fix: specify helper to qemu

[NicGrimpe]

Description

Without this change I could not launch a vm with a network configured. network="br0"

failed to create tun device: Operation not permitted
qemu-system-x86_64: -nic bridge,br=br0,model=virtio-net-pci: bridge helper failed

Tested on nixos. Maybe there is a better way to get it to work, feel free to let me know and close this PR in that case :)

Type of change

Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have performed a self-review of my code
• I have tested my code in common scenarios and confirmed there are no regressions
• I have added comments to my code, particularly in hard-to-understand sections

[2b]

Hi! Thank you for the fix!

Maybe this should be fixed at the package.nix level, if it's NixOS-specific. What do you think?
In the meantime, here is a Nix overlay for anyone who stumbled upon this, like me:

final: prev: {
  quickemu = prev.quickemu.overrideAttrs (oldAttrs: {
    postPatch = (oldAttrs.postPatch or "") + ''
      substituteInPlace quickemu \
        --replace-fail 'args+=(-nic bridge,br=''${network},model=virtio-net-pci''${MAC})' \
                       'args+=(-nic bridge,br=''${network},helper=$(type -p qemu-bridge-helper),model=virtio-net-pci''${MAC})'
    '';
  });
}

[TheMuso]

I use something similar in my nix config as well, but I have been wondering whether a programs.quickemu module needs to be created, since /etc/qemu/bridge.conf needs to contain the name of the bridge interface. Setting up a wrapper for qemu-bridge-helper could also be done there. Yes the libvirt module also sets this stuff up, but adding assertions to make sure there are no conflicts is doable.

The quickemu packaging could then be adjusted similar to the above overlay to point to the security wrapper bridge helper binary.

[nthnd]

Hi! Thank you for the fix!

Maybe this should be fixed at the package.nix level, if it's NixOS-specific. What do you think? In the meantime, here is a Nix overlay for anyone who stumbled upon this, like me:

final: prev: {
  quickemu = prev.quickemu.overrideAttrs (oldAttrs: {
    postPatch = (oldAttrs.postPatch or "") + ''
      substituteInPlace quickemu \
        --replace-fail 'args+=(-nic bridge,br=''${network},model=virtio-net-pci''${MAC})' \
                       'args+=(-nic bridge,br=''${network},helper=$(type -p qemu-bridge-helper),model=virtio-net-pci''${MAC})'
    '';
  });
}

still failing on my system with this line in the log

qemu-system-x86_64: -nic bridge,br=win-br0,helper=,model=virtio-net-pci: bridge helper failed