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514094f9 | 1 | <?xml version='1.0'?> |
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2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
db9ecf05 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
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5 | |
6 | <refentry id="sd_event_add_io" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
7 | ||
8 | <refentryinfo> | |
9 | <title>sd_event_add_io</title> | |
10 | <productname>systemd</productname> | |
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11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_event_add_io</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_event_add_io</refname> | |
20 | <refname>sd_event_source_get_io_events</refname> | |
21 | <refname>sd_event_source_set_io_events</refname> | |
22 | <refname>sd_event_source_get_io_revents</refname> | |
23 | <refname>sd_event_source_get_io_fd</refname> | |
24 | <refname>sd_event_source_set_io_fd</refname> | |
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25 | <refname>sd_event_source_get_io_fd_own</refname> |
26 | <refname>sd_event_source_set_io_fd_own</refname> | |
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27 | <refname>sd_event_source</refname> |
28 | <refname>sd_event_io_handler_t</refname> | |
29 | ||
30 | <refpurpose>Add an I/O event source to an event loop</refpurpose> | |
31 | </refnamediv> | |
32 | ||
33 | <refsynopsisdiv> | |
34 | <funcsynopsis> | |
35 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
36 | ||
37 | <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo> | |
38 | ||
39 | <funcprototype> | |
40 | <funcdef>typedef int (*<function>sd_event_io_handler_t</function>)</funcdef> | |
41 | <paramdef>sd_event_source *<parameter>s</parameter></paramdef> | |
42 | <paramdef>int <parameter>fd</parameter></paramdef> | |
43 | <paramdef>uint32_t <parameter>revents</parameter></paramdef> | |
44 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
45 | </funcprototype> | |
46 | ||
47 | <funcprototype> | |
48 | <funcdef>int <function>sd_event_add_io</function></funcdef> | |
49 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
50 | <paramdef>sd_event_source **<parameter>source</parameter></paramdef> | |
51 | <paramdef>int <parameter>fd</parameter></paramdef> | |
52 | <paramdef>uint32_t <parameter>events</parameter></paramdef> | |
53 | <paramdef>sd_event_io_handler_t <parameter>handler</parameter></paramdef> | |
54 | <paramdef>void *<parameter>userdata</parameter></paramdef> | |
55 | </funcprototype> | |
56 | ||
57 | <funcprototype> | |
58 | <funcdef>int <function>sd_event_source_get_io_events</function></funcdef> | |
59 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
60 | <paramdef>uint32_t *<parameter>events</parameter></paramdef> | |
61 | </funcprototype> | |
62 | ||
63 | <funcprototype> | |
64 | <funcdef>int <function>sd_event_source_set_io_events</function></funcdef> | |
65 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
66 | <paramdef>uint32_t <parameter>events</parameter></paramdef> | |
67 | </funcprototype> | |
68 | ||
69 | <funcprototype> | |
70 | <funcdef>int <function>sd_event_source_get_io_revents</function></funcdef> | |
71 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
72 | <paramdef>uint32_t *<parameter>revents</parameter></paramdef> | |
73 | </funcprototype> | |
74 | ||
75 | <funcprototype> | |
76 | <funcdef>int <function>sd_event_source_get_io_fd</function></funcdef> | |
77 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
78 | </funcprototype> | |
79 | ||
80 | <funcprototype> | |
81 | <funcdef>int <function>sd_event_source_set_io_fd</function></funcdef> | |
82 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
83 | <paramdef>int <parameter>fd</parameter></paramdef> | |
84 | </funcprototype> | |
85 | ||
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86 | <funcprototype> |
87 | <funcdef>int <function>sd_event_source_get_io_fd_own</function></funcdef> | |
88 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
89 | </funcprototype> | |
90 | ||
91 | <funcprototype> | |
92 | <funcdef>int <function>sd_event_source_set_io_fd_own</function></funcdef> | |
93 | <paramdef>sd_event_source *<parameter>source</parameter></paramdef> | |
94 | <paramdef>int <parameter>b</parameter></paramdef> | |
95 | </funcprototype> | |
96 | ||
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97 | </funcsynopsis> |
98 | </refsynopsisdiv> | |
99 | ||
100 | <refsect1> | |
101 | <title>Description</title> | |
102 | ||
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103 | <para><function>sd_event_add_io()</function> adds a new I/O event source to an event loop. The event loop |
104 | object is specified in the <parameter>event</parameter> parameter, the event source object is returned in | |
105 | the <parameter>source</parameter> parameter. The <parameter>fd</parameter> parameter takes the UNIX file | |
106 | descriptor to watch, which may refer to a socket, a FIFO, a message queue, a serial connection, a | |
