sd_bus_add_object_vtable, sd_bus_add_fallback_vtable, SD_BUS_VTABLE_START, SD_BUS_VTABLE_END, SD_BUS_METHOD_WITH_NAMES_OFFSET, SD_BUS_METHOD_WITH_NAMES, SD_BUS_METHOD_WITH_OFFSET, SD_BUS_METHOD, SD_BUS_SIGNAL_WITH_NAMES, SD_BUS_SIGNAL, SD_BUS_WRITABLE_PROPERTY, SD_BUS_PROPERTY, SD_BUS_PARAM — Declare properties and methods for a D-Bus path
#include <systemd/sd-bus-vtable.h>
typedef int (*sd_bus_message_handler_t)( | sd_bus_message *m, |
void *userdata, | |
sd_bus_error *ret_error) ; |
typedef int (*sd_bus_property_get_t)( | sd_bus *bus, |
const char *path, | |
const char *interface, | |
const char *property, | |
sd_bus_message *reply, | |
void *userdata, | |
sd_bus_error *ret_error) ; |
typedef int (*sd_bus_property_set_t)( | sd_bus *bus, |
const char *path, | |
const char *interface, | |
const char *property, | |
sd_bus_message *value, | |
void *userdata, | |
sd_bus_error *ret_error) ; |
typedef int (*sd_bus_object_find_t)( | const char *path, |
const char *interface, | |
void *userdata, | |
void **ret_found, | |
sd_bus_error *ret_error) ; |
int sd_bus_add_object_vtable( | sd_bus *bus, |
sd_bus_slot **slot, | |
const char *path, | |
const char *interface, | |
const sd_bus_vtable *vtable, | |
void *userdata) ; |
int sd_bus_add_fallback_vtable( | sd_bus *bus, |
sd_bus_slot **slot, | |
const char *prefix, | |
const char *interface, | |
const sd_bus_vtable *vtable, | |
sd_bus_object_find_t find, | |
void *userdata) ; |
SD_BUS_VTABLE_START(
flags
)
SD_BUS_VTABLE_END
SD_BUS_METHOD_WITH_NAMES_OFFSET(
member
,
signature
,
in_names
,
result
,
out_names
,
handler
,
offset
,
flags
)
SD_BUS_METHOD_WITH_NAMES(
member
,
signature
,
in_names
,
result
,
out_names
,
handler
,
flags
)
SD_BUS_METHOD_WITH_OFFSET(
member
,
signature
,
result
,
handler
,
offset
,
flags
)
SD_BUS_METHOD(
member
,
signature
,
result
,
handler
,
flags
)
SD_BUS_SIGNAL_WITH_NAMES(
member
,
signature
,
names
,
flags
)
SD_BUS_SIGNAL(
member
,
signature
,
flags
)
SD_BUS_WRITABLE_PROPERTY(
member
,
signature
,
get
,
set
,
offset
,
flags
)
SD_BUS_PROPERTY(
member
,
signature
,
get
,
offset
,
flags
)
SD_BUS_PARAM(
name
)
sd_bus_add_object_vtable()
is used to declare attributes for the path object
path path
connected to the bus connection bus
under the
interface interface
. The table vtable
may contain property
declarations using SD_BUS_PROPERTY()
or
SD_BUS_WRITABLE_PROPERTY()
, method declarations using
SD_BUS_METHOD()
, SD_BUS_METHOD_WITH_NAMES()
,
SD_BUS_METHOD_WITH_OFFSET()
, or
SD_BUS_METHOD_WITH_NAMES_OFFSET()
, and signal declarations using
SD_BUS_SIGNAL_WITH_NAMES()
or SD_BUS_SIGNAL()
, see below. The
userdata
parameter contains a pointer that will be passed to various callback
functions. It may be specified as NULL
if no value is necessary.
sd_bus_add_fallback_vtable()
is similar to
sd_bus_add_object_vtable()
, but is used to register "fallback" attributes. When
looking for an attribute declaration, bus object paths registered with
sd_bus_add_object_vtable()
are checked first. If no match is found, the fallback
vtables are checked for each prefix of the bus object path, i.e. with the last slash-separated components
successively removed. This allows the vtable to be used for an arbitrary number of dynamically created
objects.
Parameter find
is a function which is used to locate the target object
based on the bus object path path
. It must return 1
and
set the ret_found
output parameter if the object is found, return
0
if the object was not found, and return a negative errno-style error code or
initialize the error structure ret_error
on error. The pointer passed in
ret_found
will be used as the userdata
parameter for the
callback functions (offset by the offset
offsets as specified in the vtable
entries).
For both functions, a match slot is created internally. If the output parameter
slot
is NULL
, a "floating" slot object is created, see
sd_bus_slot_set_floating(3).
