Add libvirt domain XML option

We’re having an issue with PXE not getting the image fast enough (known issue apparently), causing some systems to hang (no boot device found typical bios msg)

What we found is that libvirt has an option to help force a reboot if that happens.
OS/Bios has the RebootTimeout

We’ve verified this works as we expect with Virsh

I’ve tried to find a way to configure this some place but it doesnt seem like there is any ability to do that.

After digging and reading lots of code, i think maybe the easiest solution would be to fork the fog-libvirt and inject my settings there (hard coded or pulled from a file, but, just something simple)

Im sure it would be awesome to really fix this the right way, but with my ruby skill i doubt you’d accept a PR :slight_smile:

Also working up the stack to expose it to the end user is likely a LOT more work than hijacking the fog-libvirt module.

So perhaps you’re wondering what the question is?!

Does this approach make sense (with the idea that speed/ease are key)
Did i over look anything that would allow us to solve this problem easily without having to modify someone else’s source.

The other method that came to mind was a plugin that hooked in to the provisioning process, but that seemed like it would be more effort with some higher odds of complication. I’ve dug enough that it seems possible but i dont know enough to judge the effort involved in this method.


I agree fog-libvirt is probably the best place - sadly we don’t maintain Fog, although we do have a couple of developers in common. I’m sure they’d help you to refine a PR though :wink:

For short term hacks, we do override Fog in a variety of places, such as here, but that kinda relies on there being the right Fog primitives in place, and it’s been ages since I messed with that.

For short-term hackery that would break on upgrade (and I’m certain I couldn’t recommend such a course of action), the XML that Fog uses will be on disk. On my Debian host it’s something like /usr/share/foreman/vendor/ruby/<ruby version>/gems/fog-libvirt-<gem version>/lib/fog/libvirt/requests/compute/mock_files/domain.xml although you’ll have to go digging. Hacking into that to match the XML in your virsh trial would at least confirm Foreman can generate the right config :wink:

Oh man, I had looked for something like that but was unable to find any reference as to where that might be. In digging through the libvirt stuff it sounded like maybe there was a file some place i was just never able to find it. I’ll see if i can find that because in this case a default of “always have that option” was really what we were going for anyways and if we need to update that upon upgrade, im sure we can get Puppet to handle that mess :slight_smile:

And as far as code, thats where i was looking

line 145,
vm = opts

I was under the impression that was the call to Fog’s services?

Which is why i figured that injecting the option in to the fog-libvirt module would just sort of magically work when used with Foreman. With how foreman is setup, I can just modify the gem setup in bundle.d to use our version of fog-libvirt (something else we can monitor with puppet to deal with upgrades)

The fog-libvirt module looks mostly like it screws with the xml and then hands that over, so just ball parking that i could edit this

rather than return the XML directly, edit it to toss in the params I need and then hand it back. The idea being that even if there are upgrades the chances of that upgrade involving fog-libvirt are probably pretty minor, and also with how little code is really in it, it shouldnt be hard if we need to merge updates. It might need to be in two places, since im not actually sure what the difference is between “define_domain” and “create_domain” is, they both make the same call and basically do the same thing (probably just edit both)

However, thats still a horrible bandaid, and if we’re going to do that, its probably better that we just modify that template xml like you mentioned (provided we can find it)

I think you might be more lucky at fog bugtracker, but for the record we want to solve the long-standing concurrency TFTP bug.

Found it on centos here

I didnt realize, until i start to dig for the path, that its listed under the mock_files… which… seems a tad odd to store the production template in a mock folder?

Will run some tests in a bit to see if this cuts it for us. really appreciate the help/insight!

Well, do you guys have any notes/directions/plans I could look at to see if its something i could attempt to do the right way? sort of doubtful I can help, but doesnt hurt to look/ask i guess :slight_smile:

Currently there are no known workarounds.

@lzap I guess i wasnt looking for a workaround to the TFTP problem (I have one, found the server.xml.erb in fog-libvirt and it works!)

Was more so curious if there was a purposed solution (correct one) that just needed to be implimented or if it was that its jsut a knoew problem that needs to be resolved and thats the extent of the information on it.

The correct solution to this problem is to file PR into fog-libvirt with the flag (assuming it is not there yet I haven’t tried) and once merged, wait until they release a new version, then pull the version into our deps, we can make RPM/DEB packages and then you can file PR to use the new flag in Foreman in UI/API/CLI. This would be perhaps new fields bootmenu and timeout in the form.

Hello in 2023!
Following @jrich523 's footsteps I’m trying to add some custom XML in my libvirtd hosts but confused to see that while server.xml.erb exists in the rubygem-fog-libvirt I can’t find that in the repo at: GitHub - fog/fog-libvirt: libvirt provider for fog! Where does the file come from?

Edit: it was replaced with some Nokogiri magic:

Does that means it will be possible to have some form of customization to the XML right from Foreman?

What I’m trying to achieve: add the qemu namespace and pass some command line options to qemu-kvm directly as documented in:

That specific PR hasn’t been released yet.

Oh hi @ekohl! Yes I’m aware it’s still in development but would love to know more about the plan for this particular change. Is there a design doc for the libvirt provider and is there a todo list somewhere for it?

I’m not aware of a design doc. I also think there’s a clear todo list, other than the current open issues.

I have released the current version as 0.12.0.

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Thanks for responding @ekohl. By todo I don’t believe you mean the Roadmap from github that was last updated in 2015? Can you share if it’s public information? I’m sure there will be people, me included, who would be really interested.

For better of worse at work we use this plugin a lot with Foreman and we might be able to help.

Turning it around, I’d say the roadmap is what users need. So if you use it at work then you know the issues you run into. IMHO the true open source way is fixing your own needs in a collaborative effort. So start with listing those.

We shouldn’t forget that fog-libvirt is not just used by Foreman, but also vagrant-libvirt.

I saw your message 4 days ago but I figure I should think about it before responding. As an individual and a support person who maintain a Foreman installation at work I’d like to see the following:

  1. Foreman able to use fog-libvirt to manage a EL9/CentOS Stream 9 compute resource.
  2. Foreman able to handle customised libvirt XML configs more gracefully.
  3. Make it possible to customize the XML either from configuration (like setting defaults like CPU passthrough and/or set qemu SMBIOS fields) or from the UI (maybe too much of an ask).

This is confirmed to work with a patch:

The PR to update it in packaging:

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