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| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
| "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
| <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
| |
| <refentry id="sd_bus_error" xmlns:xi="http://www.w3.org/2001/XInclude"> |
| |
| <refentryinfo> |
| <title>sd_bus_error</title> |
| <productname>systemd</productname> |
| </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_setfv</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_move</refname> |
| <refname>sd_bus_error_is_set</refname> |
| <refname>sd_bus_error_has_name</refname> |
| <refname>sd_bus_error_has_names_sentinel</refname> |
| <refname>sd_bus_error_has_names</refname> |
| |
| <refpurpose>sd-bus error handling</refpurpose> |
| </refnamediv> |
| |
| <refsynopsisdiv> |
| <funcsynopsis> |
| <funcsynopsisinfo>#include <systemd/sd-bus.h></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_setfv</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>va_list <parameter>ap</parameter></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 <parameter>ap</parameter></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_move</function></funcdef> |
| <paramdef>sd_bus_error *<parameter>dst</parameter></paramdef> |
| <paramdef>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> |
| |
| <funcprototype> |
| <funcdef>int <function>sd_bus_error_has_names_sentinel</function></funcdef> |
| <paramdef>const sd_bus_error *<parameter>e</parameter></paramdef> |
| <paramdef>...</paramdef> |
| </funcprototype> |
| |
| <para> |
| #define sd_bus_error_has_names(e, ...) sd_bus_error_has_names_sentinel(e, ..., NULL) |
| </para> |
| </funcsynopsis> |
| |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| |
| <para>The <structname>sd_bus_error</structname> structure carries information about a D-Bus error |
| condition, or lack thereof. The functions described below may be used to set and query fields in this |
| structure. |
| <itemizedlist> |
| <listitem><para>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="https://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.</para></listitem> |
| |
| <listitem><para>The <structfield>message</structfield> field usually contains a human-readable string |
| describing the details, but might be <constant>NULL</constant>.</para></listitem> |
| </itemizedlist> |
| An unset <structname>sd_bus_error</structname> structure should have both fields initialized to |
| <constant>NULL</constant>, and signifies lack of an error, i.e. success. Assign |
| <constant>SD_BUS_ERROR_NULL</constant> to the structure in order to initialize both fields to |
| <constant>NULL</constant>. 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 |
| contents again when they are not required anymore (see above). Do not use this call on error structures |
| that have already been set. 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_set()</function> will return an <varname>errno</varname>-like value (see |
| <citerefentry |
| project='man-pages'><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>) |
| determined from the specified error name <parameter>name</parameter>. If <parameter>name</parameter> is |
| <constant>NULL</constant>, it is assumed that no error occurred, and <constant>0</constant> is returned. |
| If <parameter>name</parameter> is nonnull, a negative value is always returned. If |
| <parameter>e</parameter> is <constant>NULL</constant>, no error structure is initialized, but |
| <parameter>name</parameter> is still converted into an <varname>errno</varname>-style value.</para> |
| |
| <para>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>. |
| </para> |
| |
| <para><function>sd_bus_error_set()</function> is designed to be conveniently used in a |
| <function>return</function> statement. If <parameter>message</parameter> is <constant>NULL</constant>, 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 will be set instead and |
| <constant>-ENOMEM</constant> returned. </para> |
| |
| <para><function>sd_bus_error_setf()</function> and <function>sd_bus_error_setfv()</function> are similar |
| to <function>sd_bus_error_set()</function>, but take a <citerefentry |
| project='man-pages'><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry> format |
| string and corresponding arguments to generate the <structfield>message</structfield> field. |
| <function>sd_bus_error_setf()</function> uses variadic arguments, and |
| <function>sd_bus_error_setfv()</function> accepts the arguments as a |
| <citerefentry |
| project='man-pages'><refentrytitle>va_arg</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| parameter list.</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> may, 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 immediately return <constant>0</constant> if the |
| specified error parameter <parameter>error</parameter> is <constant>0</constant>. Otherwise, it 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 and the absolute value is |
| used implicitly. If the specified error <parameter>error</parameter> is non-zero, 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 <constant>-ENOMEM</constant> is returned.</para> |
| |
