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<div class="section" id="file-system-abstraction">
<h1>File System Abstraction<a class="headerlink" href="#file-system-abstraction" title="Permalink to this headline"></a></h1>
<p>Mynewt provides a file system abstraction layer (<code class="docutils literal notranslate"><span class="pre">fs/fs</span></code>) to allow
client code to be file system agnostic. By accessing the file system via
the <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> API, client code can perform file system operations
without being tied to a particular implementation. When possible,
library code should use the <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> API rather than accessing the
underlying file system directly.</p>
<div class="section" id="description">
<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline"></a></h2>
<p>Applications should aim to minimize the amount of code which depends on
a particular file system implementation. When possible, only depend on
the <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> package. In terms of the Mynewt hierarchy, an <strong>app</strong>
package must depend on a specific file system package, while <strong>library</strong>
packages should only depend on <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code>.</p>
<p>Applications wanting to access a filesystem are required to include the
necessary packages in their applications pkg.yml file. In the following
example, the <code class="docutils literal notranslate"><span class="pre">`Newtron</span> <span class="pre">Flash</span> <span class="pre">File</span> <span class="pre">System</span></code> &lt;../nffs/nffs.html&gt;`__ is
used.</p>
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp"># </span>repos/apache-mynewt-core/apps/slinky/pkg.yml
<span class="go">pkg.name: repos/apache-mynewt-core/apps/slinky</span>
<span class="go">pkg.deps:</span>
<span class="go"> - fs/fs # include the file operations interfaces</span>
<span class="go"> - fs/nffs # include the NFFS filesystem implementation</span>
</pre></div>
</div>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span># repos/apache-mynewt-core/apps/slinky/syscfg.yml
# [...]
# Package: apps/&lt;example app&gt;
# [...]
CONFIG_NFFS: 1 # initialize and configure NFFS into the system
# NFFS_DETECT_FAIL: 1 # Ignore NFFS detection issues
# NFFS_DETECT_FAIL: 2 # Format a new NFFS file system on failure to detect
# [...]
</pre></div>
</div>
<p>Consult the documentation for <code class="docutils literal notranslate"><span class="pre">`nffs</span></code> &lt;../nffs/nffs.html&gt;`__ for a more
detailed explanation of NFFS_DETECT_FAIL</p>
<p>Code which uses the file system after the system has been initialized
need only depend on <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code>. For example, the <code class="docutils literal notranslate"><span class="pre">libs/imgmgr</span></code> package
is a library which provides firmware upload and download functionality
via the use of a file system. This library is only used after the system
has been initialized, and therefore only depends on the <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code>
package.</p>
<div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp"># </span>repos/apache-mynewt-core/libs/imgmgr/pkg.yml
<span class="go">pkg.name: libs/imgmgr</span>
<span class="go">pkg.deps:</span>
<span class="go"> - fs/fs</span>
<span class="gp"># </span><span class="o">[</span>...<span class="o">]</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">libs/imgmgr</span></code> package uses the <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> API for all file system
operations.</p>
</div>
<div class="section" id="support-for-multiple-filesystems">
<h2>Support for multiple filesystems<a class="headerlink" href="#support-for-multiple-filesystems" title="Permalink to this headline"></a></h2>
<p>When using a single filesystem/disk, it is valid to provide paths in the
standard unix way, eg, <code class="docutils literal notranslate"><span class="pre">/&lt;dir-name&gt;/&lt;file-name&gt;</span></code>. When trying to run
more than one filesystem or a single filesystem in multiple devices
simultaneosly, an extra name has to be given to the disk that is being
used. The abstraction for that was added as the <code class="docutils literal notranslate"><span class="pre">fs/disk</span></code> package
which is a dependency of <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code>. It adds the following extra user
function:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">disk_register</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">disk_name</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">fs_name</span><span class="p">,</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">disk_ops</span><span class="w"> </span><span class="o">*</span><span class="n">dops</span><span class="p">)</span>
</pre></div>
</div>
<p>As an example os usage:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">disk_register</span><span class="p">(</span><span class="s">&quot;mmc0&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;fatfs&quot;</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">mmc_ops</span><span class="p">);</span>
<span class="n">disk_register</span><span class="p">(</span><span class="s">&quot;flash0&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;nffs&quot;</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">);</span>
</pre></div>
