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https://github.com/systemd/systemd
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787f78b6a1
Moving them out makes it easier to run them through a compiler, use automatic indentation, and opens the possibility to provide a download link in the future. I verified that all examples compile cleanly. (2-space indentation is used because the examples are already significantly indented in the man page, and we need to keep them narrow so that they display well on standard terminals.)
161 lines
6.7 KiB
XML
161 lines
6.7 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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SPDX-License-Identifier: LGPL-2.1+
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-->
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<refentry id="sd_journal_query_unique" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_journal_query_unique</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_journal_query_unique</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_journal_query_unique</refname>
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<refname>sd_journal_enumerate_unique</refname>
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<refname>sd_journal_restart_unique</refname>
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<refname>SD_JOURNAL_FOREACH_UNIQUE</refname>
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<refpurpose>Read unique data fields from the journal</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_journal_query_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const char *<parameter>field</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_enumerate_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const void **<parameter>data</parameter></paramdef>
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<paramdef>size_t *<parameter>length</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_journal_restart_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const void *<parameter>data</parameter></paramdef>
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<paramdef>size_t <parameter>length</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_journal_query_unique()</function> queries the
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journal for all unique values the specified field can take. It
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takes two arguments: the journal to query and the field name to
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look for. Well-known field names are listed on
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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Field names must be specified without a trailing '='. After this
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function has been executed successfully the field values may be
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queried using <function>sd_journal_enumerate_unique()</function>.
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Invoking this call a second time will change the field name being
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queried and reset the enumeration index to the first field value
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that matches.</para>
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<para><function>sd_journal_enumerate_unique()</function> may be
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used to iterate through all data fields which match the previously
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selected field name as set with
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<function>sd_journal_query_unique()</function>. On each invocation
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the next field data matching the field name is returned. The order
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of the returned data fields is not defined. It takes three
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arguments: the journal context object, 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 returned data is in a read-only memory map and is
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only valid until the next invocation of
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<function>sd_journal_enumerate_unique()</function>. Note that the
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data returned will be prefixed with the field name and '='. Note
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that this call is subject to the data field size threshold as
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controlled by
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<function>sd_journal_set_data_threshold()</function>.</para>
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<para><function>sd_journal_restart_unique()</function> resets the
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data enumeration index to the beginning of the list. The next
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invocation of <function>sd_journal_enumerate_unique()</function>
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will return the first field data matching the field name
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again.</para>
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<para>Note that the
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<function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used
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as a handy wrapper around
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<function>sd_journal_restart_unique()</function> and
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<function>sd_journal_enumerate_unique()</function>.</para>
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<para>Note that these functions currently are not influenced by
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matches set with <function>sd_journal_add_match()</function> but
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this might change in a later version of this software.</para>
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<para>To enumerate all field names currently in use (and thus all suitable field parameters for
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<function>sd_journal_query_unique()</function>), use the
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<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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call.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para><function>sd_journal_query_unique()</function> returns 0 on
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success or a negative errno-style error code.
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<function>sd_journal_enumerate_unique()</function> returns a
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positive integer if the next field data has been read, 0 when no
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more fields are known, or a negative errno-style error code.
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<function>sd_journal_restart_unique()</function> returns
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nothing.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>All functions listed here are thread-agnostic and only a single thread may operate
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on a given <structname>sd_journal</structname> object.</para>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>Use the <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro
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to iterate through all values a field of the journal can take. The
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following example lists all unit names referenced in the
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journal:</para>
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<programlisting><xi:include href="journal-iterate-unique.c" parse="text" /></programlisting>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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