sd_bus_message_new_method_return(3) — Linux manual page



NAME         top

       sd_bus_message_new_method_call, sd_bus_message_new_method_return -
       Create a method call message

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       int sd_bus_message_new_method_call(sd_bus *bus, sd_bus_message **m,
                                          const char *destination,
                                          const char *path,
                                          const char *interface,
                                          const char *member);

       int sd_bus_message_new_method_return(sd_bus_message *call,
                                            sd_bus_message **m);

DESCRIPTION         top

       The sd_bus_message_new_method_call() function creates a new bus
       message object that encapsulates a D-Bus method call, and returns it
       in the m output parameter. The call will be made on the destination
       destination, path path, on the interface interface, member member.

       Briefly, the destination is a dot-separated name that identifies a
       service connected to the bus. The path is a slash-separated
       identifier of an object within the destination that resembles a file
       system path. The meaning of this path is defined by the destination.
       The interface is a dot-separated name that resembles a Java interface
       name that identifies a group of methods and signals supported by the
       object identified by path. Methods and signals are collectively
       called members and are identified by a simple name composed of ASCII
       letters, numbers, and underscores. See the D-Bus Tutorial[1] for an
       in-depth explanation.

       The destination parameter may be NULL. The interface parameter may be
       NULL, if the destination has only a single member with the given name
       and there is no ambiguity if the interface name is omitted.

       Note that this is a low level interface. See sd_bus_call_method(3)
       for a more convenient way of calling D-Bus methods.

       The sd_bus_message_new_method_return() function creates a new bus
       message object that is a reply to the method call call and returns it
       in the m output parameter. The call parameter must be a method call
       message. The sender of call is used as the destination.

RETURN VALUE         top

       On success, these functions return a non-negative integer. On
       failure, they return a negative errno-style error code.

       Returned errors may indicate the following problems:

           The output parameter m is NULL.

           The destination parameter is non-null and is not a valid D-Bus
           service name ("org.somewhere.Something"), the path parameter is
           not a valid D-Bus path ("/an/object/path"), the interface
           parameter is non-null and is not a valid D-Bus interface name
           (""), or the member parameter is not a valid
           D-Bus member ("Name").

           The call parameter is not a method call object.

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

           Memory allocation failed.

           The call parameter is not sealed.

           The call message does not have a cookie.

NOTES         top

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

EXAMPLES         top

       Example 1. Make a call to a D-Bus method that takes a single

           #include <stdio.h>
           #include <string.h>
           #include <unistd.h>
           #include <sys/types.h>

           #include <systemd/sd-bus.h>
           #define _cleanup_(f) __attribute__((cleanup(f)))

           /* This is equivalent to:
            * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
            *       org.freedesktop.systemd1.Manager GetUnitByPID $$
            * Compile with 'cc -lsystemd print-unit-path.c'

           #define DESTINATION "org.freedesktop.systemd1"
           #define PATH        "/org/freedesktop/systemd1"
           #define INTERFACE   "org.freedesktop.systemd1.Manager"
           #define MEMBER      "GetUnitByPID"

           static int log_error(int error, const char *message) {
             fprintf(stderr, "%s: %s\n", message, strerror(-error));
             return error;

           static int print_unit_path(sd_bus *bus) {
             _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
             _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
             _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
             int r;

             r = sd_bus_message_new_method_call(bus, &m,
                                                DESTINATION, PATH, INTERFACE, MEMBER);
             if (r < 0)
               return log_error(r, "Failed to create bus message");

             r = sd_bus_message_append(m, "u", (unsigned) getpid());
             if (r < 0)
               return log_error(r, "Failed to append to bus message");

             r = sd_bus_call(bus, m, -1, &error, &reply);
             if (r < 0)
               return log_error(r, "Call failed");

             const char *ans;
             r = sd_bus_message_read(reply, "o", &ans);
             if (r < 0)
               return log_error(r, "Failed to read reply");

             printf("Unit path is \"%s\".\n", ans);

             return 0;

           int main(int argc, char **argv) {
             _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
             int r;

             r = sd_bus_open_system(&bus);
             if (r < 0)
               return log_error(r, "Failed to acquire bus");


       This defines a minimally useful program that will open a connection
       to the bus, create a message object, send it, wait for the reply, and
       finally extract and print the answer. It does error handling and
       proper memory management.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_call(3), sd_bus_call_method(3),

NOTES         top

        1. D-Bus Tutorial

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 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-11-01.)  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 im‐
       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to

systemd 247                                SD_BUS_MESSAGE_NEW_METHOD_CALL(3)

Pages that refer to this page: sd_bus_message_get_bus(3)sd_bus_message_method_call(3)SD_BUS_MESSAGE_METHOD_CALL(3)sd_bus_message_method_error(3)SD_BUS_MESSAGE_METHOD_ERROR(3)sd_bus_message_method_return(3)SD_BUS_MESSAGE_METHOD_RETURN(3)sd_bus_message_new(3)sd_bus_message_ref(3)sd_bus_message_signal(3)SD_BUS_MESSAGE_SIGNAL(3)sd_bus_message_unref(3)sd_bus_message_unrefp(3)sd_bus_reply_method_return(3)sd_bus_reply_method_returnv(3)30-systemd-environment-d-generator(7)systemd.index(7)