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870c2aaf8c
The description for sd_bus_error_set_errnof/sd_bus_error_set_errnofv are adjusted to use the same pattern.
409 lines
22 KiB
XML
409 lines
22 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_bus_error" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_bus_error</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_bus_error</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_bus_error</refname>
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<refname>SD_BUS_ERROR_MAKE_CONST</refname>
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<refname>SD_BUS_ERROR_NULL</refname>
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<refname>sd_bus_error_free</refname>
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<refname>sd_bus_error_set</refname>
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<refname>sd_bus_error_setf</refname>
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<refname>sd_bus_error_setfv</refname>
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<refname>sd_bus_error_set_const</refname>
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<refname>sd_bus_error_set_errno</refname>
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<refname>sd_bus_error_set_errnof</refname>
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<refname>sd_bus_error_set_errnofv</refname>
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<refname>sd_bus_error_get_errno</refname>
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<refname>sd_bus_error_copy</refname>
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<refname>sd_bus_error_move</refname>
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<refname>sd_bus_error_is_set</refname>
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<refname>sd_bus_error_has_name</refname>
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<refname>sd_bus_error_has_names_sentinel</refname>
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<refname>sd_bus_error_has_names</refname>
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<refpurpose>sd-bus error handling</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-bus.h></funcsynopsisinfo>
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<funcsynopsisinfo>typedef struct {
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const char *name;
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const char *message;
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…
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} sd_bus_error;</funcsynopsisinfo>
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<para>
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<constant>SD_BUS_ERROR_MAKE_CONST(<replaceable>name</replaceable>, <replaceable>message</replaceable>)</constant>
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</para>
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<para>
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<constant>SD_BUS_ERROR_NULL</constant>
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</para>
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<funcprototype>
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<funcdef>void <function>sd_bus_error_free</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_set</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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<paramdef>const char *<parameter>message</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_setf</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_setfv</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>va_list <parameter>ap</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_set_const</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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<paramdef>const char *<parameter>message</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_set_errno</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>int <parameter>error</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_set_errnof</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>int <parameter>error</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>…</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_set_errnofv</function></funcdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>int <parameter>error</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>va_list <parameter>ap</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_get_errno</function></funcdef>
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<paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_copy</function></funcdef>
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<paramdef>sd_bus_error *<parameter>dst</parameter></paramdef>
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<paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_move</function></funcdef>
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<paramdef>sd_bus_error *<parameter>dst</parameter></paramdef>
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<paramdef>sd_bus_error *<parameter>e</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_is_set</function></funcdef>
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<paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_has_name</function></funcdef>
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<paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>const char *<parameter>name</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_bus_error_has_names_sentinel</function></funcdef>
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<paramdef>const sd_bus_error *<parameter>e</parameter></paramdef>
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<paramdef>...</paramdef>
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</funcprototype>
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<para>
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#define sd_bus_error_has_names(e, ...) sd_bus_error_has_names_sentinel(e, ..., NULL)
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</para>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>The <structname>sd_bus_error</structname> structure carries information about a D-Bus error
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condition, or lack thereof. The functions described below may be used to set and query fields in this
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structure.
