1SD_BUS_ADD_OBJECT_VTABLE(3)sd_bus_add_object_vtableSD_BUS_ADD_OBJECT_VTABLE(3)
2
3
4

NAME

6       sd_bus_add_object_vtable, sd_bus_add_fallback_vtable,
7       SD_BUS_VTABLE_START, SD_BUS_VTABLE_END,
8       SD_BUS_METHOD_WITH_NAMES_OFFSET, SD_BUS_METHOD_WITH_NAMES,
9       SD_BUS_METHOD_WITH_OFFSET, SD_BUS_METHOD, SD_BUS_SIGNAL_WITH_NAMES,
10       SD_BUS_SIGNAL, SD_BUS_WRITABLE_PROPERTY, SD_BUS_PROPERTY, SD_BUS_PARAM
11       - Declare properties and methods for a D-Bus path
12

SYNOPSIS

14       #include <systemd/sd-bus-vtable.h>
15
16
17       typedef int (*sd_bus_message_handler_t)(sd_bus_message *m,
18                                               void *userdata,
19                                               sd_bus_error *ret_error);
20
21       typedef int (*sd_bus_property_get_t)(sd_bus *bus, const char *path,
22                                            const char *interface,
23                                            const char *property,
24                                            sd_bus_message *reply,
25                                            void *userdata,
26                                            sd_bus_error *ret_error);
27
28       typedef int (*sd_bus_property_set_t)(sd_bus *bus, const char *path,
29                                            const char *interface,
30                                            const char *property,
31                                            sd_bus_message *value,
32                                            void *userdata,
33                                            sd_bus_error *ret_error);
34
35       typedef int (*sd_bus_object_find_t)(const char *path,
36                                           const char *interface,
37                                           void *userdata, void **ret_found,
38                                           sd_bus_error *ret_error);
39
40       int sd_bus_add_object_vtable(sd_bus *bus, sd_bus_slot **slot,
41                                    const char *path, const char *interface,
42                                    const sd_bus_vtable *vtable,
43                                    void *userdata);
44
45       int sd_bus_add_fallback_vtable(sd_bus *bus, sd_bus_slot **slot,
46                                      const char *prefix,
47                                      const char *interface,
48                                      const sd_bus_vtable *vtable,
49                                      sd_bus_object_find_t find,
50                                      void *userdata);
51
52       SD_BUS_VTABLE_START(flags)
53
54       SD_BUS_VTABLE_END
55
56       SD_BUS_METHOD_WITH_NAMES_OFFSET( member, signature, in_names, result,
57       out_names, handler, offset, flags)
58
59       SD_BUS_METHOD_WITH_NAMES( member, signature, in_names, result,
60       out_names, handler, flags)
61
62       SD_BUS_METHOD_WITH_OFFSET( member, signature, result, handler, offset,
63       flags)
64
65       SD_BUS_METHOD( member, signature, result, handler, flags)
66
67       SD_BUS_SIGNAL_WITH_NAMES( member, signature, names, flags)
68
69       SD_BUS_SIGNAL( member, signature, flags)
70
71       SD_BUS_WRITABLE_PROPERTY( member, signature, get, set, offset, flags)
72
73       SD_BUS_PROPERTY( member, signature, get, offset, flags)
74
75       SD_BUS_PARAM(name)
76

