Prep v233.3: Add missing documentation for API functions exported by elogind. (unreviewed)

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+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  This file is part of systemd.
+
+  Copyright 2014 Zbigniew Jędrzejewski-Szmek
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_bus_error">
+
+  <refentryinfo>
+    <title>sd_bus_error</title>
+    <productname>systemd</productname>
+
+    <authorgroup>
+      <author>
+        <contrib>A monkey with a typewriter</contrib>
+        <firstname>Zbigniew</firstname>
+        <surname>Jędrzejewski-Szmek</surname>
+        <email>zbyszek@in.waw.pl</email>
+      </author>
+    </authorgroup>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>sd_bus_error</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_bus_error</refname>
+    <refname>SD_BUS_ERROR_MAKE_CONST</refname>
+    <refname>SD_BUS_ERROR_NULL</refname>
+    <refname>sd_bus_error_free</refname>
+    <refname>sd_bus_error_set</refname>
+    <refname>sd_bus_error_setf</refname>
+    <refname>sd_bus_error_set_const</refname>
+    <refname>sd_bus_error_set_errno</refname>
+    <refname>sd_bus_error_set_errnof</refname>
+    <refname>sd_bus_error_set_errnofv</refname>
+    <refname>sd_bus_error_get_errno</refname>
+    <refname>sd_bus_error_copy</refname>
+    <refname>sd_bus_error_is_set</refname>
+    <refname>sd_bus_error_has_name</refname>
+
+    <refpurpose>sd-bus error handling</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
+
+      <funcsynopsisinfo>typedef struct {
+        const char *name;
+        const char *message;
+        …
+} sd_bus_error;</funcsynopsisinfo>
+
+      <para>
+        <constant>SD_BUS_ERROR_MAKE_CONST(<replaceable>name</replaceable>, <replaceable>message</replaceable>)</constant>
+      </para>
+      <para>
+        <constant>SD_BUS_ERROR_NULL</constant>
+      </para>
+
+      <funcprototype>
+        <funcdef>void <function>sd_bus_error_free</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_set</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>const char *<parameter>name</parameter></paramdef>
+        <paramdef>const char *<parameter>message</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_setf</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>const char *<parameter>name</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>…</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_set_const</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>const char *<parameter>name</parameter></paramdef>
+        <paramdef>const char *<parameter>message</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_set_errno</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>int <parameter>error</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_set_errnof</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>int <parameter>error</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>…</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_set_errnofv</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>int <parameter>error</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>va_list ap</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_get_errno</function></funcdef>
+        <paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_copy</function></funcdef>
+        <paramdef>sd_bus_error *<parameter>dst</parameter></paramdef>
+        <paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_is_set</function></funcdef>
+        <paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_bus_error_has_name</function></funcdef>
+        <paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
+        <paramdef>const char *<parameter>name</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>The <structname>sd_bus_error</structname> structure carries
+    information about a D-Bus error condition. The functions described
+    below may be used to set and query fields in this structure. The
+    <structfield>name</structfield> field contains a short identifier
+    of an error. It should follow the rules for error names described
+    in the D-Bus specification, subsection <ulink
+    url="http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names">Valid
+    Names</ulink>. A number of common, standardized error names are
+    described in
+    <citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+    but additional domain-specific errors may be defined by
+    applications. The <structfield>message</structfield> field usually
+    contains a human-readable string describing the details, but might
+    be NULL. An unset <structname>sd_bus_error</structname> structure
+    should have both fields initialized to NULL. Set an error
+    structure to <constant>SD_BUS_ERROR_NULL</constant> in order to
+    reset both fields to NULL. When no longer necessary, resources
+    held by the <structname>sd_bus_error</structname>structure should
+    be destroyed with <function>sd_bus_error_free()</function>.</para>
+
+    <para><function>sd_bus_error_set()</function> sets an error