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<itemizedlist>
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<listitem><para>The <structfield>name</structfield> field contains a short identifier of an error. It
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should follow the rules for error names described in the D-Bus specification, subsection <ulink
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url="https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names">Valid
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Names</ulink>. A number of common, standardized error names are described in
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<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>, but
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additional domain-specific errors may be defined by applications.</para></listitem>
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<listitem><para>The <structfield>message</structfield> field usually contains a human-readable string
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describing the details, but might be <constant>NULL</constant>.</para></listitem>
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</itemizedlist>
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An unset <structname>sd_bus_error</structname> structure should have both fields initialized to
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<constant>NULL</constant>, and signifies lack of an error, i.e. success. Assign
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<constant>SD_BUS_ERROR_NULL</constant> to the structure in order to initialize both fields to
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<constant>NULL</constant>. When no longer necessary, resources held by the
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<structname>sd_bus_error</structname> structure should be destroyed with
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<function>sd_bus_error_free()</function>.</para>
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<para><function>sd_bus_error_set()</function> sets an error structure to the specified name and message
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strings. The strings will be copied into internal, newly allocated memory. It is essential to free the
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contents again when they are not required anymore (see above). Do not use this call on error structures
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that have already been set. If you intend to reuse an error structure, free the old data stored in it
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with <function>sd_bus_error_free()</function> first.</para>
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<para><function>sd_bus_error_set()</function> will return an <varname>errno</varname>-like value (see
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<citerefentry
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project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>)
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determined from the specified error name <parameter>name</parameter>. If <parameter>name</parameter> is
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<constant>NULL</constant>, it is assumed that no error occurred, and <constant>0</constant> is returned.
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If <parameter>name</parameter> is nonnull, a negative value is always returned. If
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<parameter>e</parameter> is <constant>NULL</constant>, no error structure is initialized, but
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<parameter>name</parameter> is still converted into an <varname>errno</varname>-style value.</para>
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<para>Various well-known D-Bus errors are converted to well-known <varname>errno</varname> counterparts,
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and the other ones to <constant>-EIO</constant>. See
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<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry> for a
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list of well-known error names. Additional error mappings may be defined with
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<citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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</para>
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<para><function>sd_bus_error_set()</function> is designed to be conveniently used in a
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<function>return</function> statement. If <parameter>message</parameter> is <constant>NULL</constant>, no
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message is set. This call can fail if no memory may be allocated for the name and message strings, in
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which case an <constant>SD_BUS_ERROR_NO_MEMORY</constant> error will be set instead and
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<constant>-ENOMEM</constant> returned. </para>
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<para><function>sd_bus_error_setf()</function> and <function>sd_bus_error_setfv()</function> are similar
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to <function>sd_bus_error_set()</function>, but take a <citerefentry
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project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> format
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string and corresponding arguments to generate the <structfield>message</structfield> field.
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<function>sd_bus_error_setf()</function> uses variadic arguments, and
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<function>sd_bus_error_setfv()</function> accepts the arguments as a
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<citerefentry
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project='man-pages'><refentrytitle>va_arg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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parameter list.</para>
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<para><function>sd_bus_error_set_const()</function> is similar to
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<function>sd_bus_error_set()</function>, but the string parameters are not copied internally, and must
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hence remain constant and valid for the lifetime of <parameter>e</parameter>. Use this call to avoid
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memory allocations when setting error structures. Since this call does not allocate memory, it will not
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fail with an out-of-memory condition as <function>sd_bus_error_set()</function> may, as described
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above. Alternatively, the <constant>SD_BUS_ERROR_MAKE_CONST()</constant> macro may be used to generate a
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literal, constant bus error structure on-the-fly.</para>
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<para><function>sd_bus_error_set_errno()</function> will immediately return <constant>0</constant> if the
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specified error parameter <parameter>error</parameter> is <constant>0</constant>. Otherwise, it will set
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<structfield>name</structfield> from an <varname>errno</varname>-like value that is converted to a D-Bus
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error. <citerefentry
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project='die-net'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry> will
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be used to set <structfield>message</structfield>. Well-known D-Bus error names will be used for
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<structfield>name</structfield> if applicable, otherwise a name in the <literal>System.Error.</literal>
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namespace will be generated. The sign of the specified error number is ignored and the absolute value is
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used implicitly. If the specified error <parameter>error</parameter> is non-zero, the call always returns
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a negative value, for convenient usage in <function>return</function> statements. This call might fail
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due to lack of memory, in which case an <constant>SD_BUS_ERROR_NO_MEMORY</constant> error is set instead,
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and <constant>-ENOMEM</constant> is returned.</para>
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<para><function>sd_bus_error_set_errnof()</function> and <function>sd_bus_error_set_errnof()</function>
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are similar to <function>sd_bus_error_set_errno()</function>, but in addition to
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<parameter>error</parameter>, take a <citerefentry
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project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> format
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string and corresponding arguments. The <structfield>message</structfield> field will be generated from
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<parameter>format</parameter> and the arguments.
