объявление свойств и методов для пути D-Bus (declare properties and methods for a D-Bus path)
Возвращаемое значение (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.
-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.
