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Merge pull request #15253 from DaanDeMeyer/object-vtable-error-docs

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sd-bus: Add error handling info to sd_bus_add_object_vtable docs
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Zbigniew Jędrzejewski-Szmek 2020-04-01 12:25:34 +02:00 committed by GitHub
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3 changed files with 168 additions and 94 deletions
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6
man/rules/meson.build
View File

@ -121,7 +121,7 @@ manpages = [
'sd_bus_match_signal',
'sd_bus_match_signal_async'],
''],
['sd_bus_add_object_vtable',
['sd_bus_add_object',
'3',
['SD_BUS_METHOD',
'SD_BUS_METHOD_WITH_NAMES',
@ -134,7 +134,9 @@ manpages = [
'SD_BUS_VTABLE_END',
'SD_BUS_VTABLE_START',
'SD_BUS_WRITABLE_PROPERTY',
'sd_bus_add_fallback_vtable'],
'sd_bus_add_fallback',
'sd_bus_add_fallback_vtable',
'sd_bus_add_object_vtable'],
''],
['sd_bus_attach_event', '3', ['sd_bus_detach_event', 'sd_bus_get_event'], ''],
['sd_bus_call', '3', ['sd_bus_call_async'], ''],

3
man/sd-bus.xml
View File

@ -41,7 +41,10 @@
<para>See
<literallayout><citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_add_object</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_add_object_vtable</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_add_fallback</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_add_fallback_vtable</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_attach_event</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_call</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_bus_call_async</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

253
man/sd_bus_add_object_vtable.xml → man/sd_bus_add_object.xml
View File

@ -3,20 +3,22 @@
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="sd_bus_add_object_vtable"
<refentry id="sd_bus_add_object"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_bus_add_object_vtable</title>
<title>sd_bus_add_object</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_bus_add_object_vtable</refentrytitle>
<refentrytitle>sd_bus_add_object</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_bus_add_object</refname>
<refname>sd_bus_add_fallback</refname>
<refname>sd_bus_add_object_vtable</refname>
<refname>sd_bus_add_fallback_vtable</refname>
<refname>SD_BUS_VTABLE_START</refname>
@ -76,6 +78,24 @@
<paramdef>sd_bus_error *<parameter>ret_error</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_add_object</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_add_fallback</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
<paramdef>sd_bus_slot **<parameter>slot</parameter></paramdef>
<paramdef>const char *<parameter>path</parameter></paramdef>
<paramdef>sd_bus_message_handler_t <parameter>callback</parameter></paramdef>
<paramdef>void *<parameter>userdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_bus_add_object_vtable</function></funcdef>
<paramdef>sd_bus *<parameter>bus</parameter></paramdef>
@ -188,40 +208,82 @@
<refsect1>
<title>Description</title>
<para><function>sd_bus_add_object_vtable()</function> is used to declare attributes for the path object
path <parameter>path</parameter> connected to the bus connection <parameter>bus</parameter> under the
interface <parameter>interface</parameter>. The table <parameter>vtable</parameter> may contain property
declarations using <constant>SD_BUS_PROPERTY()</constant> or
<constant>SD_BUS_WRITABLE_PROPERTY()</constant>, method declarations using
<constant>SD_BUS_METHOD()</constant>, <constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
<para><function>sd_bus_add_object_vtable()</function> is used to declare attributes for the
object path <parameter>path</parameter> connected to the bus connection
<parameter>bus</parameter> under the interface <parameter>interface</parameter>. The table
<parameter>vtable</parameter> may contain property declarations using
<constant>SD_BUS_PROPERTY()</constant> or <constant>SD_BUS_WRITABLE_PROPERTY()</constant>,
method declarations using <constant>SD_BUS_METHOD()</constant>,
<constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
<constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, or
<constant>SD_BUS_METHOD_WITH_NAMES_OFFSET()</constant>, and signal declarations using
<constant>SD_BUS_SIGNAL_WITH_NAMES()</constant> or <constant>SD_BUS_SIGNAL()</constant>, see below. The
<replaceable>userdata</replaceable> parameter contains a pointer that will be passed to various callback
functions. It may be specified as <constant>NULL</constant> if no value is necessary.</para>
<constant>SD_BUS_SIGNAL_WITH_NAMES()</constant> or <constant>SD_BUS_SIGNAL()</constant>, see
below. The <replaceable>userdata</replaceable> parameter contains a pointer that will be passed
to various callback functions. It may be specified as <constant>NULL</constant> if no value is
necessary. An interface can have any number of vtables attached to it.</para>
<para><function>sd_bus_add_fallback_vtable()</function> is similar to
<function>sd_bus_add_object_vtable()</function>, but is used to register "fallback" attributes. When
looking for an attribute declaration, bus object paths registered with
<function>sd_bus_add_object_vtable()</function> are checked first. If no match is found, the fallback
vtables are checked for each prefix of the bus object path, i.e. with the last slash-separated components
successively removed. This allows the vtable to be used for an arbitrary number of dynamically created
objects.</para>
<function>sd_bus_add_object_vtable()</function>, but is used to register "fallback" attributes.
