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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 12. Kernel Cantrips</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="ch11.html" title="Chapter 11. Putting Your Stuff in the Kernel" /><link rel="next" href="ch13.html" title="Chapter 13. Thanks" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 12. Kernel Cantrips</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch11.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch13.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 12. Kernel Cantrips"><div class="titlepage"><div><div><h2 class="title"><a id="cantrips"></a>Chapter 12. Kernel Cantrips</h2></div></div></div><p>
Some favorites from browsing the source. Feel free to add to this
list.
</p><p>
<code class="filename">arch/x86/include/asm/delay.h:</code>
</p><pre class="programlisting">
#define ndelay(n) (__builtin_constant_p(n) ? \
((n) > 20000 ? __bad_ndelay() : __const_udelay((n) * 5ul)) : \
__ndelay(n))
</pre><p>
<code class="filename">include/linux/fs.h</code>:
</p><pre class="programlisting">
/*
* Kernel pointers have redundant information, so we can use a
* scheme where we can return either an error code or a dentry
* pointer with the same return value.
*
* This should be a per-architecture thing, to allow different
* error and pointer decisions.
*/
#define ERR_PTR(err) ((void *)((long)(err)))
#define PTR_ERR(ptr) ((long)(ptr))
#define IS_ERR(ptr) ((unsigned long)(ptr) > (unsigned long)(-1000))
</pre><p>
<code class="filename">arch/x86/include/asm/uaccess_32.h:</code>
</p><pre class="programlisting">
#define copy_to_user(to,from,n) \
(__builtin_constant_p(n) ? \
__constant_copy_to_user((to),(from),(n)) : \
__generic_copy_to_user((to),(from),(n)))
</pre><p>
<code class="filename">arch/sparc/kernel/head.S:</code>
</p><pre class="programlisting">
/*
* Sun people can't spell worth damn. "compatability" indeed.
* At least we *know* we can't spell, and use a spell-checker.
*/
/* Uh, actually Linus it is I who cannot spell. Too much murky
* Sparc assembly will do this to ya.
*/
C_LABEL(cputypvar):
.asciz "compatability"
/* Tested on SS-5, SS-10. Probably someone at Sun applied a spell-checker. */
.align 4
C_LABEL(cputypvar_sun4m):
.asciz "compatible"
</pre><p>
<code class="filename">arch/sparc/lib/checksum.S:</code>
</p><pre class="programlisting">
/* Sun, you just can't beat me, you just can't. Stop trying,
* give up. I'm serious, I am going to kick the living shit
* out of you, game over, lights out.
*/
</pre></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch11.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch13.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 11. Putting Your Stuff in the Kernel </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 13. Thanks</td></tr></table></div></body></html>
