# sd_bus_add_object

## NAME



           sd_bus_add_object, sd_bus_add_fallback, sd_bus_add_object_vtable,
           sd_bus_add_fallback_vtable, sd_bus_add_filter,
           SD_BUS_VTABLE_CAPABILITY, SD_BUS_VTABLE_START, SD_BUS_VTABLE_END,
           SD_BUS_METHOD_WITH_NAMES_OFFSET, SD_BUS_METHOD_WITH_NAMES,
           SD_BUS_METHOD_WITH_OFFSET, SD_BUS_METHOD,
           SD_BUS_SIGNAL_WITH_NAMES, SD_BUS_SIGNAL, SD_BUS_WRITABLE_PROPERTY,
           SD_BUS_PROPERTY, SD_BUS_PARAM - Declare properties and methods for
           a D-Bus path
    


## SYNOPSIS



           **#include <systemd/sd-bus-vtable.h>**
    
           **typedef int (*sd_bus_message_handler_t)(sd_bus_message ***_m_**,**
                                                   **void ***_userdata_**,**
                                                   **sd_bus_error ***_ret_error_**);**
    
           **typedef int (*sd_bus_property_get_t)(sd_bus ***_bus_**,**
                                                **const char ***_path_**,**
                                                **const char ***_interface_**,**
                                                **const char ***_property_**,**
                                                **sd_bus_message ***_reply_**,**
                                                **void ***_userdata_**,**
                                                **sd_bus_error ***_ret_error_**);**
    
           **typedef int (*sd_bus_property_set_t)(sd_bus ***_bus_**,**
                                                **const char ***_path_**,**
                                                **const char ***_interface_**,**
                                                **const char ***_property_**,**
                                                **sd_bus_message ***_value_**,**
                                                **void ***_userdata_**,**
                                                **sd_bus_error ***_ret_error_**);**
    
           **typedef int (*sd_bus_object_find_t)(const char ***_path_**,**
                                               **const char ***_interface_**,**
                                               **void ***_userdata_**,**
                                               **void ****_ret_found_**,**
                                               **sd_bus_error ***_ret_error_**);**
    
           **int sd_bus_add_object(sd_bus ***_bus_**, sd_bus_slot ****_slot_**,**
                                 **const char ***_path_**,**
                                 **sd_bus_message_handler_t** _callback_**,**
                                 **void ***_userdata_**);**
    
           **int sd_bus_add_fallback(sd_bus ***_bus_**, sd_bus_slot ****_slot_**,**
                                   **const char ***_path_**,**
                                   **sd_bus_message_handler_t** _callback_**,**
                                   **void ***_userdata_**);**
    
           **int sd_bus_add_object_vtable(sd_bus ***_bus_**, sd_bus_slot ****_slot_**,**
                                        **const char ***_path_**,**
                                        **const char ***_interface_**,**
                                        **const sd_bus_vtable ***_vtable_**,**
                                        **void ***_userdata_**);**
    
           **int sd_bus_add_fallback_vtable(sd_bus ***_bus_**, sd_bus_slot ****_slot_**,**
                                          **const char ***_prefix_**,**
                                          **const char ***_interface_**,**
                                          **const sd_bus_vtable ***_vtable_**,**
                                          **sd_bus_object_find_t** _find_**,**
                                          **void ***_userdata_**);**
    
           **int sd_bus_add_filter(sd_bus ***_bus_**, sd_bus_slot ****_slot_**,**
                                 **sd_bus_message_handler_t** _callback_**,**
                                 **void ***_userdata_**);**
    
           **SD_BUS_VTABLE_CAPABILITY(**_capability_**)**
    
           **SD_BUS_VTABLE_START(**_flags_**)**
    
           **SD_BUS_VTABLE_END**
    
           **SD_BUS_METHOD_WITH_ARGS_OFFSET(**_member_**,**_args_**,**_result_**,**_handler_**,**
           _offset_**,**_flags_**)**
    
           **SD_BUS_METHOD_WITH_ARGS(**_member_**,**_args_**,**_result_**,**_handler_**,**_flags_**)**
    
           **SD_BUS_METHOD_WITH_NAMES_OFFSET(**_member_**,**_signature_**,**_in_names_**,**
           _result_**,**_out_names_**,**_handler_**,**_offset_**,**_flags_**)**
    