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<function>sd_bus_error_set_errnof()</function> uses variadic arguments, and
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<function>sd_bus_error_set_errnofv()</function> accepts the arguments as a
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<citerefentry
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project='man-pages'><refentrytitle>va_arg</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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parameter list.</para>
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<para><function>sd_bus_error_get_errno()</function> converts the <structfield>name</structfield> field of
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an error structure to an <varname>errno</varname>-like (positive) value using the same rules as
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<function>sd_bus_error_set()</function>. If <parameter>e</parameter> is <constant>NULL</constant>,
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<constant>0</constant> will be returned.</para>
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<para><function>sd_bus_error_copy()</function> will initialize <parameter>dst</parameter> using the
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values in <parameter>e</parameter>, if <parameter>e</parameter> has been set with an error value before.
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Otherwise, it will return immediately. If the strings in <parameter>e</parameter> were set using
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<function>sd_bus_error_set_const()</function>, they will be shared. Otherwise, they will be
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copied. Before this call, <parameter>dst</parameter> must be unset, i.e. either freshly initialized with
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<constant>NULL</constant> or reset using <function>sd_bus_error_free()</function>.</para>
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<para><function>sd_bus_error_copy()</function> generally returns <constant>0</constant> or a negative
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<varname>errno</varname>-like value based on the input parameter <parameter>e</parameter>:
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<constant>0</constant> if it was unset and a negative integer if it was set to some error, similarly to
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<function>sd_bus_error_set()</function>. It may however also return an error generated internally, for
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example <constant>-ENOMEM</constant> if a memory allocation fails.</para>
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<para><function>sd_bus_error_move()</function> is similar to <function>sd_bus_error_copy()</function>,
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but will move any error information from <parameter>e</parameter> into <parameter>dst</parameter>,
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resetting the former. This function cannot fail, as no new memory is allocated. Note that if
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<parameter>e</parameter> is not set, <parameter>dst</parameter> is initialized to
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<constant>SD_BUS_ERROR_NULL</constant>. Moreover, if <parameter>dst</parameter> is
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<constant>NULL</constant> no operation is executed on it and resources held by <parameter>e</parameter>
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are freed and reset. Returns a converted <varname>errno</varname>-like, non-positive error value.</para>
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<para><function>sd_bus_error_is_set()</function> will return a
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non-zero value if <parameter>e</parameter> is
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non-<constant>NULL</constant> and an error has been set,
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<constant>false</constant> otherwise.</para>
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<para><function>sd_bus_error_has_name()</function> will return a
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non-zero value if <parameter>e</parameter> is
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non-<constant>NULL</constant> and an error with the same
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<parameter>name</parameter> has been set,
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<constant>false</constant> otherwise.</para>
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<para><function>sd_bus_error_has_names_sentinel()</function> is similar to
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<function>sd_bus_error_has_name()</function>, but takes multiple names to check against. The list must be
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terminated with <constant>NULL</constant>. <function>sd_bus_error_has_names()</function>
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is a macro wrapper around <function>sd_bus_error_has_names_sentinel()</function> that adds the
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<constant>NULL</constant> sentinel automatically.</para>
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<para><function>sd_bus_error_free()</function> will destroy
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resources held by <parameter>e</parameter>. The parameter itself
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will not be deallocated, and must be <citerefentry
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project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>d
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by the caller if necessary. The function may also be called safely
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on unset errors (error structures with both fields set to <constant>NULL</constant>),
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in which case it performs no operation. This call will reset the
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error structure after freeing the data, so that all fields are set
