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sd-bus: Rewrap sd_bus_get_fd docs
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Daan De Meyer
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@ -26,7 +26,8 @@
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<refname>sd_bus_get_events</refname>
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<refname>sd_bus_get_timeout</refname>
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<refpurpose>Get the file descriptor, I/O events and time-out to wait for from a message bus object</refpurpose>
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<refpurpose>Get the file descriptor, I/O events and time-out to wait for from a message bus
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object</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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@ -61,65 +62,74 @@
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<refsect1>
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<title>Description</title>
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<para><function>sd_bus_get_fd()</function> returns the file descriptor used to communicate from a message bus
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object. This descriptor can be used with <citerefentry
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project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry> or a similar
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function to wait for I/O events on the specified bus connection object. If the bus object was configured with the
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<function>sd_bus_set_fd()</function> function, then the <parameter>input_fd</parameter> file descriptor used in
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that call is returned.</para>
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<para><function>sd_bus_get_fd()</function> returns the file descriptor used to communicate from
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a message bus object. This descriptor can be used with
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<citerefentry project='man-pages'><refentrytitle>poll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or a similar function to wait for I/O events on the specified bus connection object. If the bus
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object was configured with the <function>sd_bus_set_fd()</function> function, then the
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<parameter>input_fd</parameter> file descriptor used in that call is returned.</para>
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<para><function>sd_bus_set_fd()</function> sets the file descriptors used to communicate from a message bus
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object. Both <parameter>input_fd</parameter> and <parameter>output_fd</parameter> must be valid file descriptors.
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The same file descriptor may be used as both the input and the output file descriptor. This function must be called
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before the bus is started.</para>
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<para><function>sd_bus_set_fd()</function> sets the file descriptors used to communicate from a
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message bus object. Both <parameter>input_fd</parameter> and <parameter>output_fd</parameter>
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must be valid file descriptors. The same file descriptor may be used as both the input and the
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output file descriptor. This function must be called before the bus is started.</para>
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<para><function>sd_bus_get_events()</function> returns the I/O events to wait for, suitable for passing to
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<function>poll()</function> or a similar call. Returns a combination of <constant>POLLIN</constant>,
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<constant>POLLOUT</constant>, … events, or negative on error.</para>
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<para><function>sd_bus_get_events()</function> returns the I/O events to wait for, suitable for
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passing to <function>poll()</function> or a similar call. Returns a combination of
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<constant>POLLIN</constant>, <constant>POLLOUT</constant>, … events, or negative on error.
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</para>
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<para><function>sd_bus_get_timeout()</function> returns the time-out in µs to pass to to
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<function>poll()</function> or a similar call when waiting for events on the specified bus connection. The returned
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time-out may be zero, in which case a subsequent I/O polling call should be invoked in non-blocking mode. The
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returned timeout may be <constant>UINT64_MAX</constant> in which case the I/O polling call may block indefinitely,
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without any applied time-out. Note that the returned time-out should be considered only a maximum sleeping time. It
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is permissible (and even expected) that shorter time-outs are used by the calling program, in case other event
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sources are polled in the same event loop. Note that the returned time-value is relative and specified in
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microseconds. When converting this value in order to pass it as third argument to <function>poll()</function>
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(which expects milliseconds), care should be taken to use a division that rounds up to ensure the I/O polling
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operation doesn't sleep for shorter than necessary, which might result in unintended busy looping (alternatively,
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use <citerefentry project='man-pages'><refentrytitle>ppoll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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instead of plain <function>poll()</function>, which understands time-outs with nano-second granularity).</para>
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<function>poll()</function> or a similar call when waiting for events on the specified bus
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connection. The returned time-out may be zero, in which case a subsequent I/O polling call
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should be invoked in non-blocking mode. The returned timeout may be
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<constant>UINT64_MAX</constant> in which case the I/O polling call may block indefinitely,
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without any applied time-out. Note that the returned time-out should be considered only a
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maximum sleeping time. It is permissible (and even expected) that shorter time-outs are used by
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the calling program, in case other event sources are polled in the same event loop. Note that
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the returned time-value is relative and specified in microseconds. When converting this value in
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order to pass it as third argument to <function>poll()</function> (which expects milliseconds),
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care should be taken to use a division that rounds up to ensure the I/O polling operation
