man/sd_bus_track_add_name.xml

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  10   Copyright 2016 Lennart Poettering
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  25
  26 <refentry id="sd_bus_track_add_name">
  27
  28   <refentryinfo>
  29     <title>sd_bus_track_add_name</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>Developer</contrib>
  35         <firstname>Lennart</firstname>
  36         <surname>Poettering</surname>
  37         <email>lennart@poettering.net</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_bus_track_add_name</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_bus_track_add_name</refname>
  49     <refname>sd_bus_track_add_sender</refname>
  50     <refname>sd_bus_track_remove_name</refname>
  51     <refname>sd_bus_track_remove_sender</refname>
  52     <refname>sd_bus_track_count</refname>
  53     <refname>sd_bus_track_count_sender</refname>
  54     <refname>sd_bus_track_count_name</refname>
  55     <refname>sd_bus_track_contains</refname>
  56     <refname>sd_bus_track_first</refname>
  57     <refname>sd_bus_track_next</refname>
  58
  59     <refpurpose>Add, remove and retrieve bus peers tracked in a bus peer tracking object</refpurpose>
  60   </refnamediv>
  61
  62   <refsynopsisdiv>
  63     <funcsynopsis>
  64       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  65
  66       <funcprototype>
  67         <funcdef>int <function>sd_bus_track_add_name</function></funcdef>
  68         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  69         <paramdef>const char* <parameter>name</parameter></paramdef>
  70       </funcprototype>
  71
  72       <funcprototype>
  73         <funcdef>int <function>sd_bus_track_add_sender</function></funcdef>
  74         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  75         <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
  76       </funcprototype>
  77
  78       <funcprototype>
  79         <funcdef>int <function>sd_bus_track_remove_name</function></funcdef>
  80         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  81         <paramdef>const char* <parameter>name</parameter></paramdef>
  82       </funcprototype>
  83
  84       <funcprototype>
  85         <funcdef>int <function>sd_bus_track_remove_sender</function></funcdef>
  86         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  87         <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
  88       </funcprototype>
  89
  90       <funcprototype>
  91         <funcdef>unsigned <function>sd_bus_track_count</function></funcdef>
  92         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  93       </funcprototype>
  94
  95       <funcprototype>
  96         <funcdef>int <function>sd_bus_track_count_name</function></funcdef>
  97         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
  98         <paramdef>const char* <parameter>name</parameter></paramdef>
  99       </funcprototype>
 100
 101       <funcprototype>
 102         <funcdef>int <function>sd_bus_track_count_sender</function></funcdef>
 103         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
 104         <paramdef>sd_bus_message* <parameter>message</parameter></paramdef>
 105       </funcprototype>
 106
 107       <funcprototype>
 108         <funcdef>int <function>sd_bus_track_contains</function></funcdef>
 109         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
 110         <paramdef>const char* <parameter>name</parameter></paramdef>
 111       </funcprototype>
 112
 113       <funcprototype>
 114         <funcdef>const char* <function>sd_bus_track_first</function></funcdef>
 115         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
 116       </funcprototype>
 117
 118       <funcprototype>
 119         <funcdef>const char* <function>sd_bus_track_next</function></funcdef>
 120         <paramdef>sd_bus_track* <parameter>t</parameter></paramdef>
 121       </funcprototype>
 122
 123     </funcsynopsis>
 124   </refsynopsisdiv>
 125
 126   <refsect1>
 127     <title>Description</title>
 128
 129     <para><function>sd_bus_track_add_name()</function> adds a peer to track to a bus peer tracking object. The first
 130     argument should refer to a bus peer tracking object created with
 131     <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, the second
 132     name should refer to a D-Bus peer name to track, either in unique or well-known service format. If the name is not
 133     tracked yet it will be added to the list of names to track. If it already is being tracked and non-recursive mode
 134     is enabled, no operation is executed by this call. If recursive mode is enabled a per-name counter is increased by
 135     one each time this call is invoked, and <function>sd_bus_track_remove_name()</function> has to be called as many
 136     times as <function>sd_bus_track_add_name()</function> was invoked before in order to stop tracking of the name. Use
 137     <citerefentry><refentrytitle>sd_bus_track_set_recursive</refentrytitle><manvolnum>3</manvolnum></citerefentry> to
 138     switch from the default non-recursive mode to recursive mode, or back. Note that the specified name is tracked as
 139     it is, well-known names are not resolved to unique names by this call. Note that multiple bus peer tracking objects
 140     may track the same name.</para>
 141
 142     <para><function>sd_bus_track_remove_name()</function> undoes the effect of
 143     <function>sd_bus_track_add_name()</function> and removes a bus peer name from the list of peers to watch. Depending
 144     on whether non-recursive or recursive mode is enabled for the bus peer tracking object this call will either remove
 145     the name fully from the tracking object, or will simply decrement the per-name counter by one, removing the name
 146     only when the counter reaches zero (see above). Note that a bus peer disconnecting from the bus will implicitly
 147     remove its names fully from the bus peer tracking object, regardless of the current per-name counter.</para>
 148
 149     <para><function>sd_bus_track_add_sender()</function> and <function>sd_bus_track_remove_sender()</function> are
 150     similar to <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_remove_name()</function> but
 151     take a bus message as argument. The sender of this bus message is determined and added to/removed from the bus peer
 152     tracking object. As messages always originate from unique names, and never from well-known names this means that