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to <constant>NULL</constant>. The structure may be reused afterwards.</para>
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</refsect1>
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<refsect1>
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<title>Reference ownership</title>
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<para><structname>sd_bus_error</structname> is not reference-counted. Users should destroy resources held
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by it by calling <function>sd_bus_error_free()</function>. Usually, error structures are allocated on the
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stack or passed in as function parameters, but they may also be allocated dynamically, in which case it
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is the duty of the caller to <citerefentry
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project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry> the memory
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held by the structure itself after freeing its contents with
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<function>sd_bus_error_free()</function>.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>The functions <function>sd_bus_error_set()</function>, <function>sd_bus_error_setf()</function>,
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and <function>sd_bus_error_set_const()</function> always return <constant>0</constant> when the specified
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error value is <constant>NULL</constant>, and a negative errno-like value corresponding to the
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<parameter>name</parameter> parameter otherwise. The functions
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<function>sd_bus_error_set_errno()</function>, <function>sd_bus_error_set_errnof()</function> and
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<function>sd_bus_error_set_errnofv()</function>, return <constant>0</constant> when the specified error
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value is <constant>0</constant>, and a negative errno-like value corresponding to the
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<parameter>error</parameter> parameter otherwise. If an error occurs internally, one of the negative
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error values listed below will be returned. This allows those functions to be conveniently used in a
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<constant>return</constant> statement, see the example below.</para>
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<para><function>sd_bus_error_get_errno()</function> returns
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<constant>false</constant> when <parameter>e</parameter> is
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<constant>NULL</constant>, and a positive errno value mapped from
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<parameter>e->name</parameter> otherwise.</para>
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<para><function>sd_bus_error_copy()</function> and <function>sd_bus_error_move()</function> return a
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negative error value converted from the source error, and zero if the error has not been set. This
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allows those functions to be conveniently used in a <constant>return</constant> statement, see the
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example below.</para>
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<para><function>sd_bus_error_is_set()</function> returns a
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non-zero value when <parameter>e</parameter> and the
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<structfield>name</structfield> field are
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non-<constant>NULL</constant>, zero otherwise.</para>
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<para><function>sd_bus_error_has_name()</function>, <function>sd_bus_error_has_names()</function>, and
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<function>sd_bus_error_has_names_sentinel()</function> return a non-zero value when <parameter>e</parameter> is
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non-<constant>NULL</constant> and the <structfield>name</structfield> field is equal to one of the given
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names, zero otherwise.</para>
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<refsect2>
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<title>Errors</title>
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<para>Return value may indicate the following problems in the invocation of the function itself:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>Error was already set in the <structname>sd_bus_error</structname> structure when
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one the error-setting functions was called.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>On success, <function>sd_bus_error_set()</function>, <function>sd_bus_error_setf()</function>,
|
|
<function>sd_bus_error_set_const()</function>, <function>sd_bus_error_set_errno()</function>,
|
|
<function>sd_bus_error_set_errnof()</function>, <function>sd_bus_error_set_errnofv()</function>,
|
|
<function>sd_bus_error_copy()</function>, and <function>sd_bus_error_move()</function> will return a
|
|
negative converted <varname>errno</varname>-style value, or <constant>0</constant> if the error
|
|
parameter is <constant>NULL</constant> or unset. D-Bus errors are converted to the integral
|
|
<varname>errno</varname>-style value, and the mapping mechanism is extensible, see the discussion
|
|
above. This effectively means that almost any negative <varname>errno</varname>-style value can be
|
|
returned.</para>
|
|
</refsect2>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Examples</title>
|
|
|
|
<example>
|
|
<title>Using the negative return value to propagate an error</title>
|
|
|
|
<programlisting><xi:include href="sd_bus_error-example.c" parse="text" /></programlisting>
|
|
</example>
|
|
</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-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>
|