<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
-<!--
- 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_fd">
+<refentry id="sd_journal_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_journal_get_fd</title>
<productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
</refentryinfo>
<refmeta>
immediately for all journal changes. Returns 0 if there might be a
latency involved.</para>
- <para><function>sd_journal_process()</function> and
- <function>sd_journal_wait()</function> return one of
- <constant>SD_JOURNAL_NOP</constant>,
- <constant>SD_JOURNAL_APPEND</constant> or
- <constant>SD_JOURNAL_INVALIDATE</constant> on success or a
- negative errno-style error code. If
- <constant>SD_JOURNAL_NOP</constant> is returned, the journal did
- not change since the last invocation. If
- <constant>SD_JOURNAL_APPEND</constant> is returned, new entries
- have been appended to the end of the journal. If
- <constant>SD_JOURNAL_INVALIDATE</constant>, journal files were
- added or removed (possibly due to rotation). In the latter event,
- live-view UIs should probably refresh their entire display, while
- in the case of <constant>SD_JOURNAL_APPEND</constant>, it is
- sufficient to simply continue reading at the previous end of the
- journal.</para>
+ <para><function>sd_journal_process()</function> and <function>sd_journal_wait()</function> return a negative
+ errno-style error code, or one of <constant>SD_JOURNAL_NOP</constant>, <constant>SD_JOURNAL_APPEND</constant> or
+ <constant>SD_JOURNAL_INVALIDATE</constant> on success:</para>
+
+ <itemizedlist>
+ <listitem><para>If <constant>SD_JOURNAL_NOP</constant> is returned, the journal did not change since the last
+ invocation.</para></listitem>
+
+ <listitem><para>If <constant>SD_JOURNAL_APPEND</constant> is returned, new entries have been appended to the end
+ of the journal. In this case it is sufficient to simply continue reading at the previous end location of the
+ journal, to read the newly added entries.</para></listitem>
+
+ <listitem><para>If <constant>SD_JOURNAL_INVALIDATE</constant>, journal files were added to or removed from the
+ set of journal files watched (e.g. due to rotation or vacuuming), and thus entries might have appeared or
+ disappeared at arbitrary places in the log stream, possibly before or after the previous end of the log
+ stream. If <constant>SD_JOURNAL_INVALIDATE</constant> is returned, live-view UIs that want to reflect on screen
+ the precise state of the log data on disk should probably refresh their entire display (relative to the cursor of
+ the log entry on the top of the screen). Programs only interested in a strictly sequential stream of log data may
+ treat <constant>SD_JOURNAL_INVALIDATE</constant> the same way as <constant>SD_JOURNAL_APPEND</constant>, thus
+ ignoring any changes to the log view earlier than the old end of the log stream.</para></listitem>
+ </itemizedlist>
</refsect1>
<refsect1>
<refsect1>
<title>Notes</title>
- <para>The <function>sd_journal_get_fd()</function>,
- <function>sd_journal_get_events()</function>,
- <function>sd_journal_reliable_fd()</function>,
- <function>sd_journal_process()</function> and
- <function>sd_journal_wait()</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>
+ <xi:include href="threads-aware.xml" xpointer="strict"/>
+
+ <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
</refsect1>
<refsect1>
<para>Iterating through the journal, in a live view tracking all
changes:</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;
- }
- for (;;) {
- const void *d;
- size_t l;
- r = sd_journal_next(j);
- if (r < 0) {
- fprintf(stderr, "Failed to iterate to next entry: %s\n", strerror(-r));
- break;
- }
- if (r == 0) {
- /* Reached the end, let's wait for changes, and try again */
- r = sd_journal_wait(j, (uint64_t) -1);
- if (r < 0) {
- fprintf(stderr, "Failed to wait for changes: %s\n", strerror(-r));
- break;
- }
- continue;
- }
- r = sd_journal_get_data(j, "MESSAGE", &d, &l);
- if (r < 0) {
- fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
- continue;
- }
- printf("%.*s\n", (int) l, (const char*) d);
- }
- sd_journal_close(j);
- return 0;
-}</programlisting>
+ <programlisting><xi:include href="journal-iterate-wait.c" parse="text" /></programlisting>
<para>Waiting with <function>poll()</function> (this
example lacks all error checking for the sake of
simplicity):</para>
- <programlisting>#include <poll.h>
-#include <systemd/sd-journal.h>
-
-int wait_for_changes(sd_journal *j) {
- struct pollfd pollfd;
- int msec;
-
- sd_journal_get_timeout(m, &t);
- if (t == (uint64_t) -1)
- msec = -1;
- else {
- struct timespec ts;
- uint64_t n;
- clock_gettime(CLOCK_MONOTONIC, &ts);
- n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
- msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
- }
-
- pollfd.fd = sd_journal_get_fd(j);
- pollfd.events = sd_journal_get_events(j);
- poll(&pollfd, 1, msec);
- return sd_journal_process(j);
-}</programlisting>
+ <programlisting><xi:include href="journal-iterate-poll.c" parse="text" /></programlisting>
</refsect1>
<refsect1>
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