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. An interface can have any number of vtables attached to
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).
sd_bus_add_object() attaches a callback directly to the object path
path. An object path can have any number of callbacks attached to it.
Each callback is prepended to the list of callbacks which are always
called in order. sd_bus_add_fallback() is similar to
sd_bus_add_object() but applies to fallback paths instead.
sd_bus_add_filter() installs a callback that is invoked for each
incoming D-Bus message. Filters can be used to handle logic common to
all messages received by a service (e.g. authentication or
When a request is received, any associated callbacks are called
sequentially until a callback returns a non-zero integer. Return zero
from a callback to give other callbacks the chance to process the
request. Callbacks are called in the following order: first, global
callbacks installed with sd_bus_add_filter() are called. Second,
callbacks attached directly to the request object path are called,
followed by any D-Bus method callbacks attached to the request object
path, interface and member. Finally, the property callbacks attached
to the request object path, interface and member are called. If the
final callback returns zero, an error reply is sent back to the
caller indicating no matching object for the request was found. Note
that you can return a positive integer from a callback without
immediately sending a reply. This informs sd-bus this callback will
take responsibility for replying to the request without forcing the
callback to produce a reply immediately. This allows a callback to
perform any number of asynchronous operations required to construct a
reply. Note that if producing a reply takes too long, the method call
will time out at the caller.
If a callback was invoked to handle a request that expects a reply
and the callback returns a negative value, the value is interpreted
as a negative errno-style error code and sent back to the caller as a
D-Bus error as if sd_bus_reply_method_errno(3) was called.
Additionally, all callbacks take a sd_bus_error output parameter that
can be used to provide more detailed error information. If ret_error
is set when the callback finishes, the corresponding D-Bus error is
sent back to the caller as if sd_bus_reply_method_error(3) was
called. Any error stored in ret_error takes priority over any
negative values returned by the same callback when determining which
error to send back to the caller. Use sd_bus_error_set(3) or one of
its variants to set ret_error and return a negative integer from a
callback with a single function call. To send an error reply after a
callback has already finished, use sd_bus_reply_method_errno(3) or
one of its variants.
For all 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
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
Those must always be the first and last element.
Declare a D-Bus method with the name member, arguments args and
result result. args expects a sequence of argument type/name
pairs wrapped in the SD_BUS_ARGS() macro. The elements at even
indices in this list describe the types of the method's
arguments. The method's parameter signature is the concatenation
of all the string literals at even indices in args. If a method
has no parameters, pass SD_BUS_NO_ARGS to args. The elements at
uneven indices describe the names of the method's arguments.
result expects a sequence of type/name pairs wrapped in the
SD_BUS_RESULT() macro in the same format as SD_BUS_ARGS(). The
method's result signature is the concatenation of all the string
literals at even indices in result. If a method has no result,
pass SD_BUS_NO_RESULT to result. Note that argument types are
expected to be quoted string literals and argument names are
expected to be unquoted string literals. See below for a complete
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. To send a reply from
handler, call sd_bus_reply_method_return(3) with the message the
callback was invoked with. Parameter flags is a combination of
flags, see below. SD_BUS_METHOD_WITH_ARGS() is a shorthand for
SD_BUS_METHOD_WITH_ARGS_OFFSET() with an offset of
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.
in_names and out_names should be created using the
SD_BUS_PARAM() macro, see below. In all other regards, this
macro behaves exactly the same as
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.
Prefer using SD_BUS_METHOD_WITH_ARGS_OFFSET() and
SD_BUS_METHOD_WITH_ARGS() over these macros as they allow
specifying argument types and names next to each other which
is less error-prone than first specifying all argument types
followed by specifying all argument names.
>Declare a D-Bus signal with the name member and arguments
args. args expects a sequence of argument type/name pairs
wrapped in the SD_BUS_ARGS() macro. The elements at even
indices in this list describe the types of the signal's
arguments. The signal's parameter signature is the
concatenation of all the string literals at even indices in
args. If a signal has no parameters, pass SD_BUS_NO_ARGS to
args. The elements at uneven indices describe the names of
the signal's arguments. Parameter flags is a combination of
flags. See below for a complete example.
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.
SD_BUS_SIGNAL() is equivalent to SD_BUS_SIGNAL_WITH_NAMES()
with the names parameter unset (i.e. no parameter names).
Prefer using SD_BUS_SIGNAL_WITH_ARGS() over these macros as
it allows specifying argument types and names next to each
other which is less error-prone than first specifying all
argument types followed by specifying all argument names.
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.
Parameter names should be wrapped in this macro, see the
The flags parameter is used to specify a combination of D-Busannotations.
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.
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.
Mark this vtable entry as unprivileged. If not specified, the
org.freedesktop.systemd1.Privileged annotation with value "true"
will be shown in introspection data.
Mark his vtable entry as a method that will not return a reply
using the org.freedesktop.DBus.Method.NoReply annotation in
Those three flags correspond to different values of the
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.
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.
Mark this vtable method entry as processing sensitive data. When
set, incoming method call messages and their outgoing reply
messages are marked as sensitive using
sd_bus_message_sensitive(3), so that they are erased from memory
Mark this vtable method or property entry so that the user data
pointer passed to its associated handler functions is determined
slightly differently: instead of adding the offset parameter of
the entry to the user data pointer specified during vtable
registration, the offset is passed directly, converted to a
pointer, without taking the user data pointer specified during
vtable registration into account.
On success, sd_bus_add_object_vtable() and
sd_bus_add_fallback_vtable() return a non-negative integer. On
failure, they return a negative errno-style error code.
Returned errors may indicate the following problems:
One of the required parameters is NULL or invalid. A reserved
D-Bus interface was passed as the interface parameter.
The bus cannot be resolved.
The bus was created in a different process.
Memory allocation failed.
-EPROTOTYPEsd_bus_add_object_vtable and sd_bus_add_fallback_vtable have been
both called for the same bus object path, which is not allowed.
This vtable has already been registered for this interface and
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systemd 246 SD_BUS_ADD_OBJECT(3)