OpenStack users are used to have graphical console available. They take it for granted even. But we lacked it…
When we started working on OpenStack on 64-bit ARM there were many things missing. Most of them got sorted out already. One thing was still in a queue: graphical console. So two weeks ago I started looking at the issue.
Whenever someone tried to use it Nova reported one simple message: “No free USB ports.” You can ask what it has to console? I thought similar and started digging…
As usual reason was simple: yet another aarch64<>x86 difference in libvirt. Turned out that arm64 is one of those few architectures which do not have USB host controller in default setup. When Nova is told to provide graphical console it adds Spice (or VNC) graphics, video card and USB tablet. But in our case VM instance does not have any USB ports so VM start fails with “No free USB ports” message.
Solution was simple: let’s add USB host controller into VM instance. But where? Should libvirt do that or should Nova? I discussed it with libvirt developers and got mixed answers. Opened a bug for it and went to Nova hacking.
Turned out that Nova code for building guest configuration is not that complicated. I created a patch to add USB host controller and waited for code reviews. There were many suggestions, opinions and questions. So I rewrote code. And then again. And again. Finally 15th version got “looks good” opinion from all reviewers and got merged.
And how result looks? Boring as it should: