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[thirdparty/systemd.git] / man / sd_bus_error.xml

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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_error_set_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>