>    if (unlikely (nread == -1))
> -    /* We cannot even read the head of the file.  Maybe FILDES is associated
> -       with an unseekable device.  This is nothing we can handle.  */
> -    return NULL;
> +    {
> +      __libelf_seterrno (ELF_E_INVALID_FILE);
> +      /* We cannot even read the head of the file.  Maybe FILDES is associated
> +	 with an unseekable device.  This is nothing we can handle.  */
> +      return NULL;
> +    }

That looks sensible, though I'd keep the comment at the top of the block.