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<li class="toctree-l1 has-children"><a class="reference internal" href="../chapter2/index.html">第二章：批处理系统</a><input class="toctree-checkbox" id="toctree-checkbox-7" name="toctree-checkbox-7" role="switch" type="checkbox"/><label for="toctree-checkbox-7"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul>
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<li class="toctree-l2"><a class="reference internal" href="../chapter3/2task-switching.html">任务切换</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter3/5exercise.html">chapter3练习</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter4/3sv39-implementation-1.html">实现 SV39 多级页表机制（上）</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter4/4sv39-implementation-2.html">实现 SV39 多级页表机制（下）</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter4/5kernel-app-spaces.html">内核与应用的地址空间</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter4/7exercise.html">chapter4练习</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter5/1process.html">与进程有关的重要系统调用</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter5/2core-data-structures.html">进程管理的核心数据结构</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter5/3implement-process-mechanism.html">进程管理机制的设计实现</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter5/4exercise.html">chapter5练习</a></li>
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<li class="toctree-l1 current has-children"><a class="reference internal" href="index.html">第六章：文件系统与I/O重定向</a><input checked="" class="toctree-checkbox" id="toctree-checkbox-14" name="toctree-checkbox-14" role="switch" type="checkbox"/><label for="toctree-checkbox-14"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="current">
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<li class="toctree-l2 current current-page"><a class="current reference internal" href="#">文件系统接口</a></li>
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<li class="toctree-l2"><a class="reference internal" href="2fs-implementation-1.html">简易文件系统 easy-fs (上)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="2fs-implementation-2.html">简易文件系统 easy-fs (下)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="3using-easy-fs-in-kernel.html">在内核中使用 easy-fs</a></li>
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<li class="toctree-l2"><a class="reference internal" href="4exercise.html">chapter6练习</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../chapter7/1pipe.html">管道</a></li>
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|
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</ul>
|
||
</li>
|
||
</ul>
|
||
<p class="caption" role="heading"><span class="caption-text">附录</span></p>
|
||
<ul>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-a/index.html">附录 A：Rust 系统编程资料</a><input class="toctree-checkbox" id="toctree-checkbox-17" name="toctree-checkbox-17" role="switch" type="checkbox"/><label for="toctree-checkbox-17"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-b/index.html">附录 B：常见工具的使用方法</a><input class="toctree-checkbox" id="toctree-checkbox-18" name="toctree-checkbox-18" role="switch" type="checkbox"/><label for="toctree-checkbox-18"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../appendix-c/index.html">附录 C：深入机器模式：RustSBI</a><input class="toctree-checkbox" id="toctree-checkbox-19" name="toctree-checkbox-19" role="switch" type="checkbox"/><label for="toctree-checkbox-19"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1"><a class="reference internal" href="../appendix-d/index.html">附录 D：RISC-V相关信息</a></li>
|
||
</ul>
|
||
<p class="caption" role="heading"><span class="caption-text">开发注记</span></p>
|
||
<ul>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../setup-sphinx.html">修改和构建本项目</a><input class="toctree-checkbox" id="toctree-checkbox-20" name="toctree-checkbox-20" role="switch" type="checkbox"/><label for="toctree-checkbox-20"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
|
||
</ul>
|
||
</li>
|
||
<li class="toctree-l1 has-children"><a class="reference internal" href="../rest-example.html">reStructuredText 基本语法</a><input class="toctree-checkbox" id="toctree-checkbox-21" name="toctree-checkbox-21" role="switch" type="checkbox"/><label for="toctree-checkbox-21"><div class="visually-hidden">Toggle child pages in navigation</div><i class="icon"><svg><use href="#svg-arrow-right"></use></svg></i></label><ul class="simple">
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</li>
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|
||
|
||
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</aside>
|
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<div class="main">
