systemd sd_bus_message_new_method_call 3 sd_bus_message_new_method_call sd_bus_message_new_method_return Create a method call message #include <systemd/sd-bus.h> int sd_bus_message_new_method_call sd_bus *bus sd_bus_message **m const char *destination const char *path const char *interface const char *member int sd_bus_message_new_method_return sd_bus_message *call sd_bus_message **m The sd_bus_message_new_method_call() function creates a new bus message object that encapsulates a D-Bus method call, and returns it in the m output parameter. The call will be made on the destination destination, path path, on the interface interface, member member. Briefly, the destination is a dot-separated name that identifies a service connected to the bus. The path is a slash-separated identifier of an object within the destination that resembles a file system path. The meaning of this path is defined by the destination. The interface is a dot-separated name that resembles a Java interface name that identifies a group of methods and signals supported by the object identified by path. Methods and signals are collectively called members and are identified by a simple name composed of ASCII letters, numbers, and underscores. See the D-Bus Tutorial for an in-depth explanation. The destination parameter may be NULL. The interface parameter may be NULL, if the destination has only a single member with the given name and there is no ambiguity if the interface name is omitted. Note that this is a low level interface. See sd_bus_call_method3 for a more convenient way of calling D-Bus methods. The sd_bus_message_new_method_return() function creates a new bus message object that is a reply to the method call call and returns it in the m output parameter. The call parameter must be a method call message. The sender of call is used as the destination. On success, these functions return a non-negative integer. On failure, they return a negative errno-style error code. Returned errors may indicate the following problems: -EINVAL The output parameter m is NULL. The destination parameter is non-null and is not a valid D-Bus service name (org.somewhere.Something), the path parameter is not a valid D-Bus path (/an/object/path), the interface parameter is non-null and is not a valid D-Bus interface name (an.interface.name), or the member parameter is not a valid D-Bus member (Name). The call parameter is not a method call object. -ENOTCONN The bus parameter bus is NULL or the bus is not connected. -ENOMEM Memory allocation failed. -EPERM The call parameter is not sealed. -EOPNOTSUPP The call message does not have a cookie. This defines a minimally useful program that will open a connection to the bus, create a message object, send it, wait for the reply, and finally extract and print the answer. It does error handling and proper memory management. systemd1, sd-bus3, sd_bus_call3, sd_bus_call_method3, sd_bus_path_encode3