           **SD_BUS_METHOD_WITH_NAMES(**_member_**,**_signature_**,**_in_names_**,**_result_**,**
           _out_names_**,**_handler_**,**_flags_**)**
    
           **SD_BUS_METHOD_WITH_OFFSET(**_member_**,**_signature_**,**_result_**,**_handler_**,**
           _offset_**,**_flags_**)**
    
           **SD_BUS_METHOD(**_member_**,**_signature_**,**_result_**,**_handler_**,**_flags_**)**
    
           **SD_BUS_SIGNAL_WITH_ARGS(**_member_**,**_args_**,**_flags_**)**
    
           **SD_BUS_SIGNAL_WITH_NAMES(**_member_**,**_signature_**,**_names_**,**_flags_**)**
    
           **SD_BUS_SIGNAL(**_member_**,**_signature_**,**_flags_**)**
    
           **SD_BUS_WRITABLE_PROPERTY(**_member_**,**_signature_**,**_get_**,**_set_**,**_offset_**,**
           _flags_**)**
    
           **SD_BUS_PROPERTY(**_member_**,**_signature_**,**_get_**,**_offset_**,**_flags_**)**
    
           **SD_BUS_PARAM(**_name_**)**
    
           **SD_BUS_ARGS(**_..._**)**
    
           **SD_BUS_RESULT(**_..._**)**
    
           **SD_BUS_NO_ARGS**
    
           **SD_BUS_NO_RESULT**
    


## DESCRIPTION



           **sd_bus_add_object_vtable()** is used to declare attributes for the
           object path _path_ connected to the bus connection _bus_ under the
           interface _interface_. The table _vtable_ may contain property
           declarations using **SD_BUS_PROPERTY()** or
           **SD_BUS_WRITABLE_PROPERTY()** , method declarations using
           **SD_BUS_METHOD()** , **SD_BUS_METHOD_WITH_NAMES()** ,
           **SD_BUS_METHOD_WITH_OFFSET()** , or **SD_BUS_METHOD_WITH_NAMES_OFFSET()** ,
           and signal declarations using **SD_BUS_SIGNAL_WITH_NAMES()** or
           **SD_BUS_SIGNAL()** , see below. The _userdata_ parameter contains a
           pointer that will be passed to various callback functions. It may
           be specified as **NULL** if no value is necessary. An interface can
           have any number of vtables attached to it.
    
           **sd_bus_add_fallback_vtable()** is similar to
           **sd_bus_add_object_vtable()** , but is used to register "fallback"
           attributes. When looking for an attribute declaration, bus object
           paths registered with **sd_bus_add_object_vtable()** are checked
           first. If no match is found, the fallback vtables are checked for
           each prefix of the bus object path, i.e. with the last
           slash-separated components successively removed. This allows the
           vtable to be used for an arbitrary number of dynamically created
           objects.
    
           Parameter _find_ is a function which is used to locate the target
           object based on the bus object path _path_. It must return **1** and set
           the _ret_found_ output parameter if the object is found, return **0** if
           the object was not found, and return a negative errno-style error
           code or initialize the error structure _ret_error_ on error. The
           pointer passed in _ret_found_ will be used as the _userdata_ parameter
           for the callback functions (offset by the _offset_ offsets as
           specified in the vtable entries).
    
           **sd_bus_add_object()** attaches a callback directly to the object
           path _path_. An object path can have any number of callbacks
           attached to it. Each callback is prepended to the list of
           callbacks which are always called in order.  **sd_bus_add_fallback()**
           is similar to **sd_bus_add_object()** but applies to fallback paths
           instead.
    
           **sd_bus_add_filter()** installs a callback that is invoked for each
           incoming D-Bus message. Filters can be used to handle logic common
           to all messages received by a service (e.g. authentication or
           authorization).
    
           When a request is received, any associated callbacks are called
           sequentially until a callback returns a non-zero integer. Return
           zero from a callback to give other callbacks the chance to process
           the request. Callbacks are called in the following order: first,
           global callbacks installed with **sd_bus_add_filter()** are called.
           Second, callbacks attached directly to the request object path are
           called, followed by any D-Bus method callbacks attached to the
           request object path, interface and member. Finally, the property
           callbacks attached to the request object path, interface and
           member are called. If the final callback returns zero, an error
           reply is sent back to the caller indicating no matching object for
           the request was found.
    
