x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_BUS_ADD_OBJECT(3) sd_bus_add_object SD_BUS_ADD_OBJECT(3)
NAME
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
SYNOPSIS
#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(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_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
sd_bus_slot_unref(3).
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_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 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[1].
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_sensitive(3),
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_privilege(3). 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
capabilities(7) 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[2].
The whole bus may be marked as trusted, in which case annotations
at the entry level are ignored, see sd_bus_set_trusted(3).
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-daemon(1).
EXAMPLES
Example 1. Create a simple listener on the bus
/* SPDX-License-Identifier: MIT-0 */
#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)))
#define check(x) ({ \
int r = (x); \
errno = r < 0 ? -r : 0; \
printf(#x ": %m\n"); \
if (r < 0) \
return EXIT_FAILURE; \
})
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);
if (sd_bus_message_is_method_call(m,
"org.freedesktop.systemd.VtableExample",
"Method4"))
return 1;
const char *string;
check(sd_bus_message_read(m, "s", &string));
check(sd_bus_reply_method_return(m, "s", string));
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_METHOD_WITH_ARGS_OFFSET(
"Method3",
SD_BUS_ARGS("s", string, "o", path),
SD_BUS_RESULT("s", returnstring),
method, offsetof(object, number),
SD_BUS_VTABLE_UNPRIVILEGED),
SD_BUS_METHOD_WITH_ARGS(
"Method4",
SD_BUS_NO_ARGS,
SD_BUS_NO_RESULT,
method,
SD_BUS_VTABLE_UNPRIVILEGED),
SD_BUS_SIGNAL(
"Signal1",
"so",
0),
SD_BUS_SIGNAL_WITH_NAMES(
"Signal2",
"so", SD_BUS_PARAM(string) SD_BUS_PARAM(path),
0),
SD_BUS_SIGNAL_WITH_ARGS(
"Signal3",
SD_BUS_ARGS("s", string, "o", path),
0),
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
};
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,
"/org/freedesktop/systemd/VtableExample",
"org.freedesktop.systemd.VtableExample",
vtable,
&object));
check(sd_bus_request_name(bus,
"org.freedesktop.systemd.VtableExample",
0));
for (;;) {
check(sd_bus_wait(bus, UINT64_MAX));
check(sd_bus_process(bus, NULL));
}
check(sd_bus_release_name(bus, "org.freedesktop.systemd.VtableExample"));
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"
"https://www.freedesktop.org/standards/dbus/1.0/introspect.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<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="xml_data" type="s" direction="out"/>
</method>
</interface>
<interface name="org.freedesktop.DBus.Properties">
<method name="Get">
<arg name="interface_name" direction="in" type="s"/>
<arg name="property_name" direction="in" type="s"/>
<arg name="value" direction="out" type="v"/>
</method>
<method name="GetAll">
<arg name="interface_name" direction="in" type="s"/>
<arg name="props" direction="out" type="a{sv}"/>
</method>
<method name="Set">
<arg name="interface_name" direction="in" type="s"/>
<arg name="property_name" direction="in" type="s"/>
<arg name="value" direction="in" type="v"/>
</method>
<signal name="PropertiesChanged">
<arg type="s" name="interface_name"/>
<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>
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.
NOTES
Functions described here are available as a shared library, which can
be compiled against and linked to with the libsystemd pkg-config(1)
file.
The code described here uses getenv(3), which is declared to be not
multi-thread-safe. This means that the code calling the functions
described here must not call setenv(3) from a parallel thread. It is
recommended to only do calls to setenv() from an early phase of the
program when no other threads have been started.
SEE ALSO
sd-bus(3), busctl(1), sd_bus_emit_properties_changed(3),
sd_bus_emit_object_added(3)
NOTES
1. D-Bus annotations
https://dbus.freedesktop.org/doc/dbus-specification.html#introspection-format
2. polkit
https://www.freedesktop.org/software/polkit/docs/latest/
systemd 254 SD_BUS_ADD_OBJECT(3)
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