DESCRIPTION

78       sd_bus_add_object_vtable() is used to declare attributes for the path
79       object path path connected to the bus connection bus under the
80       interface interface. The table vtable may contain property declarations
81       using SD_BUS_PROPERTY() or SD_BUS_WRITABLE_PROPERTY(), method
82       declarations using SD_BUS_METHOD(), SD_BUS_METHOD_WITH_NAMES(),
83       SD_BUS_METHOD_WITH_OFFSET(), or SD_BUS_METHOD_WITH_NAMES_OFFSET(), and
84       signal declarations using SD_BUS_SIGNAL_WITH_NAMES() or
85       SD_BUS_SIGNAL(), see below. The userdata parameter contains a pointer
86       that will be passed to various callback functions. It may be specified
87       as NULL if no value is necessary.
88
89       sd_bus_add_fallback_vtable() is similar to sd_bus_add_object_vtable(),
90       but is used to register "fallback" attributes. When looking for an
91       attribute declaration, bus object paths registered with
92       sd_bus_add_object_vtable() are checked first. If no match is found, the
93       fallback vtables are checked for each prefix of the bus object path,
94       i.e. with the last slash-separated components successively removed.
95       This allows the vtable to be used for an arbitrary number of
96       dynamically created objects.
97
98       Parameter find is a function which is used to locate the target object
99       based on the bus object path path. It must return 1 and set the
100       ret_found output parameter if the object is found, return 0 if the
101       object was not found, and return a negative errno-style error code or
102       initialize the error structure ret_error on error. The pointer passed
103       in ret_found will be used as the userdata parameter for the callback
104       functions (offset by the offset offsets as specified in the vtable
105       entries).
106
107       For both functions, a match slot is created internally. If the output
108       parameter slot is NULL, a "floating" slot object is created, see
109       sd_bus_slot_set_floating(3). Otherwise, a pointer to the slot object is
110       returned. In that case, the reference to the slot object should be
111       dropped when the vtable is not needed anymore, see
112       sd_bus_slot_unref(3).
113
114   The sd_bus_vtable array
115       The array consists of the structures of type sd_bus_vtable, but it
116       should never be filled in manually, but through one of the following
117       macros:
118
119       SD_BUS_VTABLE_START(), SD_BUS_VTABLE_END
120           Those must always be the first and last element.
121
122       SD_BUS_METHOD_WITH_NAMES_OFFSET(), SD_BUS_METHOD_WITH_NAMES(),
123       SD_BUS_METHOD_WITH_OFFSET(), SD_BUS_METHOD()
124           Declare a D-Bus method with the name member, parameter signature
125           signature, result signature result. Parameters in_names and
126           out_names specify the argument names of the input and output
127           arguments in the function signature. The handler function handler
128           must be of type sd_bus_message_handler_t. It will be called to
129           handle the incoming messages that call this method. It receives a
130           pointer that is the userdata parameter passed to the registration
131           function offset by offset bytes. This may be used to pass pointers
132           to different fields in the same data structure to different methods
133           in the same vtable.  in_names and out_names should be created using
134           the SD_BUS_PARAM() macro, see below. Parameter flags is a
135           combination of flags, see below.
136
137           SD_BUS_METHOD_WITH_NAMES(), SD_BUS_METHOD_WITH_OFFSET(), and
138           SD_BUS_METHOD() are variants which specify zero offset (userdata
139           parameter is passed with no change), leave the names unset (i.e. no
140           parameter names), or both.
141
142       SD_BUS_SIGNAL_WITH_NAMES(), SD_BUS_SIGNAL()
143           Declare a D-Bus signal with the name member, parameter signature
144           signature, and argument names names.  names should be created using
145           the SD_BUS_PARAM() macro, see below. Parameter flags is a
