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 These APIs are implemented as a shared library, which can be compiled
82 and linked to with the libsystemd pkg-config(1) file.
83
85 Example 1. Make a call to a D-Bus method that takes a single parameter
86 #include <stdio.h>
88 #include <string.h>
89 #include <unistd.h>
90 #include <sys/types.h>
91 #include <systemd/sd-bus.h>
93 #define _cleanup_(f) __attribute__((cleanup(f)))
94 /* This is equivalent to:
96 * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
97 * org.freedesktop.systemd1.Manager GetUnitByPID $$
98 *
99 * Compile with 'cc -lsystemd print-unit-path.c'
100 */
101 #define DESTINATION "org.freedesktop.systemd1"
103 #define PATH "/org/freedesktop/systemd1"
104 #define INTERFACE "org.freedesktop.systemd1.Manager"
105 #define MEMBER "GetUnitByPID"
106 static int log_error(int error, const char *message) {
108 fprintf(stderr, "%s: %s\n", message, strerror(-error));
109 return error;
110 }
111 static int print_unit_path(sd_bus *bus) {
113 _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
114 _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
115 _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
116 int r;
117 r = sd_bus_message_new_method_call(bus, &m,
119 DESTINATION, PATH, INTERFACE, MEMBER);
120 if (r < 0)
121 return log_error(r, "Failed to create bus message");
122 r = sd_bus_message_append(m, "u", (unsigned) getpid());
124 if (r < 0)
125 return log_error(r, "Failed to append to bus message");
126 r = sd_bus_call(bus, m, -1, &error, &reply);
128 if (r < 0)
129 return log_error(r, "Call failed");
130 const char *ans;
132 r = sd_bus_message_read(reply, "o", &ans);
133 if (r < 0)
134 return log_error(r, "Failed to read reply");
135 printf("Unit path is \"%s\".\n", ans);
137 return 0;
139 }
140 int main(int argc, char **argv) {
142 _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
143 int r;
144 r = sd_bus_open_system(&bus);
146 if (r < 0)
147 return log_error(r, "Failed to acquire bus");
148 print_unit_path(bus);
150 }
151 This defines a minimally useful program that will open a connection to
153 the bus, create a message object, send it, wait for the reply, and
154 finally extract and print the answer. It does error handling and proper
155 memory management.
156
158 systemd(1), sd-bus(3), sd_bus_call(3), sd_bus_call_method(3),
159 sd_bus_path_encode(3)
160
162 1. D-Bus Tutorial
163 https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts
164systemd 246 SD_BUS_MESSAGE_NEW_METHOD_CALL(3)