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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2012 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_journal_get_data">
+
+ <refentryinfo>
+ <title>sd_journal_get_data</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Lennart</firstname>
+ <surname>Poettering</surname>
+ <email>lennart@poettering.net</email>
+ </author>
+ </authorgroup>
+ </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_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>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>.
+ 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> or
+ <function>sd_journal_enumerate_data()</function>, 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
+ <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_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_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 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.</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. If the current entry
+ does not include the specified field, -ENOENT is returned. If
+ <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ has not been called at least once, -EADDRNOTAVAIL is returned.
+ <function>sd_journal_enumerate_data()</function> 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.
+ <function>sd_journal_restart_data()</function> returns nothing.
+ <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>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>The <function>sd_journal_get_data()</function>,
+ <function>sd_journal_enumerate_data()</function>,
+ <function>sd_journal_restart_data()</function>,
+ <function>sd_journal_set_data_threshold()</function> and
+ <function>sd_journal_get_data_threshold()</function> interfaces
+ are available as a shared library, which can be compiled and
+ linked to with the
+ <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ file.</para>
+ </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>