When looking for an attribute declaration, bus object paths registered with
<function>sd_bus_add_object_vtable()</function> are checked first. If no match is found, the
fallback vtables are checked for each prefix of the bus object path, i.e. with the last
slash-separated components successively removed. This allows the vtable to be used for an
arbitrary number of dynamically created objects.</para>
<para>Parameter <replaceable>find</replaceable> is a function which is used to locate the target object
based on the bus object path <replaceable>path</replaceable>. It must return <constant>1</constant> and
set the <parameter>ret_found</parameter> output parameter if the object is found, return
<constant>0</constant> if the object was not found, and return a negative errno-style error code or
initialize the error structure <replaceable>ret_error</replaceable> on error. The pointer passed in
<parameter>ret_found</parameter> will be used as the <parameter>userdata</parameter> parameter for the
callback functions (offset by the <parameter>offset</parameter> offsets as specified in the vtable
entries).</para>
<para>Parameter <replaceable>find</replaceable> is a function which is used to locate the target
object based on the bus object path <replaceable>path</replaceable>. It must return
<constant>1</constant> and set the <parameter>ret_found</parameter> output parameter if the
object is found, return <constant>0</constant> if the object was not found, and return a
negative errno-style error code or initialize the error structure
<replaceable>ret_error</replaceable> on error. The pointer passed in
<parameter>ret_found</parameter> will be used as the <parameter>userdata</parameter> parameter
for the callback functions (offset by the <parameter>offset</parameter> offsets as specified in
the vtable entries).</para>
<para>For both functions, a match slot is created internally. If the output parameter
<replaceable>slot</replaceable> is <constant>NULL</constant>, a "floating" slot object is created, see
<para><function>sd_bus_add_object()</function> attaches a callback directly to the object path
<parameter>path</parameter>. An object path can have any number of callbacks attached to it.
Each callback is prepended to the list of callbacks which are always called in order.
<function>sd_bus_add_fallback()</function> is similar to
<function>sd_bus_add_object()</function> but applies to fallback paths instead.</para>
<para>When a request is received, any associated callbacks are called sequentially until a
callback returns a non-zero integer. Return zero from a callback to give other callbacks the
chance to process the request. Callbacks are called in the following order: first, callbacks
attached directly to the request object path are called, followed by any D-Bus method callbacks
attached to the request object path, interface and member. Finally, the property callbacks
attached to the request object path, interface and member are called. If the final callback
returns zero, an error reply is sent back to the caller indicating no matching object for the
request was found. Note that you can return a positive integer from a callback without
immediately sending a reply. This informs sd-bus this callback will take responsibility for
replying to the request without forcing the callback to produce a reply immediately. This allows
a callback to perform any number of asynchronous operations required to construct a reply. Note
that if producing a reply takes too long, the method call will time out at the caller.</para>
<para>If a callback was invoked to handle a request that expects a reply and the callback
returns a negative value, the value is interpreted as a negative errno-style error code and sent
back to the caller as a D-Bus error as if
<citerefentry><refentrytitle>sd_bus_reply_method_errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
was called. Additionally, all callbacks take a <structname>sd_bus_error</structname> output
parameter that can be used to provide more detailed error information. If
<parameter>ret_error</parameter> is set when the callback finishes, the corresponding D-Bus
error is sent back to the caller as if
<citerefentry><refentrytitle>sd_bus_reply_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
was called. Any error stored in <parameter>ret_error</parameter> takes priority over any
negative values returned by the same callback when determining which error to send back to
the caller. Use
<citerefentry><refentrytitle>sd_bus_error_set</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or one of its variants to set <parameter>ret_error</parameter> and return a negative integer
from a callback with a single function call. To send an error reply after a callback has already
finished, use
<citerefentry><refentrytitle>sd_bus_reply_method_errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
or one of its variants.</para>
<para>For all functions, a match slot is created internally. If the output parameter
