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Diffstat (limited to 'man/sd_bus_get_fd.xml')
| -rw-r--r-- | man/sd_bus_get_fd.xml | 126 |
1 files changed, 103 insertions, 23 deletions
diff --git a/man/sd_bus_get_fd.xml b/man/sd_bus_get_fd.xml index a5d49074b3..2a81bddaa0 100644 --- a/man/sd_bus_get_fd.xml +++ b/man/sd_bus_get_fd.xml @@ -1,4 +1,4 @@ -<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*--> +<?xml version='1.0'?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> @@ -8,7 +8,7 @@ Copyright © 2016 Julian Orth --> -<refentry id="sd_bus_get_fd"> +<refentry id="sd_bus_get_fd" xmlns:xi="http://www.w3.org/2001/XInclude"> <refentryinfo> <title>sd_bus_get_fd</title> @@ -22,8 +22,10 @@ <refnamediv> <refname>sd_bus_get_fd</refname> + <refname>sd_bus_get_events</refname> + <refname>sd_bus_get_timeout</refname> - <refpurpose>Get the file descriptor connected to the message bus</refpurpose> + <refpurpose>Get the file descriptor, I/O events and time-out to wait for from a message bus object</refpurpose> </refnamediv> <refsynopsisdiv> @@ -34,46 +36,124 @@ <funcdef>int <function>sd_bus_get_fd</function></funcdef> <paramdef>sd_bus *<parameter>bus</parameter></paramdef> </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_bus_get_events</function></funcdef> + <paramdef>sd_bus *<parameter>bus</parameter></paramdef> + </funcprototype> + + <funcprototype> + <funcdef>int <function>sd_bus_get_timeout</function></funcdef> + <paramdef>sd_bus *<parameter>bus</parameter></paramdef> + <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef> + </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> - <para> - <function>sd_bus_get_fd()</function> returns the file descriptor used to - communicate with the message bus. This descriptor can be used with - <citerefentry - project='die-net'><refentrytitle>select</refentrytitle><manvolnum>3</manvolnum></citerefentry>, - <citerefentry - project='die-net'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>, - or similar functions to wait for incoming messages. - </para> - - <para> - If the bus was created with the - <citerefentry><refentrytitle>sd_bus_set_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry> - function, then the <parameter>input_fd</parameter> used in that call is - returned. - </para> + <para><function>sd_bus_get_fd()</function> returns the file descriptor used to communicate from a message bus + object. This descriptor can be used with <citerefentry + project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry> or a similar + function to wait for I/O events on the specified bus connection object. If the bus object was configured with the + <citerefentry><refentrytitle>sd_bus_set_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry> function, then + the <parameter>input_fd</parameter> file descriptor used in that call is returned.</para> + + <para><function>sd_bus_get_events()</function> returns the I/O events to wait for, suitable for passing to + <function>poll()</function> or a similar call. Returns a combination of <constant>POLLIN</constant>, + <constant>POLLOUT</constant>, … events, or negative on error.</para> + + <para><function>sd_bus_get_timeout()</function> returns the time-out in µs to pass to to + <function>poll()</function> or a similar call when waiting for events on the specified bus connection. The returned + time-out may be zero, in which case a subsequent I/O polling call should be invoked in non-blocking mode. The + returned timeout may be <constant>UINT64_MAX</constant> in which case the I/O polling call may block indefinitely, + without any applied time-out. Note that the returned time-out should be considered only a maximum sleeping time. It + is permissible (and even expected) that shorter time-outs are used by the calling program, in case other event + sources are polled in the same event loop. Note that the returned time-value is relative and specified in + microseconds. When converting this value in order to pass it as third argument to <function>poll()</function> + (which expects milliseconds), care should be taken to use a division that rounds up to ensure the I/O polling + operation doesn't sleep for shorter than necessary, which might result in unintended busy looping (alternatively, + use <citerefentry project='man-pages'><refentrytitle>ppoll</refentrytitle><manvolnum>3</manvolnum></citerefentry> + instead of plain <function>poll()</function>, which understands time-outs with nano-second granularity).</para> + + <para>These three functions are useful to hook up a bus connection object with an external or manual event loop + involving <function>poll()</function> or a similar I/O polling call. Before each invocation of the I/O polling + call, all three functions should be invoked: the file descriptor returned by <function>sd_bus_get_fd()</function> + should be polled for the events indicated by <function>sd_bus_get_events()</function>, and the I/O call should + block for that up to the time-out returned by <function>sd_bus_get_timeout()</function>. After each I/O polling + call the bus connection needs to process incoming or outgoing data, by invoking + <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> + + <para>Note that these function are only one of three supported ways to implement I/O event handling for bus + connections. Alternatively use + <citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry> to attach a + bus connection to an <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry> + event loop. Or use <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry> + as a simple synchronous, blocking I/O waiting call.</para> </refsect1> <refsect1> <title>Return Value</title> - <para> - Returns the file descriptor used for incoming messages from the message - bus. - </para> + <para><function>sd_bus_get_fd()</function> returns the file descriptor used for communication, or a negative + <varname>errno</varname>-style error code on error.</para> + + <para><function>sd_bus_get_events()</function> returns the I/O event mask to use for I/O event watching, or a + negative <varname>errno</varname>-style error code on error.</para> + + <para><function>sd_bus_get_timeout()</function> returns zero or positive on success, or a negative + <varname>errno</varname>-style error code on error.</para> </refsect1> <refsect1> + <title>Errors</title> + + <para>Returned errors may indicate the following problems:</para> + + <variablelist> + <varlistentry> + <term><constant>-EINVAL</constant></term> + + <listitem><para>An invalid bus object was passed.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>-ECHILD</constant></term> + + <listitem><para>The bus connection was allocated in a parent process and is being reused in a child process + after <function>fork()</function>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>-ENOTCONN</constant></term> + + <listitem><para>The bus connection has been terminated.</para></listitem> + </varlistentry> + + <varlistentry> + <term><constant>-EPERM</constant></term> + + <listitem><para>Two distinct file descriptors were passed for input and output using + <function>sd_bus_set_fd()</function>, which <function>sd_bus_get_fd()</function> cannot + return.</para></listitem> + </varlistentry> + </variablelist> + </refsect1> + + <xi:include href="libsystemd-pkgconfig.xml" /> + + <refsect1> <title>See Also</title> <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_bus_set_fd</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>, + <citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> |