feat: add initial support for 'usermode' networking

builder/libvirt/network/network.go

@@ -25,6 +25,7 @@ type NetworkInterface struct {
 
 	Bridge  BridgeNetworkInterface  `mapstructure:",squash"`
 	Managed ManagedNetworkInterface `mapstructure:",squash"`
+	User UserNetworkInterface `mapstructure:",squash"`
 }
 
 func (ni *NetworkInterface) PrepareConfig(ctx *interpolate.Context) (warnings []string, errs []error) {
@@ -46,6 +47,8 @@ func (ni *NetworkInterface) PrepareConfig(ctx *interpolate.Context) (warnings []
 		w, e = ni.Managed.PrepareConfig(ctx)
 	case "bridge":
 		w, e = ni.Bridge.PrepareConfig(ctx)
+	case "user":
+		w, e = ni.User.PrepareConfig(ctx)
 	default:
 		errs = append(errs, fmt.Errorf("unsupported network interface type '%s'", ni.Type))
 		return
@@ -78,6 +81,8 @@ func (ni NetworkInterface) DomainInterface() *libvirtxml.DomainInterface {
 		ni.Bridge.UpdateDomainInterface(&domainInterface)
 	case "managed":
 		ni.Managed.UpdateDomainInterface(&domainInterface)
+	case "user":
+		ni.User.UpdateDomainInterface(&domainInterface)
 	}
 
 	return &domainInterface

builder/libvirt/network/user.go

@@ -0,0 +1,23 @@
+package network
+
+import (
+	"github.com/hashicorp/packer-plugin-sdk/template/interpolate"
+	"libvirt.org/go/libvirtxml"
+)
+
+type UserNetworkInterface struct {
+	Dev string `mapstructure:"dev" required:"false"`
+}
+
+func (ni *UserNetworkInterface) PrepareConfig(ctx *interpolate.Context) (warnings []string, errs []error) {
+	if ni.Dev == "" {
+	}
+	return
+}
+
+func (ni *UserNetworkInterface) UpdateDomainInterface(domainInterface *libvirtxml.DomainInterface) {
+	domainInterface.Source = &libvirtxml.DomainInterfaceSource{
+		User: &libvirtxml.DomainInterfaceSourceUser{
+		},
+	}
+}

docs/builders/libvirt.mdx

@@ -250,7 +250,7 @@ volume {
 
 ### Network
 Network interfaces can be attached to a builder domain by adding a `network_interface { }` block for each.
-Currently only `managed` and `bridge` networks are supported.
+Currently only `managed`, `bridge`, and `user` networks are supported.
 
 @include 'builder/libvirt/network/NetworkInterface-required.mdx'
 @include 'builder/libvirt/network/NetworkInterface-not-required.mdx'
@@ -293,6 +293,13 @@ network_interface {
 }
 ```
 
+For usermode networking
+```hcl
+network_interface {
+  type   = "user"
+}
+```
+
 ### Graphics and video, headless domains
 Libvirt builder creates a headless domain by default with no video card or monitor attached to it. Most linux distributions
 and cloud images are fine with this setup, but you might need to add a video card and a graphical interface to your machine.