Merge pull request #3984 from poettering/refcnt

permit bus clients to pin units to avoid automatic GC

1 files changed, 261 insertions, 0 deletions

diff --git a/man/sd_bus_track_add_name.xml b/man/sd_bus_track_add_name.xml
new file mode 100644
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+++ b/man/sd_bus_track_add_name.xml
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+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!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 2016 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_bus_track_add_name">
+
+  <refentryinfo>
+    <title>sd_bus_track_add_name</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_bus_track_add_name</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_bus_track_add_name</refname>
+    <refname>sd_bus_track_add_sender</refname>
+    <refname>sd_bus_track_remove_name</refname>
+    <refname>sd_bus_track_remove_sender</refname>
+    <refname>sd_bus_track_count</refname>
+    <refname>sd_bus_track_count_sender</refname>
+    <refname>sd_bus_track_count_name</refname>
+    <refname>sd_bus_track_contains</refname>
+    <refname>sd_bus_track_first</refname>
+    <refname>sd_bus_track_next</refname>
+
+    <refpurpose>Add, remove and retrieve bus peers tracked in a bus peer tracking object</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_add_name</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>const char* <parameter>name</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_add_sender</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_remove_name</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>const char* <parameter>name</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_remove_sender</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>unsigned <function>sd_bus_track_count</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_count_name</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>const char* <parameter>name</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_count_sender</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_track_contains</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+        <paramdef>const char* <parameter>name</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>const char* <function>sd_bus_track_first</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>const char* <function>sd_bus_track_next</function></funcdef>
+        <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
+      </funcprototype>
+
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><function>sd_bus_track_add_name()</function> adds a peer to track to a bus peer tracking object. The first
+    argument should refer to a bus peer tracking object created with
+    <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, the second
+    name should refer to a D-Bus peer name to track, either in unique or well-known service format. If the name is not
+    tracked yet it will be added to the list of names to track. If it already is being tracked and non-recursive mode
+    is enabled, no operation is executed by this call. If recursive mode is enabled a per-name counter is increased by
+    one each time this call is invoked, and <function>sd_bus_track_remove_name()</function> has to be called as many
+    times as <function>sd_bus_track_add_name()</function> was invoked before in order to stop tracking of the name. Use
+    <citerefentry><refentrytitle>sd_bus_track_set_recursive</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
+    switch from the default non-recursive mode to recursive mode, or back. Note that the specified name is tracked as
+    it is, well-known names are not resolved to unique names by this call. Note that multiple bus peer tracking objects
+    may track the same name.</para>
+
+    <para><function>sd_bus_track_remove_name()</function> undoes the effect of
+    <function>sd_bus_track_add_name()</function> and removes a bus peer name from the list of peers to watch. Depending
+    on whether non-recursive or recursive mode is enabled for the bus peer tracking object this call will either remove
+    the name fully from the tracking object, or will simply decrement the per-name counter by one, removing the name
+    only when the counter reaches zero (see above). Note that a bus peer disconnecting from the bus will implicitly
+    remove its names fully from the bus peer tracking object, regardless of the current per-name counter.</para>
+
+    <para><function>sd_bus_track_add_sender()</function> and <function>sd_bus_track_remove_sender()</function> are
+    similar to <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_remove_name()</function> but
+    take a bus message as argument. The sender of this bus message is determined and added to/removed from the bus peer
+    tracking object. As messages always originate from unique names, and never from well-known names this means that
+    this call will effectively only add unique names to the bus peer tracking object.</para>
+
+    <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked by the
+    specified bus peer tracking object. Note that this function always returns the actual number of names tracked, and
+    hence if <function>sd_bus_track_add_name()</function> has been invoked multiple times for the same name it is only
+    counted as one, regardless if recursive mode is used or not.</para>
+
+    <para><function>sd_bus_track_count_name()</function> returns the current per-name counter for the specified
+    name. If non-recursive mode is used this returns either 1 or 0, depending on whether the specified name has been
+    added to the tracking object before, or not. If recursive mode has been enabled, values larger than 1 may be
+    returned too, in case <function>sd_bus_track_add_name()</function> has been called multiple times for the same
+    name.</para>
+
+    <para><function>sd_bus_track_count_sender()</function> is similar to
+    <function>sd_bus_track_count_name()</function>, but takes a bus message object and returns the per-name counter
+    matching the sender of the message.</para>
+
+    <para><function>sd_bus_track_contains()</function> may be used to determine whether the specified name has been
+    added at least once to the specified bus peer tracking object.</para>
+
+    <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> may be used to
+    enumerate all names currently being tracked by the passed bus peer tracking
+    object. <function>sd_bus_track_first()</function> returns the first entry in the object, and resets an internally
+    maintained read index. Each subsequent invocation of <function>sd_bus_track_next()</function> returns the next name
+    contained in the bus object. If the end is reached <constant>NULL</constant> is returned. If no names have been
+    added to the object yet <function>sd_bus_track_first()</function> will return <constant>NULL</constant>
+    immediately. The order in which names are returned is undefined; in particular which name is considered the first
+    returned is not defined. If recursive mode is enabled and the same name has been added multiple times to the bus
+    peer tracking object it is only returned once by this enumeration. If new names are added to or existing names
+    removed from the bus peer tracking object while it is being enumerated the enumeration ends on the next invocation
+    of <function>sd_bus_track_next()</function> as <constant>NULL</constant> is returned.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>On success, <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_add_sender()</function>
+    return 0 if the specified name has already been added to the bus peer tracking object before and positive if it
+    hasn't. On failure, they return a negative errno-style error code.</para>
+
+    <para><function>sd_bus_track_remove_name()</function> and <function>sd_bus_track_remove_sender()</function> return
+    positive if the specified name was previously tracked by the bus peer tracking object and has now been removed. In
+    non-recursive mode, 0 is returned if the specified name was not being tracked yet. In recursive mode
+    <constant>-EUNATCH</constant> is returned in this case. On failure, they return a negative errno-style error
+    code.</para>
+
+    <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked, or 0 on
+    failure.</para>
+
+    <para><function>sd_bus_track_count_name()</function> and <function>sd_bus_track_count_sender()</function> return
+    the current per-name counter for the specified name or the sender of the specified message. Zero is returned for
+    names that are not being tracked yet, a positive value for names added at least once. Larger values than 1 are only
+    returned in recursive mode. On failure, a negative errno-style error code is returned.</para>
+
+    <para><function>sd_bus_track_contains()</function> returns the passed name if it exists in the bus peer tracking
+    object. On failure, and if the name has not been added yet <constant>NULL</constant> is returned.</para>
+
+    <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> return the first/next
+    name contained in the bus peer tracking object, and <constant>NULL</constant> if the end of the enumeration is
+    reached and on error.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Errors</title>
+
+    <para>Returned errors may indicate the following problems:</para>
+
+    <variablelist>
+
+      <varlistentry>
+        <term><constant>-EUNATCH</constant></term>
+
+        <listitem><para><function>sd_bus_track_remove_name()</function> or
+        <function>sd_bus_track_remove_sender()</function> have been invoked for a name not previously added to the bus
+        peer object.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-EINVAL</constant></term>
+
+        <listitem><para>Specified parameter is invalid.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-ENOMEM</constant></term>
+
+        <listitem><para>Memory allocation failed.</para></listitem>
+      </varlistentry>
+
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Notes</title>
+
+    <para><function>sd_bus_track_add_name()</function> and the other calls described here 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>See Also</title>
+
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>