[OPTDEV-2284] Fixes for step_partition_image.go (#286)

The original code has bugs in MBR/DOS partitioniong, so narrow use cases fail miserably.

Additionally output handling is improved.

builder/step_partition_image.go

@@ -54,7 +54,7 @@ func partitionDOS(ui packer.Ui, config *Config) multistep.StepAction {
 	for i, partition := range config.ImageConfig.ImagePartitions {
 		line := fmt.Sprintf(
 			"%s%d: type=%s",
-			config.ImageConfig.ImagePath,
+			partition.Name, //config.ImageConfig.ImagePath,
 			i+1,
 			partition.Type,
 		)
@@ -67,9 +67,15 @@ func partitionDOS(ui packer.Ui, config *Config) multistep.StepAction {
 			line += fmt.Sprintf(", size=%s", partition.Size)
 		}
 
+		if partition.Name != "" {
+			line += fmt.Sprintf(", name=%s", partition.Name)
+		}
+
 		lines = append(lines, line)
 	}
 
+	ui.Error(fmt.Sprintf("** DEBUG: %s", strings.Join(lines, "\n")))
+
 	cmd := exec.Command("sfdisk", config.ImageConfig.ImagePath)
 
 	stdout, err := cmd.StdoutPipe()
@@ -79,6 +85,13 @@ func partitionDOS(ui packer.Ui, config *Config) multistep.StepAction {
 	}
 	defer stdout.Close()
 
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		ui.Error(fmt.Sprintf("error while getting stderr pipe %v", err))
+		return multistep.ActionHalt
+	}
+	defer stderr.Close()
+
 	stdin, err := cmd.StdinPipe()
 	if err != nil {
 		ui.Error(fmt.Sprintf("error while getting stdin pipe %v", err))
@@ -100,11 +113,15 @@ func partitionDOS(ui packer.Ui, config *Config) multistep.StepAction {
 	stdin.Close()
 
 	if err := cmd.Wait(); err != nil {
-		out, _ := io.ReadAll(stdout)
+		joined := io.MultiReader(stderr, stdout)
+		out, _ := io.ReadAll(joined)
 		ui.Error(fmt.Sprintf("error sfdisk %v: %s", err, string(out)))
 		return multistep.ActionHalt
 	}
 
+	out, _ := io.ReadAll(stdout)
+	ui.Message(string(out))
+
 	return multistep.ActionContinue
 }