Better support RHEL build of QEMU

[lebonez]

Required information

• Distribution: Rocky Linux
• Distribution version: 9.4
• The output of "incus info" or if that fails:
  • Kernel version: 5.14.0-427.37.1.el9_4.x86_64
  • LXC version:
  • Incus version: 6.6
  • Storage backend in use: Ceph

Issue description

High likelihood this could be a duplicate, I've built Incus on Rocky Linux 9.4 from source. I am hitting two major issues. It seems that Incus is expecting qemu-system-x86_64 to exist but on RedHat derivatives this does not exist. It technically exists at /usr/libexec/qemu-kvm. Doing a symlink from ln -s /usr/libexec/qemu-kvm /usr/bin/qemu-system-x86_64 works around it but that isn't ideal. The next major issue is the drop of Spice support in RedHat 9. Is it possible to build incus without expecting spice?

Steps to reproduce

1. Install Rocky Linux 9.4.
2. Build from source generally pretty easy I just took most of the information from the RPM spec repos.
3. Attempt to run a VM like lxc launch images:rockylinux/9/cloud --vm VM feature won't be supported even though it should be.
4. ln -s /usr/libexec/qemu-kvm /usr/bin/qemu-system-x86_64.
5. lxc launch images:rockylinux/9/cloud --vm now it will complain about the VM configs due to the spice settings not being part of qemu anymore in RedHat 9.

Questions

• Is it possible in the future that incus will support the /usr/libexec/qemu-kvm location?
• Is it also possible that incus will dynamically swap away from spice as needed if it doesn't exist?

We are definitely awaiting a EL9 zabbly incus LTS or official RPM.

[stgraber]

1. Should be possible though that's not particularly great as we normally want to use the architecture specific QEMU binaries. How does RHEL handle the case where you have the QEMU system binaries for multiple architectures installed? Is qemu-kvm some kind of shell script or the actual QEMU binary?

2. We may be able to detect the lack of SPICE support and degrade things, though that means no VGA access for your VMs which will make some use cases pretty unpleasant (like running Windows or a Linux desktop VM).

[lebonez]

Thank you for the quick response.

1. Indeed /usr/libexec/qemu-kvm on redhat is just the qemu binary unsure if it differentiates on architectures. Looking at the qemu packages available on EL9 there are no extra architecture packages like there used to be on EL8 and older.

2. Yes lack of Spice support seems most complicated but doesn't have a good solution like symlinking or a simple patch. Generally we still have virt-viewer available on EL9 but not spicy or remote-viewer. Which I assume means just have to drop to VNC only? I think the best workaround for my situation would be if there is a way to disabling spice support as a config flag or something. At a later time supporting virt-viewer VNC could be useful.

[stgraber]

We're not likely to add support for VNC as we actively use features of SPICE which VNC doesn't support, including USB passthrough, video acceleration channels, multi display support, ...

But hopefully we can degrade things in a way which just prevents attaching to the VGA console altogether on such systems.