           Note that you can return a positive integer from a _method_ callback
           without immediately sending a reply. This informs sd-bus this
           callback will take responsibility for replying to the request
           without forcing the callback to produce a reply immediately. This
           allows a callback to perform any number of asynchronous operations
           required to construct a reply. However, if producing a reply takes
           too long, the method call will time out at the caller. This is
           only available to methods and not properties.
    
           If a callback was invoked to handle a request that expects a reply
           and the callback returns a negative value, the value is
           interpreted as a negative errno-style error code and sent back to
           the caller as a D-Bus error as if sd_bus_reply_method_errno(3) was
           called. Additionally, all callbacks take a sd_bus_error output
           parameter that can be used to provide more detailed error
           information. If _ret_error_ is set when the callback finishes, the
           corresponding D-Bus error is sent back to the caller as if
           sd_bus_reply_method_error(3) was called. Any error stored in
           _ret_error_ takes priority over any negative values returned by the
           same callback when determining which error to send back to the
           caller. Use sd_bus_error_set(3) or one of its variants to set
           _ret_error_ and return a negative integer from a callback with a
           single function call. To send an error reply after a callback has
           already finished, use sd_bus_reply_method_errno(3) or one of its
           variants.
    
           For all functions, a match slot is created internally. If the
           output parameter _slot_ is **NULL** , a "floating" slot object is
           created, see sd_bus_slot_set_floating(3). Otherwise, a pointer to
           the slot object is returned. In that case, the reference to the
           slot object should be dropped when the vtable is not needed
           anymore, see sd_bus_slot_unref(3).
    
       **The sd_bus_vtable array**
           The array consists of the structures of type sd_bus_vtable, but it
           should never be filled in manually, but through one of the
           following macros:
    
           **SD_BUS_VTABLE_START(**_flags_**)** , **SD_BUS_VTABLE_END**
               Those must always be the first and last element. The _flags_
               parameter can be used to set attributes that apply to the
               whole array; see the "Flags" section below.
    
           **SD_BUS_METHOD_WITH_ARGS_OFFSET()** , **SD_BUS_METHOD_WITH_ARGS()**
               Declare a D-Bus method with the name _member_ , arguments _args_
               and result _result_.  _args_ expects a sequence of argument
               type/name pairs wrapped in the **SD_BUS_ARGS()** macro. The
               elements at even indices in this list describe the types of
               the method's arguments. The method's parameter signature is
               the concatenation of all the string literals at even indices
               in _args_. If a method has no parameters, pass **SD_BUS_NO_ARGS** to
               _args_. The elements at uneven indices describe the names of the
               method's arguments.  _result_ expects a sequence of type/name
               pairs wrapped in the **SD_BUS_RESULT()** macro in the same format
               as **SD_BUS_ARGS()**. The method's result signature is the
               concatenation of all the string literals at even indices in
               _result_. If a method has no result, pass **SD_BUS_NO_RESULT** to
               _result_. Note that argument types are expected to be quoted
               string literals and argument names are expected to be unquoted
               string literals. See below for a complete example.
    
               The handler function _handler_ must be of type
               **sd_bus_message_handler_t**. It will be called to handle the
               incoming messages that call this method. It receives a pointer
               that is the _userdata_ parameter passed to the registration
               function offset by _offset_ bytes. This may be used to pass
               pointers to different fields in the same data structure to
               different methods in the same vtable. To send a reply from
               _handler_ , call sd_bus_reply_method_return(3) with the message
               the callback was invoked with. Parameter _flags_ is a
               combination of flags, see below.
    
               **SD_BUS_METHOD_WITH_ARGS()** is a shorthand for calling
               **SD_BUS_METHOD_WITH_ARGS_OFFSET()** with an offset of zero.
    