Otherwise, a pointer to the slot object is returned. In that case, the reference to the slot object
should be dropped when the vtable is not needed anymore, see
sd_bus_slot_unref(3).
The array consists of the structures of type sd_bus_vtable, but it should never be filled in manually, but through one of the following macros:
SD_BUS_VTABLE_START()
, SD_BUS_VTABLE_END
¶Those must always be the first and last element.
SD_BUS_METHOD_WITH_NAMES_OFFSET()
, SD_BUS_METHOD_WITH_NAMES()
, SD_BUS_METHOD_WITH_OFFSET()
, SD_BUS_METHOD()
¶Declare a D-Bus method with the name member
, parameter
signature signature
, result signature result
.
Parameters in_names
and out_names
specify the
argument names of the input and output arguments in the function signature. The handler function
handler
must be of type sd_bus_message_handler_t
.
It will be called to handle the incoming messages that call this method. It receives a pointer that
is the userdata
parameter passed to the registration function offset by
offset
bytes. This may be used to pass pointers to different fields in
the same data structure to different methods in the same
vtable. in_names
and out_names
should be
created using the SD_BUS_PARAM()
macro, see below. Parameter
flags
is a combination of flags, see below.
SD_BUS_METHOD_WITH_NAMES()
,
SD_BUS_METHOD_WITH_OFFSET()
, and SD_BUS_METHOD()
are
variants which specify zero offset (userdata
parameter is passed with
no change), leave the names unset (i.e. no parameter names), or both.
SD_BUS_SIGNAL_WITH_NAMES()
, SD_BUS_SIGNAL()
¶Declare a D-Bus signal with the name member
,
parameter signature signature
, and argument names
names
. names
should be
created using the SD_BUS_PARAM()
macro, see below.
Parameter flags
is a combination of flags, see below.
Equivalent to SD_BUS_SIGNAL_WITH_NAMES()
with the
names
parameter unset (i.e. no parameter names).
SD_BUS_WRITABLE_PROPERTY()
, SD_BUS_PROPERTY()
¶Declare a D-Bus property with the name member
and value
signature signature
. Parameters get
and
set
are the getter and setter methods. They are called with a pointer
that is the userdata
parameter passed to the registration function
offset by offset
bytes. This may be used pass pointers to different
fields in the same data structure to different setters and getters in the same vtable. Parameter
flags
is a combination of flags, see below.
The setter and getter methods may be omitted (specified as NULL
), if the
property has one of the basic types or "as
" in case of read-only properties. In
those cases, the userdata
and offset
parameters must together point to valid variable of the corresponding type. A default setter and
getters will be provided, which simply copy the argument between this variable and the message.
SD_BUS_PROPERTY()
is used to define a read-only property.
SD_BUS_PARAM()
¶Parameter names should be wrapped in this macro, see the example below.
The flags
parameter is used to specify a combination of
D-Bus annotations.
SD_BUS_VTABLE_DEPRECATED
¶Mark this vtable entry as deprecated using the
org.freedesktop.DBus.Deprecated
annotation in introspection data. If
specified for SD_BUS_VTABLE_START()
, the annotation is applied to the
enclosing interface.
SD_BUS_VTABLE_HIDDEN
¶Make this vtable entry hidden. It will not be shown in introspection data. If
specified for SD_BUS_VTABLE_START()
, all entries in the array are hidden.
SD_BUS_VTABLE_UNPRIVILEGED
¶Mark this vtable entry as unprivileged. If not specified, the
org.freedesktop.systemd1.Privileged
annotation with value
"true
" will be shown in introspection data.
SD_BUS_VTABLE_METHOD_NO_REPLY
¶Mark his vtable entry as a method that will not return a reply using the
org.freedesktop.DBus.Method.NoReply
annotation in introspection data.
SD_BUS_VTABLE_PROPERTY_CONST
, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE
, SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION
¶Those three flags correspond to different values of the
org.freedesktop.DBus.Property.EmitsChangedSignal
annotation, which specifies
whether the org.freedesktop.DBus.Properties.PropertiesChanged
signal is
emitted whenever the property changes. SD_BUS_VTABLE_PROPERTY_CONST
corresponds to
const
and means that the property never changes during the lifetime of the
object it belongs to, so no signal needs to be emitted.
SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE
corresponds to true
and means
that the signal is emitted. SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION
corresponds to
invalidates
and means that the signal is emitted, but the value is not included
in the signal.
SD_BUS_VTABLE_PROPERTY_EXPLICIT
¶Mark this vtable property entry as requiring explicit request to for the value to
be shown (generally because the value is large or slow to calculate). This entry cannot be combined
with SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE
, and will not be shown in property listings by
default (e.g. busctl introspect). This corresponds to the
org.freedesktop.systemd1.Explicit
annotation in introspection data.
