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[Silvan Kaiser <silvan@xxxxxxxxxxx>]

Public bug reported:

Afaics Nova breaks with Qemu versions newer than the minimum required
version.

The change at [1] added support for setting MTU size in the libvirt settings of guests. This code checks for a minimum libvirt version 3.3.0 [2] but not for a required Qemu version.
The Nova minimum required Qemu version is 2.5 currently according to [3] (which is the latest release available with Ubuntu Xenial 16.04).
Afaics Qemu added support with release 2.9 [4] which means versions 2.5 to 2.8 of Qemu will break despite being listed as supported iiuc.
This issue broke our CIs. For verification i checked the master commit [5] which merged prior to [1] which tested ok with our CI.

The fix probably is to simply add a check for the minimum required Qemu
version beside the minimum required libvirt version.


[1] https://review.openstack.org/#/c/553072/
[2] https://github.com/openstack/nova/blob/4ea64cad3fcc4897690bfb2c02d2b06d65db4dcf/nova/virt/libvirt/vif.py#L55
[3] https://wiki.openstack.org/wiki/LibvirtDistroSupportMatrix
[4] https://wiki.qemu.org/ChangeLog/2.9)
[5] https://review.openstack.org/#/c/570656/

** Affects: nova
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1779626

Title:
  MTU setting feature conflicts with minimum Qemu version

Status in OpenStack Compute (nova):
  New

Bug description:
  Afaics Nova breaks with Qemu versions newer than the minimum required
  version.

  The change at [1] added support for setting MTU size in the libvirt settings of guests. This code checks for a minimum libvirt version 3.3.0 [2] but not for a required Qemu version.
  The Nova minimum required Qemu version is 2.5 currently according to [3] (which is the latest release available with Ubuntu Xenial 16.04).
  Afaics Qemu added support with release 2.9 [4] which means versions 2.5 to 2.8 of Qemu will break despite being listed as supported iiuc.
  This issue broke our CIs. For verification i checked the master commit [5] which merged prior to [1] which tested ok with our CI.

  The fix probably is to simply add a check for the minimum required
  Qemu version beside the minimum required libvirt version.

  
  [1] https://review.openstack.org/#/c/553072/
  [2] https://github.com/openstack/nova/blob/4ea64cad3fcc4897690bfb2c02d2b06d65db4dcf/nova/virt/libvirt/vif.py#L55
  [3] https://wiki.openstack.org/wiki/LibvirtDistroSupportMatrix
  [4] https://wiki.qemu.org/ChangeLog/2.9)
  [5] https://review.openstack.org/#/c/570656/

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