systemd sd_bus_add_object 3 sd_bus_add_object sd_bus_add_fallback sd_bus_add_object_vtable sd_bus_add_fallback_vtable 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 #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 SD_BUS_VTABLE_START(flags) SD_BUS_VTABLE_END 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_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_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. 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, 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_errno3 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_error3 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_set3 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_errno3 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_floating3. 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_unref3. 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_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. 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_return3 with the message the callback was invoked with. in_names and out_names should be created using the SD_BUS_PARAM() macro, see below. Parameter flags is a combination of flags, see below. 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. 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. Equivalent to SD_BUS_SIGNAL_WITH_NAMES() with the names parameter unset (i.e. no parameter 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. The flags parameter is used to specify a combination of D-Bus annotations. 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. 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: On success, sd_bus_add_object_vtable and sd_bus_add_fallback_vtable calls return 0 or a positive integer. On failure, they return a negative errno-style error code. 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. sd-bus3, busctl1