Adding upstream version 252.22.upstream/252.22

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 311 insertions, 0 deletions

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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_event_add_io" xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_event_add_io</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_event_add_io</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_event_add_io</refname>
+    <refname>sd_event_source_get_io_events</refname>
+    <refname>sd_event_source_set_io_events</refname>
+    <refname>sd_event_source_get_io_revents</refname>
+    <refname>sd_event_source_get_io_fd</refname>
+    <refname>sd_event_source_set_io_fd</refname>
+    <refname>sd_event_source_get_io_fd_own</refname>
+    <refname>sd_event_source_set_io_fd_own</refname>
+    <refname>sd_event_source</refname>
+    <refname>sd_event_io_handler_t</refname>
+
+    <refpurpose>Add an I/O event source to an event loop</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-event.h&gt;</funcsynopsisinfo>
+
+      <funcsynopsisinfo><token>typedef</token> struct sd_event_source sd_event_source;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>typedef int (*<function>sd_event_io_handler_t</function>)</funcdef>
+        <paramdef>sd_event_source *<parameter>s</parameter></paramdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>uint32_t <parameter>revents</parameter></paramdef>
+        <paramdef>void *<parameter>userdata</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_add_io</function></funcdef>
+        <paramdef>sd_event *<parameter>event</parameter></paramdef>
+        <paramdef>sd_event_source **<parameter>source</parameter></paramdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+        <paramdef>uint32_t <parameter>events</parameter></paramdef>
+        <paramdef>sd_event_io_handler_t <parameter>handler</parameter></paramdef>
+        <paramdef>void *<parameter>userdata</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_io_events</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint32_t *<parameter>events</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_set_io_events</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint32_t <parameter>events</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_io_revents</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>uint32_t *<parameter>revents</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_io_fd</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_set_io_fd</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>int <parameter>fd</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_get_io_fd_own</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_event_source_set_io_fd_own</function></funcdef>
+        <paramdef>sd_event_source *<parameter>source</parameter></paramdef>
+        <paramdef>int <parameter>b</parameter></paramdef>
+      </funcprototype>
+
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para><function>sd_event_add_io()</function> adds a new I/O event
+    source to an event loop. The event loop object is specified in the
+    <parameter>event</parameter> parameter, the event source object is
+    returned in the <parameter>source</parameter> parameter. The
+    <parameter>fd</parameter> parameter takes the UNIX file descriptor
+    to watch, which may refer to a socket, a FIFO, a message queue, a
+    serial connection, a character device, or any other file descriptor
+    compatible with Linux
+    <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
+    <parameter>events</parameter> parameter takes a bit mask of events
+    to watch for, a combination of the following event flags:
+    <constant>EPOLLIN</constant>, <constant>EPOLLOUT</constant>,
+    <constant>EPOLLRDHUP</constant>, <constant>EPOLLPRI</constant>,
+    and <constant>EPOLLET</constant>, see
+    <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+    for details.</para>
+
+    <para>The <parameter>handler</parameter> is a function to call when the event source is triggered or
+    <constant>NULL</constant>. The <parameter>userdata</parameter> pointer will be passed to the handler
+    function, and may be chosen freely by the caller. The handler will also be passed the file descriptor the
+    event was seen on, as well as the actual event flags. It's generally a subset of the events watched,
+    however may additionally include <constant>EPOLLERR</constant> and <constant>EPOLLHUP</constant>. The
+    handler may return negative to signal an error (see below), other return values are ignored. If
+    <parameter>handler</parameter> is <constant>NULL</constant>, a default handler that calls
+    <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry> will be
+    used.</para>
+
+    <para>By default, an event source will stay enabled continuously (<constant>SD_EVENT_ON</constant>), but
+    this may be changed with
+    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+    If the handler function returns a negative error code, it will either be disabled after the invocation,
+    even if the <constant>SD_EVENT_ON</constant> mode was requested before, or it will cause the loop to
+    terminate, see
+    <citerefentry><refentrytitle>sd_event_source_set_exit_on_failure</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+    Note that an event source set to <constant>SD_EVENT_ON</constant> will fire continuously unless data is
+    read from or written to the file descriptor to reset the mask of events seen.</para>
+
+    <para>Setting the I/O event mask to watch for to 0 does not mean
+    that the event source won't be triggered anymore, as
+    <constant>EPOLLHUP</constant> and <constant>EPOLLERR</constant>
+    may be triggered even with a zero event mask. To temporarily
+    disable an I/O event source use
+    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    with <constant>SD_EVENT_OFF</constant> instead.</para>
+
+    <para>To destroy an event source object use
+    <citerefentry><refentrytitle>sd_event_source_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+    but note that the event source is only removed from the event loop
+    when all references to the event source are dropped. To make sure
+    an event source does not fire anymore, even if it is still referenced,
+    disable the event source using
+    <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    with <constant>SD_EVENT_OFF</constant>.</para>
+
+    <para>If the second parameter of
+    <function>sd_event_add_io()</function> is
+    <constant>NULL</constant> no reference to the event source object
+    is returned. In this case the event source is considered