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||
<div class="content">
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<article role="main">
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<div class="content-icon-container">
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<div class="theme-toggle-container theme-toggle-content">
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<button class="theme-toggle">
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<div class="visually-hidden">Toggle Light / Dark / Auto color theme</div>
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<svg class="theme-icon-when-auto"><use href="#svg-sun-half"></use></svg>
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<svg class="theme-icon-when-dark"><use href="#svg-moon"></use></svg>
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<div class="visually-hidden">Toggle table of contents sidebar</div>
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<i class="icon"><svg><use href="#svg-toc"></use></svg></i>
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<div class="section" id="id1">
|
||
<h1>文件系统接口<a class="headerlink" href="#id1" title="永久链接至标题">¶</a></h1>
|
||
<div class="section" id="id2">
|
||
<h2>简易文件与目录抽象<a class="headerlink" href="#id2" title="永久链接至标题">¶</a></h2>
|
||
<p>与课堂所学相比，我们实现的文件系统进行了很大的简化：</p>
|
||
<ul class="simple">
|
||
<li><p>扁平化：仅存在根目录 <code class="docutils literal notranslate"><span class="pre">/</span></code> 一个目录，所有的文件都放在根目录内。直接以文件名索引文件。</p></li>
|
||
<li><p>不设置用户和用户组概念，不记录文件访问/修改的任何时间戳，不支持软硬链接。</p></li>
|
||
<li><p>只实现了最基本的文件系统相关系统调用。</p></li>
|
||
</ul>
|
||
</div>
|
||
<div class="section" id="id3">
|
||
<h2>打开与读写文件的系统调用<a class="headerlink" href="#id3" title="永久链接至标题">¶</a></h2>
|
||
<div class="section" id="id4">
|
||
<h3>打开文件<a class="headerlink" href="#id4" title="永久链接至标题">¶</a></h3>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="sd">/// 功能：打开一个常规文件，并返回可以访问它的文件描述符。</span>
|
||
<span class="sd">/// 参数：path 描述要打开的文件的文件名（简单起见，文件系统不需要支持目录，所有的文件都放在根目录 / 下），</span>
|
||
<span class="sd">/// flags 描述打开文件的标志，具体含义下面给出。</span>
|
||
<span class="sd">/// dirfd 和 mode 仅用于保证兼容性，忽略</span>
|
||
<span class="sd">/// 返回值：如果出现了错误则返回 -1，否则返回打开常规文件的文件描述符。可能的错误原因是：文件不存在。</span>
|
||
<span class="sd">/// syscall ID：56</span>
|
||
<span class="k">fn</span> <span class="nf">sys_openat</span><span class="p">(</span><span class="n">dirfd</span>: <span class="kt">usize</span><span class="p">,</span><span class="w"> </span><span class="n">path</span>: <span class="kp">&</span><span class="kt">str</span><span class="p">,</span><span class="w"> </span><span class="n">flags</span>: <span class="kt">u32</span><span class="p">,</span><span class="w"> </span><span class="n">mode</span>: <span class="kt">u32</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">isize</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>目前我们的内核支持以下几种标志（多种不同标志可能共存）：</p>
|
||
<ul class="simple">
|
||
<li><p>如果 <code class="docutils literal notranslate"><span class="pre">flags</span></code> 为 0，则表示以只读模式 <em>RDONLY</em> 打开；</p></li>
|
||
<li><p>如果 <code class="docutils literal notranslate"><span class="pre">flags</span></code> 第 0 位被设置（0x001），表示以只写模式 <em>WRONLY</em> 打开；</p></li>
|
||
<li><p>如果 <code class="docutils literal notranslate"><span class="pre">flags</span></code> 第 1 位被设置（0x002），表示既可读又可写 <em>RDWR</em> ；</p></li>
|
||
<li><p>如果 <code class="docutils literal notranslate"><span class="pre">flags</span></code> 第 9 位被设置（0x200），表示允许创建文件 <em>CREATE</em> ，在找不到该文件的时候应创建文件；如果该文件已经存在则应该将该文件的大小归零；</p></li>
|
||
<li><p>如果 <code class="docutils literal notranslate"><span class="pre">flags</span></code> 第 10 位被设置（0x400），则在打开文件的时候应该清空文件的内容并将该文件的大小归零，也即 <em>TRUNC</em> 。</p></li>
|
||
</ul>
|
||
<p>在用户库 <code class="docutils literal notranslate"><span class="pre">user_lib</span></code> 中，我们将该系统调用封装为 <code class="docutils literal notranslate"><span class="pre">open</span></code> 接口：</p>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="c1">// user/src/lib.rs</span>
|
||
|
||
<span class="n">bitflags</span><span class="o">!</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">pub</span><span class="w"> </span><span class="k">struct</span> <span class="nc">OpenFlags</span>: <span class="kt">u32</span> <span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">RDONLY</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">WRONLY</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">RDWR</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">CREATE</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">9</span><span class="p">;</span><span class="w"></span>
|
||
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">TRUNC</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"></span>
