Add COM port configuration for serial console output

builder/hyperv/common/config.go

@@ -156,6 +156,10 @@ type CommonConfig struct {
 	// built. When this value is set to true, the machine will start without a
 	// console.
 	Headless bool `mapstructure:"headless" required:"false"`
+	// Path to a named pipe for COM1 serial output. When set, the VM's COM1
+	// port will be configured to output to this pipe, enabling capture of
+	// boot console output. Example: `\\.\pipe\packer-console`
+	ComPortPipePath string `mapstructure:"com_port_pipe_path" required:"false"`
 	// When configured, determines the device or device type that is given preferential
 	// treatment when choosing a boot device.
 	//

builder/hyperv/common/driver.go

@@ -137,4 +137,7 @@ type Driver interface {
 
 	// Disconnect disconnects to a VM specified by the context cancel function.
 	Disconnect(context.CancelFunc)
+
+	// SetVirtualMachineComPort configures a COM port to output to a named pipe.
+	SetVirtualMachineComPort(string, int, string) error
 }

builder/hyperv/common/driver_mock.go

@@ -290,6 +290,12 @@ type DriverMock struct {
 
 	Disconnect_Called bool
 	Disconnect_Cancel context.CancelFunc
+
+	SetVirtualMachineComPort_Called     bool
+	SetVirtualMachineComPort_VmName     string
+	SetVirtualMachineComPort_PortNumber int
+	SetVirtualMachineComPort_PipePath   string
+	SetVirtualMachineComPort_Err        error
 }
 
 func (d *DriverMock) IsRunning(vmName string) (bool, error) {
@@ -673,3 +679,11 @@ func (d *DriverMock) Disconnect(cancel context.CancelFunc) {
 	d.Disconnect_Called = true
 	d.Disconnect_Cancel = cancel
 }
+
+func (d *DriverMock) SetVirtualMachineComPort(vmName string, portNumber int, pipePath string) error {
+	d.SetVirtualMachineComPort_Called = true
+	d.SetVirtualMachineComPort_VmName = vmName
+	d.SetVirtualMachineComPort_PortNumber = portNumber
+	d.SetVirtualMachineComPort_PipePath = pipePath
+	return d.SetVirtualMachineComPort_Err
+}

builder/hyperv/common/driver_ps_4.go

@@ -402,3 +402,8 @@ func (d *HypervPS4Driver) Connect(vmName string) (context.CancelFunc, error) {
 func (d *HypervPS4Driver) Disconnect(cancel context.CancelFunc) {
 	hyperv.DisconnectVirtualMachine(cancel)
 }
+
+// SetVirtualMachineComPort configures a COM port to output to a named pipe.
+func (d *HypervPS4Driver) SetVirtualMachineComPort(vmName string, portNumber int, pipePath string) error {
+	return hyperv.SetVMComPort(vmName, portNumber, pipePath)
+}

builder/hyperv/common/powershell/hyperv/hyperv.go

@@ -1627,3 +1627,13 @@ func ConnectVirtualMachine(vmName string) (context.CancelFunc, error) {
 func DisconnectVirtualMachine(cancel context.CancelFunc) {
 	cancel()
 }
+
+func SetVMComPort(vmName string, number int, pipePath string) error {
+	var script = `
+param([string]$vmName, [int]$number, [string]$pipePath)
+Set-VMComPort -VMName $vmName -Number $number -Path $pipePath
+`
+	var ps powershell.PowerShellCmd
+	err := ps.Run(script, vmName, strconv.Itoa(number), pipePath)
+	return err
+}

builder/hyperv/common/step_clone_vm.go

@@ -40,6 +40,7 @@ type StepCloneVM struct {
 	KeepRegistered                 bool
 	AdditionalDiskSize             []uint
 	DiskBlockSize                  uint
+	ComPortPipePath                string
 }
 
 func (s *StepCloneVM) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
@@ -189,6 +190,16 @@ func (s *StepCloneVM) Run(ctx context.Context, state multistep.StateBag) multist
 		}
 	}
 
+	if s.ComPortPipePath != "" {
+		err = driver.SetVirtualMachineComPort(s.VMName, 1, s.ComPortPipePath)
+		if err != nil {
+			err := fmt.Errorf("Error configuring COM port: %s", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+	}
+
 	// Set the final name in the state bag so others can use it
 	state.Put("vmName", s.VMName)
 	// instance_id is the generic term used so that users can have access to the

builder/hyperv/common/step_create_vm.go

@@ -42,6 +42,7 @@ type StepCreateVM struct {
 	FixedVHD                       bool
 	Version                        string
 	KeepRegistered                 bool
+	ComPortPipePath                string
 }
 
 func (s *StepCreateVM) Run(ctx context.Context, state multistep.StateBag) multistep.StepAction {
@@ -189,6 +190,16 @@ func (s *StepCreateVM) Run(ctx context.Context, state multistep.StateBag) multis
 		}
 	}
 
+	if s.ComPortPipePath != "" {
+		err = driver.SetVirtualMachineComPort(s.VMName, 1, s.ComPortPipePath)
+		if err != nil {
+			err := fmt.Errorf("Error configuring COM port: %s", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+	}
+
 	// Set the final name in the state bag so others can use it
 	state.Put("vmName", s.VMName)
 	// instance_id is the generic term used so that users can have access to the

builder/hyperv/iso/builder.go

@@ -248,6 +248,7 @@ func (b *Builder) Run(ctx context.Context, ui packersdk.Ui, hook packersdk.Hook)
 			FixedVHD:                       b.config.FixedVHD,
 			Version:                        b.config.Version,
 			KeepRegistered:                 b.config.KeepRegistered,
+			ComPortPipePath:                b.config.ComPortPipePath,
 		},
 		&hypervcommon.StepEnableIntegrationService{},
 

builder/hyperv/vmcx/builder.go

@@ -288,6 +288,7 @@ func (b *Builder) Run(ctx context.Context, ui packersdk.Ui, hook packersdk.Hook)
 			KeepRegistered:                 b.config.KeepRegistered,
 			AdditionalDiskSize:             b.config.AdditionalDiskSize,
 			DiskBlockSize:                  b.config.DiskBlockSize,
+			ComPortPipePath:                b.config.ComPortPipePath,
 		},
 
 		&hypervcommon.StepResizeVhd{

docs-partials/builder/hyperv/common/CommonConfig-not-required.mdx

@@ -114,6 +114,10 @@
   built. When this value is set to true, the machine will start without a
   console.
 
+- `com_port_pipe_path` (string) - Path to a named pipe for COM1 serial output. When set, the VM's COM1
+  port will be configured to output to this pipe, enabling capture of
+  boot console output. Example: `\\.\pipe\packer-console`
+
 - `first_boot_device` (string) - When configured, determines the device or device type that is given preferential
   treatment when choosing a boot device.