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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"> | |
0307f791 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
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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 | ||
103 | <para><function>sd_event_add_io()</function> adds a new I/O event | |
104 | source to an event loop. The event loop object is specified in the | |
105 | <parameter>event</parameter> parameter, the event source object is | |
106 | returned in the <parameter>source</parameter> parameter. The | |
107 | <parameter>fd</parameter> parameter takes the UNIX file descriptor | |
108 | to watch, which may refer to a socket, a FIFO, a message queue, a | |
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109 | serial connection, a character device, or any other file descriptor |
110 | compatible with Linux | |
111 | <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The | |
112 | <parameter>events</parameter> parameter takes a bit mask of events | |
113 | to watch for, a combination of the following event flags: | |
114 | <constant>EPOLLIN</constant>, <constant>EPOLLOUT</constant>, | |
115 | <constant>EPOLLRDHUP</constant>, <constant>EPOLLPRI</constant>, | |
116 | and <constant>EPOLLET</constant>, see | |
117 | <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
dc83f27a | 118 | for details. The <parameter>handler</parameter> shall reference a |
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119 | function to call when the event source is triggered. The |
120 | <parameter>userdata</parameter> pointer will be passed to the | |
121 | handler function, and may be chosen freely by the caller. The | |
122 | handler will also be passed the file descriptor the event was seen | |
123 | on, as well as the actual event flags. It's generally a subset of | |
124 | the events watched, however may additionally include | |
125 | <constant>EPOLLERR</constant> and <constant>EPOLLHUP</constant>. | |
126 | </para> | |
127 | ||
128 | <para>By default, an event source will stay enabled | |
7f3fdb7f | 129 | continuously (<constant>SD_EVENT_ON</constant>), but this may be |
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130 | changed with |
131 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
132 | If the handler function returns a negative error code, it will be | |
133 | disabled after the invocation, even if the | |
134 | <constant>SD_EVENT_ON</constant> mode was requested before. Note | |
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135 | that an event source set to <constant>SD_EVENT_ON</constant> will |
136 | fire continuously unless data is read from or written to the file | |
137 | descriptor to reset the mask of events seen. | |
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138 | </para> |
139 | ||
140 | <para>Setting the I/O event mask to watch for to 0 does not mean | |
141 | that the event source won't be triggered anymore, as | |
142 | <constant>EPOLLHUP</constant> and <constant>EPOLLERR</constant> | |
143 | may be triggered even with a zero event mask. To temporarily | |
144 | disable an I/O event source use | |
145 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
146 | with <constant>SD_EVENT_OFF</constant> instead.</para> | |
147 | ||
148 | <para>To destroy an event source object use | |
149 | <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
150 | but note that the event source is only removed from the event loop | |
151 | when all references to the event source are dropped. To make sure | |
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152 | an event source does not fire anymore, even if it is still referenced, |
153 | disable the event source using | |
154 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
155 | with <constant>SD_EVENT_OFF</constant>.</para> | |
dc83f27a | 156 | |
7f3fdb7f | 157 | <para>If the second parameter of |
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158 | <function>sd_event_add_io()</function> is |
159 | <constant>NULL</constant> no reference to the event source object | |
160 | is returned. In this case the event source is considered | |
161 | "floating", and will be destroyed implicitly when the event loop | |
162 | itself is destroyed.</para> | |
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163 | |
164 | <para>It is recommended to use | |
165 | <function>sd_event_add_io()</function> only in conjunction with | |
166 | file descriptors that have <constant>O_NONBLOCK</constant> set, to | |
167 | ensure that all I/O operations from invoked handlers are properly | |
168 | asynchronous and non-blocking. Using file descriptors without | |
169 | <constant>O_NONBLOCK</constant> might result in unexpected | |
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170 | starvation of other event sources. See |
171 | <citerefentry project='man-pages'><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry> | |
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172 | for details on enabling <constant>O_NONBLOCK</constant> mode.</para> |
173 | ||
174 | <para><function>sd_event_source_get_io_events()</function> retrieves | |
f23e83b1 | 175 | the configured mask of watched I/O events of an event source created |
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176 | previously with <function>sd_event_add_io()</function>. It takes |
177 | the event source object and a pointer to a variable to store the | |
f23e83b1 | 178 | mask in.</para> |
dc83f27a | 179 | |
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180 | <para><function>sd_event_source_set_io_events()</function> |
181 | configures the mask of watched I/O events of an event source created | |
182 | previously with <function>sd_event_add_io()</function>. It takes the | |
183 | event source object and the new event mask.</para> | |
dc83f27a | 184 | |
13b6b49f | 185 | <para><function>sd_event_source_get_io_revents()</function> |
dc83f27a | 186 | retrieves the I/O event mask of currently seen but undispatched |
f23e83b1 | 187 | events from an event source created previously with |
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188 | <function>sd_event_add_io()</function>. It takes the event source |
