<p>Suppose I want to open a file in an existing Emacs session using <code>su</code> or <code>sudo</code>, without dropping down to a shell and doing <code>sudoedit</code> or <code>sudo emacs</code>. One way to do this is</p>

<pre><code>C-x C-f /sudo::/path/to/file
</code></pre>

<p>but this requires an expensive <a href="http://www.gnu.org/software/tramp/" rel="noreferrer">round-trip through SSH</a>. Is there a more direct way?</p>

<p>[EDIT] @JBB is right. I want to be able to invoke <code>su</code>/<code>sudo</code> to save as well as open. It would be OK (but not ideal) to re-authorize when saving. What I'm looking for is variations of <code>find-file</code> and <code>save-buffer</code> that can be "piped" through <code>su</code>/<code>sudo</code>.</p>

Ugh. Perhaps you could open a shell in Emacs and exec sudo emacs.
The problem is that you presumably don't just want to open the file. You want to be able to save it later. Thus you need your root privs to persist, not just exist for opening the file.
Sounds like you want Emacs to become your window manager. It's bloated enough without that. :)