Editing libvirt xml file

vladimir franciz blando vladimir.blando at gmail.com
Wed Nov 4 18:37:20 UTC 2020


Already found a solution which entails hacking nova database, specifically
the instance_system_metadata table

Regards
Vlad


On Fri, Oct 30, 2020 at 4:57 PM vladimir franciz blando <
vladimir.blando at gmail.com> wrote:

> Yes, I am fully aware of support implications if you edit this.  But
> fortunately this is not in any way a vendor support OpenStack deployment
>
> On Fri, Oct 30, 2020 at 1:29 PM Sean Mooney <smooney at redhat.com> wrote:
>
>> On Fri, 2020-10-30 at 17:23 +0000, Stephen Finucane wrote:
>> > On Fri, 2020-10-30 at 11:56 -0500, vladimir franciz blando wrote:
>> > > Hi,
>> > > I edited the  libvirt xml (virsh edit...) file of a running Windows
>> > > server instance because I changed the video model type from cirrus to
>> > > vmvga so it can support a higher resolution on a console (cirrus
>> > > supports up to 1280 only).
>> > > After editing, i "soft-rebooted" the instance and the new
>> > > configuration sticks.  That's awesome.
>> >
>> > Please don't do this :) You shouldn't change things about an instance
>> > behind nova's back. It breaks resource tracking and can cause all sorts
>> > of horribleness.
>>
>> if you have support form an openstack vendor like redhat editing the
>> domain
>> xml also make that vm unsupported until its restroed to the way nova
>> generated.
>> it might also make other issue caused as a resulted unsupported.
>> so unless you are self supporting you cloud be very carful with doing
>> this.
>> >
>> > > But when you do a "hard-reboot" it will revert back to the original
>> > > config.
>> >
>> > Hard reboot builds configuration from scratch, dumping the existing
>> > XML. This is built from the same things used when you first create the
>> > instance (flavor + extra specs, image + metadata, host-level config,
>> > ...).
>> >
>> > What you want is the 'hw_video_model' image metadata property. Set this
>> > and rebuild your instance:
>> >
>> >         openstack image set --property hw_video_model=vmvga $IMAGE
>> this is the supported way to change this value ^
>> it will take effect for new instances.
>> >         openstack server rebuild $SERVER $IMAGE
>> and this is the only supported api action that can also change this value.
>> however i dont think rebuilding to the same image will update the image
>> metadata.
>> you currenlty need to rebuild to a new image. this is due to an
>> optiomisation we
>> have to avoid needing to go to the scheuler if we use the same image.
>>
>> the unsupported way to change this without rebuilding the instance is to
>> add
>> img_hw_video_model=vmvga to the system metadata table for that instance.
>>
>> if your cloud is supported by a vendor this will also invalidate your
>> suport
>> in all likely hood as db modificaiton generally are unsupported without
>> an exception.
>> if you can rebuild the guest that is the best approch but it wont work
>> for boot form volume
>> instances and it willl destory all data in the root disk of all other
>> instances.
>>
>> >
>> > Note that rebuild is a destructive operation so be sure you're aware of
>> > what this is doing before you do it.
>> >
>> > Stephen
>> >
>> > > I also tried to do a "shut-down" then "start" again, but it still
>> > > reads the original config.  Not sure where it  is reading the config
>> > > from...
>> > >
>> > > Regards
>> > > Vlad
>> >
>> >
>>
>>
>>
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