sd_bus_call_method, sd_bus_call_methodv, sd_bus_call_method_async, sd_bus_call_method_asyncv - Initialize

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.

Example1.MakeacalltoaD-Busmethodthattakesasingleparameter /* 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.

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.

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

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemdpkg-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.

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.

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) systemd 257.7 SD_BUS_CALL_METHOD(3)