nixos: set QEMU network options directly

Configure QEMU devices as drivers are configuration.

nixos-modules/qemu-vm.nix

@@ -48,7 +48,6 @@ let
         -name ${config.system.name} \
         -m ${toString config.virtualisation.memorySize} \
         -smp ${toString config.virtualisation.cores} \
-        ${concatStringsSep " " config.virtualisation.qemu.networkingOptions} \
         ${toString config.virtualisation.qemu.options} \
         ${
           if config.hardware.genode.usb.storage.enable then
@@ -128,7 +127,7 @@ in {
     };
 
     virtualisation.vlans = mkOption {
-      default = [ 1 ];
+      default = [ ];
       example = [ 1 2 ];
       description = ''
         Virtual networks to which the VM is connected.  Each
@@ -189,20 +188,42 @@ in {
         '';
       };
 
-      networkingOptions = mkOption {
-        default = [
-          "-net nic,netdev=user.0,model=virtio"
-          "-netdev user,id=user.0\${QEMU_NET_OPTS:+,$QEMU_NET_OPTS}"
-        ];
-        type = types.listOf types.str;
-        description = ''
-          Networking-related command-line options that should be passed to qemu.
-          The default is to use userspace networking (slirp).
-
-          If you override this option, be advised to keep
-          ''${QEMU_NET_OPTS:+,$QEMU_NET_OPTS} (as seen in the default)
-          to keep the default runtime behaviour.
-        '';
+      nics = mkOption {
+        description = "QEMU network devices.";
+        default = { };
+        type = with lib.types;
+          attrsOf (submodule {
+            options = {
+              netdev = mkOption {
+                type = submodule {
+                  options = {
+                    kind = mkOption {
+                      type = str;
+                      default = "user";
+                    };
+                    settings = mkOption {
+                      type = attrsOf str;
+                      default = { };
+                    };
+                  };
+                };
+              };
+              device = mkOption {
+                type = submodule {
+                  options = {
+                    kind = mkOption {
+                      type = str;
+                      default = "virtio-net-pci";
+                    };
+                    settings = mkOption {
+                      type = attrsOf str;
+                      default = { };
+                    };
+                  };
+                };
+              };
+            };
+          });
       };
 
       diskInterface = mkOption {
@@ -280,6 +301,15 @@ in {
       ])
       (mkIf (cfg.bios != null) [ "-bios ${cfg.bios}/bios.bin" ])
       (mkIf (!cfg.graphics) [ "-nographic" ])
+      (let
+        toFlags = bind:
+          { kind, settings }:
+          lib.strings.concatStringsSep "," ([ "${kind},${bind}" ]
+            ++ (lib.attrsets.mapAttrsToList (k: v: "${k}=${v}") settings));
+      in lib.attrsets.mapAttrsToList (id: nic: [
+        "-netdev ${toFlags "id=${id}" nic.netdev}"
+        "-device ${toFlags "netdev=${id}" nic.device}"
+      ]) cfg.qemu.nics)
     ];
 
     system.build.vm = pkgs.runCommand "nixos-vm" { preferLocalBuild = true; } ''