sd_bus_message_new_signal(3)

1SD_BUS_MESSAGE_NEW_SIGNAL(3)sd_bus_message_new_signaSlD_BUS_MESSAGE_NEW_SIGNAL(3)
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NAME

6       sd_bus_message_new_signal - Create a signal message
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SYNOPSIS

9       #include <systemd/sd-bus.h>
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11       int sd_bus_message_new_signal(sd_bus *bus, sd_bus_message **m,
12                                     const char *path, const char *interface,
13                                     const char *member);
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DESCRIPTION

16       The sd_bus_message_new_signal() function creates a new bus message
17       object that encapsulates a D-Bus signal, and returns it in the m output
18       parameter. The signal will be sent to path path, on the interface
19       interface, member member. When this message is sent, no reply is
20       expected. See sd_bus_message_new_call(1) for a short description of the
21       meaning of the path, interface, and member parameters.
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RETURN VALUE

24       This function returns 0 if the message object was successfully created,
25       and a negative errno-style error code otherwise.
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ERRORS

28       Returned errors may indicate the following problems:
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30       -EINVAL
31           The output parameter m is NULL.
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33           The path parameter is not a valid D-Bus path ("/an/object/path"),
34           the interface parameter is not a valid D-Bus interface name
35           ("an.interface.name"), or the member parameter is not a valid D-Bus
36           member ("Name").
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38       -ENOTCONN
39           The bus parameter bus is NULL or the bus is not connected.
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41       -ENOMEM
42           Memory allocation failed.
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NOTES

45       These APIs are implemented as a shared library, which can be compiled
46       and linked to with the libsystemd pkg-config(1) file.
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EXAMPLES

49       Example 1. Send a simple signal
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51           #include <systemd/sd-bus.h>
52           #define _cleanup_(f) __attribute__((cleanup(f)))
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54           int send_unit_files_changed(sd_bus *bus) {
55             _cleanup_(sd_bus_message_unrefp) sd_bus_message *message = NULL;
56             int r;
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58             r = sd_bus_message_new_signal(bus, &message,
59                                           "/org/freedesktop/systemd1",
60                                           "org.freedesktop.systemd1.Manager",
61                                           "UnitFilesChanged");
62             if (r < 0)
63               return r;
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65             return sd_bus_send(bus, message, NULL);
66           }
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68       This function in systemd sources is used to emit the "UnitFilesChanged"
69       signal when the unit files have been changed.
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