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trace: add trace_event_get_state_backends()

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Code that checks dstate is unaware of SystemTap and LTTng UST dstate, so
the following trace event will not fire when solely enabled by SystemTap
or LTTng UST:

  if (trace_event_get_state(TRACE_MY_EVENT)) {
      str = g_strdup_printf("Expensive string to generate ...",
                            ...);
      trace_my_event(str);
      g_free(str);
  }

Add trace_event_get_state_backends() to fetch backend dstate.  Those
backends that use QEMU dstate fetch it as part of
generate_h_backend_dstate().

Update existing trace_event_get_state() callers to use
trace_event_get_state_backends() instead.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170731140718.22010-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2017-07-31 15:07:18 +01:00
parent 3932ef3ffb
commit d87aa13803
5 changed files with 31 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

18
trace/control.h
View file

@ -96,7 +96,7 @@ static const char * trace_event_get_name(TraceEvent *ev);
* trace_event_get_state:
* @id: Event identifier name.
*
* Get the tracing state of an event (both static and dynamic).
* Get the tracing state of an event, both static and the QEMU dynamic state.
*
* If the event has the disabled property, the check will have no performance
* impact.
@ -104,6 +104,22 @@ static const char * trace_event_get_name(TraceEvent *ev);
#define trace_event_get_state(id) \
((id ##_ENABLED) && trace_event_get_state_dynamic_by_id(id))
/**
* trace_event_get_state_backends:
* @id: Event identifier name.
*
* Get the tracing state of an event, both static and dynamic state from all
* compiled-in backends.
*
* If the event has the disabled property, the check will have no performance
* impact.
*
* Returns: true if at least one backend has the event enabled and the event
* does not have the disabled property.
*/
#define trace_event_get_state_backends(id) \
((id ##_ENABLED) && id ##_BACKEND_DSTATE())
/**
* trace_event_get_vcpu_state:
* @vcpu: Target vCPU.