<refname>sd_bus_get_events</refname>
<refname>sd_bus_get_timeout</refname>
- <refpurpose>Get the file descriptor, I/O events and time-out to wait for from a message bus object</refpurpose>
+ <refpurpose>Get the file descriptor, I/O events and time-out to wait for from a message bus
+ object</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsect1>
<title>Description</title>
- <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
- <function>sd_bus_set_fd()</function> function, then the <parameter>input_fd</parameter> file descriptor used in
- that call is returned.</para>
-
- <para><function>sd_bus_set_fd()</function> sets the file descriptors used to communicate from a message bus
- object. Both <parameter>input_fd</parameter> and <parameter>output_fd</parameter> must be valid file descriptors.
- The same file descriptor may be used as both the input and the output file descriptor. This function must be called
- before the bus is started.</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_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 <function>sd_bus_set_fd()</function> function, then the
+ <parameter>input_fd</parameter> file descriptor used in that call is returned.</para>
+
+ <para><function>sd_bus_set_fd()</function> sets the file descriptors used to communicate from a
+ message bus object. Both <parameter>input_fd</parameter> and <parameter>output_fd</parameter>
+ must be valid file descriptors. The same file descriptor may be used as both the input and the
+ output file descriptor. This function must be called before the bus is started.</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
+ <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>
+ <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>
+ <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>On success, <function>sd_bus_get_fd()</function> returns the file descriptor used for communication. On failure,
- it returns a negative errno-style error code.</para>
+ <para>On success, <function>sd_bus_get_fd()</function> returns the file descriptor used for
+ communication. On failure, it returns a negative errno-style error code.</para>
- <para>On success, <function>sd_bus_set_fd()</function> returns a non-negative integer. On failure, it returns a
- negative errno-style error code.</para>
+ <para>On success, <function>sd_bus_set_fd()</function> returns a non-negative integer. On
+ failure, it returns a negative errno-style error code.</para>
- <para>On success, <function>sd_bus_get_events()</function> returns the I/O event mask to use for I/O event watching.
- On failure, it returns a negative errno-style error code.</para>
+ <para>On success, <function>sd_bus_get_events()</function> returns the I/O event mask to use for
+ I/O event watching. On failure, it returns a negative errno-style error code.</para>
- <para>On success, <function>sd_bus_get_timeout()</function> returns a non-negative integer. On failure, it returns a
- negative errno-style error code.</para>
+ <para>On success, <function>sd_bus_get_timeout()</function> returns a non-negative integer. On
+ failure, it returns a negative errno-style error code.</para>
<refsect2>
<title>Errors</title>
<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>
+ <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>
<varlistentry>
<term><constant>-EBADF</constant></term>
- <listitem><para>An invalid file descriptor was passed to <function>sd_bus_set_fd()</function>.
- </para></listitem>
+ <listitem><para>An invalid file descriptor was passed to
+ <function>sd_bus_set_fd()</function>.</para></listitem>
</varlistentry>
<varlistentry>
projects / thirdparty / systemd.git / commitdiff