           **SD_BUS_METHOD_WITH_NAMES_OFFSET()** , **SD_BUS_METHOD_WITH_NAMES()** ,
           **SD_BUS_METHOD_WITH_OFFSET()** , **SD_BUS_METHOD()**
               Declare a D-Bus method with the name _member_ , parameter
               signature _signature_ , result signature _result_. Parameters
               _in_names_ and _out_names_ specify the argument names of the input
               and output arguments in the function signature.  _in_names_ and
               _out_names_ should be created using the **SD_BUS_PARAM()** macro,
               see below. In all other regards, this macro behaves exactly
               the same as **SD_BUS_METHOD_WITH_ARGS_OFFSET()**.
    
               **SD_BUS_METHOD_WITH_NAMES()** , **SD_BUS_METHOD_WITH_OFFSET()** , and
               **SD_BUS_METHOD()** are variants which specify zero offset
               (_userdata_ parameter is passed with no change), leave the names
               unset (i.e. no parameter names), or both.
    
               Prefer using **SD_BUS_METHOD_WITH_ARGS_OFFSET()** and
               **SD_BUS_METHOD_WITH_ARGS()** over these macros as they allow
               specifying argument types and names next to each other which
               is less error-prone than first specifying all argument types
               followed by specifying all argument names.
    
           **SD_BUS_SIGNAL_WITH_ARGS()**
               Declare a D-Bus signal with the name _member_ and arguments
               _args_.  _args_ expects a sequence of argument type/name pairs
               wrapped in the **SD_BUS_ARGS()** macro. The elements at even
               indices in this list describe the types of the signal's
               arguments. The signal's parameter signature is the
               concatenation of all the string literals at even indices in
               _args_. If a signal has no parameters, pass **SD_BUS_NO_ARGS** to
               _args_. The elements at uneven indices describe the names of the
               signal's arguments. Parameter _flags_ is a combination of flags.
               See below for a complete example.
    
           **SD_BUS_SIGNAL_WITH_NAMES()** , **SD_BUS_SIGNAL()**
               Declare a D-Bus signal with the name _member_ , parameter
               signature _signature_ , and argument names _names_.  _names_ should
               be created using the **SD_BUS_PARAM()** macro, see below.
               Parameter _flags_ is a combination of flags, see below.
    
               **SD_BUS_SIGNAL()** is equivalent to **SD_BUS_SIGNAL_WITH_NAMES()**
               with the _names_ parameter unset (i.e. no parameter names).
    
               Prefer using **SD_BUS_SIGNAL_WITH_ARGS()** over these macros as it
               allows specifying argument types and names next to each other
               which is less error-prone than first specifying all argument
               types followed by specifying all argument names.
    
           **SD_BUS_WRITABLE_PROPERTY()** , **SD_BUS_PROPERTY()**
               Declare a D-Bus property with the name _member_ and value
               signature _signature_. Parameters _get_ and _set_ are the getter and
               setter methods. They are called with a pointer that is the
               _userdata_ parameter passed to the registration function offset
               by _offset_ bytes. This may be used pass pointers to different
               fields in the same data structure to different setters and
               getters in the same vtable. Parameter _flags_ is a combination
               of flags, see below.
    
               The setter and getter methods may be omitted (specified as
               **NULL**), if the property is one of the basic types or "as" in
               case of read-only properties. In those cases, the _userdata_ and
               _offset_ parameters must together point to a valid variable of
               the corresponding type. A default setter and getter will be
               provided, which simply copy the argument between this variable
               and the message.
    
               **SD_BUS_PROPERTY()** is used to define a read-only property.
    
           **SD_BUS_PARAM()**
               Parameter names should be wrapped in this macro, see the
               example below.
    
       **Flags**
           The _flags_ parameter is used to specify a combination of **D-Bus**
           **annotations******[1].**SD_BUS_VTABLE_DEPRECATED**
               Mark this vtable entry as deprecated using the
               **org.freedesktop.DBus.Deprecated** annotation in introspection
               data. If specified for **SD_BUS_VTABLE_START()** , the annotation
               is applied to the enclosing interface.
    
           **SD_BUS_VTABLE_HIDDEN**
               Make this vtable entry hidden. It will not be shown in
               introspection data. If specified for **SD_BUS_VTABLE_START()** ,
               all entries in the array are hidden.
    
