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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
368 lines
17 KiB
XML
368 lines
17 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+ -->
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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_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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<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_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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</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
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information about a D-Bus error condition. The functions described
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below may be used to set and query fields in this structure. The
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<structfield>name</structfield> field contains a short identifier
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of an error. It should follow the rules for error names described
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in the D-Bus specification, subsection <ulink
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url="http://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
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described in
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<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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but additional domain-specific errors may be defined by
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applications. The <structfield>message</structfield> field usually
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contains a human-readable string describing the details, but might
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be NULL. An unset <structname>sd_bus_error</structname> structure
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should have both fields initialized to NULL. Set an error
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structure to <constant>SD_BUS_ERROR_NULL</constant> in order to
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reset both fields to NULL. When no longer necessary, resources
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held by the <structname>sd_bus_error</structname> structure should
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be destroyed with <function>sd_bus_error_free()</function>.</para>
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<para><function>sd_bus_error_set()</function> sets an error
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structure to the specified name and message strings. The strings
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will be copied into internal, newly allocated memory. It is
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essential to free the error structure again when it is not
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required anymore (see above). The function will return an
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<varname>errno</varname>-like negative value (see <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. Various well-known
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D-Bus errors are converted to well-known <varname>errno</varname>
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counterparts, and the other ones to <constant>-EIO</constant>. See
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<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for a list of well-known error names. Additional error mappings
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may be defined with
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<citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>. If
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<parameter>e</parameter> is NULL, no error structure is initialized,
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but the error is still converted into an
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<varname>errno</varname>-style error. If
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<parameter>name</parameter> is <constant>NULL</constant>, it is
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assumed that no error occurred, and 0 is returned. This means that
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this function may be conveniently used in a
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<function>return</function> statement. If
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<parameter>message</parameter> is NULL, no message is set. This
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call can fail if no memory may be allocated for the name and
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message strings, in which case an
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<constant>SD_BUS_ERROR_NO_MEMORY</constant> error might be set
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instead and -ENOMEM be returned. Do not use this call on error
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structures that are already initialized. If you intend to reuse an
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error structure, free the old data stored in it with
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<function>sd_bus_error_free()</function> first.</para>
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<para><function>sd_bus_error_setf()</function> is similar to
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<function>sd_bus_error_set()</function>, but takes a <citerefentry
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project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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format string and corresponding arguments to generate the
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<structfield>message</structfield> field.</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
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are not copied internally, and must hence remain constant and
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valid for the lifetime of <parameter>e</parameter>. Use this call
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to avoid memory allocations when setting error structures. Since
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this call does not allocate memory, it will not fail with an
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out-of-memory condition as
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<function>sd_bus_error_set()</function> can, as described
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above. Alternatively, the
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<constant>SD_BUS_ERROR_MAKE_CONST()</constant> macro may be used
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to generate a literal, constant bus error structure
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on-the-fly.</para>
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<para><function>sd_bus_error_set_errno()</function> will set
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<structfield>name</structfield> from an
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<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>
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will be used to set <structfield>message</structfield>. Well-known
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D-Bus error names will be used for <structfield>name</structfield>
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if applicable, otherwise a name in the
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<literal>System.Error.</literal> namespace will be generated. The
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sign of the specified error number is ignored. The absolute value
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is used implicitly. The call always returns a negative value, for
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convenient usage in <function>return</function> statements. This
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call might fail due to lack of memory, in which case an
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<constant>SD_BUS_ERROR_NO_MEMORY</constant> error is set instead,
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and -ENOMEM is returned.</para>
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<para><function>sd_bus_error_set_errnof()</function> is similar to
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<function>sd_bus_error_set_errno()</function>, but in addition to
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<parameter>error</parameter>, takes a <citerefentry
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project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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format string and corresponding arguments. The
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<structfield>message</structfield> field will be generated from
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<parameter>format</parameter> and the arguments.</para>
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<para><function>sd_bus_error_set_errnofv()</function> is similar to
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<function>sd_bus_error_set_errnof()</function>, but takes the
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format string parameters as <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
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<structfield>name</structfield> field of an error structure to an
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<varname>errno</varname>-like (positive) value using the same
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rules as <function>sd_bus_error_set()</function>. If
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<parameter>e</parameter> is <constant>NULL</constant>, 0 will be
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returned.</para>
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<para><function>sd_bus_error_copy()</function> will initialize
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<parameter>dst</parameter> using the values in
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<parameter>e</parameter>. If the strings in
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<parameter>e</parameter> were set using
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<function>sd_bus_error_set_const()</function>, they will be shared.
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Otherwise, they will be copied. Returns a converted
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<varname>errno</varname>-like, negative error code.</para>
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<para><function>sd_bus_error_move()</function> is similar to <function>sd_bus_error_copy()</function>, but will
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move any error information from <parameter>e</parameter> into <parameter>dst</parameter>, resetting the
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former. This function cannot fail, as no new memory is allocated. Note that if <parameter>e</parameter> is not set
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(or <constant>NULL</constant>) <parameter>dst</parameter> is initializated to
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<constant>SD_BUS_ERROR_NULL</constant>. Moreover, if <parameter>dst</parameter> is <constant>NULL</constant> no
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operation is executed on it and and resources held by <parameter>e</parameter> are freed and reset. Returns a
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converted <varname>errno</varname>-like, negative error code.</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_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 NULL),
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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 NULL. The structure may be reused afterwards.</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>,
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<function>sd_bus_error_setf()</function>, and
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<function>sd_bus_error_set_const()</function>, when successful,
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return the negative errno value corresponding to the
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<parameter>name</parameter> parameter. The functions
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<function>sd_bus_error_set_errno()</function>,
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<function>sd_bus_error_set_errnof()</function> and
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<function>sd_bus_error_set_errnofv()</function>, when successful,
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return the negative value of the <parameter>error</parameter>
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parameter. If an error occurs, one of the negative error values
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listed below will be returned.</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 0 or a positive
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integer on success, and a negative error value converted from the error name otherwise.</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> returns a
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non-zero value when <parameter>e</parameter> is
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non-<constant>NULL</constant> and the
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<structfield>name</structfield> field is equal to
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<parameter>name</parameter>, zero otherwise.</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
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counted. Users should destroy resources held by it by calling
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<function>sd_bus_error_free()</function>. Usually, error structures
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are allocated on the stack or passed in as function parameters,
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but they may also be allocated dynamically, in which case it is
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the duty of the caller to <citerefentry
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project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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the memory held by the structure itself after freeing its contents
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with <function>sd_bus_error_free()</function>.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</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 <structname>sd_bus_error</structname> structure when one
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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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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-bus-errors</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_bus_error_add_map</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry project='die-net'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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