return nil
		}
	}

	// Slow path: make sure parent exists and then call Mkdir for path.
	i := len(dirPath)
	for i > 0 && os.IsPathSeparator(dirPath[i-1]) { // Skip trailing path separator.
		i--
	}

	j := i
	for j > 0 && !os.IsPathSeparator(dirPath[j-1]) { // Scan backward over element.
		j--
	}

	if j > 1 {
		// Create parent.
		if err := osMkdirAll(dirPath[:j-1], perm, baseDir); err != nil {