146           combination of flags, see below.
147
148           Equivalent to SD_BUS_SIGNAL_WITH_NAMES() with the names parameter
149           unset (i.e. no parameter names).
150
151       SD_BUS_WRITABLE_PROPERTY(), SD_BUS_PROPERTY()
152           Declare a D-Bus property with the name member and value signature
153           signature. Parameters get and set are the getter and setter
154           methods. They are called with a pointer that is the userdata
155           parameter passed to the registration function offset by offset
156           bytes. This may be used pass pointers to different fields in the
157           same data structure to different setters and getters in the same
158           vtable. Parameter flags is a combination of flags, see below.
159
160           The setter and getter methods may be omitted (specified as NULL),
161           if the property has one of the basic types or "as" in case of
162           read-only properties. In those cases, the userdata and offset
163           parameters must together point to valid variable of the
164           corresponding type. A default setter and getters will be provided,
165           which simply copy the argument between this variable and the
166           message.
167
168           SD_BUS_PROPERTY() is used to define a read-only property.
169
170       SD_BUS_PARAM()
171           Parameter names should be wrapped in this macro, see the example
172           below.
173
174   Flags
175       The flags parameter is used to specify a combination of D-Bus
176       annotations[1].
177
178       SD_BUS_VTABLE_DEPRECATED
179           Mark this vtable entry as deprecated using the
180           org.freedesktop.DBus.Deprecated annotation in introspection data.
181           If specified for SD_BUS_VTABLE_START(), the annotation is applied
182           to the enclosing interface.
183
184       SD_BUS_VTABLE_HIDDEN
185           Make this vtable entry hidden. It will not be shown in
186           introspection data. If specified for SD_BUS_VTABLE_START(), all
187           entries in the array are hidden.
188
189       SD_BUS_VTABLE_UNPRIVILEGED
190           Mark this vtable entry as unprivileged. If not specified, the
191           org.freedesktop.systemd1.Privileged annotation with value "true"
192           will be shown in introspection data.
193
194       SD_BUS_VTABLE_METHOD_NO_REPLY
195           Mark his vtable entry as a method that will not return a reply
196           using the org.freedesktop.DBus.Method.NoReply annotation in
197           introspection data.
198
199       SD_BUS_VTABLE_PROPERTY_CONST, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE,
200       SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION
201           Those three flags correspond to different values of the
202           org.freedesktop.DBus.Property.EmitsChangedSignal annotation, which
203           specifies whether the
204           org.freedesktop.DBus.Properties.PropertiesChanged signal is emitted
205           whenever the property changes.  SD_BUS_VTABLE_PROPERTY_CONST
206           corresponds to const and means that the property never changes
207           during the lifetime of the object it belongs to, so no signal needs
208           to be emitted.  SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE corresponds to
209           true and means that the signal is emitted.
210           SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION corresponds to
211           invalidates and means that the signal is emitted, but the value is
212           not included in the signal.
213
214       SD_BUS_VTABLE_PROPERTY_EXPLICIT
215           Mark this vtable property entry as requiring explicit request to
216           for the value to be shown (generally because the value is large or
217           slow to calculate). This entry cannot be combined with
218           SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE, and will not be shown in
219           property listings by default (e.g.  busctl introspect). This
220           corresponds to the org.freedesktop.systemd1.Explicit annotation in
221           introspection data.
222

