sd_bus_call_method(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | HISTORY | SEE ALSO | COLOPHON

SD_BUS_CALL_METHOD(3)      sd_bus_call_method      SD_BUS_CALL_METHOD(3)

NAME         top

       sd_bus_call_method, sd_bus_call_methodv,
       sd_bus_call_method_async, sd_bus_call_method_asyncv - Initialize
       a bus message object and invoke the corresponding D-Bus method
       call

SYNOPSIS         top

       #include <systemd/sd-bus.h>

       typedef int (*sd_bus_message_handler_t)(sd_bus_message *m,
                                               void *userdata,
                                               sd_bus_error *ret_error);

       int sd_bus_call_method(sd_bus *bus, const char *destination,
                              const char *path, const char *interface,
                              const char *member,
                              sd_bus_error *ret_error,
                              sd_bus_message **reply, const char *types,
                              ...);

       int sd_bus_call_methodv(sd_bus *bus, const char *destination,
                               const char *path, const char *interface,
                               const char *member,
                               sd_bus_error *ret_error,
                               sd_bus_message **reply,
                               const char *types, va_list ap);

       int sd_bus_call_method_async(sd_bus *bus, sd_bus_slot **slot,
                                    const char *destination,
                                    const char *path,
                                    const char *interface,
                                    const char *member,
                                    sd_bus_message_handler_t callback,
                                    void *userdata, const char *types,
                                    ...);

       int sd_bus_call_method_asyncv(sd_bus *bus, sd_bus_slot **slot,
                                     const char *destination,
                                     const char *path,
                                     const char *interface,
                                     const char *member,
                                     sd_bus_message_handler_t callback,
                                     void *userdata, const char *types,
                                     va_list ap);

DESCRIPTION         top

       sd_bus_call_method() is a convenience function for initializing a
       bus message object and calling the corresponding D-Bus method. It
       combines the sd_bus_message_new_method_call(3),
       sd_bus_message_append(3) and sd_bus_call(3) functions into a
       single function call.

       sd_bus_call_method_async() is a convenience function for
       initializing a bus message object and calling the corresponding
       D-Bus method asynchronously. It combines the
       sd_bus_message_new_method_call(3), sd_bus_message_append(3) and
       sd_bus_call_async(3) functions into a single function call.

RETURN VALUE         top

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

   Errors
       See the man pages of sd_bus_message_new_method_call(3),
       sd_bus_message_append(3), sd_bus_call(3) and sd_bus_call_async(3)
       for a list of possible errors.

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
       started.

EXAMPLES         top

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

           /* SPDX-License-Identifier: MIT-0 */

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

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

           #include <systemd/sd-bus.h>

           #define _cleanup_(f) __attribute__((cleanup(f)))
           #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) {
             errno = -error;
             fprintf(stderr, "%s: %m\n", message);
             return error;
           }

           int main(int argc, char **argv) {
             _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = 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_open_system(&bus);
             if (r < 0)
               return log_error(r, "Failed to acquire bus");

             r = sd_bus_call_method(bus, DESTINATION, PATH, INTERFACE, MEMBER, &error, &reply, "u", (unsigned) getpid());
             if (r < 0)
               return log_error(r, MEMBER " 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;
           }

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

HISTORY         top

       sd_bus_call_method(), sd_bus_call_methodv(),
       sd_bus_call_method_async(), and sd_bus_call_method_asyncv() were
       added in version 246.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_message_new_method_call(3),
       sd_bus_message_append(3), sd_bus_call(3), sd_bus_set_property(3),
       sd_bus_emit_signal(3)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http:https://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http:https://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ 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
       [email protected]

systemd 255                                        SD_BUS_CALL_METHOD(3)

Pages that refer to this page: sd-bus(3)sd_bus_call(3)sd_bus_emit_signal(3)sd_bus_interface_name_is_valid(3)sd_bus_message_new_method_call(3)sd_bus_send(3)sd_bus_set_property(3)sd_bus_slot_ref(3)systemd.directives(7)systemd.index(7)