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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>Chapter 6. Common Routines</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="index.html" title="Unreliable Guide To Hacking The Linux Kernel" /><link rel="prev" href="ch05.html" title="Chapter 5. Recipes for Deadlock" /><link rel="next" href="ch06s02.html" title="copy_[to/from]_user() / get_user() / put_user() include/asm/uaccess.h" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 6. Common Routines</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch05.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch06s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 6. Common Routines"><div class="titlepage"><div><div><h2 class="title"><a id="common-routines"></a>Chapter 6. Common Routines</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch06.html#routines-printk">
<code class="function">printk()</code>
<code class="filename">include/linux/kernel.h</code>
</a></span></dt><dt><span class="sect1"><a href="ch06s02.html">
<code class="function">copy_[to/from]_user()</code>
/
<code class="function">get_user()</code>
/
<code class="function">put_user()</code>
<code class="filename">include/asm/uaccess.h</code>
</a></span></dt><dt><span class="sect1"><a href="ch06s03.html"><code class="function">kmalloc()</code>/<code class="function">kfree()</code>
<code class="filename">include/linux/slab.h</code></a></span></dt><dt><span class="sect1"><a href="ch06s04.html"><code class="function">current</code>
<code class="filename">include/asm/current.h</code></a></span></dt><dt><span class="sect1"><a href="ch06s05.html"><code class="function">mdelay()</code>/<code class="function">udelay()</code>
<code class="filename">include/asm/delay.h</code>
<code class="filename">include/linux/delay.h</code>
</a></span></dt><dt><span class="sect1"><a href="ch06s06.html"><code class="function">cpu_to_be32()</code>/<code class="function">be32_to_cpu()</code>/<code class="function">cpu_to_le32()</code>/<code class="function">le32_to_cpu()</code>
<code class="filename">include/asm/byteorder.h</code>
</a></span></dt><dt><span class="sect1"><a href="ch06s07.html"><code class="function">local_irq_save()</code>/<code class="function">local_irq_restore()</code>
<code class="filename">include/asm/system.h</code>
</a></span></dt><dt><span class="sect1"><a href="ch06s08.html"><code class="function">local_bh_disable()</code>/<code class="function">local_bh_enable()</code>
<code class="filename">include/linux/interrupt.h</code></a></span></dt><dt><span class="sect1"><a href="ch06s09.html"><code class="function">smp_processor_id</code>()
<code class="filename">include/asm/smp.h</code></a></span></dt><dt><span class="sect1"><a href="ch06s10.html"><span class="type">__init</span>/<span class="type">__exit</span>/<span class="type">__initdata</span>
<code class="filename">include/linux/init.h</code></a></span></dt><dt><span class="sect1"><a href="ch06s11.html"><code class="function">__initcall()</code>/<code class="function">module_init()</code>
<code class="filename">include/linux/init.h</code></a></span></dt><dt><span class="sect1"><a href="ch06s12.html"> <code class="function">module_exit()</code>
<code class="filename">include/linux/init.h</code> </a></span></dt><dt><span class="sect1"><a href="ch06s13.html"> <code class="function">try_module_get()</code>/<code class="function">module_put()</code>
<code class="filename">include/linux/module.h</code></a></span></dt></dl></div><div class="sect1" title="printk() include/linux/kernel.h"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="routines-printk"></a>
<code class="function">printk()</code>
<code class="filename">include/linux/kernel.h</code>
</h2></div></div></div><p>
<code class="function">printk()</code> feeds kernel messages to the
console, dmesg, and the syslog daemon. It is useful for debugging
and reporting errors, and can be used inside interrupt context,
but use with caution: a machine which has its console flooded with
printk messages is unusable. It uses a format string mostly
compatible with ANSI C printf, and C string concatenation to give
it a first "priority" argument:
</p><pre class="programlisting">
printk(KERN_INFO "i = %u\n", i);
</pre><p>
See <code class="filename">include/linux/kernel.h</code>;
for other KERN_ values; these are interpreted by syslog as the
level. Special case: for printing an IP address use
</p><pre class="programlisting">
__be32 ipaddress;
printk(KERN_INFO "my ip: %pI4\n", &ipaddress);
</pre><p>
<code class="function">printk()</code> internally uses a 1K buffer and does
not catch overruns. Make sure that will be enough.
</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
You will know when you are a real kernel hacker
when you start typoing printf as printk in your user programs :)
</p></div><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
Another sidenote: the original Unix Version 6 sources had a
comment on top of its printf function: "Printf should not be
used for chit-chat". You should follow that advice.
</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch05.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch06s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 5. Recipes for Deadlock </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 
<code class="function">copy_[to/from]_user()</code>
/
<code class="function">get_user()</code>
/
<code class="function">put_user()</code>
<code class="filename">include/asm/uaccess.h</code>
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