Example 1. Create a simple listener on the bus
#include <errno.h> #include <stdbool.h> #include <stddef.h> #include <stdlib.h> #include <stdio.h> #include <systemd/sd-bus.h> #define _cleanup_(f) __attribute__((cleanup(f))) typedef struct object { char *name; uint32_t number; } object; static int method(sd_bus_message *m, void *userdata, sd_bus_error *error) { printf("Got called with userdata=%p\n", userdata); return 1; } static const sd_bus_vtable vtable[] = { SD_BUS_VTABLE_START(0), SD_BUS_METHOD( "Method1", "s", "s", method, 0), SD_BUS_METHOD_WITH_NAMES_OFFSET( "Method2", "so", SD_BUS_PARAM(string) SD_BUS_PARAM(path), "s", SD_BUS_PARAM(returnstring), method, offsetof(object, number), SD_BUS_VTABLE_DEPRECATED), SD_BUS_WRITABLE_PROPERTY( "AutomaticStringProperty", "s", NULL, NULL, offsetof(object, name), SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE), SD_BUS_WRITABLE_PROPERTY( "AutomaticIntegerProperty", "u", NULL, NULL, offsetof(object, number), SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION), SD_BUS_VTABLE_END }; #define check(x) ({ \ int r = x; \ errno = r < 0 ? -r : 0; \ printf(#x ": %m\n"); \ if (r < 0) \ return EXIT_FAILURE; \ }) int main(int argc, char **argv) { _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL; sd_bus_default(&bus); object object = { .number = 666 }; check((object.name = strdup("name")) != NULL); check(sd_bus_add_object_vtable(bus, NULL, "/object", "org.freedesktop.systemd.VtableExample", vtable, &object)); for (;;) { check(sd_bus_wait(bus, UINT64_MAX)); check(sd_bus_process(bus, NULL)); } free(object.name); return 0; }
This creates a simple client on the bus (the user bus, when run as normal user).
We may use the D-Bus org.freedesktop.DBus.Introspectable.Introspect
call to acquire the XML description of the interface:
<!DOCTYPE node PUBLIC "-//freedesktop//DTD D-BUS Object Introspection 1.0//EN" "http://www.freedesktop.org/standards/dbus/1.0/introspect.dtd"> <node> <interface name="org.freedesktop.DBus.Peer"> <method name="Ping"/> <method name="GetMachineId"> <arg type="s" name="machine_uuid" direction="out"/> </method> </interface> <interface name="org.freedesktop.DBus.Introspectable"> <method name="Introspect"> <arg name="data" type="s" direction="out"/> </method> </interface> <interface name="org.freedesktop.DBus.Properties"> <method name="Get"> <arg name="interface" direction="in" type="s"/> <arg name="property" direction="in" type="s"/> <arg name="value" direction="out" type="v"/> </method> <method name="GetAll"> <arg name="interface" direction="in" type="s"/> <arg name="properties" direction="out" type="a{sv}"/> </method> <method name="Set"> <arg name="interface" direction="in" type="s"/> <arg name="property" direction="in" type="s"/> <arg name="value" direction="in" type="v"/> </method> <signal name="PropertiesChanged"> <arg type="s" name="interface"/> <arg type="a{sv}" name="changed_properties"/> <arg type="as" name="invalidated_properties"/> </signal> </interface> <interface name="org.freedesktop.systemd.VtableExample"> <method name="Method1"> <arg type="s" direction="in"/> <arg type="s" direction="out"/> </method> <method name="Method2"> <arg type="s" name="string" direction="in"/> <arg type="o" name="path" direction="in"/> <arg type="s" name="returnstring" direction="out"/> <annotation name="org.freedesktop.DBus.Deprecated" value="true"/> </method> <property name="AutomaticStringProperty" type="s" access="readwrite"> </property> <property name="AutomaticIntegerProperty" type="u" access="readwrite"> <annotation name="org.freedesktop.DBus.Property.EmitsChangedSignal" value="invalidates"/> </property> </interface> </node>
On success, sd_bus_add_object_vtable
and
sd_bus_add_fallback_vtable
calls return 0 or a positive integer. On failure, they
return a negative errno-style error code.
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.
-ENOMEM
¶Memory allocation failed.
-EPROTOTYPE
¶sd_bus_add_object_vtable
and
sd_bus_add_fallback_vtable
have been both called
for the same bus object path, which is not allowed.
-EEXIST
¶This vtable has already been registered for this
interface
and path
.
These APIs are implemented as a shared
library, which can be compiled and linked to with the
libsystemd
pkg-config(1)
file.