1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>copy_[to/from]_user() / get_user() / put_user() include/asm/uaccess.h</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><link rel="home" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel"><link rel="up" href="common-routines.html" title="Chapter&#160;6.&#160;Common Routines"><link rel="prev" href="common-routines.html" title="Chapter&#160;6.&#160;Common Routines"><link rel="next" href="routines-kmalloc.html" title="kmalloc()/kfree() include/linux/slab.h"></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">
2    <code class="function">copy_[to/from]_user()</code>
3    /
4    <code class="function">get_user()</code>
5    /
6    <code class="function">put_user()</code>
7    <code class="filename">include/asm/uaccess.h</code>
8   </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="common-routines.html">Prev</a>&#160;</td><th width="60%" align="center">Chapter&#160;6.&#160;Common Routines</th><td width="20%" align="right">&#160;<a accesskey="n" href="routines-kmalloc.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="routines-copy"></a>
9    <code class="function">copy_[to/from]_user()</code>
10    /
11    <code class="function">get_user()</code>
12    /
13    <code class="function">put_user()</code>
14    <code class="filename">include/asm/uaccess.h</code>
15   </h2></div></div></div><p>
16    <span class="emphasis"><em>[SLEEPS]</em></span>
17   </p><p>
18    <code class="function">put_user()</code> and <code class="function">get_user()</code>
19    are used to get and put single values (such as an int, char, or
20    long) from and to userspace.  A pointer into userspace should
21    never be simply dereferenced: data should be copied using these
22    routines.  Both return <code class="constant">-EFAULT</code> or 0.
23   </p><p>
24    <code class="function">copy_to_user()</code> and
25    <code class="function">copy_from_user()</code> are more general: they copy
26    an arbitrary amount of data to and from userspace.
27    </p><div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Caution</h3><p>
28      Unlike <code class="function">put_user()</code> and
29      <code class="function">get_user()</code>, they return the amount of
30      uncopied data (ie. <span class="returnvalue">0</span> still means
31      success).
32     </p></div><p>
33    [Yes, this moronic interface makes me cringe.  The flamewar comes up every year or so. --RR.]
34   </p><p>
35    The functions may sleep implicitly. This should never be called
36    outside user context (it makes no sense), with interrupts
37    disabled, or a spinlock held.
38   </p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="common-routines.html">Prev</a>&#160;</td><td width="20%" align="center"><a accesskey="u" href="common-routines.html">Up</a></td><td width="40%" align="right">&#160;<a accesskey="n" href="routines-kmalloc.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter&#160;6.&#160;Common Routines&#160;</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">&#160;<code class="function">kmalloc()</code>/<code class="function">kfree()</code>
39    <code class="filename">include/linux/slab.h</code></td></tr></table></div></body></html>
40