Re: [libvirt] surprising <backingStore type='file'> setting in domain.xml
On 5/16/19 10:20 AM, Thomas Stein wrote:
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 $domain.xml contains suddenly a backingStore
setting which was not there before reboot.
Something like that:
<devices>
<emulator>/usr/bin/qemu-system-x86_64</emulator>
<disk type='file' device='disk'>
<driver name='qemu' type='qcow2'/>
<source
file='/var/lib/libvirt/shinymail/shinymail_weekly.qcow2-2019-05-15'/>
<backingStore type='file'>
<format type='qcow2'/>
<source file='/var/lib/libvirt/images/shinymail.qcow2'/>
Yes, this matches:
</backingStore>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00'
slot='0x07'
function='0x0'/>
</disk>
...
This obviousely happens after a backup has been running. The Backup
Script looks like this:
<snip>
virsh snapshot-create-as --domain shinymail weekly --diskspec
vda,file=/var/lib/libvirt/shinymail/shinymail_weekly.qcow2-$(date
+%Y-%m-%d) --disk-only --atomic --no-metadata
the effects of this command.
Ultimately, I'm TRYING to get my new 'virsh domain-backup' command
integrated into the next libvirt release, which has the advantage of
performing a backup WITHOUT having to modify the <domain> XML. But until
that happens, any time you use 'virsh snapshot-create-as' as part of a
sequence for performing backups, you ARE modifying the <domain> XML, and
if you want to revert to the external backup, or if...
cp ...
virsh blockcommit shinymail vda --active --verbose --pivot
<snip>
...blockcommit fails for whatever reason to undo the effects of
'snapshot-create-as' in creating a temporary overlay, then yes, you do
have to worry about the temporary overlay being in the way, where you'll
have to manually edit the <domain> definition to match the actual disk
layouts you really want.
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?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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