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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_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="idm139825930516144"></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 the data
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object associated with a specific field from the current journal
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entry. It takes four arguments: the journal context object, a
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string with the field name to request, plus a pair of pointers to
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pointer/size variables where the data object and its size shall be
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stored in. The field name should be an entry field name.
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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>.
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The returned data is in a read-only memory map and is only valid
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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 the read
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pointer is altered. Note that the data returned will be prefixed
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with the field name and '='. Also note that by default data fields
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larger than 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> may be used
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to iterate through all fields of the current entry. On each
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invocation the data for the next field is returned. The order of
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these fields is not defined. The data returned is in the same
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format as with <code class="function">sd_journal_get_data()</code> and also
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follows the same life-time semantics.</p><p><code class="function">sd_journal_restart_data()</code> resets the
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data enumeration index to the beginning of the entry. The next
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invocation of <code class="function">sd_journal_enumerate_data()</code>
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will return the first field of the entry again.</p><p>Note that the <code class="function">SD_JOURNAL_FOREACH_DATA()</code>
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macro 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 once, in order to
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position the read pointer at a valid entry.</p><p><code class="function">sd_journal_set_data_threshold()</code> may be
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used to change the data field size threshold for data returned by
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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 threshold
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is a hint only: it indicates that the client program is interested
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only in the initial parts of the data fields, up to the threshold
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in size -- but the library might still return larger data objects.
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That means applications should not rely exclusively on this
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setting to limit the size of the data fields returned, but need to
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apply a explicit size limit on the returned data as well. This
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threshold defaults to 64K by default. To retrieve the complete
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data fields this threshold should be turned off by setting it to
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0, so that the library always returns the complete data objects.
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It is recommended to set this threshold as low as possible since
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this relieves the library from having to decompress large
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compressed data objects in full.</p><p><code class="function">sd_journal_get_data_threshold()</code> returns
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the currently configured data field size threshold.</p></div><div class="refsect1"><a name="idm139825930490992"></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> returns 0 on
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success or a negative errno-style error code. If the current entry
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does not include the 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 returned.
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<code class="function">sd_journal_enumerate_data()</code> returns a
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positive integer if the next field has been read, 0 when no more
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fields are known, or a negative errno-style error code.
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<code class="function">sd_journal_restart_data()</code> returns nothing.
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<code class="function">sd_journal_set_data_threshold()</code> and
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<code class="function">sd_journal_get_threshold()</code> return 0 on
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success or a negative errno-style error code.</p></div><div class="refsect1"><a name="idm139825930485232"></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> and
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<code class="function">sd_journal_get_data_threshold()</code> interfaces
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are available as a shared library, which can be compiled and
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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="idm139825930478656"></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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const void *data;
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size_t length;
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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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}
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...</pre></div><div class="refsect1"><a name="idm139825925509680"></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>
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