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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_query_unique">
+
+ <refentryinfo>
+ <title>sd_journal_query_unique</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_query_unique</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_journal_query_unique</refname>
+ <refname>sd_journal_enumerate_unique</refname>
+ <refname>sd_journal_restart_unique</refname>
+ <refname>SD_JOURNAL_FOREACH_UNIQUE</refname>
+ <refpurpose>Read unique data fields from the journal</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_query_unique</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const char *<parameter>field</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_journal_enumerate_unique</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_unique</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef>
+ <paramdef>sd_journal *<parameter>j</parameter></paramdef>
+ <paramdef>const void *<parameter>data</parameter></paramdef>
+ <paramdef>size_t <parameter>length</parameter></paramdef>
+ </funcprototype>
+
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para><function>sd_journal_query_unique()</function> queries the
+ journal for all unique values the specified field can take. It
+ takes two arguments: the journal to query and the field name to
+ look for. Well-known field names are listed on
+ <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+ Field names must be specified without a trailing '='. After this
+ function has been executed successfully the field values may be
+ queried using <function>sd_journal_enumerate_unique()</function>.
+ Invoking this call a second time will change the field name being
+ queried and reset the enumeration index to the first field value
+ that matches.</para>
+
+ <para><function>sd_journal_enumerate_unique()</function> may be
+ used to iterate through all data fields which match the previously
+ selected field name as set with
+ <function>sd_journal_query_unique()</function>. On each invocation
+ the next field data matching the field name is returned. The order
+ of the returned data fields is not defined. It takes three
+ arguments: the journal context object, plus a pair of pointers to
+ pointer/size variables where the data object and its size shall be
+ stored in. The returned data is in a read-only memory map and is
+ only valid until the next invocation of
+ <function>sd_journal_enumerate_unique()</function>. Note that the
+ data returned will be prefixed with the field name and '='. Note
+ that this call is subject to the data field size threshold as
+ controlled by
+ <function>sd_journal_set_data_threshold()</function>.</para>
+
+ <para><function>sd_journal_restart_unique()</function> resets the
+ data enumeration index to the beginning of the list. The next
+ invocation of <function>sd_journal_enumerate_unique()</function>
+ will return the first field data matching the field name
+ again.</para>
+
+ <para>Note that the
+ <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used
+ as a handy wrapper around
+ <function>sd_journal_restart_unique()</function> and
+ <function>sd_journal_enumerate_unique()</function>.</para>
+
+ <para>Note that these functions currently are not influenced by
+ matches set with <function>sd_journal_add_match()</function> but
+ this might change in a later version of this software.</para>
+
+ <para>To enumerate all field names currently in use (and thus all suitable field parameters for
+ <function>sd_journal_query_unique()</function>), use the
+ <citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ call.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para><function>sd_journal_query_unique()</function> returns 0 on
+ success or a negative errno-style error code.
+ <function>sd_journal_enumerate_unique()</function> returns a
+ positive integer if the next field data has been read, 0 when no
+ more fields are known, or a negative errno-style error code.
+ <function>sd_journal_restart_unique()</function> returns
+ nothing.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>All functions listed here are thread-agnostic and only a single thread may operate
+ on a given <structname>sd_journal</structname> object.</para>
+
+ <para>The <function>sd_journal_query_unique()</function>,
+ <function>sd_journal_enumerate_unique()</function> and
+ <function>sd_journal_restart_unique()</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>Use the <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro
+ to iterate through all values a field of the journal can take. The
+ following example lists all unit names referenced in the
+ journal:</para>
+
+ <programlisting>#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+#include &lt;systemd/sd-journal.h&gt;
+
+int main(int argc, char *argv[]) {
+ sd_journal *j;
+ const void *d;
+ size_t l;
+ int r;
+
+ r = sd_journal_open(&amp;j, SD_JOURNAL_LOCAL_ONLY);
+ if (r &lt; 0) {
+ fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
+ return 1;
+ }
+ r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
+ if (r &lt; 0) {
+ fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
+ return 1;
+ }
+ SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
+ printf("%.*s\n", (int) l, (const char*) d);
+ sd_journal_close(j);
+ return 0;
+}</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_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>