           **SD_BUS_VTABLE_METHOD_NO_REPLY**
               Mark this vtable entry as a method that will not return a
               reply using the **org.freedesktop.DBus.Method.NoReply** annotation
               in introspection data.
    
           **SD_BUS_VTABLE_PROPERTY_CONST** , **SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE** ,
           **SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION**
               Those three flags correspond to different values of the
               **org.freedesktop.DBus.Property.EmitsChangedSignal** annotation,
               which specifies whether the
               **org.freedesktop.DBus.Properties.PropertiesChanged** signal is
               emitted whenever the property changes.
               **SD_BUS_VTABLE_PROPERTY_CONST** corresponds to **const** and means
               that the property never changes during the lifetime of the
               object it belongs to, so no signal needs to be emitted.
               **SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE** corresponds to **true** and
               means that the signal is emitted.
               **SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION** corresponds to
               **invalidates** and means that the signal is emitted, but the
               value is not included in the signal.
    
           **SD_BUS_VTABLE_PROPERTY_EXPLICIT**
               Mark this vtable property entry as requiring explicit request
               to for the value to be shown (generally because the value is
               large or slow to calculate). This entry cannot be combined
               with **SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE** , and will not be
               shown in property listings by default (e.g.  **busctl**
               **introspect**). This corresponds to the
               **org.freedesktop.systemd1.Explicit** annotation in introspection
               data.
    
           **SD_BUS_VTABLE_SENSITIVE**
               Mark this vtable method entry as processing sensitive data.
               When set, incoming method call messages and their outgoing
               reply messages are marked as sensitive using
               sd_bus_message_sensitive(3), so that they are erased from
               memory when freed.
    
           **SD_BUS_VTABLE_ABSOLUTE_OFFSET**
               Mark this vtable method or property entry so that the user
               data pointer passed to its associated handler functions is
               determined slightly differently: instead of adding the offset
               parameter of the entry to the user data pointer specified
               during vtable registration, the offset is passed directly,
               converted to a pointer, without taking the user data pointer
               specified during vtable registration into account.
    
           **SD_BUS_VTABLE_CAPABILITY(**_capability_**)**
               Access to this vtable entry will be allowed if the calling
               process has the capability _capability_ , as described in
               sd_bus_query_sender_privilege(3). If used for
               **SD_BUS_VTABLE_START()** , provides a default for all entries in
               the array. If not specified, either for an individual entry or
               the whole array, **CAP_SYS_ADMIN** is checked by default. See
               capabilities(7) for information about capabilities.
    
               Note that vtable entries may be marked as unprivileged and the
               whole bus may be marked as trusted, see the discussion of
               **SD_BUS_VTABLE_UNPRIVILEGED** below.
    
           **SD_BUS_VTABLE_UNPRIVILEGED**
               Mark this vtable entry as unprivileged. Access to privileged
               entries is limited to users with appropriate capabilities as
               described above. In practice many vtable entries are marked as
               unprivileged, and either are open to everyone, or the decision
               whether to allow access is taken later, e.g. by delegating to
               **polkit******[2].
    
               The whole bus may be marked as trusted, in which case
               annotations at the entry level are ignored, seesd_bus_set_trusted(3).
    
               When _not_ specified, the **org.freedesktop.systemd1.Privileged**
               annotation with value "true" will be shown in introspection
               data.
    
               **SD_BUS_VTABLE_UNPRIVILEGED** may not be applied to read-only
               properties, but read access (to both read-only and writable
               properties) is always unrestricted.
    
               Note that this page describes checks implemented in the D-Bus
               client. The D-Bus server has an additional policy that may
               permit or deny connections, see "CONFIGURATION FILE" in
               **dbus-daemon**(1).
    