<replaceable>slot</replaceable> is <constant>NULL</constant>, a "floating" slot object is
created, see
<citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
Otherwise, a pointer to the slot object is returned. In that case, the reference to the slot object
should be dropped when the vtable is not needed anymore, see
Otherwise, a pointer to the slot object is returned. In that case, the reference to the slot
object should be dropped when the vtable is not needed anymore, see
<citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
@ -245,23 +307,28 @@
<term><constant>SD_BUS_METHOD_WITH_OFFSET()</constant></term>
<term><constant>SD_BUS_METHOD()</constant></term>
<listitem><para>Declare a D-Bus method with the name <replaceable>member</replaceable>, parameter
signature <replaceable>signature</replaceable>, result signature <replaceable>result</replaceable>.
Parameters <replaceable>in_names</replaceable> and <replaceable>out_names</replaceable> specify the
argument names of the input and output arguments in the function signature. The handler function
<replaceable>handler</replaceable> must be of type <function>sd_bus_message_handler_t</function>.
It will be called to handle the incoming messages that call this method. It receives a pointer that
is the <replaceable>userdata</replaceable> parameter passed to the registration function offset by
<replaceable>offset</replaceable> bytes. This may be used to pass pointers to different fields in
the same data structure to different methods in the same
vtable. <replaceable>in_names</replaceable> and <replaceable>out_names</replaceable> should be
created using the <constant>SD_BUS_PARAM()</constant> macro, see below. Parameter
<listitem><para>Declare a D-Bus method with the name <replaceable>member</replaceable>,
parameter signature <replaceable>signature</replaceable>, result signature
<replaceable>result</replaceable>. Parameters <replaceable>in_names</replaceable> and
<replaceable>out_names</replaceable> specify the argument names of the input and output
arguments in the function signature. The handler function
<replaceable>handler</replaceable> must be of type
<function>sd_bus_message_handler_t</function>. It will be called to handle the incoming
messages that call this method. It receives a pointer that is the
<replaceable>userdata</replaceable> parameter passed to the registration function offset
by <replaceable>offset</replaceable> bytes. This may be used to pass pointers to different
fields in the same data structure to different methods in the same vtable. To send a reply
from <parameter>handler</parameter>, call
<citerefentry><refentrytitle>sd_bus_reply_method_return</refentrytitle><manvolnum>3</manvolnum></citerefentry>
with the message the callback was invoked with. <replaceable>in_names</replaceable> and
<replaceable>out_names</replaceable> should be created using the
<constant>SD_BUS_PARAM()</constant> macro, see below. Parameter
<replaceable>flags</replaceable> is a combination of flags, see below.</para>
<para><constant>SD_BUS_METHOD_WITH_NAMES()</constant>,
<constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, and <constant>SD_BUS_METHOD()</constant> are
variants which specify zero offset (<replaceable>userdata</replaceable> parameter is passed with
no change), leave the names unset (i.e. no parameter names), or both.</para>
<constant>SD_BUS_METHOD_WITH_OFFSET()</constant>, and <constant>SD_BUS_METHOD()</constant>
are variants which specify zero offset (<replaceable>userdata</replaceable> parameter is
passed with no change), leave the names unset (i.e. no parameter names), or both.</para>
</listitem>
</varlistentry>
@ -285,29 +352,31 @@
<term><constant>SD_BUS_WRITABLE_PROPERTY()</constant></term>
<term><constant>SD_BUS_PROPERTY()</constant></term>
<listitem><para>Declare a D-Bus property with the name <replaceable>member</replaceable> and value
signature <replaceable>signature</replaceable>. Parameters <replaceable>get</replaceable> and
<replaceable>set</replaceable> are the getter and setter methods. They are called with a pointer
that is the <replaceable>userdata</replaceable> parameter passed to the registration function
offset by <replaceable>offset</replaceable> bytes. This may be used pass pointers to different
fields in the same data structure to different setters and getters in the same vtable. Parameter
<replaceable>flags</replaceable> is a combination of flags, see below.</para>
<listitem><para>Declare a D-Bus property with the name <replaceable>member</replaceable>
and value signature <replaceable>signature</replaceable>. Parameters
<replaceable>get</replaceable> and <replaceable>set</replaceable> are the getter and
setter methods. They are called with a pointer that is the
<replaceable>userdata</replaceable> parameter passed to the registration function offset
by <replaceable>offset</replaceable> bytes. This may be used pass pointers to different
fields in the same data structure to different setters and getters in the same vtable.
