virsh preboot script

Question

I am running a virtual machine that requires vfio access to a PCI card. Using this script I am able to successfully bind the PCI device and its iommu group to vfio-pci, which then lets me boot up the VM:

1. ./vfio-pci-bind.sh 0000:03:00.0
2. virsh start myvm

I want to do this automatically instead of having to manually bind to vfio-pci every time. Is there some sort of preflight/preboot script I can make virsh run before it attempts to boot a vm?

Answer 1

You can use a libvirt hook to run arbitrary programs when a VM or network is started or stopped.

For instance, you can create a file /etc/libvirt/hooks/qemu which determines if your VM is being called, and then does whatever needs to be done.

#!/bin/bash

if [ "$1" = "myvm" ] && [ "$2" = "prepare" ]; then
    /path/to/vfio-pci-bind.sh '0000:03:00.0'
fi

Answer 2

@michael-hampton has the most correct answer, but for anyone's reference I was impatient and also made a systemd service called vfio-pci-bind.service that executes vfio-pci-bind.sh:

[Unit]
Description=bind PCI card to vfio

[Service]
ExecStart=/opt/vfio-pci-bind/vfio-pci-bind.sh "0000:03:00.1"
Type=oneshot
RemainAfterExit=yes

then I added to libvirt-guests.service:

[Service]
...
Wants=vfio-pci-bind.service
After=vfio-pci-bind.service

The issues with this being

• it relies on systemd rather than being self-contained to libvirt
• it executes vfio-pci-bind regardless of whether or not the affected vm will actually be started at boot

so yeah I'll switch over to libvirt hooks, thanks for the help!