## EXAMPLES



           **Example 1. Create a simple listener on the bus**
    
               /* SPDX-License-Identifier: MIT-0 */
    
               #define _GNU_SOURCE 1
               #include <errno.h>
               #include <stdbool.h>
               #include <stddef.h>
               #include <stdlib.h>
               #include <stdio.h>
               #include <systemd/sd-bus.h>
    
               #define _cleanup_(f) __attribute__((cleanup(f)))
    
               typedef struct object {
                 char *name;
                 uint32_t number;
               } object;
    
               static int method(sd_bus_message *m, void *userdata, sd_bus_error *error) {
                 int r;
    
                 printf("Got called with userdata=%p\n", userdata);
    
                 if (sd_bus_message_is_method_call(m,
                                                   "org.freedesktop.systemd.VtableExample",
                                                   "Method4"))
                   return 1;
    
                 const char *string;
                 r = sd_bus_message_read(m, "s", &string);
                 if (r < 0) {
                   fprintf(stderr, "sd_bus_message_read() failed: %s\n", strerror(-r));
                   return 0;
                 }
    
                 r = sd_bus_reply_method_return(m, "s", string);
                 if (r < 0) {
                   fprintf(stderr, "sd_bus_reply_method_return() failed: %s\n", strerror(-r));
                   return 0;
                 }
    
                 return 1;
               }
    
               static const sd_bus_vtable vtable[] = {
                       SD_BUS_VTABLE_START(0),
                       SD_BUS_METHOD(
                           "Method1", "s", "s", method, 0),
                       SD_BUS_METHOD_WITH_NAMES_OFFSET(
                           "Method2",
                           "so", SD_BUS_PARAM(string) SD_BUS_PARAM(path),
                           "s", SD_BUS_PARAM(returnstring),
                           method, offsetof(object, number),
                           SD_BUS_VTABLE_DEPRECATED),
                       SD_BUS_METHOD_WITH_ARGS_OFFSET(
                           "Method3",
                           SD_BUS_ARGS("s", string, "o", path),
                           SD_BUS_RESULT("s", returnstring),
                           method, offsetof(object, number),
                           SD_BUS_VTABLE_UNPRIVILEGED),
                       SD_BUS_METHOD_WITH_ARGS(
                           "Method4",
                           SD_BUS_NO_ARGS,
                           SD_BUS_NO_RESULT,
                           method,
                           SD_BUS_VTABLE_UNPRIVILEGED),
                       SD_BUS_SIGNAL(
                           "Signal1",
                           "so",
                           0),
                       SD_BUS_SIGNAL_WITH_NAMES(
                           "Signal2",
                           "so", SD_BUS_PARAM(string) SD_BUS_PARAM(path),
                           0),
                       SD_BUS_SIGNAL_WITH_ARGS(
                           "Signal3",
                           SD_BUS_ARGS("s", string, "o", path),
                           0),
                       SD_BUS_WRITABLE_PROPERTY(
                           "AutomaticStringProperty", "s", NULL, NULL,
                           offsetof(object, name),
                           SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
                       SD_BUS_WRITABLE_PROPERTY(
                           "AutomaticIntegerProperty", "u", NULL, NULL,
                           offsetof(object, number),
                           SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION),
                       SD_BUS_VTABLE_END
               };
    
               int main(int argc, char **argv) {
                 _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
                 int r;
    
                 sd_bus_default(&bus);
    
                 object object = { .number = 666 };
                 object.name = strdup("name");
                 if (!object.name) {
                   fprintf(stderr, "OOM\n");
                   return EXIT_FAILURE;
                 }
    
                 r = sd_bus_add_object_vtable(bus, NULL,
                                              "/org/freedesktop/systemd/VtableExample",
                                              "org.freedesktop.systemd.VtableExample",
                                              vtable,
                                              &object);
                 if (r < 0) {
                   fprintf(stderr, "sd_bus_add_object_vtable() failed: %s\n", strerror(-r));
                   return EXIT_FAILURE;
                 }
    
                 r = sd_bus_request_name(bus,
                                         "org.freedesktop.systemd.VtableExample",
                                         0);
                 if (r < 0) {
                   fprintf(stderr, "sd_bus_request_name() failed: %s\n", strerror(-r));
                   return EXIT_FAILURE;
                 }
    
                 for (;;) {
                   r = sd_bus_wait(bus, UINT64_MAX);
                   if (r < 0) {
                     fprintf(stderr, "sd_bus_wait() failed: %s\n", strerror(-r));
                     return EXIT_FAILURE;
                   }
    
                   r = sd_bus_process(bus, NULL);
                   if (r < 0) {
                     fprintf(stderr, "sd_bus_process() failed: %s\n", strerror(-r));
                     return EXIT_FAILURE;
                   }
                 }
    
                 r = sd_bus_release_name(bus, "org.freedesktop.systemd.VtableExample");
                 if (r < 0) {
                   fprintf(stderr, "sd_bus_release_name() failed: %s\n", strerror(-r));
                   return EXIT_FAILURE;
                 }
    
                 free(object.name);
    
                 return 0;
               }
    
           This creates a simple client on the bus (the user bus, when run as
           normal user). We may use the D-Bus
           **org.freedesktop.DBus.Introspectable.Introspect** call to acquire the
           XML description of the interface:
    
