Manpages - sd_bus_message_new.3

sd_bus_message_new, sd_bus_message_ref, sd_bus_message_unref, sd_bus_message_unrefp, SD_BUS_MESSAGE_METHOD_CALL, SD_BUS_MESSAGE_METHOD_RETURN, SD_BUS_MESSAGE_METHOD_ERROR, SD_BUS_MESSAGE_SIGNAL, sd_bus_message_get_bus - Create a new bus message object and create or destroy references to it

  #include <systemd/sd-bus.h>

  enum {
        SD_BUS_MESSAGE_METHOD_CALL,
        SD_BUS_MESSAGE_METHOD_RETURN,
        SD_BUS_MESSAGE_METHOD_ERROR,
        SD_BUS_MESSAGE_SIGNAL,
  };

int sd_bus_message_new(sd_bus **/bus/, sd_bus_message **/m/, uint8_t type);*

sd_bus_message *sd_bus_message_ref(sd_bus_message **/m/);*

sd_bus_message *sd_bus_message_unref(sd_bus_message **/m/);*

void sd_bus_message_unrefp(sd_bus_message ***/mp/);*

sd_bus *sd_bus_message_get_bus(sd_bus_message **/m/);*

sd_bus_message_new() creates a new bus message object attached to the bus bus and returns it in the output parameter m. This object is reference-counted, and will be destroyed when all references are gone. Initially, the caller of this function owns the sole reference to the message object. Note that the message object holds a reference to the bus object, so the bus object will not be destroyed as long as the message exists.

Note: this is a low-level call. In most cases functions like *sd_bus_message_new_method_call*(3), *sd_bus_message_new_method_error*(3), *sd_bus_message_new_method_return*(3), and *sd_bus_message_new_signal*(3) that create a message of a certain type and initialize various fields are easier to use.

The type parameter specifies the type of the message. It must be one of SD_BUS_MESSAGE_METHOD_CALL — a method call, SD_BUS_MESSAGE_METHOD_RETURN — a method call reply, SD_BUS_MESSAGE_METHOD_ERROR — an error reply to a method call, SD_BUS_MESSAGE_SIGNAL — a broadcast message with no reply.

The flag to allow interactive authorization is initialized based on the current value set in the bus object, see *sd_bus_set_allow_interactive_authorization*(3). This may be changed using *sd_bus_message_set_allow_interactive_authorization*(3).

sd_bus_message_ref() increases the reference counter of m by one.

sd_bus_message_unref() decreases the reference counter of m by one. Once the reference count has dropped to zero, message object is destroyed and cannot be used anymore, so further calls to sd_bus_message_ref() or sd_bus_message_unref() are illegal.

sd_bus_message_unrefp() is similar to sd_bus_message_unref() but takes a pointer to a pointer to an sd_bus_message object. This call is useful in conjunction with GCCs and LLVMs Clean-up Variable Attribute[1]. See *sd_bus_new*(3) for an example how to use the cleanup attribute.

sd_bus_message_ref() and sd_bus_message_unref() execute no operation if the passed in bus message object address is NULL. sd_bus_message_unrefp() will first dereference its argument, which must not be NULL, and will execute no operation if that is NULL.

sd_bus_message_get_bus() returns the bus object that message m is attached to.

On success, sd_bus_message_new() returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

sd_bus_message_ref() always returns the argument.

sd_bus_message_unref() always returns NULL.

sd_bus_message_get_bus() always returns the bus object.

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

*systemd*(1), *sd-bus*(3), *sd_bus_new*(3), *sd_bus_message_new_method_call*(3), *sd_bus_message_new_method_error*(3), *sd_bus_message_new_method_return*(3), *sd_bus_message_new_signal*(3)

1.

Clean-up Variable Attribute

https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html