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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 219</span><hr><div class="refentry"><a name="sd_event_add_child"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_event_add_child, sd_event_source_get_child_pid — Add a child state change event source to an event loop</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-bus.h></pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_add_child</b>(</code></td><td>sd_event *<var class="pdparam">event</var>, </td></tr><tr><td> </td><td>sd_event_source **<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>pid_t <var class="pdparam">pid</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">options</var>, </td></tr><tr><td> </td><td>sd_event_child_handler_t <var class="pdparam">handler</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">userdata</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef int (*<b class="fsfunc">sd_event_child_handler_t</b>)(</code></td><td>sd_event_source *<var class="pdparam">s</var>, </td></tr><tr><td> </td><td>const siginfo_t *<var class="pdparam">si</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">userdata</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_source_get_child_pid</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>pid_t *<var class="pdparam">pid</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm140121348202000"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_event_add_child()</code> adds a new child
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state change event source to an event loop object. The event loop
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is specified in <em class="parameter"><code>event</code></em>, the event source is
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returned in the <em class="parameter"><code>source</code></em> parameter. The
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<em class="parameter"><code>pid</code></em> parameter specifies the process to
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watch. The <em class="parameter"><code>handler</code></em> must reference a
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function to call when the process changes state. The handler
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function will be passed the <em class="parameter"><code>userdata</code></em>
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pointer, which may be chosen freely by the caller. The handler
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also receives a pointer to a <span class="structname">const
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siginfo_t</span> structure containing the information about
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the event. The <em class="parameter"><code>options</code></em> parameter determines
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which state changes will be watched for. It must contain an OR-ed
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mask of <code class="constant">WEXITED</code> (watch for the child
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terminating), <code class="constant">WSTOPPED</code> (watch for the child
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being stopped by a signal), and <code class="constant">WCONTINUED</code>
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(watch for the child being resumed by a signal). See
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<a href="http://man7.org/linux/man-pages/man2/waitid.2.html"><span class="citerefentry"><span class="refentrytitle">waitid</span>(2)</span></a>
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for further information.</p><p>Only a single handler may be installed for a specific
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child. The handler is enabled
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for a single event (<code class="constant">SD_EVENT_ONESHOT</code>),
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but this may be
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changed with
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<a href="sd_event_source_set_enabled.html"><span class="citerefentry"><span class="refentrytitle">sd_event_source_set_enabled</span>(3)</span></a>.
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If the handler function returns a negative error code, it will be
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disabled after the invocation, even if
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<code class="constant">SD_EVENT_ON</code> mode is set.
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</p><p><code class="function">sd_event_source_get_child_pid()</code>
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retrieves the configured <em class="parameter"><code>pid</code></em> of a child
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state change event source created previously with
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<code class="function">sd_event_add_child()</code>. It takes the event
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source object as the <em class="parameter"><code>source</code></em> parameter and a
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pointer to <span class="type">pid_t</span> to return the result in.
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</p></div><div class="refsect1"><a name="idm140121352089856"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p>On success, these functions return 0 or a positive
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integer. On failure, they return a negative errno-style error
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code.</p></div><div class="refsect1"><a name="idm140121352088528"></a><h2 id="Errors">Errors<a class="headerlink" title="Permalink to this headline" href="#Errors">¶</a></h2><p>Returned errors may indicate the following problems:</p><div class="variablelist"><dl class="variablelist"><dt id="-ENOMEM"><span class="term"><code class="constant">-ENOMEM</code></span><a class="headerlink" title="Permalink to this term" href="#-ENOMEM">¶</a></dt><dd><p>Not enough memory to allocate an object.</p></dd><dt id="-EINVAL"><span class="term"><code class="constant">-EINVAL</code></span><a class="headerlink" title="Permalink to this term" href="#-EINVAL">¶</a></dt><dd><p>An invalid argument has been passed. This includes
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specifying an empty mask in <em class="parameter"><code>options</code></em> or a mask
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which contains values different than a combination of
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<code class="constant">WEXITED</code>, <code class="constant">WSTOPPED</code>, and
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<code class="constant">WCONTINUED</code>.
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</p></dd><dt id="-EBUSY"><span class="term"><code class="constant">-EBUSY</code></span><a class="headerlink" title="Permalink to this term" href="#-EBUSY">¶</a></dt><dd><p>An handler is already installed for this
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child.</p></dd><dt id="-ESTALE"><span class="term"><code class="constant">-ESTALE</code></span><a class="headerlink" title="Permalink to this term" href="#-ESTALE">¶</a></dt><dd><p>The event loop is already terminated.</p></dd><dt id="-ECHILD"><span class="term"><code class="constant">-ECHILD</code></span><a class="headerlink" title="Permalink to this term" href="#-ECHILD">¶</a></dt><dd><p>The event loop has been created in a different process.</p></dd></dl></div></div><div class="refsect1"><a name="idm140121352070400"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p><code class="function">sd_event_add_child()</code> and the other functions
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described here are available as a shared library, which can be
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compiled and linked to with the
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<code class="constant">libsystemd</code> <a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
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file.</p></div><div class="refsect1"><a name="idm140121352066864"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
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<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
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<a href="sd-event.html"><span class="citerefentry"><span class="refentrytitle">sd-event</span>(3)</span></a>,
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<a href="sd_event_new.html"><span class="citerefentry"><span class="refentrytitle">sd_event_new</span>(3)</span></a>,
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<a href="sd_event_add_time.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_time</span>(3)</span></a>,
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<a href="sd_event_add_signal.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_signal</span>(3)</span></a>,
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<a href="sd_event_add_defer.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_defer</span>(3)</span></a>,
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<a href="sd_event_source_set_enabled.html"><span class="citerefentry"><span class="refentrytitle">sd_event_source_set_enabled</span>(3)</span></a>
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</p></div></div></body></html>
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