NAME

       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

       #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

       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

       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

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

EXAMPLES

       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.

SEE ALSO

       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)