107 | character device, or any other file descriptor compatible with Linux <citerefentry | |
108 | project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The | |
109 | <parameter>events</parameter> parameter takes a bit mask of events to watch for, a combination of the | |
110 | following event flags: <constant>EPOLLIN</constant>, <constant>EPOLLOUT</constant>, | |
111 | <constant>EPOLLRDHUP</constant>, <constant>EPOLLPRI</constant>, and <constant>EPOLLET</constant>, see | |
112 | <citerefentry | |
113 | project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> for | |
114 | details. Note that not all file descriptors are compatible with epoll, for example regular file or | |
115 | directories are not. If this function is called with a file descriptor that does not support epoll, | |
116 | <constant>-EPERM</constant> is returned (also see below). In most cases such file descriptors may be | |
117 | treated as always-readable or always-writable, so that IO event watching is unnecessary.</para> | |
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118 | |
119 | <para>The <parameter>handler</parameter> is a function to call when the event source is triggered or | |
120 | <constant>NULL</constant>. The <parameter>userdata</parameter> pointer will be passed to the handler | |
121 | function, and may be chosen freely by the caller. The handler will also be passed the file descriptor the | |
122 | event was seen on, as well as the actual event flags. It's generally a subset of the events watched, | |
123 | however may additionally include <constant>EPOLLERR</constant> and <constant>EPOLLHUP</constant>. The | |
124 | handler may return negative to signal an error (see below), other return values are ignored. If | |
125 | <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls | |
126 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be | |
127 | used.</para> | |
128 | ||
129 | <para>By default, an event source will stay enabled continuously (<constant>SD_EVENT_ON</constant>), but | |
130 | this may be changed with | |
dc83f27a | 131 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
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132 | If the handler function returns a negative error code, it will either be disabled after the invocation, |
133 | even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the loop to | |
134 | terminate, see | |
135 | <citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
136 | Note that an event source set to <constant>SD_EVENT_ON</constant> will fire continuously unless data is | |
137 | read from or written to the file descriptor to reset the mask of events seen.</para> | |
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138 | |
139 | <para>Setting the I/O event mask to watch for to 0 does not mean | |
140 | that the event source won't be triggered anymore, as | |
141 | <constant>EPOLLHUP</constant> and <constant>EPOLLERR</constant> | |
142 | may be triggered even with a zero event mask. To temporarily | |
143 | disable an I/O event source use | |
144 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
145 | with <constant>SD_EVENT_OFF</constant> instead.</para> | |
146 | ||
147 | <para>To destroy an event source object use | |
148 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
149 | but note that the event source is only removed from the event loop | |
150 | when all references to the event source are dropped. To make sure | |
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151 | an event source does not fire anymore, even if it is still referenced, |
152 | disable the event source using | |
153 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
154 | with <constant>SD_EVENT_OFF</constant>.</para> | |
dc83f27a | 155 | |
7f3fdb7f | 156 | <para>If the second parameter of |
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157 | <function>sd_event_add_io()</function> is |
158 | <constant>NULL</constant> no reference to the event source object | |
159 | is returned. In this case the event source is considered | |
160 | "floating", and will be destroyed implicitly when the event loop | |
161 | itself is destroyed.</para> | |
dc83f27a | 162 | |
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163 | <para>If the <parameter>handler</parameter> to <function>sd_event_add_io()</function> is |
164 | <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the | |
165 | event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as | |
166 | the exit code parameter to | |
167 | <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
168 | ||
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169 | <para>Note that this call does not take possession of the file descriptor passed in, ownership (and thus |
170 | the duty to close it when it is no longer needed) remains with the caller. However, with the | |
171 | <function>sd_event_source_set_io_fd_own()</function> call (see below) the event source may optionally | |
172 | take ownership of the file descriptor after the event source has been created. In that case the file | |