 153     this call will effectively only add unique names to the bus peer tracking object.</para>
 154
 155     <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked by the
 156     specified bus peer tracking object. Note that this function always returns the actual number of names tracked, and
 157     hence if <function>sd_bus_track_add_name()</function> has been invoked multiple times for the same name it is only
 158     counted as one, regardless if recursive mode is used or not.</para>
 159
 160     <para><function>sd_bus_track_count_name()</function> returns the current per-name counter for the specified
 161     name. If non-recursive mode is used this returns either 1 or 0, depending on whether the specified name has been
 162     added to the tracking object before, or not. If recursive mode has been enabled, values larger than 1 may be
 163     returned too, in case <function>sd_bus_track_add_name()</function> has been called multiple times for the same
 164     name.</para>
 165
 166     <para><function>sd_bus_track_count_sender()</function> is similar to
 167     <function>sd_bus_track_count_name()</function>, but takes a bus message object and returns the per-name counter
 168     matching the sender of the message.</para>
 169
 170     <para><function>sd_bus_track_contains()</function> may be used to determine whether the specified name has been
 171     added at least once to the specified bus peer tracking object.</para>
 172
 173     <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> may be used to
 174     enumerate all names currently being tracked by the passed bus peer tracking
 175     object. <function>sd_bus_track_first()</function> returns the first entry in the object, and resets an internally
 176     maintained read index. Each subsequent invocation of <function>sd_bus_track_next()</function> returns the next name
 177     contained in the bus object. If the end is reached <constant>NULL</constant> is returned. If no names have been
 178     added to the object yet <function>sd_bus_track_first()</function> will return <constant>NULL</constant>
 179     immediately. The order in which names are returned is undefined; in particular which name is considered the first
 180     returned is not defined. If recursive mode is enabled and the same name has been added multiple times to the bus
 181     peer tracking object it is only returned once by this enumeration. If new names are added to or existing names
 182     removed from the bus peer tracking object while it is being enumerated the enumeration ends on the next invocation
 183     of <function>sd_bus_track_next()</function> as <constant>NULL</constant> is returned.</para>
 184   </refsect1>
 185
 186   <refsect1>
 187     <title>Return Value</title>
 188
 189     <para>On success, <function>sd_bus_track_add_name()</function> and <function>sd_bus_track_add_sender()</function>
 190     return 0 if the specified name has already been added to the bus peer tracking object before and positive if it
 191     hasn't. On failure, they return a negative errno-style error code.</para>
 192
 193     <para><function>sd_bus_track_remove_name()</function> and <function>sd_bus_track_remove_sender()</function> return
 194     positive if the specified name was previously tracked by the bus peer tracking object and has now been removed. In
 195     non-recursive mode, 0 is returned if the specified name was not being tracked yet. In recursive mode
 196     <constant>-EUNATCH</constant> is returned in this case. On failure, they return a negative errno-style error
 197     code.</para>
 198
 199     <para><function>sd_bus_track_count()</function> returns the number of names currently being tracked, or 0 on
 200     failure.</para>
 201
 202     <para><function>sd_bus_track_count_name()</function> and <function>sd_bus_track_count_sender()</function> return
 203     the current per-name counter for the specified name or the sender of the specified message. Zero is returned for
 204     names that are not being tracked yet, a positive value for names added at least once. Larger values than 1 are only
 205     returned in recursive mode. On failure, a negative errno-style error code is returned.</para>
 206
 207     <para><function>sd_bus_track_contains()</function> returns the passed name if it exists in the bus peer tracking
 208     object. On failure, and if the name has not been added yet <constant>NULL</constant> is returned.</para>
 209
 210     <para><function>sd_bus_track_first()</function> and <function>sd_bus_track_next()</function> return the first/next
 211     name contained in the bus peer tracking object, and <constant>NULL</constant> if the end of the enumeration is
 212     reached and on error.</para>
 213   </refsect1>
 214
 215   <refsect1>
 216     <title>Errors</title>
 217
 218     <para>Returned errors may indicate the following problems:</para>
 219
 220     <variablelist>
 221
 222       <varlistentry>
 223         <term><constant>-EUNATCH</constant></term>
 224
 225         <listitem><para><function>sd_bus_track_remove_name()</function> or
 226         <function>sd_bus_track_remove_sender()</function> have been invoked for a name not previously added to the bus
 227         peer object.</para></listitem>
 228       </varlistentry>
 229
 230       <varlistentry>
 231         <term><constant>-EINVAL</constant></term>
 232
 233         <listitem><para>Specified parameter is invalid.</para></listitem>
 234       </varlistentry>
 235
 236       <varlistentry>
 237         <term><constant>-ENOMEM</constant></term>
 238
 239         <listitem><para>Memory allocation failed.</para></listitem>
 240       </varlistentry>
 241
 242     </variablelist>
 243   </refsect1>
 244
 245   <refsect1>
 246     <title>Notes</title>
 247
 248     <para><function>sd_bus_track_add_name()</function> and the other calls described here are available as a shared library,
 249     which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry
 250     project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para>
 251   </refsect1>
 252
 253   <refsect1>
 254     <title>See Also</title>
 255
 256     <para>
 257       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 258       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 259       <citerefentry><refentrytitle>sd_bus_track_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 260     </para>
 261   </refsect1>
 262
 263 </refentry>