+    structure to the specified name and message strings. The strings
+    will be copied into internal, newly allocated memory. It is
+    essential to free the error structure again when it is not
+    required anymore (see above). The function will return an
+    <varname>errno</varname>-like negative value (see <citerefentry
+    project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
+    determined from the specified error name.  Various well-known
+    D-Bus errors are converted to well-known <varname>errno</varname>
+    counterparts, and the other ones to <constant>-EIO</constant>. See
+    <citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    for a list of well-known error names. Additional error mappings
+    may be defined with
+    <citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
+    <parameter>e</parameter> is NULL, no error structure is initialized,
+    but the error is still converted into an
+    <varname>errno</varname>-style error. If
+    <parameter>name</parameter> is <constant>NULL</constant>, it is
+    assumed that no error occurred, and 0 is returned. This means that
+    this function may be conveniently used in a
+    <function>return</function> statement. If
+    <parameter>message</parameter> is NULL, no message is set. This
+    call can fail if no memory may be allocated for the name and
+    message strings, in which case an
+    <constant>SD_BUS_ERROR_NO_MEMORY</constant> error might be set
+    instead and -ENOMEM be returned. Do not use this call on error
+    structures that are already initialized. If you intend to reuse an
+    error structure, free the old data stored in it with
+    <function>sd_bus_error_free()</function> first.</para>
+
+    <para><function>sd_bus_error_setf()</function> is similar to
+    <function>sd_bus_error_set()</function>, but takes a <citerefentry
+    project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    format string and corresponding arguments to generate the
+    <structfield>message</structfield> field.</para>
+
+    <para><function>sd_bus_error_set_const()</function> is similar to
+    <function>sd_bus_error_set()</function>, but the string parameters
+    are not copied internally, and must hence remain constant and
+    valid for the lifetime of <parameter>e</parameter>. Use this call
+    to avoid memory allocations when setting error structures. Since
+    this call does not allocate memory, it will not fail with an
+    out-of-memory condition as
+    <function>sd_bus_error_set()</function> can, as described
+    above. Alternatively, the
+    <constant>SD_BUS_ERROR_MAKE_CONST()</constant> macro may be used
+    to generate a literal, constant bus error structure
+    on-the-fly.</para>
+
+    <para><function>sd_bus_error_set_errno()</function> will set
+    <structfield>name</structfield> from an
+    <varname>errno</varname>-like value that is converted to a D-Bus
+    error. <citerefentry
+    project='die-net'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    will be used to set <structfield>message</structfield>. Well-known
+    D-Bus error names will be used for <structfield>name</structfield>
+    if applicable, otherwise a name in the
+    <literal>System.Error.</literal> namespace will be generated. The
+    sign of the specified error number is ignored. The absolute value
+    is used implicitly. The call always returns a negative value, for
+    convenient usage in <function>return</function> statements. This
+    call might fail due to lack of memory, in which case an
+    <constant>SD_BUS_ERROR_NO_MEMORY</constant> error is set instead,
+    and -ENOMEM is returned.</para>
+
+    <para><function>sd_bus_error_set_errnof()</function> is similar to
+    <function>sd_bus_error_set_errno()</function>, but in addition to
+    <parameter>error</parameter>, takes a <citerefentry
+    project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    format string and corresponding arguments.  The
+    <structfield>message</structfield> field will be generated from
+    <parameter>format</parameter> and the arguments.</para>
+
+    <para><function>sd_bus_error_set_errnofv()</function> is similar to
+    <function>sd_bus_error_set_errnof()</function>, but takes the
+    format string parameters as <citerefentry
+    project='man-pages'><refentrytitle>va_arg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    parameter list.</para>
+
+    <para><function>sd_bus_error_get_errno()</function> converts the
+    <structfield>name</structfield> field of an error structure to an
+    <varname>errno</varname>-like (positive) value using the same
+    rules as <function>sd_bus_error_set()</function>.  If
+    <parameter>e</parameter> is <constant>NULL</constant>, 0 will be
+    returned.</para>
+
+    <para><function>sd_bus_error_copy()</function> will initialize
+    <parameter>dst</parameter> using the values in
+    <parameter>e</parameter>. If the strings in
+    <parameter>e</parameter> were set using
+    <function>sd_bus_set_error_const()</function>, they will be shared.
