SD_BUS_EMIT_SIGNAL

Section: sd_bus_emit_signal (3)
Updated:
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NAME

sd_bus_emit_signal, sd_bus_emit_signalv, 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_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_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.

-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

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