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<body class="manpage">
<div id="header">
<h1>
libtraceevent(3) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>tep_register_print_function,tep_unregister_print_function -
   Registers / Unregisters a helper function.
</p>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="verseblock">
<pre class="content"><strong>#include &lt;event-parse.h&gt;</strong>

enum <strong>tep_func_arg_type</strong> {
        TEP_FUNC_ARG_VOID,
        TEP_FUNC_ARG_INT,
        TEP_FUNC_ARG_LONG,
        TEP_FUNC_ARG_STRING,
        TEP_FUNC_ARG_PTR,
        TEP_FUNC_ARG_MAX_TYPES
};

typedef unsigned long long (<strong>*tep_func_handler</strong>)(struct trace_seq *s, unsigned long long *args);

int <strong>tep_register_print_function</strong>(struct tep_handle *<em>tep</em>, tep_func_handler <em>func</em>, enum tep_func_arg_type <em>ret_type</em>, char *<em>name</em>, <em>&#8230;</em>);
int <strong>tep_unregister_print_function</strong>(struct tep_handle *<em>tep</em>, tep_func_handler <em>func</em>, char *<em>name</em>);</pre>
<div class="attribution">
</div></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>Some events may have helper functions in the print format arguments.
This allows a plugin to dynamically create a way to process one of
these functions.</p></div>
<div class="paragraph"><p>The <strong>tep_register_print_function()</strong> registers such helper function. The <em>tep</em>
argument is the trace event parser context. The <em>func</em> argument  is a pointer
to the helper function. The <em>ret_type</em> argument is  the return type of the
helper function, value from the <em>tep_func_arg_type</em> enum. The <em>name</em> is the name
of the helper function, as seen in the print format arguments. The <em>&#8230;</em> is a
variable list of <em>tep_func_arg_type</em> enums, the <em>func</em> function arguments.
This list must end with <em>TEP_FUNC_ARG_VOID</em>. See <em>EXAMPLE</em> section.</p></div>
<div class="paragraph"><p>The <strong>tep_unregister_print_function()</strong> unregisters a helper function, previously
registered with <strong>tep_register_print_function()</strong>. The <em>tep</em> argument is the
trace event parser context. The <em>func</em> and <em>name</em> arguments are the same, used
when the helper function was registered.</p></div>
<div class="paragraph"><p>The <em>tep_func_handler</em> is the type of the helper function. The <em>s</em> argument is
the trace sequence, it can be used to create a custom string.
The <em>args</em>  is a list of arguments, defined when the helper function was
registered.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_return_value">RETURN VALUE</h2>
<div class="sectionbody">
<div class="paragraph"><p>The <strong>tep_register_print_function()</strong> function returns 0 in case of success.
In case of an error, TEP_ERRNO_&#8230; code is returned.</p></div>
<div class="paragraph"><p>The <strong>tep_unregister_print_function()</strong> returns 0 in case of success, or -1 in
case of an error.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_example">EXAMPLE</h2>
<div class="sectionbody">
<div class="paragraph"><p>Some events have internal functions calls, that appear in the print format
output. For example "tracefs/events/i915/g4x_wm/format" has:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt><span style="color: #008080">print</span> fmt<span style="color: #990000">:</span> <span style="color: #FF0000">"pipe %c, frame=%u, scanline=%u, wm %d/%d/%d, sr %s/%d/%d/%d, hpll %s/%d/%d/%d, fbc %s"</span><span style="color: #990000">,</span>
            <span style="color: #990000">((</span>REC<span style="color: #990000">-&gt;</span>pipe<span style="color: #990000">)</span> <span style="color: #990000">+</span> <span style="color: #FF0000">'A'</span><span style="color: #990000">),</span> REC<span style="color: #990000">-&gt;</span>frame<span style="color: #990000">,</span> REC<span style="color: #990000">-&gt;</span>scanline<span style="color: #990000">,</span> REC<span style="color: #990000">-&gt;</span>primary<span style="color: #990000">,</span>
            REC<span style="color: #990000">-&gt;</span>sprite<span style="color: #990000">,</span> REC<span style="color: #990000">-&gt;</span>cursor<span style="color: #990000">,</span> <span style="font-weight: bold"><span style="color: #000000">yesno</span></span><span style="color: #990000">(</span>REC<span style="color: #990000">-&gt;</span>cxsr<span style="color: #990000">),</span> REC<span style="color: #990000">-&gt;</span>sr_plane<span style="color: #990000">,</span>
            REC<span style="color: #990000">-&gt;</span>sr_cursor<span style="color: #990000">,</span> REC<span style="color: #990000">-&gt;</span>sr_fbc<span style="color: #990000">,</span> <span style="font-weight: bold"><span style="color: #000000">yesno</span></span><span style="color: #990000">(</span>REC<span style="color: #990000">-&gt;</span>hpll<span style="color: #990000">),</span> REC<span style="color: #990000">-&gt;</span>hpll_plane<span style="color: #990000">,</span>
            REC<span style="color: #990000">-&gt;</span>hpll_cursor<span style="color: #990000">,</span> REC<span style="color: #990000">-&gt;</span>hpll_fbc<span style="color: #990000">,</span> <span style="font-weight: bold"><span style="color: #000000">yesno</span></span><span style="color: #990000">(</span>REC<span style="color: #990000">-&gt;</span>fbc<span style="color: #990000">)</span></tt></pre></div></div>
<div class="paragraph"><p>Notice the call to function <strong>yesno()</strong> in the print arguments. In the kernel
context, this function has the following implementation:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt><span style="font-weight: bold"><span style="color: #0000FF">static</span></span> <span style="font-weight: bold"><span style="color: #0000FF">const</span></span> <span style="color: #009900">char</span> <span style="color: #990000">*</span><span style="font-weight: bold"><span style="color: #000000">yesno</span></span><span style="color: #990000">(</span><span style="color: #009900">int</span> x<span style="color: #990000">)</span>
<span style="color: #FF0000">{</span>
        <span style="font-weight: bold"><span style="color: #0000FF">static</span></span> <span style="font-weight: bold"><span style="color: #0000FF">const</span></span> <span style="color: #009900">char</span> <span style="color: #990000">*</span>yes <span style="color: #990000">=</span> <span style="color: #FF0000">"yes"</span><span style="color: #990000">;</span>
        <span style="font-weight: bold"><span style="color: #0000FF">static</span></span> <span style="font-weight: bold"><span style="color: #0000FF">const</span></span> <span style="color: #009900">char</span> <span style="color: #990000">*</span>no <span style="color: #990000">=</span> <span style="color: #FF0000">"no"</span><span style="color: #990000">;</span>

