x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_BUS_MESSAGE_NEW_METHOsd_bus_message_new_meSD_BUS_MESSAGE_NEW_METHOD_CALL(3)
NAME
sd_bus_message_new_method_call, sd_bus_message_new_method_return -
Create a method call message
SYNOPSIS
#include <systemd/sd-bus.h>
int sd_bus_message_new_method_call(sd_bus *bus, sd_bus_message **m,
const char *destination,
const char *path,
const char *interface,
const char *member);
int sd_bus_message_new_method_return(sd_bus_message *call,
sd_bus_message **m);
DESCRIPTION
The sd_bus_message_new_method_call() function creates a new bus message
object that encapsulates a D-Bus method call, and returns it in the m
output parameter. The call will be made on the destination destination,
path path, on the interface interface, member member.
Briefly, the destination is a dot-separated name that identifies a
service connected to the bus. The path is a slash-separated identifier
of an object within the destination that resembles a file system path.
The meaning of this path is defined by the destination. The interface
is a dot-separated name that resembles a Java interface name that
identifies a group of methods and signals supported by the object
identified by path. Methods and signals are collectively called members
and are identified by a simple name composed of ASCII letters, numbers,
and underscores. See the D-Bus Tutorial[1] for an in-depth explanation.
The destination parameter may be NULL. The interface parameter may be
NULL, if the destination has only a single member with the given name
and there is no ambiguity if the interface name is omitted.
Note that this is a low level interface. See sd_bus_call_method(3) for
a more convenient way of calling D-Bus methods.
The sd_bus_message_new_method_return() function creates a new bus
message object that is a reply to the method call call and returns it
in the m output parameter. The call parameter must be a method call
message. The sender of call is used as the destination.
RETURN VALUE
On success, these functions return a non-negative integer. On failure,
they return a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-EINVAL
The output parameter m is NULL.
The destination parameter is non-null and is not a valid D-Bus
service name ("org.somewhere.Something"), the path parameter is not
a valid D-Bus path ("/an/object/path"), the interface parameter is
non-null and is not a valid D-Bus interface name
("an.interface.name"), or the member parameter is not a valid D-Bus
member ("Name").
The call parameter is not a method call object.
-ENOTCONN
The bus parameter bus is NULL or the bus is not connected.
-ENOMEM
Memory allocation failed.
-EPERM
The call parameter is not sealed.
-EOPNOTSUPP
The call message does not have a cookie.
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.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, *m = NULL;
int r;
r = sd_bus_open_system(&bus);
if (r < 0)
return log_error(r, "Failed to acquire bus");
r = sd_bus_message_new_method_call(bus, &m,
DESTINATION, PATH, INTERFACE, MEMBER);
if (r < 0)
return log_error(r, "Failed to create bus message");
r = sd_bus_message_append(m, "u", (unsigned) getpid());
if (r < 0)
return log_error(r, "Failed to append to bus message");
r = sd_bus_call(bus, m, -1, &error, &reply);
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, create a message object, send it, 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_call(3), sd_bus_call_method(3),
sd_bus_path_encode(3)
NOTES
1. D-Bus Tutorial
https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts
systemd 254 SD_BUS_MESSAGE_NEW_METHOD_CALL(3)
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