157 lines
6.6 KiB
XML
157 lines
6.6 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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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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<xi:include href="threads-aware.xml" xpointer="strict"/>
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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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