1SD_BUS_MESSAGE_NEW_SIGNAL(3)sd_bus_message_new_signaSlD_BUS_MESSAGE_NEW_SIGNAL(3)
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6 sd_bus_message_new_signal, sd_bus_message_new_signal_to - Create a
7 signal message
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10 #include <systemd/sd-bus.h>
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12 int sd_bus_message_new_signal(sd_bus *bus, sd_bus_message **m,
13 const char *path, const char *interface,
14 const char *member);
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16 int sd_bus_message_new_signal_to(sd_bus *bus, sd_bus_message **m,
17 const char *destination,
18 const char *path,
19 const char *interface,
20 const char *member);
21
23 The sd_bus_message_new_signal() function creates a new bus message
24 object that encapsulates a D-Bus signal, and returns it in the m output
25 parameter. The signal will be sent to path path, on the interface
26 interface, member member. When this message is sent, no reply is
27 expected. See sd_bus_message_new_method_call(1) for a short description
28 of the meaning of the path, interface, and member parameters.
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30 sd_bus_message_new_signal_to() is a shorthand for creating a new bus
31 message to a specific destination. It's behavior is similar to calling
32 sd_bus_message_new_signal() followed by calling
33 sd_bus_message_set_destination(3).
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36 This function returns 0 if the message object was successfully created,
37 and a negative errno-style error code otherwise.
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39 Errors
40 Returned errors may indicate the following problems:
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42 -EINVAL
43 The output parameter m is NULL.
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45 The path parameter is not a valid D-Bus path ("/an/object/path"),
46 the interface parameter is not a valid D-Bus interface name
47 ("an.interface.name"), or the member parameter is not a valid D-Bus
48 member ("Name").
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50 -ENOTCONN
51 The bus parameter bus is NULL or the bus is not connected.
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53 -ENOMEM
54 Memory allocation failed.
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57 These APIs are implemented as a shared library, which can be compiled
58 and linked to with the libsystemd pkg-config(1) file.
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61 Example 1. Send a simple signal
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63 /* SPDX-License-Identifier: MIT-0 */
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65 #include <systemd/sd-bus.h>
66 #define _cleanup_(f) __attribute__((cleanup(f)))
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68 int send_unit_files_changed(sd_bus *bus) {
69 _cleanup_(sd_bus_message_unrefp) sd_bus_message *message = NULL;
70 int r;
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72 r = sd_bus_message_new_signal(bus, &message,
73 "/org/freedesktop/systemd1",
74 "org.freedesktop.systemd1.Manager",
75 "UnitFilesChanged");
76 if (r < 0)
77 return r;
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79 return sd_bus_send(bus, message, NULL);
80 }
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82 This function in systemd sources is used to emit the "UnitFilesChanged"
83 signal when the unit files have been changed.
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86 systemd(1), sd-bus(3), sd_bus_emit_signal(3)
87 sd_bus_message_set_destination(3)
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91systemd 253 SD_BUS_MESSAGE_NEW_SIGNAL(3)