+    "floating", and will be destroyed implicitly when the event loop
+    itself is destroyed.</para>
+
+    <para>If the <parameter>handler</parameter> to <function>sd_event_add_io()</function> is
+    <constant>NULL</constant>, and the event source fires, this will be considered a request to exit the
+    event loop. In this case, the <parameter>userdata</parameter> parameter, cast to an integer, is passed as
+    the exit code parameter to
+    <citerefentry><refentrytitle>sd_event_exit</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+    <para>Note that this call does not take possession of the file descriptor passed in, ownership (and thus
+    the duty to close it when it is no longer needed) remains with the caller. However, with the
+    <function>sd_event_source_set_io_fd_own()</function> call (see below) the event source may optionally
+    take ownership of the file descriptor after the event source has been created. In that case the file
+    descriptor is closed automatically as soon as the event source is released.</para>
+
+    <para>It is recommended to use
+    <function>sd_event_add_io()</function> only in conjunction with
+    file descriptors that have <constant>O_NONBLOCK</constant> set, to
+    ensure that all I/O operations from invoked handlers are properly
+    asynchronous and non-blocking. Using file descriptors without
+    <constant>O_NONBLOCK</constant> might result in unexpected
+    starvation of other event sources. See
+    <citerefentry project='man-pages'><refentrytitle>fcntl</refentrytitle><manvolnum>2</manvolnum></citerefentry>
+    for details on enabling <constant>O_NONBLOCK</constant> mode.</para>
+
+    <para><function>sd_event_source_get_io_events()</function> retrieves
+    the configured mask of watched I/O events of an event source created
+    previously with <function>sd_event_add_io()</function>. It takes
+    the event source object and a pointer to a variable to store the
+    mask in.</para>
+
+    <para><function>sd_event_source_set_io_events()</function>
+    configures the mask of watched I/O events of an event source created
+    previously with <function>sd_event_add_io()</function>. It takes the
+    event source object and the new event mask.</para>
+
+    <para><function>sd_event_source_get_io_revents()</function>
+    retrieves the I/O event mask of currently seen but undispatched
+    events from an event source created previously with
+    <function>sd_event_add_io()</function>. It takes the event source
+    object and a pointer to a variable to store the event mask
+    in. When called from a handler function on the handler's event
+    source object this will return the same mask as passed to the
+    handler's <parameter>revents</parameter> parameter. This call is
+    primarily useful to check for undispatched events of an event
+    source from the handler of an unrelated (possibly higher priority)
+    event source. Note the relation between
+    <function>sd_event_source_get_pending()</function> and
+    <function>sd_event_source_get_io_revents()</function>: both
+    functions will report non-zero results when there's an event
+    pending for the event source, but the former applies to all event
+    source types, the latter only to I/O event sources.</para>
+
+    <para><function>sd_event_source_get_io_fd()</function> retrieves
+    the UNIX file descriptor of an event source created previously
+    with <function>sd_event_add_io()</function>. It takes the event
+    source object and returns the non-negative file descriptor
+    or a negative error number on error (see below).</para>
+
+    <para><function>sd_event_source_set_io_fd()</function>
+    changes the UNIX file descriptor of an I/O event source created
+    previously with <function>sd_event_add_io()</function>. It takes
+    the event source object and the new file descriptor.</para>
+
+    <para><function>sd_event_source_set_io_fd_own()</function> controls whether the file descriptor of the event source
+    shall be closed automatically when the event source is freed, i.e. whether it shall be considered 'owned' by the
+    event source object. By default it is not closed automatically, and the application has to do this on its own. The
+    <parameter>b</parameter> parameter is a boolean parameter: if zero, the file descriptor is not closed automatically
+    when the event source is freed, otherwise it is closed.</para>
+
+    <para><function>sd_event_source_get_io_fd_own()</function> may be used to query the current setting of the file
+    descriptor ownership boolean flag as set with <function>sd_event_source_set_io_fd_own()</function>. It returns
+    positive if the file descriptor is closed automatically when the event source is destroyed, zero if not, and
+    negative on error.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>On success, these functions return 0 or a positive
+    integer. On failure, they return a negative errno-style error
+    code.</para>
+
+    <refsect2>
+      <title>Errors</title>
+
+      <para>Returned values may indicate the following problems:</para>
+
+      <variablelist>
+        <varlistentry>
+          <term><constant>-ENOMEM</constant></term>
+
+          <listitem><para>Not enough memory to allocate an object.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-EINVAL</constant></term>
+
+          <listitem><para>An invalid argument has been passed.</para></listitem>
+
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-ESTALE</constant></term>
+
+          <listitem><para>The event loop is already terminated.</para></listitem>
+
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-ECHILD</constant></term>
+
+          <listitem><para>The event loop has been created in a different process.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><constant>-EDOM</constant></term>
+
+          <listitem><para>The passed event source is not an I/O event source.</para></listitem>
+        </varlistentry>
+      </variablelist>
+    </refsect2>
+  </refsect1>
+
+  <xi:include href="libsystemd-pkgconfig.xml" />
+
+  <refsect1>
+    <title>See Also</title>
+
+    <para>
+      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_now</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_source_set_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_source_set_priority</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_source_set_userdata</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_source_set_description</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_source_get_pending</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_event_source_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>epoll</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>