1<html><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 V1.78.1"><link rel="home" href="index.html" title="Unreliable Guide To Hacking The Linux Kernel"><link rel="up" href="conventions.html" title="Chapter&#160;10.&#160;Routines and Conventions"><link rel="prev" href="conventions.html" title="Chapter&#160;10.&#160;Routines and Conventions"><link rel="next" href="conventions-borkedcompile.html" title="Breaking Compilation"></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">Return Conventions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="conventions.html">Prev</a>&#160;</td><th width="60%" align="center">Chapter&#160;10.&#160;Routines and Conventions</th><td width="20%" align="right">&#160;<a accesskey="n" href="conventions-borkedcompile.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="convention-returns"></a>Return Conventions</h2></div></div></div><p>
2    For code called in user context, it's very common to defy C
3    convention, and return <span class="returnvalue">0</span> for success,
4    and a negative error number
5    (eg. <span class="returnvalue">-EFAULT</span>) for failure.  This can be
6    unintuitive at first, but it's fairly widespread in the kernel.
7   </p><p>
8    Using <code class="function">ERR_PTR()</code>
9
10    <code class="filename">include/linux/err.h</code>; to
11    encode a negative error number into a pointer, and
12    <code class="function">IS_ERR()</code> and <code class="function">PTR_ERR()</code>
13    to get it back out again: avoids a separate pointer parameter for
14    the error number.  Icky, but in a good way.
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