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1 | <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | ||
5 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
9 | <refentry id="sd_event_add_io" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
10 | ||
11 | <refentryinfo> | |
12 | <title>sd_event_add_io</title> | |
13 | <productname>systemd</productname> | |
14 | ||
15 | <authorgroup> | |
16 | <author> | |
17 | <contrib>Developer</contrib> | |
18 | <firstname>Lennart</firstname> | |
19 | <surname>Poettering</surname> | |
20 | <email>lennart@poettering.net</email> | |
21 | </author> | |
22 | </authorgroup> | |
23 | </refentryinfo> | |
24 | ||
25 | <refmeta> | |
26 | <refentrytitle>sd_event_add_io</refentrytitle> | |
27 | <manvolnum>3</manvolnum> | |
28 | </refmeta> | |
29 | ||
30 | <refnamediv> | |
31 | <refname>sd_event_add_io</refname> | |
32 | <refname>sd_event_source_get_io_events</refname> | |
33 | <refname>sd_event_source_set_io_events</refname> | |
34 | <refname>sd_event_source_get_io_revents</refname> | |
35 | <refname>sd_event_source_get_io_fd</refname> | |
36 | <refname>sd_event_source_set_io_fd</refname> | |
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37 | <refname>sd_event_source_get_io_fd_own</refname> |
38 | <refname>sd_event_source_set_io_fd_own</refname> | |
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39 | <refname>sd_event_source</refname> |
40 | <refname>sd_event_io_handler_t</refname> | |
41 | ||
42 | <refpurpose>Add an I/O event source to an event loop</refpurpose> | |
43 | </refnamediv> | |
44 | ||
45 | <refsynopsisdiv> | |
46 | <funcsynopsis> | |
47 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
48 | ||
49 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
50 | ||
51 | <funcprototype> | |
52 | <funcdef>typedef int (*<function>sd_event_io_handler_t</function>)</funcdef> | |
53 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
54 | <paramdef>int <parameter>fd</parameter></paramdef> | |
55 | <paramdef>uint32_t <parameter>revents</parameter></paramdef> | |
56 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
57 | </funcprototype> | |
58 | ||
59 | <funcprototype> | |
60 | <funcdef>int <function>sd_event_add_io</function></funcdef> | |
61 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
62 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
63 | <paramdef>int <parameter>fd</parameter></paramdef> | |
64 | <paramdef>uint32_t <parameter>events</parameter></paramdef> | |
65 | <paramdef>sd_event_io_handler_t <parameter>handler</parameter></paramdef> | |
66 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
67 | </funcprototype> | |
68 | ||
69 | <funcprototype> | |
70 | <funcdef>int <function>sd_event_source_get_io_events</function></funcdef> | |
71 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
72 | <paramdef>uint32_t *<parameter>events</parameter></paramdef> | |
73 | </funcprototype> | |
74 | ||
75 | <funcprototype> | |
76 | <funcdef>int <function>sd_event_source_set_io_events</function></funcdef> | |
77 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
78 | <paramdef>uint32_t <parameter>events</parameter></paramdef> | |
79 | </funcprototype> | |
80 | ||
81 | <funcprototype> | |
82 | <funcdef>int <function>sd_event_source_get_io_revents</function></funcdef> | |
83 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
84 | <paramdef>uint32_t *<parameter>revents</parameter></paramdef> | |
85 | </funcprototype> | |
86 | ||
87 | <funcprototype> | |
88 | <funcdef>int <function>sd_event_source_get_io_fd</function></funcdef> | |
89 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
90 | </funcprototype> | |
91 | ||
92 | <funcprototype> | |
93 | <funcdef>int <function>sd_event_source_set_io_fd</function></funcdef> | |
94 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
95 | <paramdef>int <parameter>fd</parameter></paramdef> | |
96 | </funcprototype> | |
97 | ||
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98 | <funcprototype> |
99 | <funcdef>int <function>sd_event_source_get_io_fd_own</function></funcdef> | |
100 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
101 | </funcprototype> | |
102 | ||
103 | <funcprototype> | |
104 | <funcdef>int <function>sd_event_source_set_io_fd_own</function></funcdef> | |
105 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
106 | <paramdef>int <parameter>b</parameter></paramdef> | |
107 | </funcprototype> | |
108 | ||
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109 | </funcsynopsis> |
110 | </refsynopsisdiv> | |
111 | ||
112 | <refsect1> | |
113 | <title>Description</title> | |
114 | ||
115 | <para><function>sd_event_add_io()</function> adds a new I/O event | |
116 | source to an event loop. The event loop object is specified in the | |
117 | <parameter>event</parameter> parameter, the event source object is | |
118 | returned in the <parameter>source</parameter> parameter. The | |
119 | <parameter>fd</parameter> parameter takes the UNIX file descriptor | |
120 | to watch, which may refer to a socket, a FIFO, a message queue, a | |
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121 | serial connection, a character device, or any other file descriptor |
122 | compatible with Linux | |
123 | <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The | |
124 | <parameter>events</parameter> parameter takes a bit mask of events | |
