1SD_BUS_MESSAGE_NEW_METHODs_dC_AbLuLs(_3m)essage_new_metShDo_dB_UcSa_lMlESSAGE_NEW_METHOD_CALL(3)
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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>
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12 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);
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18 int sd_bus_message_new_method_return(sd_bus_message *call,
19 sd_bus_message **m);
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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.
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27 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.
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37 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.
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41 The sd_bus_message_new_method_call() function creates a new bus message
42 object that is a reply to the method call call and returns it in the m
43 output parameter. The call parameter must be a method call message. The
44 sender of call is used as the destination.
45
47 This function returns 0 if the message object was successfully created,
48 and a negative errno-style error code otherwise.
49
50 Errors
51 Returned errors may indicate the following problems:
52
53 -EINVAL
54 The output parameter m is NULL.
55
56 The destination parameter is non-null and is not a valid D-Bus
57 service name ("org.somewhere.Something"), the path parameter is not
58 a valid D-Bus path ("/an/object/path"), the interface parameter is
59 non-null and is not a valid D-Bus interface name
60 ("an.interface.name"), or the member parameter is not a valid D-Bus
61 member ("Name").
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63 The call parameter is not a method call object.
64
65 -ENOTCONN
66 The bus parameter bus is NULL or the bus is not connected.
67
68 -ENOMEM
69 Memory allocation failed.
70
71 -EPERM
72 The call parameter is not sealed.
73
74 -EOPNOTSUPP
75 The call message does not have a cookie.
76
78 These APIs are implemented as a shared library, which can be compiled
79 and linked to with the libsystemd pkg-config(1) file.
80
82 Example 1. Make a call to a D-Bus method that takes a single parameter
83
84 #include <stdio.h>
85 #include <string.h>
86 #include <unistd.h>
87 #include <sys/types.h>
88
89 #include <systemd/sd-bus.h>
90 #define _cleanup_(f) __attribute__((cleanup(f)))
91
92 /* This is equivalent to:
93 * busctl call org.freedesktop.systemd1 /org/freedesktop/systemd1 \
94 * org.freedesktop.systemd1.Manager GetUnitByPID $$
95 *
96 * Compile with 'cc -lsystemd print-unit-path.c'
97 */
98
99 #define DESTINATION "org.freedesktop.systemd1"
100 #define PATH "/org/freedesktop/systemd1"
101 #define INTERFACE "org.freedesktop.systemd1.Manager"
102 #define MEMBER "GetUnitByPID"
103
104 static int log_error(int error, const char *message) {
105 fprintf(stderr, "%s: %s\n", message, strerror(-error));
106 return error;
107 }
108
109 static int print_unit_path(sd_bus *bus) {
110 _cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
111 _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
112 _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
113 int r;
114
115 r = sd_bus_message_new_method_call(bus, &m,
116 DESTINATION, PATH, INTERFACE, MEMBER);
117 if (r < 0)
118 return log_error(r, "Failed to create bus message");
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120 r = sd_bus_message_append(m, "u", (unsigned) getpid());
121 if (r < 0)
122 return log_error(r, "Failed to append to bus message");
123
124 r = sd_bus_call(bus, m, -1, &error, &reply);
125 if (r < 0)
126 return log_error(r, "Call failed");
127
128 const char *ans;
129 r = sd_bus_message_read(reply, "o", &ans);
130 if (r < 0)
131 return log_error(r, "Failed to read reply");
132
133 printf("Unit path is \"%s\".\n", ans);
134
135 return 0;
136 }
137
138 int main(int argc, char **argv) {
139 _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
140 int r;
141
142 r = sd_bus_open_system(&bus);
143 if (r < 0)
144 return log_error(r, "Failed to acquire bus");
145
146 print_unit_path(bus);
147 }
148
149 This defines a minimally useful program that will open a connection to
150 the bus, create a message object, send it, wait for the reply, and
151 finally extract and print the answer. It does error handling and proper
152 memory management.
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155 systemd(1), sd-bus(3), sd_bus_path_encode(3)
156
158 1. D-Bus Tutorial
159 https://dbus.freedesktop.org/doc/dbus-tutorial.html#concepts
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163systemd 245 SD_BUS_MESSAGE_NEW_METHOD_CALL(3)