Manpages - sd_bus_message_new_signal.3

Table of Contents

NAME

sd_bus_message_new_signal - Create a signal message

SYNOPSIS

  #include <systemd/sd-bus.h>

int sd_bus_message_new_signal(sd_bus **/bus/, sd_bus_message **/m/, const char */path/, const char */interface/, const char */member/);*

DESCRIPTION

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*(1) for a short description of the meaning of the path, interface, and member parameters.

RETURN VALUE

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.

NOTES

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

EXAMPLES

Example 1. Send a simple signal

    #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.

SEE ALSO

*systemd*(1), *sd-bus*(3), *sd_bus_emit_signal*(3)

Author: dt

Created: 2022-02-21 Mon 13:13