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doesn't sleep for shorter than necessary, which might result in unintended busy looping
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(alternatively, use
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<citerefentry project='man-pages'><refentrytitle>ppoll</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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instead of plain <function>poll()</function>, which understands time-outs with nano-second
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granularity).</para>
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<para>These three functions are useful to hook up a bus connection object with an external or manual event loop
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involving <function>poll()</function> or a similar I/O polling call. Before each invocation of the I/O polling
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call, all three functions should be invoked: the file descriptor returned by <function>sd_bus_get_fd()</function>
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should be polled for the events indicated by <function>sd_bus_get_events()</function>, and the I/O call should
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block for that up to the time-out returned by <function>sd_bus_get_timeout()</function>. After each I/O polling
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<para>These three functions are useful to hook up a bus connection object with an external or
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manual event loop involving <function>poll()</function> or a similar I/O polling call. Before
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each invocation of the I/O polling call, all three functions should be invoked: the file
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descriptor returned by <function>sd_bus_get_fd()</function> should be polled for the events
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indicated by <function>sd_bus_get_events()</function>, and the I/O call should block for that up
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to the time-out returned by <function>sd_bus_get_timeout()</function>. After each I/O polling
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call the bus connection needs to process incoming or outgoing data, by invoking
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<citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<citerefentry><refentrytitle>sd_bus_process</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para>Note that these function are only one of three supported ways to implement I/O event handling for bus
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connections. Alternatively use
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<citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry> to attach a
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bus connection to an <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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event loop. Or use <citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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<para>Note that these function are only one of three supported ways to implement I/O event
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handling for bus connections. Alternatively use
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<citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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to attach a bus connection to an
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<citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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event loop. Or use
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<citerefentry><refentrytitle>sd_bus_wait</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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as a simple synchronous, blocking I/O waiting call.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success, <function>sd_bus_get_fd()</function> returns the file descriptor used for communication. On failure,
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it returns a negative errno-style error code.</para>
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<para>On success, <function>sd_bus_get_fd()</function> returns the file descriptor used for
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communication. On failure, it returns a negative errno-style error code.</para>
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<para>On success, <function>sd_bus_set_fd()</function> returns a non-negative integer. On failure, it returns a
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negative errno-style error code.</para>
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<para>On success, <function>sd_bus_set_fd()</function> returns a non-negative integer. On
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failure, it returns a negative errno-style error code.</para>
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<para>On success, <function>sd_bus_get_events()</function> returns the I/O event mask to use for I/O event watching.
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On failure, it returns a negative errno-style error code.</para>
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<para>On success, <function>sd_bus_get_events()</function> returns the I/O event mask to use for
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I/O event watching. On failure, it returns a negative errno-style error code.</para>
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<para>On success, <function>sd_bus_get_timeout()</function> returns a non-negative integer. On failure, it returns a
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negative errno-style error code.</para>
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<para>On success, <function>sd_bus_get_timeout()</function> returns a non-negative integer. On
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failure, it returns a negative errno-style error code.</para>
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<refsect2>
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<title>Errors</title>
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@ -136,8 +146,8 @@
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<varlistentry>
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<term><constant>-ECHILD</constant></term>
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<listitem><para>The bus connection was allocated in a parent process and is being reused in a child
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process after <function>fork()</function>.</para></listitem>
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<listitem><para>The bus connection was allocated in a parent process and is being reused
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in a child process after <function>fork()</function>.</para></listitem>
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</varlistentry>
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<varlistentry>
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@ -157,8 +167,8 @@
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<varlistentry>
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<term><constant>-EBADF</constant></term>
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<listitem><para>An invalid file descriptor was passed to <function>sd_bus_set_fd()</function>.
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</para></listitem>
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<listitem><para>An invalid file descriptor was passed to
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<function>sd_bus_set_fd()</function>.</para></listitem>
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</varlistentry>
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<varlistentry>
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