QEmu: virtiofsd prone to be garbage collected.

[YellowOnion]

Describe the bug
libvirt can't find virtfiofsd
I'm unsure how to reference virtiofsd via libvirt xml without it being garbage collected.
I'm currently hard coding nix store:

$ find /nix -name 'virtiofsd'
/nix/store/c3nr4r9ld8np3yz31circxfqipinfchq-qemu-5.2.0/libexec/virtiofsd
/nix/store/2h7s274cwhw708giflvr1p3329ypm3vr-qemu-5.2.0/libexec/virtiofsd

Expected behavior
A consistent reference to virtiofsd either via a link in /run/current-system or putting it on the $PATH.

Additional context
https://libvirt.org/kbase/virtiofs.html#host-setup

Notify maintainers
@eelco

[anton-dessiatov]

It's not perfect, but adding the following snippet to configuration.nix does the trick for me.

  environment.systemPackages = [
    (pkgs.stdenv.mkDerivation {
      name = "virtiofsd-link";
      buildCommand = ''
        mkdir -p $out/bin
        ln -s ${pkgs.qemu}/libexec/virtiofsd $out/bin/
      '';
    })
  ];

I have the following line in my virtual machine XML to make use of it:

<binary path='/run/current-system/sw/bin/virtiofsd' xattr='on'>

[stale]

I marked this as stale due to inactivity. → More info

[Madouura]

Still important to me.

[ckiee]

Sorry about the spam, I had to push to my fork in order to test it and I managed to have this crappy typo that I missed for a while.. Anyway, that PR should fix it.

[kvtb]

That's what /run/libvirt/nix-emulators/ and /run/libvirt/nix-helpers/ are for.
To have stable links in xml files which survive upgrades of libvirt and qemu, hibernation of guests, reboots of host, GCs and all of those interleaved.

Maintaining <binary path='/run/current-system/sw/bin/virtiofsd' xattr='on'> through all XML's seems ugly