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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>Return Conventions</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel" /><link rel="up" href="ch10.html" title="Chapter 10. Routines and Conventions" /><link rel="prev" href="ch10.html" title="Chapter 10. Routines and Conventions" /><link rel="next" href="ch10s03.html" title="Breaking Compilation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Return Conventions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch10.html">Prev</a> </td><th width="60%" align="center">Chapter 10. Routines and Conventions</th><td width="20%" align="right"> <a accesskey="n" href="ch10s03.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="Return Conventions"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="convention-returns"></a>Return Conventions</h2></div></div></div><p>
For code called in user context, it's very common to defy C
convention, and return <span class="returnvalue">0</span> for success,
and a negative error number
(eg. <span class="returnvalue">-EFAULT</span>) for failure. This can be
unintuitive at first, but it's fairly widespread in the kernel.
</p><p>
Using <code class="function">ERR_PTR()</code>
<code class="filename">include/linux/err.h</code>; to
encode a negative error number into a pointer, and
<code class="function">IS_ERR()</code> and <code class="function">PTR_ERR()</code>
to get it back out again: avoids a separate pointer parameter for
the error number. Icky, but in a good way.
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