|
||
<span class="w"> </span><span class="p">}</span><span class="w"></span>
|
||
<span class="p">}</span><span class="w"></span>
|
||
|
||
<span class="k">pub</span><span class="w"> </span><span class="k">fn</span> <span class="nf">open</span><span class="p">(</span><span class="n">path</span>: <span class="kp">&</span><span class="kt">str</span><span class="p">,</span><span class="w"> </span><span class="n">flags</span>: <span class="nc">OpenFlags</span><span class="p">)</span><span class="w"> </span>-> <span class="kt">isize</span> <span class="p">{</span><span class="w"></span>
|
||
<span class="w"> </span><span class="n">sys_openat</span><span class="p">(</span><span class="n">AT_FDCWD</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="kt">usize</span><span class="p">,</span><span class="w"> </span><span class="n">path</span><span class="p">,</span><span class="w"> </span><span class="n">flags</span><span class="p">.</span><span class="n">bits</span><span class="p">,</span><span class="w"> </span><span class="n">OpenFlags</span>::<span class="n">RDWR</span><span class="p">.</span><span class="n">bits</span><span class="p">)</span><span class="w"></span>
|
||
<span class="p">}</span><span class="w"></span>
|
||
</pre></div>
|
||
</div>
|
||
<p>借助 <code class="docutils literal notranslate"><span class="pre">bitflags!</span></code> 宏我们将一个 <code class="docutils literal notranslate"><span class="pre">u32</span></code> 的 flags 包装为一个 <code class="docutils literal notranslate"><span class="pre">OpenFlags</span></code> 结构体，可以从它的 <code class="docutils literal notranslate"><span class="pre">bits</span></code> 字段获得 <code class="docutils literal notranslate"><span class="pre">u32</span></code> 表示。</p>
|
||
</div>
|
||
<div class="section" id="id5">
|
||
<h3>顺序读写文件<a class="headerlink" href="#id5" title="永久链接至标题">¶</a></h3>
|
||
<p>在打开一个文件之后，我们就可以用之前的 <code class="docutils literal notranslate"><span class="pre">sys_read/sys_write</span></code> 两个系统调用来对它进行读写了。本教程只实现文件的顺序读写，而不考虑随机读写。</p>
|
||
<p>以本章的测试用例 <code class="docutils literal notranslate"><span class="pre">ch6b_filetest_simple</span></code> 来介绍文件系统接口的使用方法：</p>
|
||
<div class="highlight-rust notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 1</span><span class="c1">// user/src/bin/ch6b_filetest_simple.rs</span>
|
||
<span class="linenos"> 2</span>
|
||
<span class="linenos"> 3</span><span class="cp">#![no_std]</span><span class="w"></span>
|
||
<span class="linenos"> 4</span><span class="cp">#![no_main]</span><span class="w"></span>
|
||
<span class="linenos"> 5</span>
|
||
<span class="linenos"> 6</span><span class="cp">#[macro_use]</span><span class="w"></span>
|
||
<span class="linenos"> 7</span><span class="k">extern</span><span class="w"> </span><span class="k">crate</span><span class="w"> </span><span class="n">user_lib</span><span class="p">;</span><span class="w"></span>
|
||
<span class="linenos"> 8</span>
|
||
<span class="linenos"> 9</span><span class="k">use</span><span class="w"> </span><span class="n">user_lib</span>::<span class="p">{</span><span class="w"></span>
|
||
<span class="linenos">10</span><span class="w"> </span><span class="n">open</span><span class="p">,</span><span class="w"></span>
|
||
<span class="linenos">11</span><span class="w"> </span><span class="n">close</span><span class="p">,</span><span class="w"></span>
|
||
<span class="linenos">12</span><span class="w"> </span><span class="n">read</span><span class="p">,</span><span class="w"></span>
|
||
<span class="linenos">13</span><span class="w"> </span><span class="n">write</span><span class="p">,</span><span class="w"></span>
|
||
<span class="linenos">14</span><span class="w"> </span><span class="n">OpenFlags</span><span class="p">,</span><span class="w"></span>
|
||
<span class="linenos">15</span><span class="p">};</span><span class="w"></span>
|
||
<span class="linenos">16</span>
|
||
<span class="linenos">17</span><span class="cp">#[no_mangle]</span><span class="w"></span>
|
||
<span class="linenos">18</span><span class="k">pub</span><span class="w"> </span><span class="k">fn</span> <span class="nf">main</span><span class="p">()</span><span class="w"> </span>-> <span class="kt">i32</span> <span class="p">{</span><span class="w"></span>
|
||
<span class="linenos">19</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">test_str</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Hello, world!"</span><span class="p">;</span><span class="w"></span>
|
||
<span class="linenos">20</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">filea</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"filea</span><span class="se">\0</span><span class="s">"</span><span class="p">;</span><span class="w"></span>
