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122 lines
5.1 KiB
XML
122 lines
5.1 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-or-later -->
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<refentry id="sd_journal_enumerate_fields" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_journal_enumerate_fields</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_enumerate_fields</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_enumerate_fields</refname>
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<refname>sd_journal_restart_fields</refname>
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<refname>SD_JOURNAL_FOREACH_FIELD</refname>
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<refpurpose>Read used field names 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_enumerate_fields</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>void <function>sd_journal_restart_fields</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_FIELD</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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</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_enumerate_fields()</function> may be used to iterate through all field names used in the
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opened journal files. On each invocation the next field name is returned. The order of the returned field names is
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not defined. It takes two arguments: the journal context object, plus a pointer to a constant string pointer where
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the field name is stored in. The returned data is in a read-only memory map and is only valid until the next
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invocation of <function>sd_journal_enumerate_fields()</function>. Note that this call is subject to the data field
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size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para>
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<para><function>sd_journal_restart_fields()</function> resets the field name enumeration index to the beginning of
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the list. The next invocation of <function>sd_journal_enumerate_fields()</function> will return the first field
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name again.</para>
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<para>The <function>SD_JOURNAL_FOREACH_FIELD()</function> macro may be used as a handy wrapper around
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<function>sd_journal_restart_fields()</function> and <function>sd_journal_enumerate_fields()</function>.</para>
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<para>These functions currently are not influenced by matches set with <function>sd_journal_add_match()</function>
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but this might change in a later version of this software.</para>
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<para>To retrieve the possible values a specific field can take use
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<citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</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_enumerate_fields()</function> returns a
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positive integer if the next field name has been read, 0 when no
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more field names are known, or a negative errno-style error code.
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<function>sd_journal_restart_fields()</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_FIELD()</function> macro to iterate through all field names in use in the
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current journal.</para>
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<programlisting><xi:include href="journal-enumerate-fields.c" parse="text" /></programlisting>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para><function>sd_journal_enumerate_fields()</function>,
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<function>sd_journal_restart_fields()</function>, and
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<function>SD_JOURNAL_FOREACH_FIELD()</function> were added in version 229.</para>
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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_query_unique</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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