man: let's document explicitly that method reply handlers won't get ret_error set to method error

Fixes: #8108

1 files changed, 21 insertions, 20 deletions

diff --git a/man/sd_bus_call.xml b/man/sd_bus_call.xml
index b93efb2622..f47f9c8526 100644
--- a/man/sd_bus_call.xml
+++ b/man/sd_bus_call.xml
@@ -61,32 +61,33 @@
     received a D-Bus error reply), <parameter>ret_error</parameter> is initialized to an instance of
     <structname>sd_bus_error</structname> describing the error.</para>
 
-    <para><function>sd_bus_call_async()</function> is like <function>sd_bus_call()</function> but
-    works asynchronously. The <parameter>callback</parameter> indicates the function to call when
-    the response arrives. The <parameter>userdata</parameter> pointer will be passed to the callback
-    function, and may be chosen freely by the caller. If <parameter>slot</parameter> is not
-    <constant>NULL</constant> and <function>sd_bus_call_async()</function> succeeds,
-    <parameter>slot</parameter> is set to a slot object which can be used to cancel the method call
-    at a later time using
+    <para><function>sd_bus_call_async()</function> is like <function>sd_bus_call()</function> but works
+    asynchronously. The <parameter>callback</parameter> indicates the function to call when the response
+    arrives. The <parameter>userdata</parameter> pointer will be passed to the callback function, and may be
+    chosen freely by the caller. If <parameter>slot</parameter> is not <constant>NULL</constant> and
+    <function>sd_bus_call_async()</function> succeeds, <parameter>slot</parameter> is set to a slot object
+    which can be used to cancel the method call at a later time using
     <citerefentry><refentrytitle>sd_bus_slot_unref</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
-    If <parameter>slot</parameter> is <constant>NULL</constant>, the lifetime of the method call is
-    bound to the lifetime of the bus object itself, and it cannot be cancelled independently. See
+    If <parameter>slot</parameter> is <constant>NULL</constant>, the lifetime of the method call is bound to
+    the lifetime of the bus object itself, and it cannot be cancelled independently. See
     <citerefentry><refentrytitle>sd_bus_slot_set_floating</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     for details. <parameter>callback</parameter> is called when a reply arrives with the reply,
-    <parameter>userdata</parameter> and an <structname>sd_bus_error</structname> output
-    parameter as its arguments. Unlike <function>sd_bus_call()</function>, the
-    <structname>sd_bus_error</structname> output parameter passed to the callback will be empty. To
-    determine whether the method call succeeded, use
+    <parameter>userdata</parameter> and an <structname>sd_bus_error</structname> output parameter as its
+    arguments. Unlike <function>sd_bus_call()</function>, the <structname>sd_bus_error</structname> output
+    parameter passed to the callback will be empty. To determine whether the method call succeeded, use
     <citerefentry><refentrytitle>sd_bus_message_is_method_error</refentrytitle><manvolnum>3</manvolnum></citerefentry>
     on the reply message passed to the callback instead. If the callback returns zero and the
-    <structname>sd_bus_error</structname> output parameter is still empty when the callback
-    inishes, other handlers registered with functions such as
+    <structname>sd_bus_error</structname> output parameter is still empty when the callback finishes, other
+    handlers registered with functions such as
     <citerefentry><refentrytitle>sd_bus_add_filter</refentrytitle><manvolnum>3</manvolnum></citerefentry> or
-    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
-    are given a chance to process the message. If the callback returns a non-zero value or the
-    <structname>sd_bus_error</structname> output parameter is not empty when the callback finishes,
-    no further processing of the message is done. Generally, you want to return zero from the
-    callback to give other registered handlers a chance to process the reply as well.</para>
+    <citerefentry><refentrytitle>sd_bus_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> are
+    given a chance to process the message. If the callback returns a non-zero value or the
+    <structname>sd_bus_error</structname> output parameter is not empty when the callback finishes, no
+    further processing of the message is done. Generally, you want to return zero from the callback to give
+    other registered handlers a chance to process the reply as well. (Note that the
+    <structname>sd_bus_error</structname> parameter is an output parameter of the callback function, not an
+    input parameter; it can be used to propagate errors from the callback handler, it will not receive any
+    error that was received as method reply.)</para>
 
     <para>If <parameter>usec</parameter> is zero, the default D-Bus method call timeout is used. See
     <citerefentry><refentrytitle>sd_bus_get_method_call_timeout</refentrytitle><manvolnum>3</manvolnum></citerefentry>.