|
||
<span class="linenos">21</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">open</span><span class="p">(</span><span class="n">filea</span><span class="p">,</span><span class="w"> </span><span class="n">OpenFlags</span>::<span class="n">CREATE</span><span class="w"> </span><span class="o">|</span><span class="w"> </span><span class="n">OpenFlags</span>::<span class="n">WRONLY</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">22</span><span class="w"> </span><span class="fm">assert!</span><span class="p">(</span><span class="n">fd</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="mi">0</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">23</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">fd</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="kt">usize</span><span class="p">;</span><span class="w"></span>
|
||
<span class="linenos">24</span><span class="w"> </span><span class="n">write</span><span class="p">(</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="n">test_str</span><span class="p">.</span><span class="n">as_bytes</span><span class="p">());</span><span class="w"></span>
|
||
<span class="linenos">25</span><span class="w"> </span><span class="n">close</span><span class="p">(</span><span class="n">fd</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">26</span>
|
||
<span class="linenos">27</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">open</span><span class="p">(</span><span class="n">filea</span><span class="p">,</span><span class="w"> </span><span class="n">OpenFlags</span>::<span class="n">RDONLY</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">28</span><span class="w"> </span><span class="fm">assert!</span><span class="p">(</span><span class="n">fd</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="mi">0</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">29</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">fd</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="kt">usize</span><span class="p">;</span><span class="w"></span>
|
||
<span class="linenos">30</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="k">mut</span><span class="w"> </span><span class="n">buffer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">[</span><span class="mi">0</span><span class="k">u8</span><span class="p">;</span><span class="w"> </span><span class="mi">100</span><span class="p">];</span><span class="w"></span>
|
||
<span class="linenos">31</span><span class="w"> </span><span class="kd">let</span><span class="w"> </span><span class="n">read_len</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">read</span><span class="p">(</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="k">mut</span><span class="w"> </span><span class="n">buffer</span><span class="p">)</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="kt">usize</span><span class="p">;</span><span class="w"></span>
|
||
<span class="linenos">32</span><span class="w"> </span><span class="n">close</span><span class="p">(</span><span class="n">fd</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">33</span>
|
||
<span class="linenos">34</span><span class="w"> </span><span class="fm">assert_eq!</span><span class="p">(</span><span class="w"></span>
|
||
<span class="linenos">35</span><span class="w"> </span><span class="n">test_str</span><span class="p">,</span><span class="w"></span>
|
||
<span class="linenos">36</span><span class="w"> </span><span class="n">core</span>::<span class="kt">str</span>::<span class="n">from_utf8</span><span class="p">(</span><span class="o">&</span><span class="n">buffer</span><span class="p">[</span><span class="o">..</span><span class="n">read_len</span><span class="p">]).</span><span class="n">unwrap</span><span class="p">(),</span><span class="w"></span>
|
||
<span class="linenos">37</span><span class="w"> </span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">38</span><span class="w"> </span><span class="fm">println!</span><span class="p">(</span><span class="s">"file_test passed!"</span><span class="p">);</span><span class="w"></span>
|
||
<span class="linenos">39</span><span class="w"> </span><span class="mi">0</span><span class="w"></span>
|
||
<span class="linenos">40</span><span class="p">}</span><span class="w"></span>
|
||
</pre></div>
|
||
</div>
|
||
<ul class="simple">
|
||
<li><p>第 20~25 行，我们以 <em>只写 + 创建</em> 的模式打开文件 <code class="docutils literal notranslate"><span class="pre">filea</span></code> ，向其中写入字符串 <code class="docutils literal notranslate"><span class="pre">Hello,</span> <span class="pre">world!</span></code> 而后关闭文件。</p></li>
|
||
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