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<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>libsystemd</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>