1<html><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 V1.78.1"><link rel="home" href="index.html" title="The Linux-USB Host Side API"><link rel="up" href="usbcore.html" title="Chapter&#160;5.&#160;USB Core APIs"><link rel="prev" href="API-usb-sg-cancel.html" title="usb_sg_cancel"><link rel="next" href="API-usb-string.html" title="usb_string"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center"><span class="phrase">usb_get_descriptor</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API-usb-sg-cancel.html">Prev</a>&#160;</td><th width="60%" align="center">Chapter&#160;5.&#160;USB Core APIs</th><td width="20%" align="right">&#160;<a accesskey="n" href="API-usb-string.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API-usb-get-descriptor"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>usb_get_descriptor &#8212; 
2     issues a generic GET_DESCRIPTOR request
3 </p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><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>&#160;</td><td>unsigned char <var class="pdparam">type</var>, </td></tr><tr><td>&#160;</td><td>unsigned char <var class="pdparam">index</var>, </td></tr><tr><td>&#160;</td><td>void * <var class="pdparam">buf</var>, </td></tr><tr><td>&#160;</td><td>int <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer">&#160;</div></div></div><div class="refsect1"><a name="idp1116208292"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>dev</code></em></span></dt><dd><p>
4     the device whose descriptor is being retrieved
5    </p></dd><dt><span class="term"><em class="parameter"><code>type</code></em></span></dt><dd><p>
6     the descriptor type (USB_DT_*)
7    </p></dd><dt><span class="term"><em class="parameter"><code>index</code></em></span></dt><dd><p>
8     the number of the descriptor
9    </p></dd><dt><span class="term"><em class="parameter"><code>buf</code></em></span></dt><dd><p>
10     where to put the descriptor
11    </p></dd><dt><span class="term"><em class="parameter"><code>size</code></em></span></dt><dd><p>
12     how big is <span class="quote">&#8220;<span class="quote">buf</span>&#8221;</span>?
13    </p></dd></dl></div></div><div class="refsect1"><a name="idp1116214028"></a><h2>Context</h2><p>
14   !in_interrupt ()
15</p></div><div class="refsect1"><a name="idp1116214604"></a><h2>Description</h2><p>
16   Gets a USB descriptor.  Convenience functions exist to simplify
17   getting some types of descriptors.  Use
18   <code class="function">usb_get_string</code> or <code class="function">usb_string</code> for USB_DT_STRING.
19   Device (USB_DT_DEVICE) and configuration descriptors (USB_DT_CONFIG)
20   are part of the device structure.
21   In addition to a number of USB-standard descriptors, some
22   devices also use class-specific or vendor-specific descriptors.
23   </p><p>
24
25   This call is synchronous, and may not be used in an interrupt context.
26</p></div><div class="refsect1"><a name="idp1116216412"></a><h2>Return</h2><p>
27   The number of bytes received on success, or else the status code
28   returned by the underlying <code class="function">usb_control_msg</code> call.
29</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="API-usb-sg-cancel.html">Prev</a>&#160;</td><td width="20%" align="center"><a accesskey="u" href="usbcore.html">Up</a></td><td width="40%" align="right">&#160;<a accesskey="n" href="API-usb-string.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span class="phrase">usb_sg_cancel</span>&#160;</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">&#160;<span class="phrase">usb_string</span></td></tr></table></div></body></html>
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