sd_bus_emit_signal(3) — Linux manual page


SD_BUS_EMIT_SIGNAL(3)      sd_bus_emit_signal      SD_BUS_EMIT_SIGNAL(3)

NAME         top

       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_properties_changed_strv, sd_bus_emit_object_added,
       sd_bus_emit_object_removed - Convenience functions for emitting
       (standard) D-Bus signals

SYNOPSIS         top

       #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         top

       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

       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         top

       On success, these functions return a non-negative integer. On
       failure, they return a negative errno-style error code.

       Returned errors may indicate the following problems:

           One of the required parameters is NULL or invalid. A reserved
           D-Bus interface was passed as the interface parameter.

           Added in version 246.

           The bus cannot be resolved.

           Added in version 246.

           The bus was created in a different process, library or module

           Added in version 246.

           Memory allocation failed.

           Added in version 246.

           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.

           Added in version 246.

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

NOTES         top

       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

HISTORY         top

       sd_bus_emit_signal(), sd_bus_emit_signalv(),
       sd_bus_emit_object_added(), and sd_bus_emit_object_removed() were
       added in version 246.

       sd_bus_emit_signal_to() and sd_bus_emit_signal_tov() were added
       in version 253.

SEE ALSO         top

       sd-bus(3), busctl(1), sd_bus_message_new_signal(3),
       sd_bus_message_append(3), sd_bus_send(3), sd_bus_call_method(3)

COLOPHON         top

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       manager) project.  Information about the project can be found at
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       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
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       (which is not part of the original manual page), send a mail to

systemd 255                                        SD_BUS_EMIT_SIGNAL(3)

Pages that refer to this page: sd-bus(3)sd_bus_add_object(3)sd_bus_add_object_manager(3)sd_bus_call_method(3)sd_bus_message_new_signal(3)systemd.directives(7)systemd.index(7)