rem: size_t prefix_length = FILESYSTEM_PREFIX_LEN (path);
add: size_t prefix_length = FILE_SYSTEM_PREFIX_LEN (path);
context: dir_len (char const *path){  size_t prefix_length = FILESYSTEM_PREFIX_LEN (path);  size_t length;  /* Strip the basename and any redundant slashes before it.  */  for (length = base_name (path) - path;  prefix_length < length;  length--)    if (! ISSLASH (path[length - 1]))      return length;  /* But don't strip the only slash from "/".  */  return prefix_length + ISSLASH (path[prefix_length]);}