sd_bus_message_new(3) — Linux manual page


SD_BUS_MESSAGE_NEW(3)      sd_bus_message_new      SD_BUS_MESSAGE_NEW(3)

NAME         top

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

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       enum {

       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         top

       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_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_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

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

RETURN VALUE         top

       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.

       Returned errors may indicate the following problems:

           Specified type is invalid.

           The bus parameter bus is NULL or the bus is not connected.

           Memory allocation failed.

NOTES         top

       Functions described here are available as a shared library, which
       can be compiled against and linked to with the
       libsystemd pkg-config(1) file.

       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

HISTORY         top

       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.

SEE ALSO         top

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

NOTES         top

        1. Clean-up Variable Attribute

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 255                                        SD_BUS_MESSAGE_NEW(3)

Pages that refer to this page: 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)