1SD_EVENT_GET_FD(3) sd_event_get_fd SD_EVENT_GET_FD(3)
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6 sd_event_get_fd - Obtain a file descriptor to poll for event loop
7 events
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10 #include <systemd/sd-event.h>
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12 int sd_event_get_fd(sd_event *event);
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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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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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29 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, library or
37 module instance.
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40 Example 1. Integration in the GLib event loop
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42 /* SPDX-License-Identifier: MIT-0 */
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44 #include <stdlib.h>
45 #include <glib.h>
46 #include <systemd/sd-event.h>
47
48 typedef struct SDEventSource {
49 GSource source;
50 GPollFD pollfd;
51 sd_event *event;
52 } SDEventSource;
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54 static gboolean event_prepare(GSource *source, gint *timeout_) {
55 return sd_event_prepare(((SDEventSource *)source)->event) > 0;
56 }
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58 static gboolean event_check(GSource *source) {
59 return sd_event_wait(((SDEventSource *)source)->event, 0) > 0;
60 }
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62 static gboolean event_dispatch(GSource *source, GSourceFunc callback, gpointer user_data) {
63 return sd_event_dispatch(((SDEventSource *)source)->event) > 0;
64 }
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66 static void event_finalize(GSource *source) {
67 sd_event_unref(((SDEventSource *)source)->event);
68 }
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70 static GSourceFuncs event_funcs = {
71 .prepare = event_prepare,
72 .check = event_check,
73 .dispatch = event_dispatch,
74 .finalize = event_finalize,
75 };
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77 GSource *g_sd_event_create_source(sd_event *event) {
78 SDEventSource *source;
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80 source = (SDEventSource *)g_source_new(&event_funcs, sizeof(SDEventSource));
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82 source->event = sd_event_ref(event);
83 source->pollfd.fd = sd_event_get_fd(event);
84 source->pollfd.events = G_IO_IN | G_IO_HUP | G_IO_ERR;
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86 g_source_add_poll((GSource *)source, &source->pollfd);
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88 return (GSource *)source;
89 }
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92 Functions described here are available as a shared library, which can
93 be compiled against and linked to with the libsystemd pkg-config(1)
94 file.
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96 The code described here uses getenv(3), which is declared to be not
97 multi-thread-safe. This means that the code calling the functions
98 described here must not call setenv(3) from a parallel thread. It is
99 recommended to only do calls to setenv() from an early phase of the
100 program when no other threads have been started.
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103 sd-event(3), sd_event_new(3), sd_event_wait(3), epoll_ctl(2), epoll(7)
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107systemd 254 SD_EVENT_GET_FD(3)