125 | to watch for, a combination of the following event flags: | |
126 | <constant>EPOLLIN</constant>, <constant>EPOLLOUT</constant>, | |
127 | <constant>EPOLLRDHUP</constant>, <constant>EPOLLPRI</constant>, | |
128 | and <constant>EPOLLET</constant>, see | |
129 | <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
dc83f27a | 130 | for details. The <parameter>handler</parameter> shall reference a |
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131 | function to call when the event source is triggered. The |
132 | <parameter>userdata</parameter> pointer will be passed to the | |
133 | handler function, and may be chosen freely by the caller. The | |
134 | handler will also be passed the file descriptor the event was seen | |
135 | on, as well as the actual event flags. It's generally a subset of | |
136 | the events watched, however may additionally include | |
137 | <constant>EPOLLERR</constant> and <constant>EPOLLHUP</constant>. | |
138 | </para> | |
139 | ||
140 | <para>By default, an event source will stay enabled | |
7f3fdb7f | 141 | continuously (<constant>SD_EVENT_ON</constant>), but this may be |
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142 | changed with |
143 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
144 | If the handler function returns a negative error code, it will be | |
145 | disabled after the invocation, even if the | |
146 | <constant>SD_EVENT_ON</constant> mode was requested before. Note | |
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147 | that an event source set to <constant>SD_EVENT_ON</constant> will |
148 | fire continuously unless data is read from or written to the file | |
149 | descriptor to reset the mask of events seen. | |
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150 | </para> |
151 | ||
152 | <para>Setting the I/O event mask to watch for to 0 does not mean | |
153 | that the event source won't be triggered anymore, as | |
154 | <constant>EPOLLHUP</constant> and <constant>EPOLLERR</constant> | |
155 | may be triggered even with a zero event mask. To temporarily | |
156 | disable an I/O event source use | |
157 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
158 | with <constant>SD_EVENT_OFF</constant> instead.</para> | |
159 | ||
160 | <para>To destroy an event source object use | |
161 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
162 | but note that the event source is only removed from the event loop | |
163 | when all references to the event source are dropped. To make sure | |
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164 | an event source does not fire anymore, even if it is still referenced, |
165 | disable the event source using | |
166 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
167 | with <constant>SD_EVENT_OFF</constant>.</para> | |
dc83f27a | 168 | |
7f3fdb7f | 169 | <para>If the second parameter of |
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170 | <function>sd_event_add_io()</function> is |
171 | <constant>NULL</constant> no reference to the event source object | |
172 | is returned. In this case the event source is considered | |
173 | "floating", and will be destroyed implicitly when the event loop | |
174 | itself is destroyed.</para> | |
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175 | |
176 | <para>It is recommended to use | |
177 | <function>sd_event_add_io()</function> only in conjunction with | |
178 | file descriptors that have <constant>O_NONBLOCK</constant> set, to | |
179 | ensure that all I/O operations from invoked handlers are properly | |
180 | asynchronous and non-blocking. Using file descriptors without | |
181 | <constant>O_NONBLOCK</constant> might result in unexpected | |
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182 | starvation of other event sources. See |
183 | <citerefentry project='man-pages'><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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184 | for details on enabling <constant>O_NONBLOCK</constant> mode.</para> |
185 | ||
186 | <para><function>sd_event_source_get_io_events()</function> retrieves | |
f23e83b1 | 187 | the configured mask of watched I/O events of an event source created |
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188 | previously with <function>sd_event_add_io()</function>. It takes |
189 | the event source object and a pointer to a variable to store the | |
f23e83b1 | 190 | mask in.</para> |
dc83f27a | 191 | |
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192 | <para><function>sd_event_source_set_io_events()</function> |
193 | configures the mask of watched I/O events of an event source created | |
194 | previously with <function>sd_event_add_io()</function>. It takes the | |
195 | event source object and the new event mask.</para> | |
dc83f27a | 196 | |
13b6b49f | 197 | <para><function>sd_event_source_get_io_revents()</function> |
dc83f27a | 198 | retrieves the I/O event mask of currently seen but undispatched |
f23e83b1 | 199 | events from an event source created previously with |
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200 | <function>sd_event_add_io()</function>. It takes the event source |
201 | object and a pointer to a variable to store the event mask | |
202 | in. When called from a handler function on the handler's event | |
203 | source object this will return the same mask as passed to the | |