EXAMPLES

224       Example 1. Create a simple listener on the bus
225
226           #include <errno.h>
227           #include <stdbool.h>
228           #include <stddef.h>
229           #include <stdlib.h>
230           #include <stdio.h>
231           #include <systemd/sd-bus.h>
232
233           #define _cleanup_(f) __attribute__((cleanup(f)))
234
235           typedef struct object {
236             char *name;
237             uint32_t number;
238           } object;
239
240           static int method(sd_bus_message *m, void *userdata, sd_bus_error *error) {
241             printf("Got called with userdata=%p\n", userdata);
242             return 1;
243           }
244
245           static const sd_bus_vtable vtable[] = {
246                   SD_BUS_VTABLE_START(0),
247                   SD_BUS_METHOD(
248                       "Method1", "s", "s", method, 0),
249                   SD_BUS_METHOD_WITH_NAMES_OFFSET(
250                       "Method2",
251                       "so", SD_BUS_PARAM(string) SD_BUS_PARAM(path),
252                       "s", SD_BUS_PARAM(returnstring),
253                       method, offsetof(object, number),
254                       SD_BUS_VTABLE_DEPRECATED),
255                   SD_BUS_WRITABLE_PROPERTY(
256                       "AutomaticStringProperty", "s", NULL, NULL,
257                       offsetof(object, name),
258                       SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
259                   SD_BUS_WRITABLE_PROPERTY(
260                       "AutomaticIntegerProperty", "u", NULL, NULL,
261                       offsetof(object, number),
262                       SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
263                   SD_BUS_VTABLE_END
264           };
265
266           #define check(x) ({                             \
267             int r = x;                                    \
268             errno = r < 0 ? -r : 0;                       \
269             printf(#x ": %m\n");                          \
270             if (r < 0)                                    \
271               return EXIT_FAILURE;                        \
272             })
273
274           int main(int argc, char **argv) {
275             _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
276
277             sd_bus_default(&bus);
278
279             object object = { .number = 666 };
280             check((object.name = strdup("name")) != NULL);
281
282             check(sd_bus_add_object_vtable(bus, NULL, "/object",
283                                            "org.freedesktop.systemd.VtableExample",
284                                            vtable,
285                                            &object));
286
287             for (;;) {
288               check(sd_bus_wait(bus, UINT64_MAX));
289               check(sd_bus_process(bus, NULL));
290             }
291
292             free(object.name);
293
294             return 0;
295           }
296
297       This creates a simple client on the bus (the user bus, when run as
298       normal user). We may use the D-Bus
299       org.freedesktop.DBus.Introspectable.Introspect call to acquire the XML
300       description of the interface:
301
302           <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
303           "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
304           <node>
305            <interface name="org.freedesktop.DBus.Peer">
306             <method name="Ping"/>
307             <method name="GetMachineId">
308              <arg type="s" name="machine_uuid" direction="out"/>
309             </method>
310            </interface>
311            <interface name="org.freedesktop.DBus.Introspectable">
312             <method name="Introspect">
313              <arg name="data" type="s" direction="out"/>
314             </method>
315            </interface>
316            <interface name="org.freedesktop.DBus.Properties">
317             <method name="Get">
318              <arg name="interface" direction="in" type="s"/>
319              <arg name="property" direction="in" type="s"/>
320              <arg name="value" direction="out" type="v"/>
321             </method>
322             <method name="GetAll">
323              <arg name="interface" direction="in" type="s"/>
324              <arg name="properties" direction="out" type="a{sv}"/>
325             </method>
326             <method name="Set">
327              <arg name="interface" direction="in" type="s"/>
328              <arg name="property" direction="in" type="s"/>
329              <arg name="value" direction="in" type="v"/>
330             </method>
331             <signal name="PropertiesChanged">
332              <arg type="s" name="interface"/>
333              <arg type="a{sv}" name="changed_properties"/>
334              <arg type="as" name="invalidated_properties"/>
335             </signal>
336            </interface>
337            <interface name="org.freedesktop.systemd.VtableExample">
338             <method name="Method1">
339              <arg type="s" direction="in"/>
340              <arg type="s" direction="out"/>
341             </method>
342             <method name="Method2">
343              <arg type="s" name="string" direction="in"/>
344              <arg type="o" name="path" direction="in"/>
345              <arg type="s" name="returnstring" direction="out"/>
346              <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
347             </method>
348             <property name="AutomaticStringProperty" type="s" access="readwrite">
349             </property>
350             <property name="AutomaticIntegerProperty" type="u" access="readwrite">
351              <annotation name="org.freedesktop.DBus.Property.EmitsChangedSignal" value="invalidates"/>
352             </property>
353            </interface>
354           </node>
355
356

RETURN VALUE

358       On success, sd_bus_add_object_vtable and sd_bus_add_fallback_vtable
359       calls return 0 or a positive integer. On failure, they return a
360       negative errno-style error code.
361
362   Errors
363       Returned errors may indicate the following problems:
364
365       -EINVAL
366           One of the required parameters is NULL or invalid. A reserved D-Bus
367           interface was passed as the interface parameter.
368
369       -ENOPKG
370           The bus cannot be resolved.
371
372       -ECHILD
373           The bus was created in a different process.
374
375       -ENOMEM
376           Memory allocation failed.
377
378       -EPROTOTYPE
379           sd_bus_add_object_vtable and sd_bus_add_fallback_vtable have been
380           both called for the same bus object path, which is not allowed.
381
382       -EEXIST
383           This vtable has already been registered for this interface and
384           path.
385

NOTES

387       These APIs are implemented as a shared library, which can be compiled
388       and linked to with the libsystemd pkg-config(1) file.
389

SEE ALSO

391       sd-bus(3), busctl(1)
392

NOTES

394        1. D-Bus annotations
395           https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format
396
397
398
399systemd 243                                        SD_BUS_ADD_OBJECT_VTABLE(3)
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