Parameter <replaceable>flags</replaceable> is a combination of flags, see below.</para>
<para>The setter and getter methods may be omitted (specified as <constant>NULL</constant>), if the
property has one of the basic types or <literal>as</literal> in case of read-only properties. In
those cases, the <replaceable>userdata</replaceable> and <replaceable>offset</replaceable>
parameters must together point to valid variable of the corresponding type. A default setter and
getters will be provided, which simply copy the argument between this variable and the message.
<para>The setter and getter methods may be omitted (specified as
<constant>NULL</constant>), if the property is one of the basic types or
<literal>as</literal> in case of read-only properties. In those cases, the
<replaceable>userdata</replaceable> and <replaceable>offset</replaceable> parameters must
together point to a valid variable of the corresponding type. A default setter and getter
will be provided, which simply copy the argument between this variable and the message.
</para>
<para><constant>SD_BUS_PROPERTY()</constant> is used to define a read-only property.</para>
</listitem>
<para><constant>SD_BUS_PROPERTY()</constant> is used to define a read-only property.
</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>SD_BUS_PARAM()</constant></term>
<listitem><para>Parameter names should be wrapped in this macro, see the example below.</para>
</listitem>
<listitem><para>Parameter names should be wrapped in this macro, see the example below.
</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
@ -324,7 +393,7 @@
<term><constant>SD_BUS_VTABLE_DEPRECATED</constant></term>
<listitem><para>Mark this vtable entry as deprecated using the
<constant>org.freedesktop.DBus.Deprecated</constant> annotation in introspection data. If
<constant>org.freedesktop.DBus.Deprecated</constant> annotation in introspection data. If
specified for <constant>SD_BUS_VTABLE_START()</constant>, the annotation is applied to the
enclosing interface.</para></listitem>
</varlistentry>
@ -332,10 +401,9 @@
<varlistentry>
<term><constant>SD_BUS_VTABLE_HIDDEN</constant></term>
<listitem><para>Make this vtable entry hidden. It will not be shown in introspection data. If
specified for <constant>SD_BUS_VTABLE_START()</constant>, all entries in the array are hidden.
</para>
</listitem>
<listitem><para>Make this vtable entry hidden. It will not be shown in introspection data.
If specified for <constant>SD_BUS_VTABLE_START()</constant>, all entries in the array are
hidden.</para></listitem>
</varlistentry>
<varlistentry>
@ -343,8 +411,7 @@
<listitem><para>Mark this vtable entry as unprivileged. If not specified, the
<constant>org.freedesktop.systemd1.Privileged</constant> annotation with value
<literal>true</literal> will be shown in introspection data.</para>
</listitem>
<literal>true</literal> will be shown in introspection data.</para></listitem>
</varlistentry>
<varlistentry>
@ -361,27 +428,28 @@
<term><constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant></term>
<listitem><para>Those three flags correspond to different values of the
<constant>org.freedesktop.DBus.Property.EmitsChangedSignal</constant> annotation, which specifies
whether the <constant>org.freedesktop.DBus.Properties.PropertiesChanged</constant> signal is
emitted whenever the property changes. <constant>SD_BUS_VTABLE_PROPERTY_CONST</constant> corresponds to
<constant>const</constant> and means that the property never changes during the lifetime of the
object it belongs to, so no signal needs to be emitted.
<constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant> corresponds to <constant>true</constant> and means
that the signal is emitted. <constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant> corresponds to
<constant>invalidates</constant> and means that the signal is emitted, but the value is not included
in the signal.</para>
</listitem>
<constant>org.freedesktop.DBus.Property.EmitsChangedSignal</constant> annotation, which
specifies whether the
<constant>org.freedesktop.DBus.Properties.PropertiesChanged</constant> signal is emitted
whenever the property changes. <constant>SD_BUS_VTABLE_PROPERTY_CONST</constant>
corresponds to <constant>const</constant> and means that the property never changes during
the lifetime of the object it belongs to, so no signal needs to be emitted.
<constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant> corresponds to
<constant>true</constant> and means that the signal is emitted.
<constant>SD_BUS_VTABLE_PROPERTY_EMITS_INVALIDATION</constant> corresponds to
<constant>invalidates</constant> and means that the signal is emitted, but the value is
not included in the signal.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>SD_BUS_VTABLE_PROPERTY_EXPLICIT</constant></term>
<listitem><para>Mark this vtable property entry as requiring explicit request to for the value to
be shown (generally because the value is large or slow to calculate). This entry cannot be combined
with <constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant>, and will not be shown in property listings by
default (e.g. <command>busctl introspect</command>). This corresponds to the
<constant>org.freedesktop.systemd1.Explicit</constant> annotation in introspection data.</para>
</listitem>
<listitem><para>Mark this vtable property entry as requiring explicit request to for the
value to be shown (generally because the value is large or slow to calculate). This entry
cannot be combined with <constant>SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE</constant>, and will
not be shown in property listings by default (e.g. <command>busctl introspect</command>).
This corresponds to the <constant>org.freedesktop.systemd1.Explicit</constant> annotation
in introspection data.</para></listitem>
</varlistentry>
</variablelist>
</refsect2>
@ -395,9 +463,9 @@
<programlisting><xi:include href="vtable-example.c" parse="text" /></programlisting>
<para>This creates a simple client on the bus (the user bus, when run as normal user).
We may use the D-Bus <constant>org.freedesktop.DBus.Introspectable.Introspect</constant>
call to acquire the XML description of the interface:</para>
<para>This creates a simple client on the bus (the user bus, when run as normal user). We may
use the D-Bus <constant>org.freedesktop.DBus.Introspectable.Introspect</constant> call to
acquire the XML description of the interface:</para>
<programlisting><xi:include href="vtable-example.xml" parse="text" /></programlisting>
</example>
@ -407,8 +475,8 @@
<title>Return Value</title>
<para>On success, <function>sd_bus_add_object_vtable</function> and
<function>sd_bus_add_fallback_vtable</function> calls return 0 or a positive integer. On failure, they
return a negative errno-style error code.</para>
<function>sd_bus_add_fallback_vtable</function> calls return 0 or a positive integer. On
failure, they return a negative errno-style error code.</para>
<refsect2>
<title>Errors</title>
@ -419,8 +487,9 @@
<varlistentry>
<term><constant>-EINVAL</constant></term>
<listitem><para>One of the required parameters is <constant>NULL</constant> or invalid. A reserved
D-Bus interface was passed as the <replaceable>interface</replaceable> parameter.</para></listitem>
<listitem><para>One of the required parameters is <constant>NULL</constant> or invalid. A
reserved D-Bus interface was passed as the <replaceable>interface</replaceable> parameter.
</para></listitem>
</varlistentry>
<varlistentry>
@ -445,8 +514,8 @@
<term><constant>-EPROTOTYPE</constant></term>
<listitem><para><function>sd_bus_add_object_vtable</function> and
<function>sd_bus_add_fallback_vtable</function> have been both called
for the same bus object path, which is not allowed.</para></listitem>
<function>sd_bus_add_fallback_vtable</function> have been both called for the same bus
object path, which is not allowed.</para></listitem>
</varlistentry>
<varlistentry>