sd_bus_message

Name

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

Synopsis

#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);

Description¶

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 internal reference counter of m by one.

sd_bus_message_unref() decreases the internal 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 GCC's and LLVM's Clean-up Variable Attribute. 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.

Return Value¶

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.

Errors¶

Returned errors may indicate the following problems:

-EINVAL¶: Specified type is invalid.
-ENOTCONN¶: The bus parameter bus is NULL or the bus is not connected.
-ENOMEM¶: Memory allocation failed.

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.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel.

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.

History¶

sd_bus_message_new(), sd_bus_message_ref(), sd_bus_message_unref(), sd_bus_message_unrefp(), and sd_bus_message_get_bus() were added in version 240.