189 | object and a pointer to a variable to store the event mask | |
190 | in. When called from a handler function on the handler's event | |
191 | source object this will return the same mask as passed to the | |
192 | handler's <parameter>revents</parameter> parameter. This call is | |
193 | primarily useful to check for undispatched events of an event | |
194 | source from the handler of an unrelated (possibly higher priority) | |
195 | event source. Note the relation between | |
196 | <function>sd_event_source_get_pending()</function> and | |
197 | <function>sd_event_source_get_io_revents()</function>: both | |
198 | functions will report non-zero results when there's an event | |
199 | pending for the event source, but the former applies to all event | |
200 | source types, the latter only to I/O event sources.</para> | |
201 | ||
202 | <para><function>sd_event_source_get_io_fd()</function> retrieves | |
f23e83b1 | 203 | the UNIX file descriptor of an event source created previously |
dc83f27a | 204 | with <function>sd_event_add_io()</function>. It takes the event |
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205 | source object and returns the non-negative file descriptor |
206 | or a negative error number on error (see below).</para> | |
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207 | |
208 | <para><function>sd_event_source_set_io_fd()</function> | |
209 | changes the UNIX file descriptor of an I/O event source created | |
210 | previously with <function>sd_event_add_io()</function>. It takes | |
f23e83b1 | 211 | the event source object and the new file descriptor.</para> |
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212 | |
213 | <para><function>sd_event_source_set_io_fd_own()</function> controls whether the file descriptor of the event source | |
214 | shall be closed automatically when the event source is freed, i.e. whether it shall be considered 'owned' by the | |
215 | event source object. By default it is not closed automatically, and the application has to do this on its own. The | |
216 | <parameter>b</parameter> parameter is a boolean parameter: if zero, the file descriptor is not closed automatically | |
217 | when the event source is freed, otherwise it is closed.</para> | |
218 | ||
219 | <para><function>sd_event_source_get_io_fd_own()</function> may be used to query the current setting of the file | |
220 | descriptor ownership boolean flag as set with <function>sd_event_source_set_io_fd_own()</function>. It returns | |
221 | positive if the file descriptor is closed automatically when the event source is destroyed, zero if not, and | |
222 | negative on error.</para> | |
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223 | </refsect1> |
224 | ||
225 | <refsect1> | |
226 | <title>Return Value</title> | |
227 | ||
228 | <para>On success, these functions return 0 or a positive | |
229 | integer. On failure, they return a negative errno-style error | |
f23e83b1 | 230 | code.</para> |
dc83f27a | 231 | |
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232 | <refsect2> |
233 | <title>Errors</title> | |
dc83f27a | 234 | |
b1de39de | 235 | <para>Returned values may indicate the following problems:</para> |
dc83f27a | 236 | |
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237 | <variablelist> |
238 | <varlistentry> | |
239 | <term><constant>-ENOMEM</constant></term> | |
dc83f27a | 240 | |
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241 | <listitem><para>Not enough memory to allocate an object.</para></listitem> |
242 | </varlistentry> | |
dc83f27a | 243 | |
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244 | <varlistentry> |
245 | <term><constant>-EINVAL</constant></term> | |
dc83f27a | 246 | |
b1de39de | 247 | <listitem><para>An invalid argument has been passed.</para></listitem> |
dc83f27a | 248 | |
b1de39de | 249 | </varlistentry> |
dc83f27a | 250 | |
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251 | <varlistentry> |
252 | <term><constant>-ESTALE</constant></term> | |
dc83f27a | 253 | |
b1de39de | 254 | <listitem><para>The event loop is already terminated.</para></listitem> |
dc83f27a | 255 | |
b1de39de | 256 | </varlistentry> |
dc83f27a | 257 | |
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258 | <varlistentry> |
259 | <term><constant>-ECHILD</constant></term> | |
dc83f27a | 260 | |
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261 | <listitem><para>The event loop has been created in a different process.</para></listitem> |
262 | </varlistentry> | |
dc83f27a | 263 | |
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264 | <varlistentry> |
265 | <term><constant>-EDOM</constant></term> | |
dc83f27a | 266 | |
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267 | <listitem><para>The passed event source is not an I/O event source.</para></listitem> |
268 | </varlistentry> | |
269 | </variablelist> | |
270 | </refsect2> | |
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271 | </refsect1> |
272 | ||
273 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
274 | ||
275 | <refsect1> | |
276 | <title>See Also</title> | |
277 | ||
278 | <para> | |
279 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
280 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
281 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
282 | <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
283 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
284 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
285 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
1eb54dc6 | 286 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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287 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
288 | <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
289 | <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
290 | <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
291 | <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
292 | <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
d3c05587 | 293 | <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>, |
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294 | <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
295 | </para> | |
296 | </refsect1> | |
297 | ||
298 | </refentry> |