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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_BUS_TRACK_ADD_NAME(3) sd_bus_track_add_name SD_BUS_TRACK_ADD_NAME(3)
sd_bus_track_add_name, sd_bus_track_add_sender,
sd_bus_track_remove_name, sd_bus_track_remove_sender,
sd_bus_track_count, sd_bus_track_count_sender,
sd_bus_track_count_name, sd_bus_track_contains,
sd_bus_track_first, sd_bus_track_next - Add, remove and retrieve
bus peers tracked in a bus peer tracking object
#include <systemd/sd-bus.h>
int sd_bus_track_add_name(sd_bus_track* t, const char* name);
int sd_bus_track_add_sender(sd_bus_track* t,
sd_bus_message* message);
int sd_bus_track_remove_name(sd_bus_track* t, const char* name);
int sd_bus_track_remove_sender(sd_bus_track* t,
sd_bus_message* message);
unsigned sd_bus_track_count(sd_bus_track* t);
int sd_bus_track_count_name(sd_bus_track* t, const char* name);
int sd_bus_track_count_sender(sd_bus_track* t,
sd_bus_message* message);
int sd_bus_track_contains(sd_bus_track* t, const char* name);
const char* sd_bus_track_first(sd_bus_track* t);
const char* sd_bus_track_next(sd_bus_track* t);
sd_bus_track_add_name() adds a peer to track to a bus peer
tracking object. The first argument should refer to a bus peer
tracking object created with sd_bus_track_new(3), the second name
should refer to a D-Bus peer name to track, either in unique or
well-known service format. If the name is not tracked yet it will
be added to the list of names to track. If it already is being
tracked and non-recursive mode is enabled, no operation is
executed by this call. If recursive mode is enabled a per-name
counter is increased by one each time this call is invoked, and
sd_bus_track_remove_name() has to be called as many times as
sd_bus_track_add_name() was invoked before in order to stop
tracking of the name. Use sd_bus_track_set_recursive(3) to switch
from the default non-recursive mode to recursive mode, or back.
Note that the specified name is tracked as it is, well-known names
are not resolved to unique names by this call. Note that multiple
bus peer tracking objects may track the same name.
sd_bus_track_remove_name() undoes the effect of
sd_bus_track_add_name() and removes a bus peer name from the list
of peers to watch. Depending on whether non-recursive or recursive
mode is enabled for the bus peer tracking object this call will
either remove the name fully from the tracking object, or will
simply decrement the per-name counter by one, removing the name
only when the counter reaches zero (see above). Note that a bus
peer disconnecting from the bus will implicitly remove its names
fully from the bus peer tracking object, regardless of the current
per-name counter.
sd_bus_track_add_sender() and sd_bus_track_remove_sender() are
similar to sd_bus_track_add_name() and sd_bus_track_remove_name()
but take a bus message as argument. The sender of this bus message
is determined and added to/removed from the bus peer tracking
object. As messages always originate from unique names, and never
from well-known names this means that this call will effectively
only add unique names to the bus peer tracking object.
sd_bus_track_count() returns the number of names currently being
tracked by the specified bus peer tracking object. Note that this
function always returns the actual number of names tracked, and
hence if sd_bus_track_add_name() has been invoked multiple times
for the same name it is only counted as one, regardless of whether
recursive mode is used or not.
sd_bus_track_count_name() returns the current per-name counter for
the specified name. If non-recursive mode is used this returns
either 1 or 0, depending on whether the specified name has been
added to the tracking object before, or not. If recursive mode has
been enabled, values larger than 1 may be returned too, in case
sd_bus_track_add_name() has been called multiple times for the
same name.
sd_bus_track_count_sender() is similar to
sd_bus_track_count_name(), but takes a bus message object and
returns the per-name counter matching the sender of the message.
sd_bus_track_contains() may be used to determine whether the
specified name has been added at least once to the specified bus
peer tracking object.
sd_bus_track_first() and sd_bus_track_next() may be used to
enumerate all names currently being tracked by the passed bus peer
tracking object. sd_bus_track_first() returns the first entry in
the object, and resets an internally maintained read index. Each
subsequent invocation of sd_bus_track_next() returns the next name
contained in the bus object. If the end is reached NULL is
returned. If no names have been added to the object yet
sd_bus_track_first() will return NULL immediately. The order in
which names are returned is undefined; in particular which name is
considered the first returned is not defined. If recursive mode is
enabled and the same name has been added multiple times to the bus
peer tracking object it is only returned once by this enumeration.
If new names are added to or existing names removed from the bus
peer tracking object while it is being enumerated the enumeration
ends on the next invocation of sd_bus_track_next() as NULL is
returned.
On success, sd_bus_track_add_name() and sd_bus_track_add_sender()
return 0 if the specified name has already been added to the bus
peer tracking object before and positive if it has not. On
failure, they return a negative errno-style error code.
sd_bus_track_remove_name() and sd_bus_track_remove_sender() return
positive if the specified name was previously tracked by the bus
peer tracking object and has now been removed. In non-recursive
mode, 0 is returned if the specified name was not being tracked
yet. In recursive mode -EUNATCH is returned in this case. On
failure, they return a negative errno-style error code.
sd_bus_track_count() returns the number of names currently being
tracked, or 0 on failure.
sd_bus_track_count_name() and sd_bus_track_count_sender() return
the current per-name counter for the specified name or the sender
of the specified message. Zero is returned for names that are not
being tracked yet, a positive value for names added at least once.
Larger values than 1 are only returned in recursive mode. On
failure, a negative errno-style error code is returned.
sd_bus_track_contains() returns the passed name if it exists in
the bus peer tracking object. On failure, and if the name has not
been added yet NULL is returned.
sd_bus_track_first() and sd_bus_track_next() return the first/next
name contained in the bus peer tracking object, and NULL if the
end of the enumeration is reached and on error.
Errors
Returned errors may indicate the following problems:
-EUNATCH
sd_bus_track_remove_name() or sd_bus_track_remove_sender()
have been invoked for a name not previously added to the bus
peer object.
-EINVAL
Specified parameter is invalid.
-ENOMEM
Memory allocation failed.
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.
sd_bus_track_add_name(), sd_bus_track_add_sender(),
sd_bus_track_remove_name(), sd_bus_track_remove_sender(),
sd_bus_track_count(), sd_bus_track_count_name(),
sd_bus_track_count_sender(), sd_bus_track_contains(),
sd_bus_track_first(), and sd_bus_track_next() were added in
version 232.
systemd(1), sd-bus(3), sd_bus_track_new(3)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SD_BUS_TRACK_ADD_NAME(3)
Pages that refer to this page: sd-bus(3), sd_bus_track_new(3), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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