nixos/kvmgt: add udev rules for unprivileged access

nixos/modules/virtualisation/kvmgt.nix

@@ -19,7 +19,8 @@ in {
     virtualisation.kvmgt = {
       enable = mkEnableOption ''
         KVMGT (iGVT-g) VGPU support. Allows Qemu/KVM guests to share host's Intel integrated graphics card.
-        Currently only one graphical device can be shared
+        Currently only one graphical device can be shared. To allow users to access the device without root add them
+        to the kvm group: <literal>users.extraUsers.&lt;yourusername&gt;.extraGroups = [ "kvm" ];</literal>
       '';
       # multi GPU support is under the question
       device = mkOption {
@@ -35,9 +36,7 @@ in {
           and find info about device via <command>cat /sys/bus/pci/devices/*/mdev_supported_types/i915-GVTg_V5_4/description</command>
         '';
         example = {
-          i915-GVTg_V5_8 = {
-            uuid = "a297db4a-f4c2-11e6-90f6-d3b88d6c9525";
-          };
+          i915-GVTg_V5_8.uuid = "a297db4a-f4c2-11e6-90f6-d3b88d6c9525";
         };
       };
     };
@@ -62,6 +61,10 @@ in {
       }
     ) cfg.vgpus;
 
+    services.udev.extraRules = ''
+      SUBSYSTEM=="vfio", OWNER="root", GROUP="kvm"
+    '';
+
     systemd.services = mapAttrs' (name: value:
       nameValuePair "kvmgt-${name}" {
         description = "KVMGT VGPU ${name}";