[PULL 6/8] docs/qapi-code-gen: update to cover trace events code generation

[Markus Armbruster <armbru@redhat.com>]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Previous commits enabled trace events generation for most of QAPI
generated code (except for tests/ and qga/). Let's update documentation
to illustrate it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20220126161130.3240892-6-vsementsov@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 docs/devel/qapi-code-gen.rst | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst
index feafed79b5..246709ede8 100644
--- a/docs/devel/qapi-code-gen.rst
+++ b/docs/devel/qapi-code-gen.rst
@@ -1630,6 +1630,9 @@ The following files are generated:
  ``$(prefix)qapi-commands.h``
      Function prototypes for the QMP commands specified in the schema
 
+ ``$(prefix)qapi-commands.trace-events``
+     Trace event declarations, see :ref:`tracing`.
+
  ``$(prefix)qapi-init-commands.h``
      Command initialization prototype
 
@@ -1650,6 +1653,13 @@ Example::
     void qmp_marshal_my_command(QDict *args, QObject **ret, Error **errp);
 
     #endif /* EXAMPLE_QAPI_COMMANDS_H */
+
+    $ cat qapi-generated/example-qapi-commands.trace-events
+    # AUTOMATICALLY GENERATED, DO NOT MODIFY
+
+    qmp_enter_my_command(const char *json) "%s"
+    qmp_exit_my_command(const char *result, bool succeeded) "%s %d"
+
     $ cat qapi-generated/example-qapi-commands.c
     [Uninteresting stuff omitted...]
 
@@ -1689,14 +1699,27 @@ Example::
             goto out;
         }
 
+        if (trace_event_get_state_backends(TRACE_QMP_ENTER_MY_COMMAND)) {
+            g_autoptr(GString) req_json = qobject_to_json(QOBJECT(args));
+
+            trace_qmp_enter_my_command(req_json->str);
+        }
+
         retval = qmp_my_command(arg.arg1, &err);
         if (err) {
+            trace_qmp_exit_my_command(error_get_pretty(err), false);
             error_propagate(errp, err);
             goto out;
         }
 
         qmp_marshal_output_UserDefOne(retval, ret, errp);
 
+        if (trace_event_get_state_backends(TRACE_QMP_EXIT_MY_COMMAND)) {
+            g_autoptr(GString) ret_json = qobject_to_json(*ret);
+
+            trace_qmp_exit_my_command(ret_json->str, true);
+        }
+
     out:
         visit_free(v);
         v = qapi_dealloc_visitor_new();
-- 
2.31.1