добавление, удаление и получение одноранговых узлов шины, отслеживаемых в объекте отслеживания узлов шины (add, remove and retrieve bus peers tracked in a bus peer tracking object)
Имя (Name)
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
Синопсис (Synopsis)
#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);
Описание (Description)
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 if
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.
Возвращаемое значение (Return value)
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 hasn't. 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.
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (See also)
systemd(1), sd-bus(3), sd_bus_track_new(3)
