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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
232 lines
11 KiB
XML
232 lines
11 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_bus_track_new" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_track_new</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_track_new</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_track_new</refname>
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<refname>sd_bus_track_ref</refname>
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<refname>sd_bus_track_unref</refname>
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<refname>sd_bus_track_unrefp</refname>
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<refname>sd_bus_track_set_recursive</refname>
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<refname>sd_bus_track_get_recursive</refname>
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<refname>sd_bus_track_get_bus</refname>
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<refname>sd_bus_track_get_userdata</refname>
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<refname>sd_bus_track_set_userdata</refname>
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<refpurpose>Track bus peers</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_new</function></funcdef>
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<paramdef>sd_bus* <parameter>bus</parameter></paramdef>
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<paramdef>sd_bus_track** <parameter>ret</parameter></paramdef>
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<paramdef>sd_bus_track_handler_t <parameter>handler</parameter></paramdef>
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<paramdef>void* <parameter>userdata</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus_track *<function>sd_bus_track_ref</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus_track *<function>sd_bus_track_unref</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_bus_track_unrefp</function></funcdef>
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<paramdef>sd_bus_track **<parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_get_recursive</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_track_set_recursive</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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<paramdef>int <parameter>b</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_bus* <function>sd_bus_track_get_bus</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void* <function>sd_bus_track_get_userdata</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void* <function>sd_bus_track_set_userdata</function></funcdef>
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<paramdef>sd_bus_track *<parameter>t</parameter></paramdef>
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<paramdef>void *userdata</paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_track_new()</function> creates a new bus peer tracking object. The object is allocated for
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the specified bus, and returned in the <parameter>*ret</parameter> parameter. After use, the object should be freed
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again by dropping the acquired reference with <function>sd_bus_track_unref()</function> (see below). A bus peer
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tracking object may be used to keep track of peers on a specific IPC bus, for cases where peers are making use of
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one or more local objects, in order to control the lifecycle of the local objects and ensure they stay around as
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long as the peers needing them are around, and unreferenced (and possibly destroyed) as soon as all relevant peers
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have vanished. Each bus peer tracking object may be used to track zero, one or more peers add a time. References to
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specific bus peers are added via
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<citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
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<function>sd_bus_track_add_sender()</function>. They may be dropped again via
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<function>sd_bus_track_remove_name()</function> and
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<function>sd_bus_track_remove_sender()</function>. Alternatively, references on peers are removed automatically
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when they disconnect from the bus. If non-NULL the <parameter>handler</parameter> may specify a function that is
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invoked whenever the last reference is dropped, regardless whether the reference is dropped explicitly via
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<function>sd_bus_track_remove_name()</function> or implicitly because the peer disconnected from the bus. The final
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argument <parameter>userdata</parameter> may be used to attach a generic user data pointer to the object. This
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pointer is passed to the handler callback when it is invoked.</para>
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<para><function>sd_bus_track_ref()</function> creates a new reference to a bus peer tracking object. This object
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will not be destroyed until <function>sd_bus_track_unref()</function> has been called as many times plus once
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more. Once the reference count has dropped to zero, the specified object cannot be used anymore, further calls to
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<function>sd_bus_track_ref()</function> or <function>sd_bus_track_unref()</function> on the same object are
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illegal.</para>
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<para><function>sd_bus_track_unref()</function> destroys a reference to a bus peer tracking object.</para>
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<para><function>sd_bus_track_unrefp()</function> is similar to <function>sd_bus_track_unref()</function> but takes
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a pointer to a pointer to an <type>sd_bus_track</type> object. This call is useful in conjunction with GCC's and
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LLVM's <ulink url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up Variable
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Attribute</ulink>. Note that this function is defined as inline function.</para>
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<para><function>sd_bus_track_ref()</function>, <function>sd_bus_track_unref()</function> and
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<function>sd_bus_track_unrefp()</function> execute no operation if the passed in bus peer tracking object is
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<constant>NULL</constant>.</para>
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<para>Bus peer tracking objects may exist in two modes: by default they operate in non-recursive mode, but may
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optionally be switched into recursive mode. If operating in the default non-recursive mode a peer is either tracked
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or not tracked. In this mode invoking <function>sd_bus_track_add_name()</function> multiple times in a row for the
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same peer is fully equivalent to calling it just once, as the call adds the peer to the set of tracked peers if
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necessary, and executes no operation if the peer is already being tracked. A single invocation of
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<function>sd_bus_track_remove_name()</function> removes the reference on the peer again, regardless how many times
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<function>sd_bus_track_add_name()</function> was called before. If operating in recursive mode, the number of times
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<function>sd_bus_track_add_name()</function> is invoked for the same peer name is counted and
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<function>sd_bus_track_remove_name()</function> must be called the same number of times before the peer is not
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tracked anymore, with the exception when the tracked peer vanishes from the bus, in which case the count is
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irrelevant and the tracking of the specific peer is immediately
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removed. <function>sd_bus_track_get_recursive()</function> may be used to determine whether the bus peer tracking
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object is operating in recursive mode. <function>sd_bus_track_set_recursive()</function> may be used to enable or
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disable recursive mode. By default a bus peer tracking object operates in non-recursive mode, and
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<function>sd_bus_track_get_recursive()</function> for a newly allocated object hence returns a value equal to
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zero. Use <function>sd_bus_track_set_recursive()</function> to enable recursive mode, right after allocation. It
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takes a boolean argument to enable or disable recursive mode. Note that tracking objects for which
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<function>sd_bus_track_add_name()</function> was already invoked at least once (and which hence track already one
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or more peers) may not be switched from recursive to non-recursive mode anymore.</para>
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<para><function>sd_bus_track_get_bus()</function> returns the bus object the bus peer tracking object belongs
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to. It returns the bus object initially passed to <function>sd_bus_track_new()</function> when the object was
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allocated.</para>
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<para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer set on the bus peer
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tracking object at the time of creation using <function>sd_bus_track_new()</function> or at a later time, using
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<function>sd_bus_track_set_userdata()</function>.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, <function>sd_bus_track_new()</function> and <function>sd_bus_track_set_recursive()</function>
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return 0 or a positive integer. On failure, they return a negative errno-style error code.</para>
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<para><function>sd_bus_track_ref()</function> always returns the argument.</para>
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<para><function>sd_bus_track_unref()</function> always returns <constant>NULL</constant>.</para>
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<para><function>sd_bus_track_get_recursive()</function> returns 0 if non-recursive mode is selected (default), and
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greater than 0 if recursive mode is selected. On failure a negative errno-style error code is returned.</para>
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<para><function>sd_bus_track_get_bus()</function> returns the bus object associated to the bus peer tracking
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object.</para>
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<para><function>sd_bus_track_get_userdata()</function> returns the generic user data pointer associated with the
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bus peer tracking object. <function>sd_bus_track_set_userdata()</function> returns the previous user data pointer
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set.</para>
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</refsect1>
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<refsect1>
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<title>Reference ownership</title>
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<para>The <function>sd_bus_track_new()</function> function creates a new object and the caller owns the sole
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reference. When not needed anymore, this reference should be destroyed with
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<function>sd_bus_track_unref()</function>.
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</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EBUSY</constant></term>
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<listitem><para>Bus peers have already been added to the bus peer tracking object and
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<function>sd_bus_track_set_recursive()</function> was called to change tracking mode.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>Specified parameter is invalid
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(<constant>NULL</constant> in case of output
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parameters).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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<citerefentry><refentrytitle>sd_bus_track_add_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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