sd_bus_emit

Name

sd_bus_emit_signal, sd_bus_emit_signalv, sd_bus_emit_signal_to, sd_bus_emit_signal_tov, sd_bus_emit_interfaces_added, sd_bus_emit_interfaces_added_strv, sd_bus_emit_interfaces_removed, sd_bus_emit_interfaces_removed_strv, sd_bus_emit_properties_changed, sd_bus_emit_properties_changed_strv, sd_bus_emit_object_added, sd_bus_emit_object_removed — Convenience functions for emitting (standard) D-Bus signals

Synopsis

#include <systemd/sd-bus-vtable.h>

`int sd_bus_emit_signal(`	sd_bus *`bus`,
	const char *`path`,
	const char *`interface`,
	const char *`member`,
	const char *`types`,
	...`)`;

`int sd_bus_emit_signalv(`	sd_bus *`bus`,
	const char *`path`,
	const char *`interface`,
	const char *`member`,
	const char *`types`,
	va_list `ap)`;

`int sd_bus_emit_signal_to(`	sd_bus *`bus`,
	const char *`destination`,
	const char *`path`,
	const char *`interface`,
	const char *`member`,
	const char *`types`,
	...`)`;

`int sd_bus_emit_signal_tov(`	sd_bus *`bus`,
	const char *`destination`,
	const char *`path`,
	const char *`interface`,
	const char *`member`,
	const char *`types`,
	va_list `ap)`;

`int sd_bus_emit_interfaces_added(`	sd_bus *`bus`,
	const char *`path`,
	const char *`interface`,
	...`)`;

`int sd_bus_emit_interfaces_added_strv(`	sd_bus *`bus`,
	const char *`path`,
	const char **`interfaces)`;

`int sd_bus_emit_interfaces_removed(`	sd_bus *`bus`,
	const char *`path`,
	const char *`interface`,
	...`)`;

`int sd_bus_emit_interfaces_removed_strv(`	sd_bus *`bus`,
	const char *`path`,
	const char **`interfaces)`;

`int sd_bus_emit_properties_changed(`	sd_bus *`bus`,
	const char *`path`,
	const char *`interface`,
	const char *`name`,
	...`)`;

`int sd_bus_emit_properties_changed_strv(`	sd_bus *`bus`,
	const char *`path`,
	const char *`interface`,
	const char **`names)`;

`int sd_bus_emit_object_added(`	sd_bus *`bus`,
	const char *`path)`;

`int sd_bus_emit_object_removed(`	sd_bus *`bus`,
	const char *`path)`;

Description¶

sd_bus_emit_signal() is a convenience function for initializing a bus message object and emitting the corresponding D-Bus signal. It combines the sd_bus_message_new_signal(3), sd_bus_message_append(3) and sd_bus_send(3) functions into a single function call. sd_bus_emit_signalv() is equivalent to sd_bus_message_append(), except that it is called with a "va_list" instead of a variable number of arguments.

sd_bus_emit_signal_to() and sd_bus_emit_signal_tov() are identical to sd_bus_emit_signal() and sd_bus_emit_signalv(), except that they can emit the signal to a single destination. Give destination as NULL to broadcast the signal.

sd_bus_emit_interfaces_added() and sd_bus_emit_interfaces_removed() are used to implement the InterfacesAdded and InterfacesRemoved signals of the org.freedesktop.DBus.ObjectManager interface. They take a path whose interfaces have been modified as an argument and a variable list of interfaces that have been added or removed, respectively. The final argument passed to sd_bus_emit_interfaces_added() and sd_bus_emit_interfaces_removed() must be NULL. This allows both functions to safely determine the number of passed interface arguments. sd_bus_emit_interfaces_added_strv() and sd_bus_emit_interfaces_removed_strv() are identical to their respective counterparts but both take the list of interfaces as a single argument instead of a variable number of arguments.

sd_bus_emit_properties_changed() is used to implement the PropertiesChanged signal of the org.freedesktop.DBus.Properties interface. It takes an object path, interface and a variable list of property names as its arguments. The final argument passed to sd_bus_emit_properties_changed() must be NULL. This allows it to safely determine the number of passed property names. sd_bus_emit_properties_changed_strv() is identical to sd_bus_emit_properties_changed() but takes the list of property names as a single argument instead of a variable number of arguments.

sd_bus_emit_object_added() and sd_bus_emit_object_removed() are convenience functions for emitting the InterfacesAdded or InterfacesRemoved signals for all interfaces registered on a specific object path, respectively. This includes any parent fallback vtables if they are not overridden by a more applicable child vtable. It also includes all the standard D-Bus interfaces implemented by sd-bus itself on any registered object.

Note that sd_bus_emit_interfaces_added(), sd_bus_emit_interfaces_removed(), sd_bus_emit_object_added() and sd_bus_emit_object_removed() require an object manager to have been registered on the given object path or one of its parent object paths using sd_bus_add_object_manager(3).

Return Value¶

On success, these functions 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.
-ESRCH¶: One of sd_bus_emit_interfaces_added(), sd_bus_emit_interfaces_removed(), sd_bus_emit_object_added() or sd_bus_emit_object_removed() was called on an object without an object manager registered on its own object path or one of its parent object paths.

See the man pages of sd_bus_message_new_signal(3), sd_bus_message_append(3) and sd_bus_send(3) for more possible errors.

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.