               <!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN"
               "https://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
               <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
               <node>
                <interface name="org.freedesktop.DBus.Peer">
                 <method name="Ping"/>
                 <method name="GetMachineId">
                  <arg type="s" name="machine_uuid" direction="out"/>
                 </method>
                </interface>
                <interface name="org.freedesktop.DBus.Introspectable">
                 <method name="Introspect">
                  <arg name="xml_data" type="s" direction="out"/>
                 </method>
                </interface>
                <interface name="org.freedesktop.DBus.Properties">
                 <method name="Get">
                  <arg name="interface_name" direction="in" type="s"/>
                  <arg name="property_name" direction="in" type="s"/>
                  <arg name="value" direction="out" type="v"/>
                 </method>
                 <method name="GetAll">
                  <arg name="interface_name" direction="in" type="s"/>
                  <arg name="props" direction="out" type="a{sv}"/>
                 </method>
                 <method name="Set">
                  <arg name="interface_name" direction="in" type="s"/>
                  <arg name="property_name" direction="in" type="s"/>
                  <arg name="value" direction="in" type="v"/>
                 </method>
                 <signal name="PropertiesChanged">
                  <arg type="s" name="interface_name"/>
                  <arg type="a{sv}" name="changed_properties"/>
                  <arg type="as" name="invalidated_properties"/>
                 </signal>
                </interface>
                <interface name="org.freedesktop.systemd.VtableExample">
                 <method name="Method1">
                  <arg type="s" direction="in"/>
                  <arg type="s" direction="out"/>
                 </method>
                 <method name="Method2">
                  <arg type="s" name="string" direction="in"/>
                  <arg type="o" name="path" direction="in"/>
                  <arg type="s" name="returnstring" direction="out"/>
                  <annotation name="org.freedesktop.DBus.Deprecated" value="true"/>
                 </method>
                 <property name="AutomaticStringProperty" type="s" access="readwrite">
                 </property>
                 <property name="AutomaticIntegerProperty" type="u" access="readwrite">
                  <annotation name="org.freedesktop.DBus.Property.EmitsChangedSignal" value="invalidates"/>
                 </property>
                </interface>
               </node>
    


## RETURN VALUE



           On success, **sd_bus_add_object_vtable()** and
           **sd_bus_add_fallback_vtable()** return a non-negative integer. On
           failure, they return a negative errno-style error code.
    
       **Errors**
           Returned errors may indicate the following problems:
    
           **-EINVAL**
               One of the required parameters is **NULL** or invalid. A reserved
               D-Bus interface was passed as the _interface_ parameter.
    
           **-ENOPKG**
               The bus cannot be resolved.
    
           **-ECHILD**
               The bus was created in a different process, library or module
               instance.
    
           **-ENOMEM**
               Memory allocation failed.
    
           **-EPROTOTYPE**
               **sd_bus_add_object_vtable()** and **sd_bus_add_fallback_vtable()**
               have been both called for the same bus object path, which is
               not allowed.
    
           **-EEXIST**
               This vtable has already been registered for this _interface_ and
               _path_.
    


## NOTES



           Functions described here are available as a shared library, which
           can be compiled against and linked to with the
           **libsystemd pkg-config**(1) file.
    
           The code described here uses getenv(3), which is declared to be
           not multi-thread-safe. This means that the code calling the
           functions described here must not call setenv(3) from a parallel
           thread. It is recommended to only do calls to **setenv()** from an
           early phase of the program when no other threads have been
           started.
    


## NOTES



            1. D-Bus annotations
               https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format
    
            2. polkit
               https://www.freedesktop.org/software/polkit/docs/latest/
    


* * *