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277 lines
12 KiB
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277 lines
12 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_get_data" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_journal_get_data</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_get_data</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_get_data</refname>
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<refname>sd_journal_enumerate_data</refname>
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<refname>sd_journal_enumerate_available_data</refname>
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<refname>sd_journal_restart_data</refname>
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<refname>SD_JOURNAL_FOREACH_DATA</refname>
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<refname>sd_journal_set_data_threshold</refname>
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<refname>sd_journal_get_data_threshold</refname>
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<refpurpose>Read data fields from the current journal entry</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_get_data</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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<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>int <function>sd_journal_enumerate_data</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>int <function>sd_journal_enumerate_available_data</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_data</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_DATA</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>int <function>sd_journal_set_data_threshold</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>size_t <parameter>sz</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_get_data_threshold</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>size_t *<parameter>sz</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_get_data()</function> gets the data object associated with a specific field
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from the current journal entry. It takes four arguments: the journal context object, a string with the
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field name to request, plus a pair of pointers to pointer/size variables where the data object and its
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size shall be stored in. The field name should be an entry field name. Well-known field names are listed in
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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but any field can be specified. The returned data is in a read-only memory map and is only valid until
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the next invocation of <function>sd_journal_get_data()</function>,
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<function>sd_journal_enumerate_data()</function>,
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<function>sd_journal_enumerate_available_data()</function>, or when the read pointer is altered. Note
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that the data returned will be prefixed with the field name and <literal>=</literal>. Also note that, by
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default, data fields larger than 64K might get truncated to 64K. This threshold may be changed and turned
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off with <function>sd_journal_set_data_threshold()</function> (see below).</para>
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<para><function>sd_journal_enumerate_data()</function> may be used
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to iterate through all fields of the current entry. On each
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invocation the data for the next field is returned. The order of
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these fields is not defined. The data returned is in the same
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format as with <function>sd_journal_get_data()</function> and also
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follows the same life-time semantics.</para>
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<para><function>sd_journal_enumerate_available_data()</function> is similar to
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<function>sd_journal_enumerate_data()</function>, but silently skips any fields which may be valid, but
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are too large or not supported by current implementation.</para>
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<para><function>sd_journal_restart_data()</function> resets the
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data enumeration index to the beginning of the entry. The next
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invocation of <function>sd_journal_enumerate_data()</function>
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will return the first field of the entry again.</para>
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<para>Note that the <function>SD_JOURNAL_FOREACH_DATA()</function> macro may be used as a handy wrapper
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around <function>sd_journal_restart_data()</function> and
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<function>sd_journal_enumerate_available_data()</function>.</para>
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<para>Note that these functions will not work before
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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(or related call) has been called at least once, in order to
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position the read pointer at a valid entry.</para>
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<para><function>sd_journal_set_data_threshold()</function> may be
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used to change the data field size threshold for data returned by
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<function>sd_journal_get_data()</function>,
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<function>sd_journal_enumerate_data()</function> and
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<function>sd_journal_enumerate_unique()</function>. This threshold
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is a hint only: it indicates that the client program is interested
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only in the initial parts of the data fields, up to the threshold
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in size — but the library might still return larger data objects.
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That means applications should not rely exclusively on this
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setting to limit the size of the data fields returned, but need to
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apply an explicit size limit on the returned data as well. This
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threshold defaults to 64K by default. To retrieve the complete
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data fields this threshold should be turned off by setting it to
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0, so that the library always returns the complete data objects.
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It is recommended to set this threshold as low as possible since
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this relieves the library from having to decompress large
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compressed data objects in full.</para>
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<para><function>sd_journal_get_data_threshold()</function> returns
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the currently configured data field size threshold.</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_get_data()</function> returns 0 on success or a negative errno-style error
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code. <function>sd_journal_enumerate_data()</function> and
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<function>sd_journal_enumerate_available_data()</function> return a positive integer if the next field
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has been read, 0 when no more fields remain, or a negative errno-style error code.
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<function>sd_journal_restart_data()</function> doesn't return anything.
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<function>sd_journal_set_data_threshold()</function> and <function>sd_journal_get_threshold()</function>
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return 0 on success or a negative errno-style error code.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry id='EINVAL'>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>One of the required parameters is <constant>NULL</constant> or invalid.
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</para></listitem>
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</varlistentry>
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<varlistentry id='ECHILD'>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The journal object was created in a different process.</para></listitem>
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</varlistentry>
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<varlistentry id='EADDRNOTAVAIL'>
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<term><constant>-EADDRNOTAVAIL</constant></term>
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<listitem><para>The read pointer is not positioned at a valid entry;
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or a related call has not been called at least once.</para></listitem>
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</varlistentry>
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<varlistentry id='ENOENT'>
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<term><constant>-ENOENT</constant></term>
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<listitem><para>The current entry does not include the specified field.</para>
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</listitem>
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</varlistentry>
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<varlistentry id='ENOMEM'>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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<varlistentry id='ENOBUFS'>
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<term><constant>-ENOBUFS</constant></term>
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<listitem><para>A compressed entry is too large.</para></listitem>
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</varlistentry>
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<varlistentry id='E2BIG'>
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<term><constant>-E2BIG</constant></term>
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<listitem><para>The data field is too large for this computer architecture (e.g. above 4 GB on a
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32-bit architecture).</para></listitem>
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</varlistentry>
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<varlistentry id='EPROTONOSUPPORT'>
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<term><constant>-EPROTONOSUPPORT</constant></term>
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<listitem><para>The journal is compressed with an unsupported method or the journal uses an
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unsupported feature.</para></listitem>
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</varlistentry>
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<varlistentry id='EBADMSG'>
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<term><constant>-EBADMSG</constant></term>
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<listitem><para>The journal is corrupted (possibly just the entry being iterated over).
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</para></listitem>
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</varlistentry>
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<varlistentry id='EIO'>
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<term><constant>-EIO</constant></term>
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<listitem><para>An I/O error was reported by the kernel.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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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>See
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for a complete example how to use
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<function>sd_journal_get_data()</function>.</para>
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<para>Use the
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<function>SD_JOURNAL_FOREACH_DATA()</function> macro to
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iterate through all fields of the current journal
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entry:</para>
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<programlisting>…
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int print_fields(sd_journal *j) {
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const void *data;
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size_t length;
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SD_JOURNAL_FOREACH_DATA(j, data, length)
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printf("%.*s\n", (int) length, data);
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}
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…</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_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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