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1004b2c7bc
Also extend the memory management description of sd-bus highlighting the effect of "floating" slot objects a bit.
119 lines
5.0 KiB
XML
119 lines
5.0 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//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_slot_set_floating">
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<refentryinfo>
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<title>sd_bus_slot_set_floating</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_slot_set_floating</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_slot_set_floating</refname>
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<refname>sd_bus_slot_get_floating</refname>
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<refpurpose>Control whether a bus slot object is "floating".</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_slot_set_floating</function></funcdef>
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<paramdef>sd_bus_slot *<parameter>bus</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>int <function>sd_bus_slot_get_floating</function></funcdef>
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<paramdef>sd_bus_slot *<parameter>slot</parameter></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_slot_set_floating()</function> controls whether the specified bus slot object
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<parameter>slot</parameter> shall be "floating" or not. A floating bus slot object's lifetime is bound to the
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lifetime of the bus object it is associated with, meaning that it remains allocated as long as the bus object
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itself and is freed automatically when the bus object is freed. Regular (i.e. non-floating) bus slot objects keep
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the bus referenced, hence the bus object remains allocated at least as long as there remains at least one
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referenced bus slot object around. The floating state hence controls the direction of referencing between the bus
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object and the bus slot objects: if floating the bus pins the the bus slot, and otherwise the bus slot pins the bus
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objects. Use <function>sd_bus_slot_set_floating()</function> to switch between both modes: if the
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<parameter>b</parameter> parameter is zero, the slot object is considered floating, otherwise it is made a regular
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(non-floating) slot object.</para>
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<para>Bus slot objects may be allocated with calls such as
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<citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If the
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<parameter>slot</parameter> of these functions is non-<constant>NULL</constant> the slot object will be of the
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regular kind (i.e. non-floating), otherwise it will be created floating. With
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<function>sd_bus_slot_set_floating()</function> a bus slot object allocated as regular can be converted into a
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floating object and back. This is particularly useful for creating a bus slot object, then changing parameters of
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it, and then turning it into a floating object, whose lifecycle is managed by the bus object.</para>
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<para><function>sd_bus_slot_get_floating()</function> returns the current floating state of the specified bus slot
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object. It returns negative on error, zero if the bus slot object is a regular (non-floating) object and positive
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otherwise.</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, these functions return 0 or a positive integer. On failure, they return a negative errno-style
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error code.</para>
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</refsect1>
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<refsect1>
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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>-ECHILD</constant></term>
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<listitem><para>The bus connection has been created in a different process.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ESTALE</constant></term>
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<listitem><para>The bus object the specified bus slot object is associated with has already been freed, and
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hence no change in the floating state can be made anymore.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para><function>sd_bus_slot_set_floating()</function> and <function>sd_bus_slot_get_floating()</function> are
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available as a shared library, which can be compiled and linked to with the
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<constant>libsystemd</constant> <citerefentry
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project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
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</refsect1>
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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_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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