man: document sd_journal_get_data() and friends
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Lennart Poettering
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15
Makefile.am
15
Makefile.am
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@ -502,7 +502,8 @@ MANPAGES = \
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man/sd_journal_print.3 \
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man/sd_journal_stream_fd.3 \
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man/sd_journal_open.3 \
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man/sd_journal_next.3
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man/sd_journal_next.3 \
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man/sd_journal_get_data.3
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MANPAGES_ALIAS = \
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man/reboot.8 \
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@ -547,7 +548,12 @@ MANPAGES_ALIAS = \
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man/sd_journal_close.3 \
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man/sd_journal_previous.3 \
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man/sd_journal_next_skip.3 \
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man/sd_journal_previous_skip.3
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man/sd_journal_previous_skip.3 \
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man/SD_JOURNAL_FOREACH.3 \
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man/SD_JOURNAL_FOREACH_BACKWARDS.3 \
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man/sd_journal_enumerate_data.3 \
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man/sd_journal_restart_data.3 \
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man/SD_JOURNAL_FOREACH_DATA.3
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man/reboot.8: man/halt.8
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man/poweroff.8: man/halt.8
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@ -592,6 +598,11 @@ man/sd_journal_close.3: man/sd_journal_open.3
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man/sd_journal_previous.3: man/sd_journal_next.3
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man/sd_journal_next_skip.3: man/sd_journal_next.3
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man/sd_journal_previous_skip.3: man/sd_journal_next.3
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man/SD_JOURNAL_FOREACH.3: man/sd_journal_next.3
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man/SD_JOURNAL_FOREACH_BACKWARDS.3: man/sd_journal_next.3
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man/sd_journal_enumerate_data.3: man/sd_journal_get_data.3
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man/sd_journal_restart_data.3: man/sd_journal_get_data.3
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man/SD_JOURNAL_FOREACH_DATA.3: man/sd_journal_get_data.3
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XML_FILES = \
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${patsubst %.1,%.xml,${patsubst %.3,%.xml,${patsubst %.5,%.xml,${patsubst %.7,%.xml,${patsubst %.8,%.xml,$(MANPAGES)}}}}}
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@ -0,0 +1,199 @@
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<?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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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_journal_get_data">
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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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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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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_restart_data</refname>
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<refname>SD_JOURNAL_FOREACH_DATA</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_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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</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
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the data object associated with a specific field from
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the current journal entry. It takes four arguments:
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the journal context object, a string with the field
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name to request, plus a pair of pointers to
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pointer/size variables where the data object and its
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size shall be stored in. The field name should be an
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entry field name. Well-known field names are listed in
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
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returned data is in a read-only memory map and is only
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valid until the next invocation of
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<function>sd_journal_get_data()</function> or
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<function>sd_journal_enumerate_data()</function>, or
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the read pointer is altered. Note that the data
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returned will be prefixed with the field name and
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'='.</para>
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<para><function>sd_journal_enumerate_data()</function>
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may be used to iterate through all fields of the
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current entry. On each invocation the data for the
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next field is returned. The order of these fields is
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not defined. The data returned is in the same format
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as with <function>sd_journal_get_data()</function> and
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also follows the same life-time semantics.</para>
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<para><function>sd_journal_restart_data()</function>
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resets the data enumeration index to the beginning of
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the entry. The next invocation of
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<function>sd_journal_enumerate_data()</function> will return the first
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field of the entry again.</para>
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<para>Note that the
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<function>SD_JOURNAL_FOREACH_DATA()</function> macro
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may be used as a wrapper around
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<function>sd_journal_restart_data()</function> and
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<function>sd_journal_enumerate_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 not been called at least
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once.</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>
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returns 0 on success or a negative errno-style error
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code. If the current entry does not include the
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specified field -ENOENT is returned. If
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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has not been called at least once -EADDRNOTAVAIL is
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returned. <function>sd_journal_enumerate_data()</function>
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returns a positive integer if the next field has been
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read, 0 when no more fields are known, or a negative
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errno-style error
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code. <function>sd_journal_restart_data()</function>
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returns nothing.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>The <function>sd_journal_get_data()</function>,
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<function>sd_journal_enumerate_data()</function> and
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<function>sd_journal_restart_data()</function>
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interfaces are available as shared library, which can
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be compiled and linked to with the
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<literal>libsystemd-journal</literal>
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<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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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 l;
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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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</para>
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</refsect1>
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</refentry>
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@ -47,6 +47,8 @@
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<refname>sd_journal_previous</refname>
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<refname>sd_journal_next_skip</refname>
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<refname>sd_journal_previous_skip</refname>
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<refname>SD_JOURNAL_FOREACH</refname>
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<refname>SD_JOURNAL_FOREACH_BACKWARDS</refname>
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<refpurpose>Advance or set back the read pointer in the journal</refpurpose>
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</refnamediv>
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@ -76,6 +78,15 @@
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<paramdef>uint64_t <parameter>skip</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef><function>SD_JOURNAL_FOREACH</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_BACKWARDS</function></funcdef>
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<paramdef>sd_journal* <parameter>j</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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@ -105,6 +116,13 @@
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that the entry then pointing to is later in time than
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then previous one, or has the same timestamp.</para>
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<para>Note that
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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and related calls will fail unless
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<function>sd_journal_next()</function> has been
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invoked at least once in order to position the read
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pointer on a journal entry.</para>
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<para>Note that the
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<function>SD_JOURNAL_FOREACH()</function> macro may be used
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as a wrapper around
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@ -85,6 +85,7 @@ int sd_journal_next_skip(sd_journal *j, uint64_t skip);
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int sd_journal_get_realtime_usec(sd_journal *j, uint64_t *ret);
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int sd_journal_get_monotonic_usec(sd_journal *j, uint64_t *ret, sd_id128_t *ret_boot_id);
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int sd_journal_get_data(sd_journal *j, const char *field, const void **data, size_t *l);
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int sd_journal_enumerate_data(sd_journal *j, const void **data, size_t *l);
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void sd_journal_restart_data(sd_journal *j);
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