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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_signal"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_event_add_signal, sd_event_source_get_signal — Add a signal 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_signal</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>int <var class="pdparam">signal</var>, </td></tr><tr><td> </td><td>sd_event_signal_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_signal_handler_t</b>)(</code></td><td>sd_event_source *<var class="pdparam">s</var>, </td></tr><tr><td> </td><td>const struct signalfd_siginfo *<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_signal</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm139637450605920"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_event_add_signal()</code> adds a new signal
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event source to an event loop object. The event loop is specified
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in <em class="parameter"><code>event</code></em>, the event source is returned in
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the <em class="parameter"><code>source</code></em> parameter. The
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<em class="parameter"><code>signal</code></em> parameter specifies the signal to be handled
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(see
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<a href="signal.html"><span class="citerefentry"><span class="refentrytitle">signal</span>(7)</span></a>).
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The <em class="parameter"><code>handler</code></em> must reference a function to
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call when the signal is delivered or be <code class="constant">NULL</code>.
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The handler function will be passed the
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<em class="parameter"><code>userdata</code></em> pointer, which may be chosen
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freely by the caller. The handler also receives a pointer to a
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<span class="structname">const struct signalfd_siginfo</span> containing
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the information about the received signal. See
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<a href="http://man7.org/linux/man-pages/man2/signalfd.2.html"><span class="citerefentry"><span class="refentrytitle">signalfd</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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signal. The signal will be unblocked, and must be
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blocked when the function is called. If the handler is not
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specified (<em class="parameter"><code>handler</code></em> is
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<code class="constant">NULL</code>), a default handler which causes the
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program to exit will be used. By default, the handler is enabled
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permanently (<code class="constant">SD_EVENT_ON</code>), 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_signal()</code> retrieves
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the configured signal number of a signal event source created
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previously with <code class="function">sd_event_add_signal()</code>. It
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takes the event source object as the <em class="parameter"><code>source</code></em>
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parameter.</p></div><div class="refsect1"><a name="idm139637454494336"></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="idm139637454493008"></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.</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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signal or the signal was not blocked previously.</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="idm139637454484032"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p><code class="function">sd_event_add_signal()</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="idm139637454473296"></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_child.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_child</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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