drivers/virtualbox/disk.go
func createDiskImage(dest string, size int, r io.Reader) error {
	// Convert a raw image from stdin to the dest VMDK image.
	sizeBytes := int64(size) << 20 // usually won't fit in 32-bit int (max 2GB)
	// FIXME: why isn't this just using the vbm*() functions?
	cmd := exec.Command(vboxManageCmd, "convertfromraw", "stdin", dest,
		fmt.Sprintf("%d", sizeBytes), "--format", "VMDK")

	log.Debug(cmd)

	if os.Getenv("MACHINE_DEBUG") != "" {
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
	}

	stdin, err := cmd.StdinPipe()
	if err != nil {
		return err
	}

	log.Debug("Starting command")

	if err := cmd.Start(); err != nil {
		return err
	}

	log.Debug("Copying to stdin")

	n, err := io.Copy(stdin, r)
	if err != nil {
		return err
	}

	log.Debug("Filling zeroes")

	// The total number of bytes written to stdin must match sizeBytes, or
	// VBoxManage.exe on Windows will fail. Fill remaining with zeros.
	if left := sizeBytes - n; left > 0 {
		if err := zeroFill(stdin, left); err != nil {
			return err
		}
	}

	log.Debug("Closing STDIN")

	// cmd won't exit until the stdin is closed.
	if err := stdin.Close(); err != nil {
		return err
	}

	log.Debug("Waiting on cmd")

	return cmd.Wait()
}
func createDiskImage(dest string, size int, r io.Reader) error {
	// Convert a raw image from stdin to the dest VMDK image.
	sizeBytes := int64(size) << 20 // usually won't fit in 32-bit int (max 2GB)
	// FIXME: why isn't this just using the vbm*() functions?
	cmd := exec.Command(vboxManageCmd, "convertfromraw", "stdin", dest,
		fmt.Sprintf("%d", sizeBytes), "--format", "VMDK")

	log.Debug(cmd)

	if os.Getenv("MACHINE_DEBUG") != "" {
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
	}

	stdin, err := cmd.StdinPipe()
	if err != nil {
		return err
	}

	log.Debug("Starting command")

	if err := cmd.Start(); err != nil {
		return err
	}

	log.Debug("Copying to stdin")

	n, err := io.Copy(stdin, r)
	if err != nil {
		return err
	}

	log.Debug("Filling zeroes")

	// The total number of bytes written to stdin must match sizeBytes, or
	// VBoxManage.exe on Windows will fail. Fill remaining with zeros.
	if left := sizeBytes - n; left > 0 {
		if err := zeroFill(stdin, left); err != nil {
			return err
		}
	}

	log.Debug("Closing STDIN")

	// cmd won't exit until the stdin is closed.
	if err := stdin.Close(); err != nil {
		return err
	}

	log.Debug("Waiting on cmd")

	return cmd.Wait()
}
// createDiskImage makes a disk image at dest with the given size in MB. If r is
// not nil, it will be read as a raw disk image to convert from.