x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_BUS_CALL_METHOD(3) sd_bus_call_method 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.
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) {
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)
systemd 254 SD_BUS_CALL_METHOD(3)
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