Introduce $QEMU_BRIDGE_HELPER

default.nix

@@ -29,6 +29,10 @@ pkgs.python3.pkgs.buildPythonPackage rec {
     license = pkgs.lib.licenses.asl20;
   };
 
+  postInstall = ''
+    install -Dm755 ${create_bridge} $out/bin/${pname}-create-bridge
+  '';
+
   nativeCheckInputs = [
     pkgs.shellcheck
     pkgs.pylint

nixos-module.nix

@@ -0,0 +1,50 @@
+# nixos-module.nix
+{ config, lib, pkgs, ... }:
+let
+  qemuPkg = config.services.vmrunner.qemuPackage or pkgs.qemu;
+  vmrunnerPkg = config.services.vmrunner.package or (pkgs.callPackage ./default.nix { });
+
+  qemuBridgeHelperPath  = "/run/wrappers/bin/qemu-bridge-helper";
+  bridge = "bridge43";
+in
+  {
+  options.services.vmrunner.qemuPackage = lib.mkOption {
+    type = lib.types.package;
+    default = pkgs.qemu;
+    description = "QEMU with capabilities enabled for IncludeOS unikernels";
+  };
+
+  config = {
+    security.wrappers = {
+      # https://wiki.qemu.org/Features/HelperNetworking
+      qemu-bridge-helper = {
+        source = "${qemuPkg}/libexec/qemu-bridge-helper";
+        owner = "root";
+        group = "root";
+        capabilities = "cap_net_admin+ep";  # required for attaching TAP devices to bridges
+      };
+
+      ping = {
+        source = "${pkgs.iputils}/bin/ping";
+        owner = "root";
+        group = "root";
+        capabilities = "cap_net_raw+ep";  # required to send ICMP packets
+      };
+    };
+
+    environment = {
+      etc."qemu/bridge.conf".text = ''
+        allow ${bridge}
+      '';
+
+      systemPackages = [ vmrunnerPkg ];
+
+      variables.QEMU_BRIDGE_HELPER = qemuBridgeHelperPath;
+    };
+
+    networking.firewall = {
+      trustedInterfaces = [ bridge ];
+    };
+  };
+}
+

vmrunner/vmrunner.py

@@ -471,7 +471,7 @@ def mod_args(self, mods):
                              for mod in mods])
         return ["-initrd", mods_list]
 
-    def net_arg(self, backend, device, if_name = "net0", mac = None, bridge = None, scripts = None):
+    def net_arg(self, backend, device, if_name = "net0", mac = None, bridge = None, scripts = None, helper = None):
         """ creates network argument for hypervisor """
         if scripts:
             qemu_ifup = scripts + "qemu-ifup"
@@ -503,6 +503,8 @@ def net_arg(self, backend, device, if_name = "net0", mac = None, bridge = None,
 
         if bridge:
             netdev = "bridge,id=" + if_name + ",br=" + bridge
+            if helper:
+                netdev += ",helper=" + helper
 
 
         # Device - e.g. guest side of nic
@@ -655,7 +657,8 @@ def boot_in_hypervisor(self, multiboot=True, debug = False, kernel_args = "", im
                 mac = net["mac"] if "mac" in net else None
                 bridge = net["bridge"] if "bridge" in net else None
                 scripts = net["scripts"] if "scripts" in net else None
-                net_args += self.net_arg(net["backend"], net["device"], "net"+str(i), mac, bridge, scripts)
+                helper = net.get("helper", os.environ.get("QEMU_BRIDGE_HELPER"))
+                net_args += self.net_arg(net["backend"], net["device"], "net"+str(i), mac, bridge, scripts, helper)
                 i+=1
 
         mem_arg = []