sd_event_add_io(3)

1SD_EVENT_ADD_IO(3)              sd_event_add_io             SD_EVENT_ADD_IO(3)
2
3
4

NAME

6       sd_event_add_io, sd_event_source_get_io_events,
7       sd_event_source_set_io_events, sd_event_source_get_io_revents,
8       sd_event_source_get_io_fd, sd_event_source_set_io_fd,
9       sd_event_source_get_io_fd_own, sd_event_source_set_io_fd_own,
10       sd_event_source, sd_event_io_handler_t - Add an I/O event source to an
11       event loop
12

SYNOPSIS

14       #include <systemd/sd-event.h>
15
16       typedef struct sd_event_source sd_event_source;
17
18       typedef int (*sd_event_io_handler_t)(sd_event_source *s, int fd,
19                                            uint32_t revents, void *userdata);
20
21       int sd_event_add_io(sd_event *event, sd_event_source **source, int fd,
22                           uint32_t events, sd_event_io_handler_t handler,
23                           void *userdata);
24
25       int sd_event_source_get_io_events(sd_event_source *source,
26                                         uint32_t *events);
27
28       int sd_event_source_set_io_events(sd_event_source *source,
29                                         uint32_t events);
30
31       int sd_event_source_get_io_revents(sd_event_source *source,
32                                          uint32_t *revents);
33
34       int sd_event_source_get_io_fd(sd_event_source *source);
35
36       int sd_event_source_set_io_fd(sd_event_source *source, int fd);
37
38       int sd_event_source_get_io_fd_own(sd_event_source *source);
39
40       int sd_event_source_set_io_fd_own(sd_event_source *source, int b);
41

DESCRIPTION

43       sd_event_add_io() adds a new I/O event source to an event loop. The
44       event loop object is specified in the event parameter, the event source
45       object is returned in the source parameter. The fd parameter takes the
46       UNIX file descriptor to watch, which may refer to a socket, a FIFO, a
47       message queue, a serial connection, a character device, or any other
48       file descriptor compatible with Linux epoll(7). The events parameter
49       takes a bit mask of events to watch for, a combination of the following
50       event flags: EPOLLIN, EPOLLOUT, EPOLLRDHUP, EPOLLPRI, and EPOLLET, see
51       epoll_ctl(2) for details. The handler shall reference a function to
52       call when the event source is triggered. The userdata pointer will be
53       passed to the handler function, and may be chosen freely by the caller.
54       The handler will also be passed the file descriptor the event was seen
55       on, as well as the actual event flags. It's generally a subset of the
56       events watched, however may additionally include EPOLLERR and EPOLLHUP.
57
58       By default, an event source will stay enabled continuously
59       (SD_EVENT_ON), but this may be changed with
60       sd_event_source_set_enabled(3). If the handler function returns a
61       negative error code, it will be disabled after the invocation, even if
62       the SD_EVENT_ON mode was requested before. Note that an event source
63       set to SD_EVENT_ON will fire continuously unless data is read from or
64       written to the file descriptor to reset the mask of events seen.
65
66       Setting the I/O event mask to watch for to 0 does not mean that the
67       event source won't be triggered anymore, as EPOLLHUP and EPOLLERR may
68       be triggered even with a zero event mask. To temporarily disable an I/O
69       event source use sd_event_source_set_enabled(3) with SD_EVENT_OFF
70       instead.
71
72       To destroy an event source object use sd_event_source_unref(3), but
73       note that the event source is only removed from the event loop when all
74       references to the event source are dropped. To make sure an event
75       source does not fire anymore, even if it is still referenced, disable
76       the event source using sd_event_source_set_enabled(3) with
77       SD_EVENT_OFF.
78
79       If the second parameter of sd_event_add_io() is NULL no reference to
80       the event source object is returned. In this case the event source is
81       considered "floating", and will be destroyed implicitly when the event
82       loop itself is destroyed.
83
84       It is recommended to use sd_event_add_io() only in conjunction with
85       file descriptors that have O_NONBLOCK set, to ensure that all I/O
86       operations from invoked handlers are properly asynchronous and
87       non-blocking. Using file descriptors without O_NONBLOCK might result in
88       unexpected starvation of other event sources. See fcntl(2) for details
89       on enabling O_NONBLOCK mode.
90
91       sd_event_source_get_io_events() retrieves the configured mask of
92       watched I/O events of an event source created previously with
93       sd_event_add_io(). It takes the event source object and a pointer to a
94       variable to store the mask in.
95
96       sd_event_source_set_io_events() configures the mask of watched I/O
97       events of an event source created previously with sd_event_add_io(). It
98       takes the event source object and the new event mask.
99
100       sd_event_source_get_io_revents() retrieves the I/O event mask of
101       currently seen but undispatched events from an event source created
102       previously with sd_event_add_io(). It takes the event source object and
103       a pointer to a variable to store the event mask in. When called from a
104       handler function on the handler's event source object this will return
105       the same mask as passed to the handler's revents parameter. This call
106       is primarily useful to check for undispatched events of an event source
107       from the handler of an unrelated (possibly higher priority) event
108       source. Note the relation between sd_event_source_get_pending() and
109       sd_event_source_get_io_revents(): both functions will report non-zero
110       results when there's an event pending for the event source, but the
111       former applies to all event source types, the latter only to I/O event
112       sources.
113
114       sd_event_source_get_io_fd() retrieves the UNIX file descriptor of an
115       event source created previously with sd_event_add_io(). It takes the
116       event source object and returns the non-negative file descriptor or a
117       negative error number on error (see below).
118
119       sd_event_source_set_io_fd() changes the UNIX file descriptor of an I/O
120       event source created previously with sd_event_add_io(). It takes the
121       event source object and the new file descriptor.
122
123       sd_event_source_set_io_fd_own() controls whether the file descriptor of
124       the event source shall be closed automatically when the event source is
125       freed, i.e. whether it shall be considered 'owned' by the event source
126       object. By default it is not closed automatically, and the application
127       has to do this on its own. The b parameter is a boolean parameter: if
128       zero, the file descriptor is not closed automatically when the event
129       source is freed, otherwise it is closed.
130
131       sd_event_source_get_io_fd_own() may be used to query the current
132       setting of the file descriptor ownership boolean flag as set with
133       sd_event_source_set_io_fd_own(). It returns positive if the file
134       descriptor is closed automatically when the event source is destroyed,
135       zero if not, and negative on error.
136

RETURN VALUE

138       On success, these functions return 0 or a positive integer. On failure,
139       they return a negative errno-style error code.
140

ERRORS

142       Returned values may indicate the following problems:
143
144       -ENOMEM
145           Not enough memory to allocate an object.
146
147       -EINVAL
148           An invalid argument has been passed.
149
150       -ESTALE
151           The event loop is already terminated.
152
153       -ECHILD
154           The event loop has been created in a different process.
155
156       -EDOM
157           The passed event source is not an I/O event source.
158

NOTES

160       These APIs are implemented as a shared library, which can be compiled
161       and linked to with the libsystemd pkg-config(1) file.
162

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

NOTES

SEE ALSO