1SD_BUS_MESSAGE_NEW_METHODs_dC_AbLuLs(_3m)essage_new_metShDo_dB_UcSa_lMlESSAGE_NEW_METHOD_CALL(3)
2
6 sd_bus_message_new_method_call, sd_bus_message_new_method_return -
7 Create a method call message
8
10 #include <systemd/sd-bus.h>
11 int sd_bus_message_new_method_call(sd_bus *bus, sd_bus_message **m,
13 const char *destination,
14 const char *path,
15 const char *interface,
16 const char *member);
17 int sd_bus_message_new_method_return(sd_bus_message *call,
19 sd_bus_message **m);
20
22 The sd_bus_message_new_method_call() function creates a new bus message
23 object that encapsulates a D-Bus method call, and returns it in the m
24 output parameter. The call will be made on the destination destination,
25 path path, on the interface interface, member member.
26 Briefly, the destination is a dot-separated name that identifies a
28 service connected to the bus. The path is a slash-separated identifier
29 of an object within the destination that resembles a file system path.
30 The meaning of this path is defined by the destination. The interface
31 is a dot-separated name that resembles a Java interface name that
32 identifies a group of methods and signals supported by the object
33 identified by path. Methods and signals are collectively called members
34 and are identified by a simple name composed of ASCII letters, numbers,
35 and underscores. See the D-Bus Tutorial[1] for an in-depth explanation.
36 The destination parameter may be NULL. The interface parameter may be
38 NULL, if the destination has only a single member with the given name
39 and there is no ambiguity if the interface name is omitted.
40 Note that this is a low level interface. See sd_bus_call_method(3) for
42 a more convenient way of calling D-Bus methods.
43 The sd_bus_message_new_method_return() function creates a new bus
45 message object that is a reply to the method call call and returns it
46 in the m output parameter. The call parameter must be a method call
47 message. The sender of call is used as the destination.
48
50 On success, these functions return a non-negative integer. On failure,
51 they return a negative errno-style error code.
52 Errors
54 Returned errors may indicate the following problems:
55 -EINVAL
57 The output parameter m is NULL.
58 The destination parameter is non-null and is not a valid D-Bus
60 service name ("org.somewhere.Something"), the path parameter is not
61 a valid D-Bus path ("/an/object/path"), the interface parameter is
62 non-null and is not a valid D-Bus interface name
63 ("an.interface.name"), or the member parameter is not a valid D-Bus
64 member ("Name").
65 The call parameter is not a method call object.
67 -ENOTCONN
69 The bus parameter bus is NULL or the bus is not connected.
70 -ENOMEM
72 Memory allocation failed.
73 -EPERM
75 The call parameter is not sealed.
76 -EOPNOTSUPP
78 The call message does not have a cookie.
79
81 Functions described here are available as a shared library, which can
82 be compiled against and linked to with the libsystemd pkg-config(1)
83 file.
84 The code described here uses getenv(3), which is declared to be not
86 multi-thread-safe. This means that the code calling the functions
87 described here must not call setenv(3) from a parallel thread. It is
88 recommended to only do calls to setenv() from an early phase of the
89 program when no other threads have been started.
90
92 Example 1. Make a call to a D-Bus method that takes a single parameter
93 /* SPDX-License-Identifier: MIT-0 */
95 /* This is equivalent to:
97 * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
98 * org.freedesktop.systemd1.Manager GetUnitByPID $$
99 *
100 * Compile with 'cc print-unit-path.c -lsystemd'
101 */
102 #include <errno.h>
104 #include <stdio.h>
105 #include <sys/types.h>
106 #include <unistd.h>
107 #include <systemd/sd-bus.h>
109 #define _cleanup_(f) __attribute__((cleanup(f)))
111 #define DESTINATION "org.freedesktop.systemd1"
112 #define PATH "/org/freedesktop/systemd1"
113 #define INTERFACE "org.freedesktop.systemd1.Manager"
114 #define MEMBER "GetUnitByPID"
115 static int log_error(int error, const char *message) {
117 errno = -error;
118 fprintf(stderr, "%s: %m\n", message);
119 return error;
120 }
121 int main(int argc, char **argv) {
123 _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
124 _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
125 _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL, *m = NULL;
126 int r;
127 r = sd_bus_open_system(&bus);
129 if (r < 0)
130 return log_error(r, "Failed to acquire bus");
131 r = sd_bus_message_new_method_call(bus, &m,
133 DESTINATION, PATH, INTERFACE, MEMBER);
134 if (r < 0)
135 return log_error(r, "Failed to create bus message");
136 r = sd_bus_message_append(m, "u", (unsigned) getpid());
138 if (r < 0)
139 return log_error(r, "Failed to append to bus message");
140 r = sd_bus_call(bus, m, -1, &error, &reply);
142 if (r < 0)
143 return log_error(r, MEMBER " call failed");
144 const char *ans;
146 r = sd_bus_message_read(reply, "o", &ans);
147 if (r < 0)
148 return log_error(r, "Failed to read reply");
149 printf("Unit path is \"%s\".\n", ans);
151 return 0;
153 }
154 This defines a minimally useful program that will open a connection to
156 the bus, create a message object, send it, wait for the reply, and
157 finally extract and print the answer. It does error handling and proper
158 memory management.
159
161 systemd(1), sd-bus(3), sd_bus_call(3), sd_bus_call_method(3),
162 sd_bus_path_encode(3)
163
165 1. D-Bus Tutorial
166 https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts
167systemd 254 SD_BUS_MESSAGE_NEW_METHOD_CALL(3)