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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 1. utrace concepts</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="The utrace User Debugging Infrastructure" /><link rel="up" href="index.html" title="The utrace User Debugging Infrastructure" /><link rel="prev" href="index.html" title="The utrace User Debugging Infrastructure" /><link rel="next" href="ch01s02.html" title="Events and Callbacks" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 1. utrace concepts</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="index.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch01s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 1. utrace concepts"><div class="titlepage"><div><div><h2 class="title"><a id="concepts"></a>Chapter 1. utrace concepts</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch01.html#intro">Introduction</a></span></dt><dt><span class="sect1"><a href="ch01s02.html">Events and Callbacks</a></span></dt><dt><span class="sect1"><a href="ch01s03.html">Stopping Safely</a></span></dt><dd><dl><dt><span class="sect2"><a href="ch01s03.html#well-behaved">Writing well-behaved callbacks</a></span></dt><dt><span class="sect2"><a href="ch01s03.html#UTRACE_STOP">Using <code class="constant">UTRACE_STOP</code></a></span></dt></dl></dd><dt><span class="sect1"><a href="ch01s04.html">Tear-down Races</a></span></dt><dd><dl><dt><span class="sect2"><a href="ch01s04.html#SIGKILL">Primacy of <code class="constant">SIGKILL</code></a></span></dt><dt><span class="sect2"><a href="ch01s04.html#reap">Final callbacks</a></span></dt><dt><span class="sect2"><a href="ch01s04.html#refcount">Engine and task pointers</a></span></dt><dt><span class="sect2"><a href="ch01s04.html#reap-after-death">
Serialization of <code class="constant">DEATH</code> and <code class="constant">REAP</code>
</a></span></dt><dt><span class="sect2"><a href="ch01s04.html#interlock">Interlock with final callbacks</a></span></dt><dt><span class="sect2"><a href="ch01s04.html#barrier">Using <code class="function">utrace_barrier</code></a></span></dt></dl></dd></dl></div><div class="sect1" title="Introduction"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="intro"></a>Introduction</h2></div></div></div><p>
<span class="application">utrace</span> is infrastructure code for tracing
and controlling user threads. This is the foundation for writing
tracing engines, which can be loadable kernel modules.
</p><p>
The basic actors in <span class="application">utrace</span> are the thread
and the tracing engine. A tracing engine is some body of code that
calls into the <code class="filename"><linux/utrace.h></code>
interfaces, represented by a <span class="structname">struct
utrace_engine_ops</span>. (Usually it's a kernel module,
though the legacy <code class="function">ptrace</code> support is a tracing
engine that is not in a kernel module.) The interface operates on
individual threads (<span class="structname">struct task_struct</span>).
If an engine wants to treat several threads as a group, that is up
to its higher-level code.
</p><p>
Tracing begins by attaching an engine to a thread, using
<code class="function">utrace_attach_task</code> or
<code class="function">utrace_attach_pid</code>. If successful, it returns a
pointer that is the handle used in all other calls.
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