SD_BUS_MESSAGE_NEW(3)

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 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 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 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

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

SEE ALSO

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)

NOTES

1.  Clean-up Variable Attribute
    https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html