173 | descriptor is closed automatically as soon as the event source is released.</para> | |
174 | ||
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175 | <para>It is recommended to use |
176 | <function>sd_event_add_io()</function> only in conjunction with | |
177 | file descriptors that have <constant>O_NONBLOCK</constant> set, to | |
178 | ensure that all I/O operations from invoked handlers are properly | |
179 | asynchronous and non-blocking. Using file descriptors without | |
180 | <constant>O_NONBLOCK</constant> might result in unexpected | |
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181 | starvation of other event sources. See |
182 | <citerefentry project='man-pages'><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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183 | for details on enabling <constant>O_NONBLOCK</constant> mode.</para> |
184 | ||
185 | <para><function>sd_event_source_get_io_events()</function> retrieves | |
f23e83b1 | 186 | the configured mask of watched I/O events of an event source created |
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187 | previously with <function>sd_event_add_io()</function>. It takes |
188 | the event source object and a pointer to a variable to store the | |
f23e83b1 | 189 | mask in.</para> |
dc83f27a | 190 | |
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191 | <para><function>sd_event_source_set_io_events()</function> |
192 | configures the mask of watched I/O events of an event source created | |
193 | previously with <function>sd_event_add_io()</function>. It takes the | |
194 | event source object and the new event mask.</para> | |
dc83f27a | 195 | |
13b6b49f | 196 | <para><function>sd_event_source_get_io_revents()</function> |
dc83f27a | 197 | retrieves the I/O event mask of currently seen but undispatched |
f23e83b1 | 198 | events from an event source created previously with |
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199 | <function>sd_event_add_io()</function>. It takes the event source |
200 | object and a pointer to a variable to store the event mask | |
201 | in. When called from a handler function on the handler's event | |
202 | source object this will return the same mask as passed to the | |
203 | handler's <parameter>revents</parameter> parameter. This call is | |
204 | primarily useful to check for undispatched events of an event | |
205 | source from the handler of an unrelated (possibly higher priority) | |
206 | event source. Note the relation between | |
207 | <function>sd_event_source_get_pending()</function> and | |
208 | <function>sd_event_source_get_io_revents()</function>: both | |
209 | functions will report non-zero results when there's an event | |
210 | pending for the event source, but the former applies to all event | |
211 | source types, the latter only to I/O event sources.</para> | |
212 | ||
213 | <para><function>sd_event_source_get_io_fd()</function> retrieves | |
f23e83b1 | 214 | the UNIX file descriptor of an event source created previously |
dc83f27a | 215 | with <function>sd_event_add_io()</function>. It takes the event |
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216 | source object and returns the non-negative file descriptor |
217 | or a negative error number on error (see below).</para> | |
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218 | |
219 | <para><function>sd_event_source_set_io_fd()</function> | |
220 | changes the UNIX file descriptor of an I/O event source created | |
221 | previously with <function>sd_event_add_io()</function>. It takes | |
f23e83b1 | 222 | the event source object and the new file descriptor.</para> |
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223 | |
224 | <para><function>sd_event_source_set_io_fd_own()</function> controls whether the file descriptor of the event source | |
225 | shall be closed automatically when the event source is freed, i.e. whether it shall be considered 'owned' by the | |
226 | event source object. By default it is not closed automatically, and the application has to do this on its own. The | |
227 | <parameter>b</parameter> parameter is a boolean parameter: if zero, the file descriptor is not closed automatically | |
228 | when the event source is freed, otherwise it is closed.</para> | |
229 | ||
230 | <para><function>sd_event_source_get_io_fd_own()</function> may be used to query the current setting of the file | |
231 | descriptor ownership boolean flag as set with <function>sd_event_source_set_io_fd_own()</function>. It returns | |
232 | positive if the file descriptor is closed automatically when the event source is destroyed, zero if not, and | |
233 | negative on error.</para> | |
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234 | </refsect1> |
235 | ||
236 | <refsect1> | |
237 | <title>Return Value</title> | |
238 | ||
239 | <para>On success, these functions return 0 or a positive | |
240 | integer. On failure, they return a negative errno-style error | |
f23e83b1 | 241 | code.</para> |
