SD_BUS_CALL_METHOD(3)

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.

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel.

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.

HISTORY

sd_bus_call_method(), and sd_bus_call_method_async() were added in version 221.

sd_bus_call_methodv(), sd_bus_call_method_asyncv() were added in version 246.

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)