+    Otherwise, they will be copied. Returns a converted
+    <varname>errno</varname>-like, negative error code.</para>
+
+    <para><function>sd_bus_error_is_set()</function> will return a
+    non-zero value if <parameter>e</parameter> is
+    non-<constant>NULL</constant> and an error has been set,
+    <constant>false</constant> otherwise.</para>
+
+    <para><function>sd_bus_error_has_name()</function> will return a
+    non-zero value if <parameter>e</parameter> is
+    non-<constant>NULL</constant> and an error with the same
+    <parameter>name</parameter> has been set,
+    <constant>false</constant> otherwise.</para>
+
+    <para><function>sd_bus_error_free()</function> will destroy
+    resources held by <parameter>e</parameter>. The parameter itself
+    will not be deallocated, and must be <citerefentry
+    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>d
+    by the caller if necessary. The function may also be called safely
+    on unset errors (error structures with both fields set to NULL),
+    in which case it performs no operation. This call will reset the
+    error structure after freeing the data, so that all fields are set
+    to NULL. The structure may be reused afterwards.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>The functions <function>sd_bus_error_set()</function>,
+    <function>sd_bus_error_setf()</function>, and
+    <function>sd_bus_error_set_const()</function>, when successful,
+    return the negative errno value corresponding to the
+    <parameter>name</parameter> parameter. The functions
+    <function>sd_bus_error_set_errno()</function>,
+    <function>sd_bus_error_set_errnof()</function> and
+    <function>sd_bus_error_set_errnofv()</function>, when successful,
+    return the negative value of the <parameter>error</parameter>
+    parameter. If an error occurs, one of the negative error values
+    listed below will be returned.</para>
+
+    <para><function>sd_bus_error_get_errno()</function> returns
+    <constant>false</constant> when <parameter>e</parameter> is
+    <constant>NULL</constant>, and a positive errno value mapped from
+    <parameter>e-&gt;name</parameter> otherwise.</para>
+
+    <para><function>sd_bus_error_copy()</function> returns 0 or a
+    positive integer on success, and a negative error value converted
+    from the error name otherwise.</para>
+
+    <para><function>sd_bus_error_is_set()</function> returns a
+    non-zero value when <parameter>e</parameter> and the
+    <structfield>name</structfield> field are
+    non-<constant>NULL</constant>, zero otherwise.</para>
+
+    <para><function>sd_bus_error_has_name()</function> returns a
+    non-zero value when <parameter>e</parameter> is
+    non-<constant>NULL</constant> and the
+    <structfield>name</structfield> field is equal to
+    <parameter>name</parameter>, zero otherwise.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Reference ownership</title>
+    <para><structname>sd_bus_error</structname> is not reference
+    counted. Users should destroy resources held by it by calling
+    <function>sd_bus_error_free()</function>. Usually, error structures
+    are allocated on the stack or passed in as function parameters,
+    but they may also be allocated dynamically, in which case it is
+    the duty of the caller to <citerefentry
+    project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    the memory held by the structure itself after freeing its contents
+    with <function>sd_bus_error_free()</function>.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Errors</title>
+
+    <para>Returned errors may indicate the following problems:</para>
+
+    <variablelist>
+
+      <varlistentry>
+        <term><constant>-EINVAL</constant></term>
+
+        <listitem><para>Error was already set in
+        <structname>sd_bus_error</structname> structure when one the
+        error-setting functions was called.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>-ENOMEM</constant></term>
+
+        <listitem><para>Memory allocation failed.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Notes</title>
+
+    <para><function>sd_bus_set_error()</function> and other functions
+    described here are available as a shared library, which can be
+    compiled and linked to with the
+    <constant>libelogind</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+    file.</para>
+  </refsect1>
+
+  <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-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry project='die-net'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>