<span style="font-weight: bold"><span style="color: #0000FF">return</span></span> x <span style="color: #990000">?</span> yes <span style="color: #990000">:</span> no<span style="color: #990000">;</span>
<span style="color: #FF0000">}</span></tt></pre></div></div>
<div class="paragraph"><p>The user space event parser has no idea how to handle this <strong>yesno()</strong> function.
The <strong>tep_register_print_function()</strong> API can be used to register a user space
helper function, mapped to the kernel&#8217;s <strong>yesno()</strong>:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt><span style="font-weight: bold"><span style="color: #000080">#include</span></span> <span style="color: #FF0000">&lt;event-parse.h&gt;</span>
<span style="font-weight: bold"><span style="color: #000080">#include</span></span> <span style="color: #FF0000">&lt;trace-seq.h&gt;</span>
<span style="color: #990000">...</span>
<span style="font-weight: bold"><span style="color: #0000FF">struct</span></span> <span style="color: #008080">tep_handle</span> <span style="color: #990000">*</span>tep <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">tep_alloc</span></span><span style="color: #990000">();</span>
<span style="color: #990000">...</span>
<span style="font-weight: bold"><span style="color: #0000FF">static</span></span> <span style="font-weight: bold"><span style="color: #0000FF">const</span></span> <span style="color: #009900">char</span> <span style="color: #990000">*</span><span style="font-weight: bold"><span style="color: #000000">yes_no_helper</span></span><span style="color: #990000">(</span><span style="color: #009900">int</span> x<span style="color: #990000">)</span>
<span style="color: #FF0000">{</span>
        <span style="font-weight: bold"><span style="color: #0000FF">return</span></span> x <span style="color: #990000">?</span> <span style="color: #FF0000">"yes"</span> <span style="color: #990000">:</span> <span style="color: #FF0000">"no"</span><span style="color: #990000">;</span>
<span style="color: #FF0000">}</span>
<span style="color: #990000">...</span>
        <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #990000">(</span> <span style="font-weight: bold"><span style="color: #000000">tep_register_print_function</span></span><span style="color: #990000">(</span>tep<span style="color: #990000">,</span>
                                    yes_no_helper<span style="color: #990000">,</span>
                                    TEP_FUNC_ARG_STRING<span style="color: #990000">,</span>
                                    <span style="color: #FF0000">"yesno"</span><span style="color: #990000">,</span>
                                    TEP_FUNC_ARG_INT<span style="color: #990000">,</span>
                                    TEP_FUNC_ARG_VOID<span style="color: #990000">)</span> <span style="color: #990000">!=</span> <span style="color: #993399">0</span><span style="color: #990000">)</span> <span style="color: #FF0000">{</span>
                <span style="font-style: italic"><span style="color: #9A1900">/* Failed to register yes_no_helper function */</span></span>
        <span style="color: #FF0000">}</span>

