doc: choose different words to improve clarity

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

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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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_free</refname>
    <refname>sd_bus_error_set</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_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>int <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_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>

    <para>
      <constant>SD_BUS_ERROR_FAILED</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_NO_MEMORY</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_SERVICE_UNKNOWN</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_NAME_HAS_NO_OWNER</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_NO_REPLY</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_IO_ERROR</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_BAD_ADDRESS</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_NOT_SUPPORTED</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_LIMITS_EXCEEDED</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_ACCESS_DENIED</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_AUTH_FAILED</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_NO_SERVER</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_TIMEOUT</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_NO_NETWORK</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_ADDRESS_IN_USE</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_DISCONNECTED</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_INVALID_ARGS</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_FILE_NOT_FOUND</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_FILE_EXISTS</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_UNKNOWN_METHOD</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_UNKNOWN_OBJECT</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_UNKNOWN_INTERFACE</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_UNKNOWN_PROPERTY</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_PROPERTY_READ_ONLY</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_UNIX_PROCESS_ID_UNKNOWN</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_INVALID_SIGNATURE</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_INCONSISTENT_MESSAGE</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_MATCH_RULE_NOT_FOUND</constant>
    </para>
    <para>
      <constant>SD_BUS_ERROR_MATCH_RULE_INVALID</constant>
    </para>

  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para>The <structname>sd_bus_error</structname> structure carries
    information for a <filename>sd-bus</filename> error.
    Functions described below can 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>. The <structfield>message</structfield> is a human
    readable string describing the details. When no longer necessary,
    resources held by this structure should be destroyed with
    <function>sd_bus_error_free</function>.</para>

    <para><function>sd_bus_error_set</function> will return an
    errno-like negative value returned based on parameter
    <parameter>name</parameter> (see
    <citerefentry><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
    Various well-known D-Bus errors are converted to specific values,
    and the remaining ones to <constant>-ENXIO</constant>. Well-known
    D-Bus error names are available as constants
    <constant>SD_BUS_ERROR_FAILED</constant>, etc., listed above. If
    <parameter>name</parameter> is <constant>NULL</constant>, it is
    assumed that no error occured, and 0 is returned. This means that
    this function may be conveniently used in a
    <function>return</function> statement.</para>

    <para>If <parameter>e</parameter> is not
    <constant>NULL</constant>, <structfield>name</structfield> and
    <structfield>message</structfield> in the
    <structname>sd_bus_error</structname> structure
    <parameter>e</parameter> points at will be filled in. As described above,
    <parameter>name</parameter> may be <constant>NULL</constant>,
    which is treated as no error. Parameter
    <parameter>message</parameter> may also be
    <constant>NULL</constant>, in which case no message is specified.
    <function>sd_bus_error_set</function> will make internal copies of
    specified strings.</para>

    <para><function>sd_bus_error_setf</function> is similar to
    <function>sd_bus_error_set</function>, but takes a
    <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    format string and corresponding arguments to generate
    <structname>message</structname>.</para>

    <para><function>sd_bus_error_set_const</function> is similar to
    <function>sd_bus_error_set</function>, but string parameters are
    not copied internally, and must remain valid for the lifetime of
    <parameter>e</parameter>.</para>

    <para><function>sd_bus_error_set_errno</function> will set
    <structfield>name</structfield> based on an errno-like value.
    <citerefentry><refentrytitle>strerror</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 available, otherwise a name in the
    <literal>System.Error</literal> namespace will be generated.
    </para>

    <para><function>sd_bus_error_set_errnof</function> is similar to
    <function>sd_bus_error_set_errno</function>, but in addition to
    <parameter>name</parameter>, takes a
    <citerefentry><refentrytitle>printf</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    format and corresponding arguments.
    <structfield>name</structfield> will be generated from
    <parameter>format</parameter> and the arguments.</para>

    <para><function>sd_bus_error_get_errno</function> is will convert
    <structname>e->name</structname> to an errno-like 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.</para>

    <para><function>sd_bus_error_is_set</function> will return
    <constant>true</constant> 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 true
    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><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>d
    by the caller if necessary.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para>Functions <function>sd_bus_error_set</function>,
    <function>sd_bus_error_setf</function>,
    <function>sd_bus_error_set_const</function>, when successful,
    return the negative errno value corresponding to the
    <parameter>name</parameter> parameter. Functions
    <function>sd_bus_error_set_errno</function> and
    <function>sd_bus_error_set_errnof</function>, when successful,
    return the value of the <parameter>errno</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->name</parameter> otherwise.</para>

    <para><function>sd_bus_error_copy</function> returns 0 or a
    positive integer on success, and one of the negative error values
    listed below otherwise.</para>

    <para><function>sd_bus_error_is_set</function> returns
    <constant>true</constant> when <parameter>e</parameter> and
    <parameter>e->name</parameter> are non-<constant>NULL</constant>,
    <constant>false</constant> otherwise.</para>

    <para><function>sd_bus_error_has_name</function> returns
    <constant>true</constant> when <parameter>e</parameter> is
    non-<constant>NULL</constant> and <parameter>e->name</parameter>
    is equal to <parameter>name</parameter>,
    <constant>false</constant> 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>.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para>Returned errors may indicate the following problems:</para>

    <variablelist>

      <varlistentry>
        <term><varname>-EINVAL</varname></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><varname>-ENOMEM</varname></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><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>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>strerror</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>