sd_bus_add_object
systemd
sd_bus_add_object
3
sd_bus_add_object
sd_bus_add_fallback
sd_bus_add_object_vtable
sd_bus_add_fallback_vtable
sd_bus_add_filter
SD_BUS_VTABLE_CAPABILITY
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_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
sd_bus *bus
sd_bus_slot **slot
const char *path
sd_bus_message_handler_t callback
void *userdata
int sd_bus_add_fallback
sd_bus *bus
sd_bus_slot **slot
const char *path
sd_bus_message_handler_t callback
void *userdata
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
int sd_bus_add_filter
sd_bus *bus
sd_bus_slot **slot
sd_bus_message_handler_t callback
void *userdata
SD_BUS_VTABLE_CAPABILITY(capability)
SD_BUS_VTABLE_START(flags)
SD_BUS_VTABLE_END
SD_BUS_METHOD_WITH_ARGS_OFFSET(member,
args,
result,
handler,
offset,
flags)
SD_BUS_METHOD_WITH_ARGS(member,
args,
result,
handler,
flags)
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_ARGS(member,
args,
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_ARGS(...)
SD_BUS_RESULT(...)
SD_BUS_NO_ARGS
SD_BUS_NO_RESULT
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. An interface can have any number of vtables attached to it.
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 authorization).
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 method 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.
However, if producing a reply takes too long, the method call will time out at the caller. This is
only available to methods and not properties.
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_errno3
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_error3
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_set3
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_errno3
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_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(flags)
SD_BUS_VTABLE_END
Those must always be the first and last element. The
flags parameter can be used to set attributes that apply to the whole
array; see the "Flags" section below.
SD_BUS_METHOD_WITH_ARGS_OFFSET()
SD_BUS_METHOD_WITH_ARGS()
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 example.
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_return3
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 calling
SD_BUS_METHOD_WITH_ARGS_OFFSET() with an offset of zero.
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. 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_ARGS_OFFSET().
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.
SD_BUS_SIGNAL_WITH_ARGS()
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.
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.
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.
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_METHOD_NO_REPLY
Mark this 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.
SD_BUS_VTABLE_SENSITIVE
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_sensitive3,
so that they are erased from memory when freed.
SD_BUS_VTABLE_ABSOLUTE_OFFSET
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.
SD_BUS_VTABLE_CAPABILITY(capability)
Access to this vtable entry will be allowed if the calling process has the
capability capability, as described in
sd_bus_query_sender_privilege3.
If used for SD_BUS_VTABLE_START(), provides a default for all entries in the
array. If not specified, either for an individual entry or the whole array,
CAP_SYS_ADMIN is checked by default. See capabilities7
for information about capabilities.
Note that vtable entries may be marked as unprivileged and the whole bus may be marked as
trusted, see the discussion of SD_BUS_VTABLE_UNPRIVILEGED below.
SD_BUS_VTABLE_UNPRIVILEGED
Mark this vtable entry as unprivileged. Access to privileged entries is limited to
users with appropriate capabilities as described above. In practice many vtable entries are marked
as unprivileged, and either are open to everyone, or the decision whether to allow access is taken
later, e.g. by delegating to polkit.
The whole bus may be marked as trusted, in which case annotations at the entry level are
ignored, see
sd_bus_set_trusted3.
When not specified, the
org.freedesktop.systemd1.Privileged annotation with value
true will be shown in introspection data.
SD_BUS_VTABLE_UNPRIVILEGED may not be applied to read-only properties,
but read access (to both read-only and writable properties) is always unrestricted.
Note that this page describes checks implemented in the D-Bus client. The D-Bus server has an
additional policy that may permit or deny connections, see
"CONFIGURATION FILE" in
dbus-daemon1.
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() return a non-negative 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, library or module instance.
-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.
History
sd_bus_property_get_t(),
sd_bus_property_set_t(),
sd_bus_object_find_t(),
sd_bus_add_object(),
sd_bus_add_fallback(),
sd_bus_add_object_vtable(),
sd_bus_add_fallback_vtable(), and
sd_bus_add_filter() were added in version 221.
See Also
sd-bus3
busctl1
sd_bus_emit_properties_changed3
sd_bus_emit_object_added3