sd_bus_message_new - Man Page

#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 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​^[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​.

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​.

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​.

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

sd-bus(3), sd_bus_add_match(3), sd_bus_call(3), sd_bus_message_get_signature(3), sd_bus_message_get_type(3), sd_bus_process(3), sd_bus_slot_ref(3), systemd.directives(7), systemd.index(7).

The man pages sd_bus_message_get_bus(3), SD_BUS_MESSAGE_METHOD_CALL(3), SD_BUS_MESSAGE_METHOD_ERROR(3), SD_BUS_MESSAGE_METHOD_RETURN(3), sd_bus_message_ref(3), SD_BUS_MESSAGE_SIGNAL(3), sd_bus_message_unref(3) and sd_bus_message_unrefp(3) are aliases of sd_bus_message_new(3).