sd_bus_add_object_vtable

systemd
sd_bus_add_object_vtable 3
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_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)`

## Description

`sd_bus_add_object_vtable()` is used to declare attributes for the path 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.

`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).

For both 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_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. 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 has 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 valid variable of the corresponding type. A default setter and getters 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.

`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.

## Examples

Create a simple listener on the bus

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:

## Return Value

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.

### 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.

## See Also

sd-bus 3, busctl 1