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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>sd_journal_get_data</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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</style><a href="index.html">Index </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 208</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="idm274684373776"></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 object associated with a specific field from
the current journal entry. It takes four arguments:
the journal context object, a string with the field
name to request, plus a pair of pointers to
pointer/size variables where the data object and its
size shall be stored in. The field name should be an
entry field name. Well-known field names are listed in
<a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>. The
returned data is in a read-only memory map and is only
valid until the next invocation of
<code class="function">sd_journal_get_data()</code> or
<code class="function">sd_journal_enumerate_data()</code>, or
the read pointer is altered. Note that the data
returned will be prefixed with the field name and
'='. Also note that by default data fields larger than
64K might get truncated to 64K. This threshold may be
changed and turned off with
<code class="function">sd_journal_set_data_threshold()</code> (see
below).</p><p><code class="function">sd_journal_enumerate_data()</code>
may be used to iterate through all fields of the
current entry. On each invocation the data for the
next field is returned. The order of these fields is
not defined. The data returned is in the same format
as with <code class="function">sd_journal_get_data()</code> and
also follows the same life-time semantics.</p><p><code class="function">sd_journal_restart_data()</code>
resets the data enumeration index to the beginning of
the entry. The next invocation of
<code class="function">sd_journal_enumerate_data()</code> will return the first
field of the entry again.</p><p>Note that the
<code class="function">SD_JOURNAL_FOREACH_DATA()</code> macro
may be used as a handy wrapper around
<code class="function">sd_journal_restart_data()</code> and
<code class="function">sd_journal_enumerate_data()</code>.</p><p>Note that these functions will not work before
<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
(or related call) has been called at least
once, in order to position the read pointer at a valid entry.</p><p><code class="function">sd_journal_set_data_threshold()</code>
may be used to change the data field size threshold
for data returned by
<code class="function">sd_journal_get_data()</code>,
<code class="function">sd_journal_enumerate_data()</code> and
<code class="function">sd_journal_enumerate_unique()</code>. This
threshold is a hint only: it indicates that the client
program is interested only in the initial parts of the
data fields, up to the threshold in size -- but the
library might still return larger data objects. That
means applications should not rely exclusively on this
setting to limit the size of the data fields returned,
but need to apply a explicit size limit on the
returned data as well. This threshold defaults to 64K
by default. To retrieve the complete data fields this
threshold should be turned off by setting it to 0, so
that the library always returns the complete data
objects. It is recommended to set this threshold as
low as possible since this relieves the library from
having to decompress large compressed data objects in
full.</p><p><code class="function">sd_journal_get_data_threshold()</code>
returns the currently configured data field size
threshold.</p></div><div class="refsect1"><a name="idm274684347840"></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 success or a negative errno-style error
code. If the current entry does not include the
specified field, -ENOENT is returned. If
<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
has not been called at least once, -EADDRNOTAVAIL is
returned. <code class="function">sd_journal_enumerate_data()</code>
returns a positive integer if the next field has been
read, 0 when no more fields are known, or a negative
errno-style error
code. <code class="function">sd_journal_restart_data()</code>
returns
nothing. <code class="function">sd_journal_set_data_threshold()</code>
and <code class="function">sd_journal_get_threshold()</code>
return 0 on success or a negative errno-style error
code.</p></div><div class="refsect1"><a name="idm274684341792"></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>,
<code class="function">sd_journal_enumerate_data()</code>,
<code class="function">sd_journal_restart_data()</code>,
<code class="function">sd_journal_set_data_threshold()</code>
and
<code class="function">sd_journal_get_data_threshold()</code>
interfaces are available as shared library, which can
be compiled and linked to with the
<code class="constant">libsystemd-journal</code> <a href="pkg-config.html"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
file.</p></div><div class="refsect1"><a name="idm274679375856"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>See
<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>
for a complete example how to use
<code class="function">sd_journal_get_data()</code>.</p><p>Use the
<code class="function">SD_JOURNAL_FOREACH_DATA</code> macro to
iterate through all fields of the current journal
entry:</p><pre class="programlisting">...
int print_fields(sd_journal *j) {
const void *data;
size_t l;
SD_JOURNAL_FOREACH_DATA(j, data, length)
printf("%.*s\n", (int) length, data);
}
...</pre></div><div class="refsect1"><a name="idm274679371360"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
<a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>,
<a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>,
<a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>,
<a href="sd_journal_next.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_next</span>(3)</span></a>,
<a href="sd_journal_get_realtime_usec.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_realtime_usec</span>(3)</span></a>,
<a href="sd_journal_query_unique.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_query_unique</span>(3)</span></a>
</p></div></div></body></html>
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