feature: add pre mount commands step for chroot builder

builder/osc/chroot/builder.go

@@ -249,6 +249,9 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 		},
 		&StepLinkVolume{},
 		&StepEarlyUnflock{},
+		&StepPreMountCommands{
+			Commands: b.config.PreMountCommands,
+		},
 	)
 
 	// Run!

builder/osc/chroot/run_local_commands.go

@@ -0,0 +1,39 @@
+package chroot
+
+import (
+	"fmt"
+
+	sl "github.com/hashicorp/packer/common/shell-local"
+	"github.com/hashicorp/packer/packer"
+	"github.com/hashicorp/packer/template/interpolate"
+)
+
+func RunLocalCommands(commands []string, wrappedCommand CommandWrapper, ctx interpolate.Context, ui packer.Ui) error {
+	for _, rawCmd := range commands {
+		intCmd, err := interpolate.Render(rawCmd, &ctx)
+		if err != nil {
+			return fmt.Errorf("Error interpolating: %s", err)
+		}
+
+		command, err := wrappedCommand(intCmd)
+		if err != nil {
+			return fmt.Errorf("Error wrapping command: %s", err)
+		}
+
+		ui.Say(fmt.Sprintf("Executing command: %s", command))
+		comm := &sl.Communicator{
+			ExecuteCommand: []string{"sh", "-c", command},
+		}
+		cmd := &packer.RemoteCmd{Command: command}
+		if err := cmd.StartWithUi(comm, ui); err != nil {
+			return fmt.Errorf("Error executing command: %s", err)
+		}
+		if cmd.ExitStatus != 0 {
+			return fmt.Errorf(
+				"Received non-zero exit code %d from command: %s",
+				cmd.ExitStatus,
+				command)
+		}
+	}
+	return nil
+}

builder/osc/chroot/step_pre_mount_commands.go

@@ -0,0 +1,41 @@
+package chroot
+
+import (
+	"context"
+
+	"github.com/hashicorp/packer/helper/multistep"
+	"github.com/hashicorp/packer/packer"
+)
+
+type preMountCommandsData struct {
+	Device string
+}
+
+// StepPreMountCommands sets up the a new block device when building from scratch
+type StepPreMountCommands struct {
+	Commands []string
+}
+
+func (s *StepPreMountCommands) Run(_ context.Context, state multistep.StateBag) multistep.StepAction {
+	config := state.Get("config").(*Config)
+	device := state.Get("device").(string)
+	ui := state.Get("ui").(packer.Ui)
+	wrappedCommand := state.Get("wrappedCommand").(CommandWrapper)
+
+	if len(s.Commands) == 0 {
+		return multistep.ActionContinue
+	}
+
+	ctx := config.ctx
+	ctx.Data = &preMountCommandsData{Device: device}
+
+	ui.Say("Running device setup commands...")
+	if err := RunLocalCommands(s.Commands, wrappedCommand, ctx, ui); err != nil {
+		state.Put("error", err)
+		ui.Error(err.Error())
+		return multistep.ActionHalt
+	}
+	return multistep.ActionContinue
+}
+
+func (s *StepPreMountCommands) Cleanup(state multistep.StateBag) {}