From: Tanish Desai <tanishdesai37@gmail.com>

Add a new attribute CHECK_TRACE_EVENT_GET_STATE to the backends.
When present and True, the code generated by the generate function
is wrapped in a conditional that checks whether the event is enabled;
this removes the need for repeating the same conditional in multiple
backends.

Signed-off-by: Tanish Desai <tanishdesai37@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 scripts/tracetool/backend/__init__.py | 39 ++++++++++++++++++---------
 scripts/tracetool/format/h.py         | 11 +++++---
 2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/scripts/tracetool/backend/__init__.py b/scripts/tracetool/backend/__init__.py
index bf91e443e99..9109a783c72 100644
--- a/scripts/tracetool/backend/__init__.py
+++ b/scripts/tracetool/backend/__init__.py
@@ -19,11 +19,15 @@
 Backend attributes
 ------------------
 
-========= ====================================================================
-Attribute Description
-========= ====================================================================
-PUBLIC    If exists and is set to 'True', the backend is considered "public".
-========= ====================================================================
+=========================== ====================================================
+Attribute                   Description
+=========================== ====================================================
+PUBLIC                      If exists and is set to 'True', the backend is
+                            considered "public".
+CHECK_TRACE_EVENT_GET_STATE If exists and is set to 'True', the backend-specific
+                            code inside the tracepoint is emitted within an
+                            ``if trace_event_get_state()`` conditional.
+=========================== ====================================================
 
 
 Backend functions
@@ -101,22 +105,33 @@ class Wrapper:
     def __init__(self, backends, format):
         self._backends = [backend.replace("-", "_") for backend in backends]
         self._format = format.replace("-", "_")
+        self.check_trace_event_get_state = False
         for backend in self._backends:
             assert exists(backend)
         assert tracetool.format.exists(self._format)
+        for backend in self.backend_modules():
+            check_trace_event_get_state = getattr(backend, "CHECK_TRACE_EVENT_GET_STATE", False)
+            self.check_trace_event_get_state = self.check_trace_event_get_state or check_trace_event_get_state
 
-    def _run_function(self, name, *args, **kwargs):
+    def backend_modules(self):
         for backend in self._backends:
-            func = tracetool.try_import("tracetool.backend." + backend,
-                                        name % self._format, None)[1]
-            if func is not None:
-                func(*args, **kwargs)
+             module = tracetool.try_import("tracetool.backend." + backend)[1]
+             if module is not None:
+                 yield module
+
+    def _run_function(self, name, *args, check_trace_event_get_state=None, **kwargs):
+        for backend in self.backend_modules():
+            func = getattr(backend, name % self._format, None)
+            if func is not None and \
+                (check_trace_event_get_state is None or
+                 check_trace_event_get_state == getattr(backend, 'CHECK_TRACE_EVENT_GET_STATE', False)):
+                    func(*args, **kwargs)
 
     def generate_begin(self, events, group):
         self._run_function("generate_%s_begin", events, group)
 
-    def generate(self, event, group):
-        self._run_function("generate_%s", event, group)
+    def generate(self, event, group, check_trace_event_get_state=None):
+        self._run_function("generate_%s", event, group, check_trace_event_get_state=check_trace_event_get_state)
 
     def generate_backend_dstate(self, event, group):
         self._run_function("generate_%s_backend_dstate", event, group)
diff --git a/scripts/tracetool/format/h.py b/scripts/tracetool/format/h.py
index be7f32e67b9..dd58713a158 100644
--- a/scripts/tracetool/format/h.py
+++ b/scripts/tracetool/format/h.py
@@ -55,7 +55,6 @@ def generate(events, backend, group):
 
         out('    false)')
 
-        # tracer without checks
         out('',
             'static inline void %(api)s(%(args)s)',
             '{',
@@ -63,11 +62,17 @@ def generate(events, backend, group):
             args=e.args)
 
         if "disable" not in e.properties:
-            backend.generate(e, group)
+            backend.generate(e, group, check_trace_event_get_state=False)
 
+            if backend.check_trace_event_get_state:
+                event_id = 'TRACE_' + e.name.upper()
+                cond = "trace_event_get_state(%s)" % event_id
+                out('    if (%(cond)s) {',
+                        cond=cond)
+                backend.generate(e, group, check_trace_event_get_state=True)
+                out('    }')
         out('}')
 
-
     backend.generate_end(events, group)
 
     out('#endif /* TRACE_%s_GENERATED_TRACERS_H */' % group.upper())
-- 
2.51.0