1<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>__copy_from_user</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="The Linux Kernel API"><link rel="up" href="ch04s02.html" title="User Space Memory Access"><link rel="prev" href="API---copy-to-user.html" title="__copy_to_user"><link rel="next" href="API-clear-user.html" title="clear_user"></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">__copy_from_user</span></th></tr><tr><td width="20%" align="left"><a accesskey="p" href="API---copy-to-user.html">Prev</a> </td><th width="60%" align="center">User Space Memory Access</th><td width="20%" align="right"> <a accesskey="n" href="API-clear-user.html">Next</a></td></tr></table><hr></div><div class="refentry"><a name="API---copy-from-user"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>__copy_from_user — 
2     Copy a block of data from user space, with less checking.
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">unsigned long <b class="fsfunc">__copy_from_user </b>(</code></td><td>void * <var class="pdparam">to</var>, </td></tr><tr><td> </td><td>const void __user * <var class="pdparam">from</var>, </td></tr><tr><td> </td><td>unsigned long <var class="pdparam">n</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="id-1.6.3.4.5"></a><h2>Arguments</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="parameter"><code>to</code></em></span></dt><dd><p>
4     Destination address, in kernel space.
5    </p></dd><dt><span class="term"><em class="parameter"><code>from</code></em></span></dt><dd><p>
6     Source address, in user space.
7    </p></dd><dt><span class="term"><em class="parameter"><code>n</code></em></span></dt><dd><p>
8     Number of bytes to copy.
9    </p></dd></dl></div></div><div class="refsect1"><a name="id-1.6.3.4.6"></a><h2>Context</h2><p>
10   User context only. This function may sleep if pagefaults are
11   enabled.
12</p></div><div class="refsect1"><a name="id-1.6.3.4.7"></a><h2>Description</h2><p>
13   Copy data from user space to kernel space.  Caller must check
14   the specified block with <code class="function">access_ok</code> before calling this function.
15   </p><p>
16
17   Returns number of bytes that could not be copied.
18   On success, this will be zero.
19   </p><p>
20
21   If some data could not be copied, this function will pad the copied
22   data to the requested size using zero bytes.
23   </p><p>
24
25   An alternate version - <code class="function">__copy_from_user_inatomic</code> - may be called from
26   atomic context and will fail rather than sleep.  In this case the
27   uncopied bytes will *NOT* be padded with zeros.  See fs/filemap.h
28   for explanation of why this is needed.
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---copy-to-user.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch04s02.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="API-clear-user.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"><span class="phrase">__copy_to_user</span> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> <span class="phrase">clear_user</span></td></tr></table></div></body></html>
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