| <para><function>sd_bus_error_set_errnof()</function> and <function>sd_bus_error_set_errnof()</function> |
| are similar to <function>sd_bus_error_set_errno()</function>, but in addition to |
| <parameter>error</parameter>, take 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. |
| <function>sd_bus_error_set_errnof()</function> uses variadic arguments, and |
| <function>sd_bus_error_set_errnofv()</function> accepts the arguments as a |
| <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>, |
| <constant>0</constant> will be returned.</para> |
| |
| <para><function>sd_bus_error_copy()</function> will initialize <parameter>dst</parameter> using the |
| values in <parameter>e</parameter>, if <parameter>e</parameter> has been set with an error value before. |
| Otherwise, it will return immediately. If the strings in <parameter>e</parameter> were set using |
| <function>sd_bus_error_set_const()</function>, they will be shared. Otherwise, they will be |
| copied. Before this call, <parameter>dst</parameter> must be unset, i.e. either freshly initialized with |
| <constant>NULL</constant> or reset using <function>sd_bus_error_free()</function>.</para> |
| |
| <para><function>sd_bus_error_copy()</function> generally returns <constant>0</constant> or a negative |
| <varname>errno</varname>-like value based on the input parameter <parameter>e</parameter>: |
| <constant>0</constant> if it was unset and a negative integer if it was set to some error, similarly to |
| <function>sd_bus_error_set()</function>. It may however also return an error generated internally, for |
| example <constant>-ENOMEM</constant> if a memory allocation fails.</para> |
| |
| <para><function>sd_bus_error_move()</function> is similar to <function>sd_bus_error_copy()</function>, |
| but will move any error information from <parameter>e</parameter> into <parameter>dst</parameter>, |
| resetting the former. This function cannot fail, as no new memory is allocated. Note that if |
| <parameter>e</parameter> is not set, <parameter>dst</parameter> is initialized to |
| <constant>SD_BUS_ERROR_NULL</constant>. Moreover, if <parameter>dst</parameter> is |
| <constant>NULL</constant> no operation is executed on it and resources held by <parameter>e</parameter> |
| are freed and reset. Returns a converted <varname>errno</varname>-like, non-positive error value.</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_has_names_sentinel()</function> is similar to |
| <function>sd_bus_error_has_name()</function>, but takes multiple names to check against. The list must be |
| terminated with <constant>NULL</constant>. <function>sd_bus_error_has_names()</function> |
| is a macro wrapper around <function>sd_bus_error_has_names_sentinel()</function> that adds the |
| <constant>NULL</constant> sentinel automatically.</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 <constant>NULL</constant>), |
| 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 <constant>NULL</constant>. The structure may be reused afterwards.</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>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> always return <constant>0</constant> when the specified |
| error value is <constant>NULL</constant>, and a negative errno-like value corresponding to the |
| <parameter>name</parameter> parameter otherwise. The functions |
| <function>sd_bus_error_set_errno()</function>, <function>sd_bus_error_set_errnof()</function> and |
| <function>sd_bus_error_set_errnofv()</function>, return <constant>0</constant> when the specified error |
| value is <constant>0</constant>, and a negative errno-like value corresponding to the |
| <parameter>error</parameter> parameter otherwise. If an error occurs internally, one of the negative |
| error values listed below will be returned. This allows those functions to be conveniently used in a |
| <constant>return</constant> statement, see the example below.</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->name</parameter> otherwise.</para> |
| |
| <para><function>sd_bus_error_copy()</function> and <function>sd_bus_error_move()</function> return a |
| negative error value converted from the source error, and zero if the error has not been set. This |
| allows those functions to be conveniently used in a <constant>return</constant> statement, see the |
| example below.</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>, <function>sd_bus_error_has_names()</function>, and |
| <function>sd_bus_error_has_names_sentinel()</function> return a non-zero value when <parameter>e</parameter> is |
| non-<constant>NULL</constant> and the <structfield>name</structfield> field is equal to one of the given |
| names, zero otherwise.</para> |
| |
| <refsect2> |
| <title>Errors</title> |
| |
| <para>Return value may indicate the following problems in the invocation of the function itself:</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><constant>-EINVAL</constant></term> |
| |
| <listitem><para>Error was already set in the <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> |
| |
| <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='man-pages'><refentrytitle>strerror_r</refentrytitle><manvolnum>3</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |
