sd_bus_message_new_signal, sd_bus_message_new_signal_to - Create a signal message

The sd_bus_message_new_signal() function creates a new bus message object that encapsulates a D-Bus signal, and returns it in the m output parameter. The signal will be sent to path path, on the interface interface, member member. When this message is sent, no reply is expected. See sd_bus_message_new_method_call(3) for a short description of the meaning of the path, interface, and member parameters. sd_bus_message_new_signal_to() is a shorthand for creating a new bus message to a specific destination. It's behavior is similar to calling sd_bus_message_new_signal() followed by calling sd_bus_message_set_destination(3).

Example1.Sendasimplesignal /* SPDX-License-Identifier: MIT-0 */ #include <systemd/sd-bus.h> #define _cleanup_(f) __attribute__((cleanup(f))) int send_unit_files_changed(sd_bus *bus) { _cleanup_(sd_bus_message_unrefp) sd_bus_message *message = NULL; int r; r = sd_bus_message_new_signal(bus, &message, "/org/freedesktop/systemd1", "org.freedesktop.systemd1.Manager", "UnitFilesChanged"); if (r < 0) return r; return sd_bus_send(bus, message, NULL); } This function in systemd sources is used to emit the "UnitFilesChanged" signal when the unit files have been changed.

sd_bus_message_new_signal, sd_bus_message_new_signal_to - Create a signal message

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemdpkg-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.

This function returns 0 if the message object was successfully created, and a negative errno-style error code otherwise. Errors Returned errors may indicate the following problems: -EINVAL The output parameter m is NULL. The path parameter is not a valid D-Bus path ("/an/object/path"), the interface parameter is not a valid D-Bus interface name ("an.interface.name"), or the member parameter is not a valid D-Bus member ("Name"). -ENOTCONN The bus parameter bus is NULL or the bus is not connected. -ENOMEM Memory allocation failed.

systemd(1), sd-bus(3), sd_bus_emit_signal(3), sd_bus_message_set_destination(3) systemd 257.7 SD_BUS_MESSAGE_NEW_SIGNAL(3)