leads to filesystem errors.

Someone has an idea what could cause such a behaviour?


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