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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
SPDX-License-Identifier: LGPL-2.1+
This file is part of systemd.
Copyright 2012 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd_journal_get_data">
<refentryinfo>
<title>sd_journal_get_data</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_get_data</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_get_data</refname>
<refname>sd_journal_enumerate_data</refname>
<refname>sd_journal_restart_data</refname>
<refname>SD_JOURNAL_FOREACH_DATA</refname>
<refname>sd_journal_set_data_threshold</refname>
<refname>sd_journal_get_data_threshold</refname>
<refpurpose>Read data fields from the current journal entry</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_get_data</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>const char *<parameter>field</parameter></paramdef>
<paramdef>const void **<parameter>data</parameter></paramdef>
<paramdef>size_t *<parameter>length</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_enumerate_data</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>const void **<parameter>data</parameter></paramdef>
<paramdef>size_t *<parameter>length</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sd_journal_restart_data</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef><function>SD_JOURNAL_FOREACH_DATA</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>const void *<parameter>data</parameter></paramdef>
<paramdef>size_t <parameter>length</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_set_data_threshold</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>size_t <parameter>sz</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_get_data_threshold</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>size_t *<parameter>sz</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_journal_get_data()</function> gets the data
object associated with a specific field from the current journal
entry. It takes four arguments: the journal context object, a
string with the field name to request, plus a pair of pointers to
pointer/size variables where the data object and its size shall be
stored in. The field name should be an entry field name.
Well-known field names are listed in
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
The returned data is in a read-only memory map and is only valid
until the next invocation of
<function>sd_journal_get_data()</function> or
<function>sd_journal_enumerate_data()</function>, or the read
pointer is altered. Note that the data returned will be prefixed
with the field name and '='. Also note that, by default, data fields
larger than 64K might get truncated to 64K. This threshold may be
changed and turned off with
<function>sd_journal_set_data_threshold()</function> (see
below).</para>
<para><function>sd_journal_enumerate_data()</function> may be used
to iterate through all fields of the current entry. On each
invocation the data for the next field is returned. The order of
these fields is not defined. The data returned is in the same
format as with <function>sd_journal_get_data()</function> and also
follows the same life-time semantics.</para>
<para><function>sd_journal_restart_data()</function> resets the
data enumeration index to the beginning of the entry. The next
invocation of <function>sd_journal_enumerate_data()</function>
will return the first field of the entry again.</para>
<para>Note that the <function>SD_JOURNAL_FOREACH_DATA()</function>
macro may be used as a handy wrapper around
<function>sd_journal_restart_data()</function> and
<function>sd_journal_enumerate_data()</function>.</para>
<para>Note that these functions will not work before
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
(or related call) has been called at least once, in order to
position the read pointer at a valid entry.</para>
<para><function>sd_journal_set_data_threshold()</function> may be
used to change the data field size threshold for data returned by
<function>sd_journal_get_data()</function>,
<function>sd_journal_enumerate_data()</function> and
<function>sd_journal_enumerate_unique()</function>. This threshold
is a hint only: it indicates that the client program is interested
only in the initial parts of the data fields, up to the threshold
in size — but the library might still return larger data objects.
That means applications should not rely exclusively on this
setting to limit the size of the data fields returned, but need to
apply an explicit size limit on the returned data as well. This
threshold defaults to 64K by default. To retrieve the complete
data fields this threshold should be turned off by setting it to
0, so that the library always returns the complete data objects.
It is recommended to set this threshold as low as possible since
this relieves the library from having to decompress large
compressed data objects in full.</para>
<para><function>sd_journal_get_data_threshold()</function> returns
the currently configured data field size threshold.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para><function>sd_journal_get_data()</function> returns 0 on
success or a negative errno-style error code. If the current entry
does not include the specified field, -ENOENT is returned. If
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
has not been called at least once, -EADDRNOTAVAIL is returned.
<function>sd_journal_enumerate_data()</function> returns a
positive integer if the next field has been read, 0 when no more
fields are known, or a negative errno-style error code.
<function>sd_journal_restart_data()</function> returns nothing.
<function>sd_journal_set_data_threshold()</function> and
<function>sd_journal_get_threshold()</function> return 0 on
success or a negative errno-style error code.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>The <function>sd_journal_get_data()</function>,
<function>sd_journal_enumerate_data()</function>,
<function>sd_journal_restart_data()</function>,
<function>sd_journal_set_data_threshold()</function> and
<function>sd_journal_get_data_threshold()</function> interfaces
are available as a shared library, which can be compiled and
linked to with the
<constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
file.</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>See
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for a complete example how to use
<function>sd_journal_get_data()</function>.</para>
<para>Use the
<function>SD_JOURNAL_FOREACH_DATA</function> macro to
iterate through all fields of the current journal
entry:</para>
<programlisting>…
int print_fields(sd_journal *j) {
const void *data;
size_t length;
SD_JOURNAL_FOREACH_DATA(j, data, length)
printf("%.*s\n", (int) length, data);
}
…</programlisting>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
|
