[Bug 1620407] Re: vm startup broken when interface definition has script tag

[Matthias Ferdinand]

On Thu, Jan 12, 2017 at 01:25:28PM -0000, ChristianEhrhardt wrote:
> On libvirt 1.3 I got:
> error: Failed to start domain testguest-X-on-X
> error: Unable to get index for interface mf_testet: No such device

on xenial, that is the exact error message we get, while on "precise"
kvm hosts (libvirt 0.9.8) the same setup works.

> As well as (other distro but same applies) https://fedoraproject.org/wiki/How_to_debug_Virtualization_problems?rd=Tools/Virtualization/BugReporting#Errors_using_.3Cinterface_type.3D.27ethernet.27.2F.3E
Yes, "ethernet" type networking is made difficult by standard security
settings, and we do have our own infrastructure installed to overcome
these restrictions. One such measure is having a daemon running as root
that does the actual interface creation, triggered by the interface
setup script.

This error message "Unable to get index..." is generated by libvirt,
before qemu is even invoked. While it is perfectly ok for interfaces
with setup scripts to not yet exist before qemu can invoke the script,
libvirt 1.3 nonetheless pre-checks for its existence. 

This is what the bug report and the patch is about. With the patch
applied (removal of existence check for scripted interfaces), libvirt
1.3 again does the right thing.

Regards
Matthias

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https://bugs.launchpad.net/bugs/1620407

Title:
  vm startup broken when interface definition has script tag

Status in libvirt package in Ubuntu:
  Incomplete

Bug description:
  Ubuntu 16.04.1 LTS (amd64)
  libvirt-bin 1.3.1-1ubuntu10.1

  We use external scripts to setup tap interfaces, e.g.

      <interface type='ethernet'>
        <mac address='52:54:00:18:0d:a3'/>
        <script path='/etc/libvirt/14v/mf_testet.sh'/>
        <target dev='mf_testet'/>
        <model type='virtio'/>
        <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
      </interface>

  Starting the VM throws an error message ("interface not found" or
  something like that).

  IIUC, the script invocation is done by qemu, so the interface
  may not yet exist when libvirt is constructing the qemu cmd args.
  Checking for that interface in advance therefore is a bug.

  Attached patch skips the check if a <script> parameter is provided.

  Regards
  Matthias Ferdinand

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