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Diffstat (limited to 'src/libsystemd/sd_journal_next.xml')
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diff --git a/src/libsystemd/sd_journal_next.xml b/src/libsystemd/sd_journal_next.xml new file mode 100644 index 0000000000..7c385de260 --- /dev/null +++ b/src/libsystemd/sd_journal_next.xml @@ -0,0 +1,210 @@ +<?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_next"> + + <refentryinfo> + <title>sd_journal_next</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_next</refentrytitle> + <manvolnum>3</manvolnum> + </refmeta> + + <refnamediv> + <refname>sd_journal_next</refname> + <refname>sd_journal_previous</refname> + <refname>sd_journal_next_skip</refname> + <refname>sd_journal_previous_skip</refname> + <refname>SD_JOURNAL_FOREACH</refname> + <refname>SD_JOURNAL_FOREACH_BACKWARDS</refname> + <refpurpose>Advance or set back the read pointer in the journal</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <funcsynopsis> + <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> + + <funcprototype> + <funcdef>int <function>sd_journal_next</function></funcdef> + <paramdef>sd_journal *<parameter>j</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_journal_previous</function></funcdef> + <paramdef>sd_journal *<parameter>j</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_journal_next_skip</function></funcdef> + <paramdef>sd_journal *<parameter>j</parameter></paramdef> + <paramdef>uint64_t <parameter>skip</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_journal_previous_skip</function></funcdef> + <paramdef>sd_journal *<parameter>j</parameter></paramdef> + <paramdef>uint64_t <parameter>skip</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef><function>SD_JOURNAL_FOREACH</function></funcdef> + <paramdef>sd_journal *<parameter>j</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef> + <paramdef>sd_journal *<parameter>j</parameter></paramdef> + </funcprototype> + </funcsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Description</title> + + <para><function>sd_journal_next()</function> advances the read + pointer into the journal by one entry. The only argument taken is + a journal context object as allocated via + <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>. + After successful invocation the entry may be read with functions + such as + <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> + + <para>Similarly, <function>sd_journal_previous()</function> sets + the read pointer back one entry.</para> + + <para><function>sd_journal_next_skip()</function> and + <function>sd_journal_previous_skip()</function> advance/set back + the read pointer by multiple entries at once, as specified in the + <varname>skip</varname> parameter.</para> + + <para>The journal is strictly ordered by reception time, and hence + advancing to the next entry guarantees that the entry then + pointing to is later in time than then previous one, or has the + same timestamp.</para> + + <para>Note that + <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> + and related calls will fail unless + <function>sd_journal_next()</function> has been invoked at least + once in order to position the read pointer on a journal + entry.</para> + + <para>Note that the <function>SD_JOURNAL_FOREACH()</function> + macro may be used as a wrapper around + <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry> + and <function>sd_journal_next()</function> in order to make + iterating through the journal easier. See below for an example. + Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may + be used for iterating the journal in reverse order.</para> + </refsect1> + + <refsect1> + <title>Return Value</title> + + <para>The four calls return the number of entries advanced/set + back on success or a negative errno-style error code. When the end + or beginning of the journal is reached, a number smaller than + requested is returned. More specifically, if + <function>sd_journal_next()</function> or + <function>sd_journal_previous()</function> reach the end/beginning + of the journal they will return 0, instead of 1 when they are + successful. This should be considered an EOF marker.</para> + </refsect1> + + <refsect1> + <title>Notes</title> + + <para>All functions listed here are thread-agnostic and only a single thread may operate + on a given <structname>sd_journal</structname> object.</para> + + <para>The <function>sd_journal_next()</function>, + <function>sd_journal_previous()</function>, + <function>sd_journal_next_skip()</function> and + <function>sd_journal_previous_skip()</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>Iterating through the journal:</para> + + <programlisting>#include <stdio.h> +#include <string.h> +#include <systemd/sd-journal.h> + +int main(int argc, char *argv[]) { + int r; + sd_journal *j; + r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); + if (r < 0) { + fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); + return 1; + } + SD_JOURNAL_FOREACH(j) { + const char *d; + size_t l; + + r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l); + if (r < 0) { + fprintf(stderr, "Failed to read message field: %s\n", strerror(-r)); + continue; + } + + printf("%.*s\n", (int) l, d); + } + sd_journal_close(j); + return 0; +}</programlisting> + + </refsect1> + + <refsect1> + <title>See Also</title> + + <para> + <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</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_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry> + </para> + </refsect1> + +</refentry> |