qemu-devenv.nix

qemu-devenv.nix

{ pkgs, lib, config, ... }: {
  inputs.microvm.url = "github:astro/microvm.nix";

  packages = [ 
    pkgs.qemu 
    pkgs.microvm 
    pkgs.utillinux # For kvm-ok check
  ];

  env = {
    VM_NAME = builtins.baseNameOf (builtins.toString ./.);
    KVM_AVAILABLE = let
      kvmCheck = pkgs.runCommand "check-kvm" {} ''
        ${pkgs.utillinux}/bin/kvm-ok >/dev/null 2>&1 && touch $out || exit 1
      '';
    in if builtins.pathExists kvmCheck then "1" else "0";
  };

  tasks.vm-setup = {
    exec = ''
      mkdir -p .devenv/microvm
      cat > .devenv/microvm/flake.nix <<EOF
      {
        inputs.microvm.url = "github:astro/microvm.nix";
        inputs.nixpkgs.url = "nixpkgs/nixos-unstable";

        outputs = { self, microvm, nixpkgs, ... }: {
          nixosConfigurations.${config.env.VM_NAME} = nixpkgs.lib.nixosSystem {
            system = "x86_64-linux";
            modules = [
              microvm.nixosModules.microvm
              {
                microvm = {
                  hypervisor = "qemu";
                  vcpu = 2;
                  mem = 2048;
                  shares = [{
                    source = "\${builtins.toString ./.}";
                    mountPoint = "/project";
                    proto = "virtiofs";
                  }];
                  qemu.extraArgs = lib.optional (config.env.KVM_AVAILABLE == "0") "-enable-kvm";
                  writableStoreOverlay = "/nix/.rwstore";
                };
                users.users.root.password = "";
                services.getty.autologinUser = "root";
                environment.sessionVariables = config.env;
                environment.systemPackages = config.packages;
              }
            ];
          };
        };
      }
      EOF
    '';
    onEnter = true;
  };

  enterShell = ''
    if [ -z "$IN_MICROVM" ]; then
      export IN_MICROVM=1
      devenv tasks run vm-setup
      
      echo "Starting QEMU MicroVM (KVM: ${config.env.KVM_AVAILABLE})..."
      nix run .devenv/microvm#nixosConfigurations.${config.env.VM_NAME}.config.microvm.declaredRunner
      exit
    fi
  '';

  cachix.pull = [ "devenv" ];
}