SD_BUS_EMIT_SIGNAL(3)

💅 NAME 💅

okay so bestie, welcome to SD_BUS_EMIT_SIGNAL(3) — aka the sd_bus_emit_signal page. These are all convenience functions for emitting (standard) D-Bus signals, and the whole friend group is: 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. No cap, that's a whole squad of signal besties. 💖

✨ 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,
                                      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,
                                        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,
                                        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 🦋

So sd_bus_emit_signal() is the convenience function for initializing a bus message object and emitting the corresponding D-Bus signal. It literally combines sd_bus_message_new_signal(3), sd_bus_message_append(3) and sd_bus_send(3) into a single function call — it's giving three-step combo meal, but make it one 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. iykyk.

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. broadcast queen behavior. 👑

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). Don't skip that step, bestie. 🚨

💜 RETURN VALUE 💜

On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code. That's the whole vibe check. ✅

😭 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. slay, linkage. 🔗

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel. so yes, parallel objects are fine — just don't gang up on one object at the same time. 🧚

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. seriously, don't do the parallel setenv() thing. 💀

🎀 HISTORY 🎀

• Added in version 221: sd_bus_emit_signal(), 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().
• Added in version 222: sd_bus_emit_object_added(), and sd_bus_emit_object_removed().
• Added in version 246: sd_bus_emit_signalv().
• Added in version 253: sd_bus_emit_signal_to() and sd_bus_emit_signal_tov().

⭐ SEE ALSO ⭐

• 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)

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And that's the whole vibe. Signed with love by systemd 261.3 💖 — this manual page is SD_BUS_EMIT_SIGNAL(3), periodt. 🫶