sd_bus_add_object_vtable
systemd
sd_bus_add_object_vtable
3
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)
Description
sd_bus_add_object_vtable() is used to declare attributes for the
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_floating3.
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_unref3.
The sd_bus_vtable array
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 is 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 a valid variable of the corresponding type. A default setter and getter
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.
Flags
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.
Examples
Create a simple listener on the bus
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:
Return Value
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.
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.
-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.
See Also
sd-bus3,
busctl1