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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>usb_get_descriptor</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="The Linux-USB Host Side API" /><link rel="up" href="ch05.html" title="Chapter 5. USB Core APIs" /><link rel="prev" href="re64.html" title="usb_sg_cancel" /><link rel="next" href="re66.html" title="usb_string" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span>usb_get_descriptor</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="re64.html">Prev</a> </td><th width="60%" align="center">Chapter 5. USB Core APIs</th><td width="20%" align="right"> <a accesskey="n" href="re66.html">Next</a></td></tr></table><hr /></div><div class="refentry" title="usb_get_descriptor"><a id="API-usb-get-descriptor"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>usb_get_descriptor —
issues a generic GET_DESCRIPTOR request
</p></div><div class="refsynopsisdiv" title="Synopsis"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">usb_get_descriptor </b>(</code></td><td>struct usb_device * <var class="pdparam">dev</var>, </td></tr><tr><td> </td><td>unsigned char <var class="pdparam">type</var>, </td></tr><tr><td> </td><td>unsigned char <var class="pdparam">index</var>, </td></tr><tr><td> </td><td>void * <var class="pdparam">buf</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1" title="Arguments"><a id="id3111451"></a><h2>Arguments</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>dev</code></em></span></dt><dd><p>
the device whose descriptor is being retrieved
</p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>
the descriptor type (USB_DT_*)
</p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>
the number of the descriptor
</p></dd><dt><span class="term"><em class="parameter"><code>buf</code></em></span></dt><dd><p>
where to put the descriptor
</p></dd><dt><span class="term"><em class="parameter"><code>size</code></em></span></dt><dd><p>
how big is <span class="quote">“<span class="quote">buf</span>”</span>?
</p></dd></dl></div></div><div class="refsect1" title="Context"><a id="id3111547"></a><h2>Context</h2><p>
!in_interrupt ()
</p></div><div class="refsect1" title="Description"><a id="id3111556"></a><h2>Description</h2><p>
Gets a USB descriptor. Convenience functions exist to simplify
getting some types of descriptors. Use
<code class="function">usb_get_string</code> or <code class="function">usb_string</code> for USB_DT_STRING.
Device (USB_DT_DEVICE) and configuration descriptors (USB_DT_CONFIG)
are part of the device structure.
In addition to a number of USB-standard descriptors, some
devices also use class-specific or vendor-specific descriptors.
</p><p>
This call is synchronous, and may not be used in an interrupt context.
</p><p>
Returns the number of bytes received on success, or else the status code
returned by the underlying <code class="function">usb_control_msg</code> call.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="re64.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch05.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="re66.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span>usb_sg_cancel</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span>usb_string</span></td></tr></table></div></body></html>
