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krisyotam.net/reference/pmikkelsen/pmikkelsen.com/plan9/mounting-9p-over-drawterm.html -rw-r--r-- 9.4 KiB
8bfa4b74 — Kris Yotam ci: declare SourceHut source for push builds a month ago 
                                                                                
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    <title>plan9 - mounting-9p over drawterm</title>
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    <h1><a href="../index.html">Peter&#39;s website <span id="headerSubTitle">- random notes</span></a></h1>
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<article>
<h1>Mounting a 9P connection over drawterm</h1>
<p>I sometimes use drawterm on linux to connect to my 9front server. While it is possible to access the host system's files under <code>/mnt/term</code>, there is no builtin way to access the remote system's file under linux. Now, why would anybody want to do this? In my case, I often want to write some code under 9front, but for languages which aren't supported such as prolog in this case, so there are three options as I see it:</p>
<ul>
<li>
Store the files on the host machine, and access them under <code>/mnt/term</code>.
</li><li>
Store the files on the server and somehow mount the server's filesystem on the host.
</li><li>
Store the files on a third machine that both the host and server can access.
</li>
</ul>
<p>Option number two seems best for me, so I asked around and it seems like the best tool to mount a 9P connection on linux is <a href="https://github.com/bunny351/9pfs">9pfs</a>.</p>
<h2>How it works</h2>
<p>Before I could mount the connection, I had to serve it somehow. Normally I already serve 9P directly from my server's filesystem, but that requires some authentication that 9pfs does not support, so I had to serve it without authentication. Serving directly to the internet without authentication is of course pretty dumb since everyone can then access my files, so thanks to a hint from hiro, I figured out that it is actually possible to use the host's network stack on the server by binding <code>/mnt/term/net</code> over <code>/net</code>.</p>
<p>I'll just show the final script below and explain it afterwards:</p>
<code><pre>
#!/bin/rc

rfork n
bind /mnt/term/net /net
aux/listen1 -t tcp!*!12335 /bin/exportfs -r / &amp;
os mkdir -p /tmp/drawterm
os 9pfs localhost -p 12335 /tmp/drawterm
</pre></code>
<p>So the first thing that happens is that I bind the host's network in, and from that point on, every network connection in this namespace actually goes out from the host instead of from the server!</p>
<p>Then <code>exportfs</code> is started and it is serving the <code>/</code> directory over 9P at port 12335. The <code>os</code> command runs a command on the host, so it just creates the folder that the system will be mounted to, and then uses <code>9pfs</code> to actually mount it. The nice thing here is that <code>9pfs</code> just connects to localhost.</p>
<h2>Using it</h2>
<p>As I said in the beginning, I did this to be able to edit files on the 9front server, and run compilers/interpreters on linux. The <code>os</code> command goes a long way, but the following script makes it even easier (I have this installed as <code>linux</code>):</p>
<code><pre>
#!/bin/rc

dir=/tmp/drawterm/`{pwd}
os -d $dir $*
</pre></code>
<p>This means I can just go into any directory on the server, type <code>linux ghci</code> and I get a haskell repl running in the correct directory, as seen in the gif below.</p>

<p><a href="https://images.pmikkelsen.com/linuxreverse.gif" /><img src="https://images.pmikkelsen.com/linuxreverse.gif" alt="An animated gif showing ghci loading a file on the 9front server" /></a></p>
<h2>Final notes</h2>
<p>The bind net trick still blows my mind a bit, since it is so trivial, yet so powerful. It is also fun to think about how one would do this on other systems than plan9, which I can't even imagine.</p>

</article>
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