Index · Directives systemd 250


sd_bus_add_node_enumerator — Add a node enumerator for a D-Bus object path prefix


#include <systemd/sd-bus.h>
typedef int (*sd_bus_node_enumerator_t)(sd_bus *bus,
 const char *prefix,
 void *userdata,
 char ***ret_nodes,
 sd_bus_error *ret_error);
int sd_bus_add_node_enumerator(sd_bus *bus,
 sd_bus_slot **slot,
 const char *path,
 sd_bus_node_enumerator_t callback,
 void *userdata);


sd_bus_add_node_enumerator() adds a D-Bus node enumerator for the given path prefix. The given callback is called to enumerate all the available objects with the given path prefix when required (e.g. when org.freedesktop.DBus.Introspectable.Introspect or org.freedesktop.DBus.ObjectManager.GetManagedObjects are called on a D-Bus service managed by sd-bus).

callback is called with the path and userdata pointer registered with sd_bus_add_node_enumerator(). When called, it should store all the child object paths of the given path prefix in ret_nodes with a NULL terminator item. The callback should return a non-negative value on success. If an error occurs, it can either return a negative integer, set ret_error to a non-empty error or do both. Any errors returned by the callback are encoded as D-Bus errors and sent back to the caller. Errors in ret_error take priority over negative return values.

Note that a node enumerator callback will only ever be called for a single path prefix and hence, for normal operation, prefix can be ignored. Also, a node enumerator is only used to enumerate the available child objects under a given prefix. To install a handler for a set of dynamic child objects, use sd_bus_add_fallback_vtable(3).

When sd_bus_add_node_enumerator() succeeds, a 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 node enumerator is not needed anymore, see sd_bus_slot_unref(3).

Return Value

On success, sd_bus_add_node_enumerator() returns a non-negative integer. On failure, it returns a negative errno-style error code.


Returned errors may indicate the following problems:


One of the required parameters is NULL or path is not a valid object path.


The bus cannot be resolved.


The bus was created in a different process.


Memory allocation failed.


These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.

See Also

sd-bus(3), busctl(1), sd_bus_add_fallback_vtable(3), sd_bus_slot_unref(3)