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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_journal_get_data" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_journal_get_data</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_journal_get_data</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_journal_get_data</refname>
+ <refname>sd_journal_enumerate_data</refname>
+ <refname>sd_journal_enumerate_available_data</refname>
+ <refname>sd_journal_restart_data</refname>
+ <refname>SD_JOURNAL_FOREACH_DATA</refname>
+ <refname>sd_journal_set_data_threshold</refname>
+ <refname>sd_journal_get_data_threshold</refname>
+ <refpurpose>Read data fields from the current journal entry</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_get_data</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const char *<parameter>field</parameter></paramdef>
+ <paramdef>const void **<parameter>data</parameter></paramdef>
+ <paramdef>size_t *<parameter>length</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_enumerate_data</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const void **<parameter>data</parameter></paramdef>
+ <paramdef>size_t *<parameter>length</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_enumerate_available_data</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const void **<parameter>data</parameter></paramdef>
+ <paramdef>size_t *<parameter>length</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>void <function>sd_journal_restart_data</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const void *<parameter>data</parameter></paramdef>
+ <paramdef>size_t <parameter>length</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_set_data_threshold</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>size_t <parameter>sz</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_get_data_threshold</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>size_t *<parameter>sz</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_journal_get_data()</function> 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
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ but any field can be specified. The returned data is in a read-only memory map and is only valid until
+ the next invocation of <function>sd_journal_get_data()</function>,
+ <function>sd_journal_enumerate_data()</function>,
+ <function>sd_journal_enumerate_available_data()</function>, or when the read pointer is altered. Note
+ that the data returned will be prefixed with the field name and <literal>=</literal>. Also note that, by
+ default, data fields larger than 64K might get truncated to 64K. This threshold may be changed and turned
+ off with <function>sd_journal_set_data_threshold()</function> (see below).</para>
+
+ <para><function>sd_journal_enumerate_data()</function> 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 <function>sd_journal_get_data()</function> and also
+ follows the same life-time semantics.</para>
+
+ <para><function>sd_journal_enumerate_available_data()</function> is similar to
+ <function>sd_journal_enumerate_data()</function>, but silently skips any fields which may be valid, but
+ are too large or not supported by current implementation.</para>
+
+ <para><function>sd_journal_restart_data()</function> resets the
+ data enumeration index to the beginning of the entry. The next
+ invocation of <function>sd_journal_enumerate_data()</function>
+ will return the first field of the entry again.</para>
+
+ <para>Note that the <function>SD_JOURNAL_FOREACH_DATA()</function> macro may be used as a handy wrapper
+ around <function>sd_journal_restart_data()</function> and
+ <function>sd_journal_enumerate_available_data()</function>.</para>
+
+ <para>Note that these functions will not work before
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ (or related call) has been called at least once, in order to
+ position the read pointer at a valid entry.</para>
+
+ <para><function>sd_journal_set_data_threshold()</function> may be
+ used to change the data field size threshold for data returned by
+ <function>sd_journal_get_data()</function>,
+ <function>sd_journal_enumerate_data()</function> and
+ <function>sd_journal_enumerate_unique()</function>. 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 an 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.</para>
+
+ <para><function>sd_journal_get_data_threshold()</function> returns
+ the currently configured data field size threshold.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para><function>sd_journal_get_data()</function> returns 0 on success or a negative errno-style error
+ code. <function>sd_journal_enumerate_data()</function> and
+ <function>sd_journal_enumerate_available_data()</function> return a positive integer if the next field
+ has been read, 0 when no more fields remain, or a negative errno-style error code.
+ <function>sd_journal_restart_data()</function> doesn't return anything.
+ <function>sd_journal_set_data_threshold()</function> and <function>sd_journal_get_threshold()</function>
+ return 0 on success or a negative errno-style error code.</para>
+
+ <refsect2>
+ <title>Errors</title>
+
+ <para>Returned errors may indicate the following problems:</para>
+
+ <variablelist>
+ <varlistentry id='EINVAL'>
+ <term><constant>-EINVAL</constant></term>
+
+ <listitem><para>One of the required parameters is <constant>NULL</constant> or invalid.
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry id='ECHILD'>
+ <term><constant>-ECHILD</constant></term>
+
+ <listitem><para>The journal object was created in a different process.</para></listitem>
+ </varlistentry>
+
+ <varlistentry id='EADDRNOTAVAIL'>
+ <term><constant>-EADDRNOTAVAIL</constant></term>
+
+ <listitem><para>The read pointer is not positioned at a valid entry;
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ or a related call has not been called at least once.</para></listitem>
+ </varlistentry>
+
+ <varlistentry id='ENOENT'>
+ <term><constant>-ENOENT</constant></term>
+
+ <listitem><para>The current entry does not include the specified field.</para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id='ENOMEM'>
+ <term><constant>-ENOMEM</constant></term>
+
+ <listitem><para>Memory allocation failed.</para></listitem>
+ </varlistentry>
+
+ <varlistentry id='ENOBUFS'>
+ <term><constant>-ENOBUFS</constant></term>
+
+ <listitem><para>A compressed entry is too large.</para></listitem>
+ </varlistentry>
+
+ <varlistentry id='E2BIG'>
+ <term><constant>-E2BIG</constant></term>
+
+ <listitem><para>The data field is too large for this computer architecture (e.g. above 4 GB on a
+ 32-bit architecture).</para></listitem>
+ </varlistentry>
+
+ <varlistentry id='EPROTONOSUPPORT'>
+ <term><constant>-EPROTONOSUPPORT</constant></term>
+
+ <listitem><para>The journal is compressed with an unsupported method or the journal uses an
+ unsupported feature.</para></listitem>
+ </varlistentry>
+
+ <varlistentry id='EBADMSG'>
+ <term><constant>-EBADMSG</constant></term>
+
+ <listitem><para>The journal is corrupted (possibly just the entry being iterated over).
+ </para></listitem>
+ </varlistentry>
+
+ <varlistentry id='EIO'>
+ <term><constant>-EIO</constant></term>
+
+ <listitem><para>An I/O error was reported by the kernel.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect2>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <xi:include href="threads-aware.xml" xpointer="strict"/>
+
+ <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+
+ <para>See
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ for a complete example how to use
+ <function>sd_journal_get_data()</function>.</para>
+
+ <para>Use the
+ <function>SD_JOURNAL_FOREACH_DATA()</function> macro to
+ iterate through all fields of the current journal
+ entry:</para>
+
+ <programlisting>…
+int print_fields(sd_journal *j) {
+ const void *data;
+ size_t length;
+ SD_JOURNAL_FOREACH_DATA(j, data, length)
+ printf("%.*s\n", (int) length, data);
+}
+…</programlisting>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>