<span style="font-style: italic"><span style="color: #9A1900">/*</span></span>
<span style="font-style: italic"><span style="color: #9A1900">   Now, when the event parser encounters this yesno() function, it will know</span></span>
<span style="font-style: italic"><span style="color: #9A1900">   how to handle it.</span></span>
<span style="font-style: italic"><span style="color: #9A1900">*/</span></span>
<span style="color: #990000">...</span>
        <span style="font-weight: bold"><span style="color: #0000FF">if</span></span> <span style="color: #990000">(</span><span style="font-weight: bold"><span style="color: #000000">tep_unregister_print_function</span></span><span style="color: #990000">(</span>tep<span style="color: #990000">,</span> yes_no_helper<span style="color: #990000">,</span> <span style="color: #FF0000">"yesno"</span><span style="color: #990000">)</span> <span style="color: #990000">!=</span> <span style="color: #993399">0</span><span style="color: #990000">)</span> <span style="color: #FF0000">{</span>
                <span style="font-style: italic"><span style="color: #9A1900">/* Failed to unregister yes_no_helper function */</span></span>
        <span style="color: #FF0000">}</span></tt></pre></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_files">FILES</h2>
<div class="sectionbody">
<div class="verseblock">
<pre class="content"><strong>event-parse.h</strong>
        Header file to include in order to have access to the library APIs.
<strong>trace-seq.h</strong>
        Header file to include in order to have access to trace sequences
        related APIs. Trace sequences are used to allow a function to call
        several other functions to create a string of data to use.
<strong>-ltraceevent</strong>
        Linker switch to add when building a program that uses the library.</pre>
<div class="attribution">
</div></div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph"><p><strong>libtraceevent</strong>(3), <strong>trace-cmd</strong>(1)</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_author">AUTHOR</h2>
<div class="sectionbody">
<div class="verseblock">
<pre class="content"><strong>Steven Rostedt</strong> &lt;<a href="mailto:rostedt@goodmis.org">rostedt@goodmis.org</a>&gt;, author of <strong>libtraceevent</strong>.
<strong>Tzvetomir Stoyanov</strong> &lt;<a href="mailto:tz.stoyanov@gmail.com">tz.stoyanov@gmail.com</a>&gt;, author of this man page.</pre>
<div class="attribution">
</div></div>
</div>
</div>
<div class="sect1">
<h2 id="_reporting_bugs">REPORTING BUGS</h2>
<div class="sectionbody">
<div class="paragraph"><p>Report bugs to  &lt;<a href="mailto:linux-trace-devel@vger.kernel.org">linux-trace-devel@vger.kernel.org</a>&gt;</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_license">LICENSE</h2>
<div class="sectionbody">
<div class="paragraph"><p>libtraceevent is Free Software licensed under the GNU LGPL 2.1</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_resources">RESOURCES</h2>
<div class="sectionbody">
<div class="paragraph"><p><a href="https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/">https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/</a></p></div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Last updated
 2022-03-24 23:40:51 UTC
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