proxmox-mutex

Proxmox tool to manage mutually exclusive guest VMs

This repository contains a tool that helps to run a proxmox system with alternate main guest VMs that have host hardware (like a PCIe GPU and USB inputs) passed thru to them.

Scenario

Let's say we have

• a headless proxmox server install
• a PCIe GPU and one or more USB devices that are used only by two or more main guest VMs
  • VM 101 is a Windows VM for gaming
  • VM 102 is a Linux VM for productivity

Problem: hardware conflict between main guest VMs

Without any additional setup, what one must do to switch between VM 101 and 102 is: to first stop one, wait, and then start the other.

In other words, the best one can do is to issue a command like qm shutdown 102 && qm start 101 at a proxmox console using the qm management command.

Solution: a proxmox qemu hookscript

We can start to do better by automating the "shutdown any conflicting VMs" part.

This can be achieved during the pre-start phase of a qm hookscript.

The qmexmut.go tool in this repository currently implements just that. It does so by finding any overlap of hostpciX: ... or usbX: host=... configuration in the VM that's trying to start, and any currently running VMs. So there's no need for static rules to be configured like "stop X before starting Y"; proxmox's existing config is sufficient.

To install qmexmut:

• clone this repository and build the binary
  • you'll need Go (tested on 1.18, but should work on 1.17)
  • just type go build ./qmexmut.go
• copy the qmexmut binary into your proxmox's snippet storage
  • you may need to first enable snippets on your local (/var/lib/vz) storage directory
  • the binary should end up at /var/lib/vz/snippets/qmexmut on your proxmox server(s)
• then set the hookscript on any relevant VMs
  • run commands like qm set <vmid> --hookscript local:snippets/qmexmut for all involved VMs (101 and 102 in our example here)

After this point, now you can simply start each VM, and it will first shutdown any conflicting siblings. So the qm shutdown 102 && qm start 101 above can just be qm start 101.

TODO

• implement automatic installation of qmexmut so that the above install advice can be boiled down to "just build it, upload it, and run it"
• if it's possible to detect "guest shutdown voluntarily", we could boot up the other/last/next sibling for fast swapping trigger from withing a guest
• alternatively, it'd be neat to leverage something like a macro pad attached to the host to trigger main guest start without access to a console or the proxmox webui