mirror of
https://github.com/systemd/systemd.git
synced 2024-11-01 17:51:22 +03:00
236 lines
10 KiB
XML
236 lines
10 KiB
XML
<?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">
|
||
|
||
<!--
|
||
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 a 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>
|