sd_bus_add_match(3) — Linux manual page
SD_BUS_ADD_MATCH(3) sd_bus_add_match SD_BUS_ADD_MATCH(3)
NAME
sd_bus_add_match, sd_bus_add_match_async, sd_bus_match_signal,
sd_bus_match_signal_async - Add a match rule for incoming message
dispatching
SYNOPSIS
#include <systemd/sd-bus.h>
typedef int (*sd_bus_message_handler_t)(sd_bus_message *m,
void *userdata,
sd_bus_error *ret_error);
int sd_bus_add_match(sd_bus *bus, sd_bus_slot **slot,
const char *match,
sd_bus_message_handler_t callback,
void *userdata);
int sd_bus_add_match_async(sd_bus *bus, sd_bus_slot **slot,
const char *match,
sd_bus_message_handler_t callback,
sd_bus_message_handler_t install_callback,
void *userdata);
int sd_bus_match_signal(sd_bus *bus, sd_bus_slot **slot,
const char *sender, const char *path,
const char *interface,
const char *member,
sd_bus_message_handler_t callback,
void *userdata);
int sd_bus_match_signal_async(sd_bus *bus, sd_bus_slot **slot,
const char *sender,
const char *path,
const char *interface,
const char *member,
sd_bus_message_handler_t callback,
sd_bus_message_handler_t install_callback,
void *userdata);
DESCRIPTION
sd_bus_add_match() installs a match rule for messages received on
the specified bus connection object bus. The syntax of the match
rule expression passed in match is described in the D-Bus
Specification[1]. The specified handler function callback is
called for each incoming message matching the specified
expression, the userdata parameter is passed as-is to the
callback function. The match is installed synchronously when
connected to a bus broker, i.e. the call sends a control message
requested the match to be added to the broker and waits until the
broker confirms the match has been installed successfully.
sd_bus_add_match_async() operates very similarly to
sd_bus_add_match(), however it installs the match asynchronously,
in a non-blocking fashion: a request is sent to the broker, but
the call does not wait for a response. The install_callback
function is called when the response is later received, with the
response message from the broker as parameter. If this function
is specified as NULL a default implementation is used that
terminates the bus connection should installing the match fail.
sd_bus_match_signal() is very similar to sd_bus_add_match(), but
only matches signals, and instead of a match expression accepts
four parameters: sender (the service name of the sender), path
(the object path of the emitting object), interface (the
interface the signal belongs to), member (the signal name), from
which the match string is internally generated. Optionally, these
parameters may be specified as NULL in which case the relevant
field of incoming signals is not tested.
sd_bus_match_signal_async() combines the signal matching logic of
sd_bus_match_signal() with the asynchronous behaviour of
sd_bus_add_match_async().
On success, and if non-NULL, the slot return parameter will be
set to a slot object that may be used as a reference to the
installed match, and may be utilized to remove it again at a
later time with sd_bus_slot_unref(3). If specified as NULL the
lifetime of the match is bound to the lifetime of the bus object
itself, and the match is generally not removed independently. See
sd_bus_slot_set_floating(3) for details.
The message m passed to the callback is only borrowed, that is,
the callback should not call sd_bus_message_unref(3) on it. If
the callback wants to hold on to the message beyond the lifetime
of the callback, it needs to call sd_bus_message_ref(3) to create
a new reference.
If an error occurs during the callback invocation, the callback
should return a negative error number (optionally, a more precise
error may be returned in ret_error, as well). If it wants other
callbacks that match the same rule to be called, it should return
0. Otherwise it should return a positive integer.
If the bus refers to a direct connection (i.e. not a bus
connection, as set with sd_bus_set_bus_client(3)) the match is
only installed on the client side, and the synchronous and
asynchronous functions operate the same.
RETURN VALUE
On success, sd_bus_add_match() and the other calls return 0 or a
positive integer. On failure, they return a negative errno-style
error code.
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.
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.
HISTORY
sd_bus_add_match() and sd_bus_message_handler_t() were added in
version 221.
sd_bus_add_match_async(), sd_bus_match_signal(), and
sd_bus_match_signal_async() were added in version 237.
SEE ALSO
systemd(1), sd-bus(3), sd_bus_slot_unref(3),
sd_bus_message_ref(3), sd_bus_set_bus_client(3),
sd_bus_slot_set_floating(3)
NOTES
1. D-Bus Specification
https://dbus.freedesktop.org/doc/dbus-specification.html
COLOPHON
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systemd 257~devel SD_BUS_ADD_MATCH(3)
Pages that refer to this page: busctl(1), sd-bus(3), sd_bus_call(3), sd_bus_default(3), sd_bus_set_connected_signal(3), sd_bus_set_watch_bind(3), sd_bus_slot_set_destroy_callback(3), sd_bus_slot_set_floating(3), sd_bus_slot_set_userdata(3), systemd.directives(7), systemd.index(7)