204 | handler's <parameter>revents</parameter> parameter. This call is | |
205 | primarily useful to check for undispatched events of an event | |
206 | source from the handler of an unrelated (possibly higher priority) | |
207 | event source. Note the relation between | |
208 | <function>sd_event_source_get_pending()</function> and | |
209 | <function>sd_event_source_get_io_revents()</function>: both | |
210 | functions will report non-zero results when there's an event | |
211 | pending for the event source, but the former applies to all event | |
212 | source types, the latter only to I/O event sources.</para> | |
213 | ||
214 | <para><function>sd_event_source_get_io_fd()</function> retrieves | |
f23e83b1 | 215 | the UNIX file descriptor of an event source created previously |
dc83f27a | 216 | with <function>sd_event_add_io()</function>. It takes the event |
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217 | source object and returns the non-negative file descriptor |
218 | or a negative error number on error (see below).</para> | |
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219 | |
220 | <para><function>sd_event_source_set_io_fd()</function> | |
221 | changes the UNIX file descriptor of an I/O event source created | |
222 | previously with <function>sd_event_add_io()</function>. It takes | |
f23e83b1 | 223 | the event source object and the new file descriptor.</para> |
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224 | |
225 | <para><function>sd_event_source_set_io_fd_own()</function> controls whether the file descriptor of the event source | |
226 | shall be closed automatically when the event source is freed, i.e. whether it shall be considered 'owned' by the | |
227 | event source object. By default it is not closed automatically, and the application has to do this on its own. The | |
228 | <parameter>b</parameter> parameter is a boolean parameter: if zero, the file descriptor is not closed automatically | |
229 | when the event source is freed, otherwise it is closed.</para> | |
230 | ||
231 | <para><function>sd_event_source_get_io_fd_own()</function> may be used to query the current setting of the file | |
232 | descriptor ownership boolean flag as set with <function>sd_event_source_set_io_fd_own()</function>. It returns | |
233 | positive if the file descriptor is closed automatically when the event source is destroyed, zero if not, and | |
234 | negative on error.</para> | |
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235 | </refsect1> |
236 | ||
237 | <refsect1> | |
238 | <title>Return Value</title> | |
239 | ||
240 | <para>On success, these functions return 0 or a positive | |
241 | integer. On failure, they return a negative errno-style error | |
f23e83b1 | 242 | code.</para> |
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243 | </refsect1> |
244 | ||
245 | <refsect1> | |
246 | <title>Errors</title> | |
247 | ||
f23e83b1 | 248 | <para>Returned values may indicate the following problems:</para> |
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249 | |
250 | <variablelist> | |
251 | <varlistentry> | |
252 | <term><constant>-ENOMEM</constant></term> | |
253 | ||
254 | <listitem><para>Not enough memory to allocate an object.</para></listitem> | |
255 | </varlistentry> | |
256 | ||
257 | <varlistentry> | |
258 | <term><constant>-EINVAL</constant></term> | |
259 | ||
260 | <listitem><para>An invalid argument has been passed.</para></listitem> | |
261 | ||
262 | </varlistentry> | |
263 | ||
264 | <varlistentry> | |
265 | <term><constant>-ESTALE</constant></term> | |
266 | ||
267 | <listitem><para>The event loop is already terminated.</para></listitem> | |
268 | ||
269 | </varlistentry> | |
270 | ||
271 | <varlistentry> | |
272 | <term><constant>-ECHILD</constant></term> | |
273 | ||
274 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
275 | </varlistentry> | |
276 | ||
277 | <varlistentry> | |
278 | <term><constant>-EDOM</constant></term> | |
279 | ||
280 | <listitem><para>The passed event source is not an I/O event source.</para></listitem> | |
281 | </varlistentry> | |
282 | </variablelist> | |
283 | </refsect1> | |
284 | ||
285 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
286 | ||
287 | <refsect1> | |
288 | <title>See Also</title> | |
289 | ||
290 | <para> | |
291 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
292 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
293 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
294 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
295 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
296 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
297 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
1eb54dc6 | 298 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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299 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
300 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
301 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
302 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
303 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
304 | <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
305 | <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
306 | <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
307 | </para> | |
308 | </refsect1> | |
309 | ||
310 | </refentry> |