# sd_bus_call_method

## 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



           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



           **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) {
                 fprintf(stderr, "%s: %s\n", message, strerror(-error));
                 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.
    


* * *