feature: add mount extra step in chroot builder

builder/osc/chroot/builder.go

@@ -259,6 +259,7 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 		&StepPostMountCommands{
 			Commands: b.config.PostMountCommands,
 		},
+		&StepMountExtra{},
 	)
 
 	// Run!

builder/osc/chroot/step_mount_extra.go

@@ -0,0 +1,137 @@
+package chroot
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"syscall"
+
+	"github.com/hashicorp/packer/helper/multistep"
+	"github.com/hashicorp/packer/packer"
+)
+
+// StepMountExtra mounts the attached device.
+//
+// Produces:
+//   mount_extra_cleanup CleanupFunc - To perform early cleanup
+type StepMountExtra struct {
+	mounts []string
+}
+
+func (s *StepMountExtra) Run(_ context.Context, state multistep.StateBag) multistep.StepAction {
+	config := state.Get("config").(*Config)
+	mountPath := state.Get("mount_path").(string)
+	ui := state.Get("ui").(packer.Ui)
+	wrappedCommand := state.Get("wrappedCommand").(CommandWrapper)
+
+	s.mounts = make([]string, 0, len(config.ChrootMounts))
+
+	ui.Say("Mounting additional paths within the chroot...")
+	for _, mountInfo := range config.ChrootMounts {
+		innerPath := mountPath + mountInfo[2]
+
+		if err := os.MkdirAll(innerPath, 0755); err != nil {
+			err := fmt.Errorf("Error creating mount directory: %s", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		flags := "-t " + mountInfo[0]
+		if mountInfo[0] == "bind" {
+			flags = "--bind"
+		}
+
+		ui.Message(fmt.Sprintf("Mounting: %s", mountInfo[2]))
+		stderr := new(bytes.Buffer)
+		mountCommand, err := wrappedCommand(fmt.Sprintf(
+			"mount %s %s %s",
+			flags,
+			mountInfo[1],
+			innerPath))
+		if err != nil {
+			err := fmt.Errorf("Error creating mount command: %s", err)
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		cmd := ShellCommand(mountCommand)
+		cmd.Stderr = stderr
+		if err := cmd.Run(); err != nil {
+			err := fmt.Errorf(
+				"Error mounting: %s\nStderr: %s", err, stderr.String())
+			state.Put("error", err)
+			ui.Error(err.Error())
+			return multistep.ActionHalt
+		}
+
+		s.mounts = append(s.mounts, innerPath)
+	}
+
+	state.Put("mount_extra_cleanup", s)
+	return multistep.ActionContinue
+}
+
+func (s *StepMountExtra) Cleanup(state multistep.StateBag) {
+	ui := state.Get("ui").(packer.Ui)
+
+	if err := s.CleanupFunc(state); err != nil {
+		ui.Error(err.Error())
+		return
+	}
+}
+
+func (s *StepMountExtra) CleanupFunc(state multistep.StateBag) error {
+	if s.mounts == nil {
+		return nil
+	}
+
+	wrappedCommand := state.Get("wrappedCommand").(CommandWrapper)
+	for len(s.mounts) > 0 {
+		var path string
+		lastIndex := len(s.mounts) - 1
+		path, s.mounts = s.mounts[lastIndex], s.mounts[:lastIndex]
+
+		grepCommand, err := wrappedCommand(fmt.Sprintf("grep %s /proc/mounts", path))
+		if err != nil {
+			return fmt.Errorf("Error creating grep command: %s", err)
+		}
+
+		// Before attempting to unmount,
+		// check to see if path is already unmounted
+		stderr := new(bytes.Buffer)
+		cmd := ShellCommand(grepCommand)
+		cmd.Stderr = stderr
+		if err := cmd.Run(); err != nil {
+			if exitError, ok := err.(*exec.ExitError); ok {
+				if status, ok := exitError.Sys().(syscall.WaitStatus); ok {
+					exitStatus := status.ExitStatus()
+					if exitStatus == 1 {
+						// path has already been unmounted
+						// just skip this path
+						continue
+					}
+				}
+			}
+		}
+
+		unmountCommand, err := wrappedCommand(fmt.Sprintf("umount %s", path))
+		if err != nil {
+			return fmt.Errorf("Error creating unmount command: %s", err)
+		}
+
+		stderr = new(bytes.Buffer)
+		cmd = ShellCommand(unmountCommand)
+		cmd.Stderr = stderr
+		if err := cmd.Run(); err != nil {
+			return fmt.Errorf(
+				"Error unmounting device: %s\nStderr: %s", err, stderr.String())
+		}
+	}
+
+	s.mounts = nil
+	return nil
+}