dc83f27a | 242 | |
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243 | <refsect2> |
244 | <title>Errors</title> | |
dc83f27a | 245 | |
b1de39de | 246 | <para>Returned values may indicate the following problems:</para> |
dc83f27a | 247 | |
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248 | <variablelist> |
249 | <varlistentry> | |
250 | <term><constant>-ENOMEM</constant></term> | |
dc83f27a | 251 | |
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252 | <listitem><para>Not enough memory to allocate an object.</para></listitem> |
253 | </varlistentry> | |
dc83f27a | 254 | |
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255 | <varlistentry> |
256 | <term><constant>-EINVAL</constant></term> | |
dc83f27a | 257 | |
b1de39de | 258 | <listitem><para>An invalid argument has been passed.</para></listitem> |
dc83f27a | 259 | |
b1de39de | 260 | </varlistentry> |
dc83f27a | 261 | |
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262 | <varlistentry> |
263 | <term><constant>-ESTALE</constant></term> | |
dc83f27a | 264 | |
b1de39de | 265 | <listitem><para>The event loop is already terminated.</para></listitem> |
dc83f27a | 266 | |
b1de39de | 267 | </varlistentry> |
dc83f27a | 268 | |
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269 | <varlistentry> |
270 | <term><constant>-ECHILD</constant></term> | |
dc83f27a | 271 | |
2eeff0f4 | 272 | <listitem><para>The event loop has been created in a different process, library or module instance.</para></listitem> |
b1de39de | 273 | </varlistentry> |
dc83f27a | 274 | |
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275 | <varlistentry> |
276 | <term><constant>-EDOM</constant></term> | |
dc83f27a | 277 | |
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278 | <listitem><para>The passed event source is not an I/O event source.</para></listitem> |
279 | </varlistentry> | |
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280 | |
281 | <varlistentry> | |
282 | <term><constant>-EPERM</constant></term> | |
283 | ||
284 | <listitem><para>The passed file descriptor does not support the <citerefentry | |
285 | project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry> | |
286 | API, for example because it is a regular file or directory. See <citerefentry | |
287 | project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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288 | for details.</para> |
289 | ||
290 | <xi:include href="version-info.xml" xpointer="v255"/></listitem> | |
a06c92eb | 291 | </varlistentry> |
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292 | </variablelist> |
293 | </refsect2> | |
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294 | </refsect1> |
295 | ||
296 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
297 | ||
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298 | <refsect1> |
299 | <title>History</title> | |
300 | <para><function>sd_event_add_io()</function> was added in version 229.</para> | |
301 | <para><function>sd_event_source_get_io_events()</function> was added in version 229.</para> | |
302 | <para><function>sd_event_source_get_io_fd()</function> was added in version 229.</para> | |
303 | <para><function>sd_event_source_get_io_revents()</function> was added in version 229.</para> | |
304 | <para><function>sd_event_source_set_io_events()</function> was added in version 229.</para> | |
305 | <para><function>sd_event_source_set_io_fd()</function> was added in version 229.</para> | |
306 | <para><function>sd_event_source_get_io_fd_own()</function> was added in version 239.</para> | |
307 | <para><function>sd_event_source_set_io_fd_own()</function> was added in version 239.</para> | |
308 | </refsect1> | |
309 | ||
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310 | <refsect1> |
311 | <title>See Also</title> | |
312 | ||
313 | <para> | |
314 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
315 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
316 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
317 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
318 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
319 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
320 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
1eb54dc6 | 321 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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322 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
323 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
324 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
325 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
326 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
327 | <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
0bca2831 | 328 | <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
d3c05587 | 329 | <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>, |
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330 | <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
331 | </para> | |
332 | </refsect1> | |
333 | ||
334 | </refentry> |