sd_event_get_fd(3)

1SD_EVENT_GET_FD(3)              sd_event_get_fd             SD_EVENT_GET_FD(3)
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NAME

6       sd_event_get_fd - Obtain a file descriptor to poll for event loop
7       events
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SYNOPSIS

10       #include <systemd/sd-event.h>
11
12       int sd_event_get_fd(sd_event *event);
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DESCRIPTION

15       sd_event_get_fd() returns the file descriptor that an event loop object
16       returned by the sd_event_new(3) function uses to wait for events. This
17       file descriptor may itself be polled for POLLIN/EPOLLIN events. This
18       makes it possible to embed an sd-event(3) event loop into another,
19       possibly foreign, event loop.
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21       The returned file descriptor refers to an epoll(7) object. It is
22       recommended not to alter it by invoking epoll_ctl(2) on it, in order to
23       avoid interference with the event loop's inner logic and assumptions.
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RETURN VALUE

26       On success, sd_event_get_fd() returns a non-negative file descriptor.
27       On failure, it returns a negative errno-style error code.
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ERRORS

30       Returned errors may indicate the following problems:
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32       -EINVAL
33           event is not a valid pointer to an sd_event structure.
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35       -ECHILD
36           The event loop has been created in a different process.
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EXAMPLES

39       Example 1. Integration in the GLib event loop
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41           /* SPDX-License-Identifier: MIT */
42
43           #include <stdlib.h>
44           #include <glib.h>
45           #include <systemd/sd-event.h>
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47           typedef struct SDEventSource {
48             GSource source;
49             GPollFD pollfd;
50             sd_event *event;
51           } SDEventSource;
52
53           static gboolean event_prepare(GSource *source, gint *timeout_) {
54             return sd_event_prepare(((SDEventSource *)source)->event) > 0;
55           }
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57           static gboolean event_check(GSource *source) {
58             return sd_event_wait(((SDEventSource *)source)->event, 0) > 0;
59           }
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61           static gboolean event_dispatch(GSource *source, GSourceFunc callback, gpointer user_data) {
62             return sd_event_dispatch(((SDEventSource *)source)->event) > 0;
63           }
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65           static void event_finalize(GSource *source) {
66             sd_event_unref(((SDEventSource *)source)->event);
67           }
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69           static GSourceFuncs event_funcs = {
70             .prepare = event_prepare,
71             .check = event_check,
72             .dispatch = event_dispatch,
73             .finalize = event_finalize,
74           };
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76           GSource *g_sd_event_create_source(sd_event *event) {
77             SDEventSource *source;
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79             source = (SDEventSource *)g_source_new(&event_funcs, sizeof(SDEventSource));
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81             source->event = sd_event_ref(event);
82             source->pollfd.fd = sd_event_get_fd(event);
83             source->pollfd.events = G_IO_IN | G_IO_HUP | G_IO_ERR;
84
85             g_source_add_poll((GSource *)source, &source->pollfd);
86
87             return (GSource *)source;
88           }
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NOTES

91       These APIs are implemented as a shared library, which can be compiled
92       and linked to with the libsystemd pkg-config(1) file.
93