SD_BUS_VTABLE_END(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | RETURN VALUE | NOTES | SEE ALSO | NOTES | COLOPHON

SD_BUS_ADD_OBJECT(3)          sd_bus_add_object         SD_BUS_ADD_OBJECT(3)

NAME         top

       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_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         top

       #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_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         top

       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 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. Note that if producing a reply takes too long, the method call
       will time out at the caller.

       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(), SD_BUS_VTABLE_END
           Those must always be the first and last element.

       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.
                     .RE

           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_UNPRIVILEGED
           Mark this vtable entry as unprivileged. If not specified, the
           org.freedesktop.systemd1.Privileged annotation with value "true"
           will be shown in introspection data.

       SD_BUS_VTABLE_METHOD_NO_REPLY
           Mark his 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.

EXAMPLES         top

       Example 1. Create a simple listener on the bus

           #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) {
             printf("Got called with userdata=%p\n", userdata);
             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
           };

           #define check(x) ({                             \
             int r = x;                                    \
             errno = r < 0 ? -r : 0;                       \
             printf(#x ": %m\n");                          \
             if (r < 0)                                    \
               return EXIT_FAILURE;                        \
             })

           int main(int argc, char **argv) {
             _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;

             sd_bus_default(&bus);

             object object = { .number = 666 };
             check((object.name = strdup("name")) != NULL);

             check(sd_bus_add_object_vtable(bus, NULL, "/object",
                                            "org.freedesktop.systemd.VtableExample",
                                            vtable,
                                            &object));

             for (;;) {
               check(sd_bus_wait(bus, UINT64_MAX));
               check(sd_bus_process(bus, NULL));
             }

             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"
           "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
           <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="data" type="s" direction="out"/>
             </method>
            </interface>
            <interface name="org.freedesktop.DBus.Properties">
             <method name="Get">
              <arg name="interface" direction="in" type="s"/>
              <arg name="property" direction="in" type="s"/>
              <arg name="value" direction="out" type="v"/>
             </method>
             <method name="GetAll">
              <arg name="interface" direction="in" type="s"/>
              <arg name="properties" direction="out" type="a{sv}"/>
             </method>
             <method name="Set">
              <arg name="interface" direction="in" type="s"/>
              <arg name="property" direction="in" type="s"/>
              <arg name="value" direction="in" type="v"/>
             </method>
             <signal name="PropertiesChanged">
              <arg type="s" name="interface"/>
              <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         top

       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.

       -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         top

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

SEE ALSO         top

       sd-bus(3), busctl(1), sd_bus_emit_properties_changed(3),
       sd_bus_emit_object_added(3)

NOTES         top

        1. D-Bus annotations
           https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format

COLOPHON         top

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       project.  Information about the project can be found at 
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a bug
       report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.  This
       page was obtained from the project's upstream Git repository
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systemd 247                                             SD_BUS_ADD_OBJECT(3)

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