</div>
<p>This registers the name <code class="docutils literal notranslate"><span class="pre">mmc0</span></code> to use <code class="docutils literal notranslate"><span class="pre">fatfs</span></code> as the filesystem and
<code class="docutils literal notranslate"><span class="pre">mmc_ops</span></code> for the low-level disk driver and also registers <code class="docutils literal notranslate"><span class="pre">flash0</span></code>
to use <code class="docutils literal notranslate"><span class="pre">nffs</span></code>. <code class="docutils literal notranslate"><span class="pre">nffs</span></code> is currently strongly bound to the
<code class="docutils literal notranslate"><span class="pre">hal_flash</span></code> interface, ignoring any other possible <code class="docutils literal notranslate"><span class="pre">disk_ops</span></code> given.</p>
<div class="section" id="struct-disk-ops">
<h3>struct disk_ops<a class="headerlink" href="#struct-disk-ops" title="Permalink to this headline"></a></h3>
<p>To support a new low-level disk interface, the <code class="docutils literal notranslate"><span class="pre">struct</span> <span class="pre">disk_ops</span></code>
interface must be implemented by the low-level driver. Currently only
<code class="docutils literal notranslate"><span class="pre">read</span></code> and <code class="docutils literal notranslate"><span class="pre">write</span></code> are effectively used (by <code class="docutils literal notranslate"><span class="pre">fatfs</span></code>).</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">disk_ops</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">read</span><span class="p">)(</span><span class="kt">uint8_t</span><span class="p">,</span><span class="w"> </span><span class="kt">uint32_t</span><span class="p">,</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="p">,</span><span class="w"> </span><span class="kt">uint32_t</span><span class="p">);</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">write</span><span class="p">)(</span><span class="kt">uint8_t</span><span class="p">,</span><span class="w"> </span><span class="kt">uint32_t</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="p">,</span><span class="w"> </span><span class="kt">uint32_t</span><span class="p">);</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">ioctl</span><span class="p">)(</span><span class="kt">uint8_t</span><span class="p">,</span><span class="w"> </span><span class="kt">uint32_t</span><span class="p">,</span><span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="p">);</span>
<span class="w"> </span><span class="n">SLIST_ENTRY</span><span class="p">(</span><span class="n">disk_ops</span><span class="p">)</span><span class="w"> </span><span class="n">sc_next</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="thread-safety">
<h2>Thread Safety<a class="headerlink" href="#thread-safety" title="Permalink to this headline"></a></h2>
<p>All <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> functions are thread safe.</p>
</div>
<div class="section" id="header-files">
<h2>Header Files<a class="headerlink" href="#header-files" title="Permalink to this headline"></a></h2>
<p>All code which uses the <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> package needs to include the following
header:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">&quot;fs/fs.h&quot;</span>
</pre></div>
</div>
</div>
<div class="section" id="data-structures">
<h2>Data Structures<a class="headerlink" href="#data-structures" title="Permalink to this headline"></a></h2>
<p>All <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> data structures are opaque to client code.</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">fs_file</span><span class="p">;</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">fs_dir</span><span class="p">;</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">fs_dirent</span><span class="p">;</span>
</pre></div>
</div>
</div>
<div class="section" id="api">
<h2>API<a class="headerlink" href="#api" title="Permalink to this headline"></a></h2>
<p>Functions in <code class="docutils literal notranslate"><span class="pre">fs/fs</span></code> that indicate success or failure do so with the
following set of return codes:</p>
<ul class="simple">
<li><p><a class="reference external" href="fs_return_codes.html">Return Codes</a></p></li>
</ul>
<p>The functions available in this OS feature are:</p>
<p>Additional file system utilities that bundle some of the basic functions
above are:</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 43%" />
<col style="width: 57%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Function</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><a href="#id3"><span class="problematic" id="id4">`fsutil\_r
ead\_file
&lt;fsutil_re
ad_file.md
&gt;`__</span></a></p></td>
<td><p>Opens a file
at the
specified
path, retrieve
data from the
file starting
from the
specified
offset, and
close the file
and invalidate
the file
handle.</p></td>
</tr>
<tr class="row-odd"><td><p><a href="#id1"><span class="problematic" id="id2">`</span></a>fsutil_w
rite_file</p>
<blockquote>
<div><p>&lt;fsutil_w</p>
</div></blockquote>
<p>rite_file.
md&gt;`__</p>
</td>
<td><p>Open a file at
the specified
path, write
the supplied
data to the
current offset
of the
specified file
handle, and
close the file
and invalidate
the file
handle.</p></td>
</tr>
</tbody>
</table>
</div>
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