title: Why return a negative errno? (e.g. return -EIO)
body: <p>Another simple example:</p>
  
  <pre><code>if (wpa_s-&gt;mlme.ssid_len == 0)
      return -EINVAL;
  </code></pre>
  
  <p>Why the unary minus? Is this (usually) done for functions that return >0 on success and &lt;(=)0 on failure, or is there some other reason?</p>