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<!DOCTYPE HTML>
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User Memory
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Extend File Descriptor (Extra)
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Introduction
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Memory Mapped Files
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Indexed and Extensible Files
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Buffer Cache
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Synchronization
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Mount (Extra)
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Threads
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Synchronization
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Memory Allocation
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Virtual Address
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Page Table
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Debugging Tools
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Development Tools
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<h2 id="extend-file-descriptor-extra">Extend File Descriptor (Extra)</h2>
<p><strong> Make your pintos to support closing of stdin, stdout and dup2 system call in
linux </strong></p>
<p>The closing the fd of <code>stdin</code> and <code>stdout</code> is forbidden in current
implementation of pintos. In this extra point requirements, you first allow user
to close <code>stdin</code> and <code>stdout</code> as same as the linux. That is, the process should
never read the inputs if you close <code>stdin</code>, and the process should never print
out anything if you close <code>stdout</code>.</p>
<p>Next, implement the <code>dup2</code> system call.</p>
<hr>
<pre><code class="lang-C"><span class="hljs-function"><span class="hljs-keyword">int</span> <span class="hljs-title">dup2</span><span class="hljs-params">(<span class="hljs-keyword">int</span> oldfd, <span class="hljs-keyword">int</span> newfd)</span></span>;
</code></pre>
<blockquote>
<p>The <code>dup2()</code> system call creates a copy of the file descriptor <code>oldfd</code> with
the file descriptor number specified in <code>newfd</code>, and returns <code>newfd</code> on
success. If the file descriptor <code>newfd</code> was previously open, it is silently
closed before being reused.</p>
<p>Note the following points:</p>
<ul>
<li><p>If <code>oldfd</code> is not a valid file descriptor, then the call fails
(returns <code>-1</code>), and <code>newfd</code> is not closed.</p>
</li>
<li><p>If <code>oldfd</code> is a valid file descriptor, and <code>newfd</code> has the same value as
<code>oldfd</code>, then <code>dup2()</code> does nothing, and returns <code>newfd</code>.</p>
</li>
</ul>
<p>After a successful return from this system call, the old and new file
descriptors may be used interchangeably. Although they are <strong>different file
descriptors</strong>, they <strong>refer to the same open file description</strong> and thus share
<em>file offset</em> and <em>status flags</em>; for example, if the file offset is modified
by using <code>seek</code> on one of the descriptors, the offset is also changed for the
other.</p>
</blockquote>
<p>Note that <code>dup</code>ed file descriptors must preserve their semantic after the
forking.</p>
<p><strong>YOU SHOULD PASS ALL TESTCASES FOR EXTRA TO GET THE CREDIT.
TAKE ALL OR NOTHING.</strong></p>
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