nixos/virtualisation: add option for explicitly named network interfaces

nixos/doc/manual/from_md/release-notes/rl-2305.section.xml

@@ -687,6 +687,15 @@
           been fixed to allow more than one plugin in the path.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          A new option was added to the virtualisation module that
+          enables specifying explicitly named network interfaces in QEMU
+          VMs. The existing <literal>virtualisation.vlans</literal> is
+          still supported for cases where the name of the network
+          interface is irrelevant.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
 </section>

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -170,3 +170,5 @@ In addition to numerous new and upgraded packages, this release has the followin
 - `nixos-version` now accepts `--configuration-revision` to display more information about the current generation revision
 
 - The option `services.nomad.extraSettingsPlugins` has been fixed to allow more than one plugin in the path.
+
+- A new option was added to the virtualisation module that enables specifying explicitly named network interfaces in QEMU VMs. The existing `virtualisation.vlans` is still supported for cases where the name of the network interface is irrelevant.

nixos/lib/testing/driver.nix

@@ -12,7 +12,9 @@ let
   };
 
 
-  vlans = map (m: m.virtualisation.vlans) (lib.attrValues config.nodes);
+  vlans = map (m: (
+    m.virtualisation.vlans ++
+    (lib.mapAttrsToList (_: v: v.vlan) m.virtualisation.interfaces))) (lib.attrValues config.nodes);
   vms = map (m: m.system.build.vm) (lib.attrValues config.nodes);
 
   nodeHostNames =

nixos/lib/testing/network.nix

@@ -18,24 +18,40 @@ let
 
   networkModule = { config, nodes, pkgs, ... }:
     let
-      interfacesNumbered = zipLists config.virtualisation.vlans (range 1 255);
-      interfaces = forEach interfacesNumbered ({ fst, snd }:
-        nameValuePair "eth${toString snd}" {
-          ipv4.addresses =
-            [{
-              address = "192.168.${toString fst}.${toString config.virtualisation.test.nodeNumber}";
+      qemu-common = import ../qemu-common.nix { inherit lib pkgs; };
+
+      # Convert legacy VLANs to named interfaces and merge with explicit interfaces.
+      vlansNumbered = forEach (zipLists config.virtualisation.vlans (range 1 255)) (v: {
+        name = "eth${toString v.snd}";
+        vlan = v.fst;
+        assignIP = true;
+      });
+      explicitInterfaces = lib.mapAttrsToList (n: v: v // { name = n; }) config.virtualisation.interfaces;
+      interfaces = vlansNumbered ++ explicitInterfaces;
+      interfacesNumbered = zipLists interfaces (range 1 255);
+
+      # Automatically assign IP addresses to requested interfaces.
+      assignIPs = lib.filter (i: i.assignIP) interfaces;
+      ipInterfaces = forEach assignIPs (i:
+        nameValuePair i.name { ipv4.addresses =
+          [ { address = "192.168.${toString i.vlan}.${toString config.virtualisation.test.nodeNumber}";
               prefixLength = 24;
             }];
         });
 
+      qemuOptions = lib.flatten (forEach interfacesNumbered ({ fst, snd }:
+        qemu-common.qemuNICFlags snd fst.vlan config.virtualisation.test.nodeNumber));
+      udevRules = forEach interfacesNumbered ({ fst, snd }:
+        "SUBSYSTEM==\"net\",ACTION==\"add\",ATTR{address}==\"${qemu-common.qemuNicMac fst.vlan config.virtualisation.test.nodeNumber}\",NAME=\"${fst.name}\"");
+
       networkConfig =
         {
           networking.hostName = mkDefault config.virtualisation.test.nodeName;
 
-          networking.interfaces = listToAttrs interfaces;
+          networking.interfaces = listToAttrs ipInterfaces;
 
           networking.primaryIPAddress =
-            optionalString (interfaces != [ ]) (head (head interfaces).value.ipv4.addresses).address;
+            optionalString (ipInterfaces != [ ]) (head (head ipInterfaces).value.ipv4.addresses).address;
 
           # Put the IP addresses of all VMs in this machine's
           # /etc/hosts file.  If a machine has multiple
@@ -51,16 +67,13 @@ let
                     "${config.networking.hostName}.${config.networking.domain} " +
                   "${config.networking.hostName}\n"));
 
-          virtualisation.qemu.options =
-            let qemu-common = import ../qemu-common.nix { inherit lib pkgs; };
-            in
-            flip concatMap interfacesNumbered
-              ({ fst, snd }: qemu-common.qemuNICFlags snd fst config.virtualisation.test.nodeNumber);
+          virtualisation.qemu.options = qemuOptions;
+          boot.initrd.services.udev.rules = concatMapStrings (x: x + "\n") udevRules;
         };
 
     in
     {
-      key = "ip-address";
+      key = "network-interfaces";
       config = networkConfig // {
         # Expose the networkConfig items for tests like nixops
         # that need to recreate the network config.

nixos/modules/virtualisation/qemu-vm.nix

@@ -545,7 +545,8 @@ in
     virtualisation.vlans =
       mkOption {
         type = types.listOf types.ints.unsigned;
-        default = [ 1 ];
+        default = if config.virtualisation.interfaces == {} then [ 1 ] else [ ];
+        defaultText = lib.literalExpression ''if config.virtualisation.interfaces == {} then [ 1 ] else [ ]'';
         example = [ 1 2 ];
         description =
           lib.mdDoc ''
@@ -560,6 +561,35 @@ in
           '';
       };
 
+    virtualisation.interfaces = mkOption {
+      default = {};
+      example = {
+        enp1s0.vlan = 1;
+      };
+      description = lib.mdDoc ''
+        Network interfaces to add to the VM.
+      '';
+      type = with types; attrsOf (submodule {
+        options = {
+          vlan = mkOption {
+            type = types.ints.unsigned;
+            description = lib.mdDoc ''
+              VLAN to which the network interface is connected.
+            '';
+          };
+
+          assignIP = mkOption {
+            type = types.bool;
+            default = false;
+            description = lib.mdDoc ''
+              Automatically assign an IP address to the network interface using the same scheme as
+              virtualisation.vlans.
+            '';
+          };
+        };
+      });
+    };
+
     virtualisation.writableStore =
       mkOption {
         type = types.bool;