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514094f9 | 1 | <?xml version='1.0'?> |
3a54a157 ZJS |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
e382c49f | 4 | |
5 | <!-- | |
572eb058 ZJS |
6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
96b2fb93 | 8 | Copyright © 2016 Julian Orth |
e382c49f | 9 | --> |
10 | ||
ffd1a3f6 | 11 | <refentry id="sd_bus_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude"> |
e382c49f | 12 | |
13 | <refentryinfo> | |
14 | <title>sd_bus_get_fd</title> | |
15 | <productname>systemd</productname> | |
e382c49f | 16 | </refentryinfo> |
17 | ||
18 | <refmeta> | |
19 | <refentrytitle>sd_bus_get_fd</refentrytitle> | |
20 | <manvolnum>3</manvolnum> | |
21 | </refmeta> | |
22 | ||
23 | <refnamediv> | |
24 | <refname>sd_bus_get_fd</refname> | |
aaf6c750 | 25 | <refname>sd_bus_set_fd</refname> |
ffd1a3f6 LP |
26 | <refname>sd_bus_get_events</refname> |
27 | <refname>sd_bus_get_timeout</refname> | |
e382c49f | 28 | |
201632e3 | 29 | <refpurpose>Get the file descriptor, I/O events and timeout to wait for from a message bus |
d4169bf8 | 30 | object</refpurpose> |
e382c49f | 31 | </refnamediv> |
32 | ||
33 | <refsynopsisdiv> | |
34 | <funcsynopsis> | |
35 | <funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo> | |
36 | ||
37 | <funcprototype> | |
38 | <funcdef>int <function>sd_bus_get_fd</function></funcdef> | |
39 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
40 | </funcprototype> | |
ffd1a3f6 | 41 | |
aaf6c750 DDM |
42 | <funcprototype> |
43 | <funcdef>int <function>sd_bus_set_fd</function></funcdef> | |
44 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
45 | <paramdef>int <parameter>input_fd</parameter></paramdef> | |
46 | <paramdef>int <parameter>output_fd</parameter></paramdef> | |
47 | </funcprototype> | |
48 | ||
ffd1a3f6 LP |
49 | <funcprototype> |
50 | <funcdef>int <function>sd_bus_get_events</function></funcdef> | |
51 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
52 | </funcprototype> | |
53 | ||
54 | <funcprototype> | |
55 | <funcdef>int <function>sd_bus_get_timeout</function></funcdef> | |
56 | <paramdef>sd_bus *<parameter>bus</parameter></paramdef> | |
57 | <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef> | |
58 | </funcprototype> | |
e382c49f | 59 | </funcsynopsis> |
60 | </refsynopsisdiv> | |
61 | ||
62 | <refsect1> | |
63 | <title>Description</title> | |
64 | ||
d4169bf8 DDM |
65 | <para><function>sd_bus_get_fd()</function> returns the file descriptor used to communicate from |
66 | a message bus object. This descriptor can be used with | |
67 | <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
68 | or a similar function to wait for I/O events on the specified bus connection object. If the bus | |
69 | object was configured with the <function>sd_bus_set_fd()</function> function, then the | |
70 | <parameter>input_fd</parameter> file descriptor used in that call is returned.</para> | |
aaf6c750 | 71 | |
d4169bf8 DDM |
72 | <para><function>sd_bus_set_fd()</function> sets the file descriptors used to communicate from a |
73 | message bus object. Both <parameter>input_fd</parameter> and <parameter>output_fd</parameter> | |
74 | must be valid file descriptors. The same file descriptor may be used as both the input and the | |
75 | output file descriptor. This function must be called before the bus is started.</para> | |
ffd1a3f6 | 76 | |
d4169bf8 DDM |
77 | <para><function>sd_bus_get_events()</function> returns the I/O events to wait for, suitable for |
78 | passing to <function>poll()</function> or a similar call. Returns a combination of | |
79 | <constant>POLLIN</constant>, <constant>POLLOUT</constant>, … events, or negative on error. | |
80 | </para> | |
ffd1a3f6 | 81 | |
201632e3 | 82 | <para><function>sd_bus_get_timeout()</function> returns the timeout in µs to pass to to |
d4169bf8 | 83 | <function>poll()</function> or a similar call when waiting for events on the specified bus |
201632e3 | 84 | connection. The returned timeout may be zero, in which case a subsequent I/O polling call |
d4169bf8 DDM |
85 | should be invoked in non-blocking mode. The returned timeout may be |
86 | <constant>UINT64_MAX</constant> in which case the I/O polling call may block indefinitely, | |
201632e3 ZJS |
87 | without any applied timeout. Note that the returned timeout should be considered only a |
88 | maximum sleeping time. It is permissible (and even expected) that shorter timeouts are used by | |
d4169bf8 DDM |
89 | the calling program, in case other event sources are polled in the same event loop. Note that |
90 | the returned time-value is relative and specified in microseconds. When converting this value in | |
91 | order to pass it as third argument to <function>poll()</function> (which expects milliseconds), | |
92 | care should be taken to use a division that rounds up to ensure the I/O polling operation | |
93 | doesn't sleep for shorter than necessary, which might result in unintended busy looping | |
94 | (alternatively, use | |
95 | <citerefentry project='man-pages'><refentrytitle>ppoll</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
