allow user to mount entire block device in chroot builder

builder/amazon/chroot/builder.go

@@ -35,7 +35,7 @@ type Config struct {
 	DevicePath        string                     `mapstructure:"device_path"`
 	FromScratch       bool                       `mapstructure:"from_scratch"`
 	MountOptions      []string                   `mapstructure:"mount_options"`
-	MountPartition    int                        `mapstructure:"mount_partition"`
+	MountPartition    string                     `mapstructure:"mount_partition"`
 	MountPath         string                     `mapstructure:"mount_path"`
 	PostMountCommands []string                   `mapstructure:"post_mount_commands"`
 	PreMountCommands  []string                   `mapstructure:"pre_mount_commands"`
@@ -112,8 +112,8 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 		b.config.MountPath = "/mnt/packer-amazon-chroot-volumes/{{.Device}}"
 	}
 
-	if b.config.MountPartition == 0 {
+	if b.config.MountPartition == "" {
-		b.config.MountPartition = 1
+		b.config.MountPartition = "1"
 	}
 
 	// Accumulate any errors or warnings

builder/amazon/chroot/step_mount_device.go

@@ -26,7 +26,7 @@ type mountPathData struct {
 //   mount_device_cleanup CleanupFunc - To perform early cleanup
 type StepMountDevice struct {
 	MountOptions   []string
-	MountPartition int
+	MountPartition string
 
 	mountPath string
 }
@@ -75,8 +75,9 @@ func (s *StepMountDevice) Run(_ context.Context, state multistep.StateBag) multi
 	}
 
 	deviceMount := device
-	if virtualizationType == "hvm" {
+
-		deviceMount = fmt.Sprintf("%s%d", device, s.MountPartition)
+	if virtualizationType == "hvm" && s.MountPartition != "0" {
+		deviceMount = fmt.Sprintf("%s%s", device, s.MountPartition)
 	}
 	state.Put("deviceMount", deviceMount)
 

website/source/docs/builders/amazon-chroot.html.md

@@ -213,8 +213,10 @@ each category, the available configuration keys are alphabetized.
     where the `.Device` variable is replaced with the name of the device where
     the volume is attached.
 
--   `mount_partition` (number) - The partition number containing the
+-   `mount_partition` (string) - The partition number containing the
-    / partition. By default this is the first partition of the volume.
+    / partition. By default this is the first partition of the volume, (for
+    example, `xvda1`) but you can designate the entire block device by setting
+    `"mount_partition": "0"` in your config, which will mount `xvda` instead.
 
 -   `mount_options` (array of strings) - Options to supply the `mount` command
     when mounting devices. Each option will be prefixed with `-o` and supplied