|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
SD_BUS_MESSAGE_NEW_METHOD_CALL(3)sage_new_method_callSAGE_NEW_METHOD_CALL(3)
sd_bus_message_new_method_call, sd_bus_message_new_method_return -
Create a method call message
#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);
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.
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.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
Example 1. Make a call to a D-Bus method that takes a single
parameter
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <systemd/sd-bus.h>
#define _cleanup_(f) __attribute__((cleanup(f)))
/* This is equivalent to:
* busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
* org.freedesktop.systemd1.Manager GetUnitByPID $$
*
* Compile with 'cc -lsystemd print-unit-path.c'
*/
#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;
}
static int print_unit_path(sd_bus *bus) {
_cleanup_(sd_bus_message_unrefp) sd_bus_message *m = 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_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, "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;
}
int main(int argc, char **argv) {
_cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
int r;
r = sd_bus_open_system(&bus);
if (r < 0)
return log_error(r, "Failed to acquire bus");
print_unit_path(bus);
}
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.
systemd(1), sd-bus(3), sd_bus_call(3), sd_bus_call_method(3),
sd_bus_path_encode(3)
1. D-Bus Tutorial
https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to man-pages@man7.org
systemd 246 SD_BUS_MESSAGE_NEW_METHOD_CALL(3)
Pages that refer to this page: sd-bus(3) , sd_bus_call(3) , sd_bus_call_async(3) , sd_bus_call_method(3) , sd_bus_call_method_async(3) , sd_bus_call_method_asyncv(3) , sd_bus_call_methodv(3) , sd_bus_message_get_bus(3) , sd_bus_message_get_creds(3) , sd_bus_message_get_destination(3) , sd_bus_message_get_errno(3) , sd_bus_message_get_error(3) , sd_bus_message_get_interface(3) , sd_bus_message_get_member(3) , sd_bus_message_get_path(3) , sd_bus_message_get_sender(3) , sd_bus_message_get_type(3) , sd_bus_message_is_method_call(3) , sd_bus_message_is_method_error(3) , sd_bus_message_is_signal(3) , sd_bus_message_method_call(3) , SD_BUS_MESSAGE_METHOD_CALL(3) , sd_bus_message_method_error(3) , SD_BUS_MESSAGE_METHOD_ERROR(3) , sd_bus_message_method_return(3) , SD_BUS_MESSAGE_METHOD_RETURN(3) , sd_bus_message_new(3) , sd_bus_message_ref(3) , sd_bus_message_sensitive(3) , sd_bus_message_set_destination(3) , sd_bus_message_set_sender(3) , sd_bus_message_signal(3) , SD_BUS_MESSAGE_SIGNAL(3) , sd_bus_message_unref(3) , sd_bus_message_unrefp(3) , 30-systemd-environment-d-generator(7) , systemd.directives(7) , systemd.index(7)