201632e3 | 96 | instead of plain <function>poll()</function>, which understands timeouts with nano-second |
d4169bf8 DDM |
97 | granularity).</para> |
98 | ||
99 | <para>These three functions are useful to hook up a bus connection object with an external or | |
100 | manual event loop involving <function>poll()</function> or a similar I/O polling call. Before | |
101 | each invocation of the I/O polling call, all three functions should be invoked: the file | |
102 | descriptor returned by <function>sd_bus_get_fd()</function> should be polled for the events | |
103 | indicated by <function>sd_bus_get_events()</function>, and the I/O call should block for that up | |
201632e3 | 104 | to the timeout returned by <function>sd_bus_get_timeout()</function>. After each I/O polling |
ffd1a3f6 | 105 | call the bus connection needs to process incoming or outgoing data, by invoking |
d4169bf8 DDM |
106 | <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>. |
107 | </para> | |
108 | ||
75358555 | 109 | <para>Note that these functions are only one of three supported ways to implement I/O event |
d4169bf8 DDM |
110 | handling for bus connections. Alternatively use |
111 | <citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
112 | to attach a bus connection to an | |
113 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
114 | event loop. Or use | |
115 | <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
ffd1a3f6 | 116 | as a simple synchronous, blocking I/O waiting call.</para> |
e382c49f | 117 | </refsect1> |
118 | ||
119 | <refsect1> | |
120 | <title>Return Value</title> | |
121 | ||
d4169bf8 DDM |
122 | <para>On success, <function>sd_bus_get_fd()</function> returns the file descriptor used for |
123 | communication. On failure, it returns a negative errno-style error code.</para> | |
aaf6c750 | 124 | |
d4169bf8 DDM |
125 | <para>On success, <function>sd_bus_set_fd()</function> returns a non-negative integer. On |
126 | failure, it returns a negative errno-style error code.</para> | |
ffd1a3f6 | 127 | |
d4169bf8 DDM |
128 | <para>On success, <function>sd_bus_get_events()</function> returns the I/O event mask to use for |
129 | I/O event watching. On failure, it returns a negative errno-style error code.</para> | |
ffd1a3f6 | 130 | |
d4169bf8 DDM |
131 | <para>On success, <function>sd_bus_get_timeout()</function> returns a non-negative integer. On |
132 | failure, it returns a negative errno-style error code.</para> | |
e382c49f | 133 | |
b1de39de ZJS |
134 | <refsect2> |
135 | <title>Errors</title> | |
ffd1a3f6 | 136 | |
b1de39de | 137 | <para>Returned errors may indicate the following problems:</para> |
ffd1a3f6 | 138 | |
b1de39de ZJS |
139 | <variablelist> |
140 | <varlistentry> | |
141 | <term><constant>-EINVAL</constant></term> | |
ffd1a3f6 | 142 | |
b1de39de ZJS |
143 | <listitem><para>An invalid bus object was passed.</para></listitem> |
144 | </varlistentry> | |
ffd1a3f6 | 145 | |
b1de39de ZJS |
146 | <varlistentry> |
147 | <term><constant>-ECHILD</constant></term> | |
ffd1a3f6 | 148 | |
d4169bf8 DDM |
149 | <listitem><para>The bus connection was allocated in a parent process and is being reused |
150 | in a child process after <function>fork()</function>.</para></listitem> | |
b1de39de | 151 | </varlistentry> |
ffd1a3f6 | 152 | |
b1de39de ZJS |
153 | <varlistentry> |
154 | <term><constant>-ENOTCONN</constant></term> | |
ffd1a3f6 | 155 | |
b1de39de ZJS |
156 | <listitem><para>The bus connection has been terminated.</para></listitem> |
157 | </varlistentry> | |
ffd1a3f6 | 158 | |
b1de39de ZJS |
159 | <varlistentry> |
160 | <term><constant>-EPERM</constant></term> | |
ffd1a3f6 | 161 | |
b1de39de ZJS |
162 | <listitem><para>Two distinct file descriptors were passed for input and output using |
163 | <function>sd_bus_set_fd()</function>, which <function>sd_bus_get_fd()</function> cannot | |
164 | return.</para></listitem> | |
165 | </varlistentry> | |
aaf6c750 DDM |
166 | |
167 | <varlistentry> | |
168 | <term><constant>-EBADF</constant></term> | |
169 | ||
d4169bf8 DDM |
170 | <listitem><para>An invalid file descriptor was passed to |
171 | <function>sd_bus_set_fd()</function>.</para></listitem> | |
aaf6c750 DDM |
172 | </varlistentry> |
173 | ||
174 | <varlistentry> | |
175 | <term><constant>-ENOPKG</constant></term> | |
176 | ||
177 | <listitem><para>The bus cannot be resolved.</para></listitem> | |
178 | </varlistentry> | |
b1de39de ZJS |
179 | </variablelist> |
180 | </refsect2> | |
ffd1a3f6 LP |
181 | </refsect1> |
182 | ||
183 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
184 | ||
e382c49f | 185 | <refsect1> |
186 | <title>See Also</title> | |
187 | ||
188 | <para> | |
189 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
190 | <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
ffd1a3f6 LP |
191 | <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
192 | <citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
193 | <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
194 | <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
e382c49f | 195 | </para> |
196 | </refsect1> | |
197 | ||
198 | </refentry> |