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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 204</span><hr><div class="refentry"><a name="sd_journal_get_data"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_journal_get_data, sd_journal_enumerate_data, sd_journal_restart_data, SD_JOURNAL_FOREACH_DATA, sd_journal_set_data_threshold, sd_journal_get_data_threshold — Read data fields from the current journal entry</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-journal.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_journal_get_data</b>(</code></td><td>sd_journal* <var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const char* <var class="pdparam">field</var>, </td></tr><tr><td> </td><td>const void** <var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t* <var class="pdparam">length</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_journal_enumerate_data</b>(</code></td><td>sd_journal* <var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void** <var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t* <var class="pdparam">length</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">void <b class="fsfunc">sd_journal_restart_data</b>(</code></td><td>sd_journal* <var class="pdparam">j</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"><b class="fsfunc">SD_JOURNAL_FOREACH_DATA</b>(</code></td><td>sd_journal* <var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void* <var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">length</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_journal_set_data_threshold</b>(</code></td><td>sd_journal* <var class="pdparam">j</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">sz</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_journal_get_data_threshold</b>(</code></td><td>sd_journal* <var class="pdparam">j</var>, </td></tr><tr><td> </td><td>size_t* <var class="pdparam">sz</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm259782712960"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_journal_get_data()</code> gets
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the data object associated with a specific field from
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the current journal entry. It takes four arguments:
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the journal context object, a string with the field
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name to request, plus a pair of pointers to
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pointer/size variables where the data object and its
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size shall be stored in. The field name should be an
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entry field name. Well-known field names are listed in
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<a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>. The
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returned data is in a read-only memory map and is only
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valid until the next invocation of
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<code class="function">sd_journal_get_data()</code> or
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<code class="function">sd_journal_enumerate_data()</code>, or
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the read pointer is altered. Note that the data
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returned will be prefixed with the field name and
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'='. Also note that by default data fields larger than
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64K might get truncated to 64K. This threshold may be
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changed and turned off with
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<code class="function">sd_journal_set_data_threshold()</code> (see
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below).</p><p><code class="function">sd_journal_enumerate_data()</code>
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may be used to iterate through all fields of the
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current entry. On each invocation the data for the
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next field is returned. The order of these fields is
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not defined. The data returned is in the same format
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as with <code class="function">sd_journal_get_data()</code> and
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also follows the same life-time semantics.</p><p><code class="function">sd_journal_restart_data()</code>
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resets the data enumeration index to the beginning of
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the entry. The next invocation of
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<code class="function">sd_journal_enumerate_data()</code> will return the first
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field of the entry again.</p><p>Note that the
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<code class="function">SD_JOURNAL_FOREACH_DATA()</code> macro
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may be used as a handy wrapper around
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<code class="function">sd_journal_restart_data()</code> and
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<code class="function">sd_journal_enumerate_data()</code>.</p><p>Note that these functions will not work before
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<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
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(or related call) has been called at least
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once, in order to position the read pointer at a valid entry.</p><p><code class="function">sd_journal_set_data_threshold()</code>
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may be used to change the data field size threshold
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<code class="function">sd_journal_get_data()</code>,
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<code class="function">sd_journal_enumerate_data()</code> and
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<code class="function">sd_journal_enumerate_unique()</code>. This
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threshold is a hint only: it indicates that the client
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program is interested only in the initial parts of the
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data fields, up to the threshold in size -- but the
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library might still return larger data objects. That
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means applications should not rely exclusively on this
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setting to limit the size of the data fields returned,
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but need to apply a explicit size limit on the
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returned data as well. This threshold defaults to 64K
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by default. To retrieve the complete data fields this
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threshold should be turned off by setting it to 0, so
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that the library always returns the complete data
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objects. It is recommended to set this threshold as
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low as possible since this relieves the library from
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having to decompress large compressed data objects in
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full.</p><p><code class="function">sd_journal_get_data_threshold()</code>
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returns the currently configured data field size
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threshold.</p></div><div class="refsect1"><a name="idm259782687296"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p><code class="function">sd_journal_get_data()</code>
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returns 0 on success or a negative errno-style error
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code. If the current entry does not include the
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specified field -ENOENT is returned. If
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<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
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has not been called at least once -EADDRNOTAVAIL is
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returned. <code class="function">sd_journal_enumerate_data()</code>
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returns a positive integer if the next field has been
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read, 0 when no more fields are known, or a negative
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code. <code class="function">sd_journal_restart_data()</code>
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nothing. <code class="function">sd_journal_set_data_threshold()</code>
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and <code class="function">sd_journal_get_threshold()</code>
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return 0 on success or a negative errno-style error
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code.</p></div><div class="refsect1"><a name="idm259782681248"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p>The <code class="function">sd_journal_get_data()</code>,
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<code class="function">sd_journal_enumerate_data()</code>,
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<code class="function">sd_journal_restart_data()</code>,
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<code class="function">sd_journal_set_data_threshold()</code>
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<code class="function">sd_journal_get_data_threshold()</code>
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interfaces are available as shared library, which can
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be compiled and linked to with the
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<code class="literal">libsystemd-journal</code>
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<a href="pkg-config.html"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
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file.</p></div><div class="refsect1"><a name="idm259777759888"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>See
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<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
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for a complete example how to use
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<code class="function">sd_journal_get_data()</code>.</p><p>Use the
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<code class="function">SD_JOURNAL_FOREACH_DATA</code> macro to
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iterate through all fields of the current journal
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entry:</p><pre class="programlisting">...
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int print_fields(sd_journal *j) {
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SD_JOURNAL_FOREACH_DATA(j, data, length)
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printf("%.*s\n", (int) length, data);
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...</pre></div><div class="refsect1"><a name="idm259777755392"></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="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>,
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<a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>,
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<a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>,
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<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>,
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<a href="sd_journal_get_realtime_usec.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_realtime_usec</span>(3)</span></a>,
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<a href="sd_journal_query_unique.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_query_unique</span>(3)</span></a>
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</p></div></div></body></html>