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trace: add TRACE_<event>_BACKEND_DSTATE()

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QEMU keeps track of trace event enabled/disabled state and provides
monitor commands to inspect and modify the "dstate".  SystemTap and
LTTng UST maintain independent enabled/disabled states for each trace
event, the other backends rely on QEMU dstate.

Introduce a new per-event macro that combines backend-specific dstate
like this:

  #define TRACE_MY_EVENT_BACKEND_DSTATE() ( \
      QEMU_MY_EVENT_ENABLED() || /* SystemTap */ \
      tracepoint_enabled(qemu, my_event) /* LTTng UST */ || \
      false)

This will be used to extend trace_event_get_state() in the next patch.

[Daniel Berrange pointed out that QEMU_MY_EVENT_ENABLED() must be true
by default, not false.  This way events will fire even if the DTrace
implementation does not implement the SystemTap semaphores feature.

Ubuntu Precise uses lttng-ust-dev 2.0.2 which does not have
tracepoint_enabled(), so we need a compatibility wrapper to keep Travis
builds passing.
--Stefan]

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20170731140718.22010-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

fixup! trace: add TRACE_<event>_BACKEND_DSTATE()
This commit is contained in:
Stefan Hajnoczi 2017-07-31 15:07:17 +01:00
parent ea1ff54f7d
commit 3932ef3ffb
9 changed files with 56 additions and 0 deletions
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5
scripts/tracetool/backend/simple.py
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@ -42,6 +42,11 @@ def generate_h(event, group):
args=", ".join(event.args.names()))
def generate_h_backend_dstate(event, group):
out(' trace_event_get_state_dynamic_by_id(%(event_id)s) || \\',
event_id="TRACE_" + event.name.upper())
def generate_c_begin(events, group):
out('#include "qemu/osdep.h"',
'#include "trace/control.h"',