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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Mon, 08 Feb 2016 18:01:55 +0000
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Subject: Re: [Qemu-devel] trace: timestamps, core IDs, and file creation
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To: Hollis Blanchard <hollis_blanchard@mentor.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, QEMU Developers <qemu-devel@nongnu.org>


Hollis Blanchard <hollis_blanchard@mentor.com> writes:

> Hi Stefan, I've been starting to use qemu tracing and found it quite
> useful. I have a couple comments about the trace events in general:
>
<snip>
> Right now, the simple tracepoint backend creates a trace file even when
> no events are active and no -trace options are present. Compounding the
> situation, omitting "-trace file=foo" results in the directory being
> littered with trace-NNNN files... could we create the file only when
> tracing is activated? And maybe with a more predictable name?

Yeah I've run into trouble when running "make check" with the simple
backend enabled. I'm not sure exactly what mechanism breaks the test but
it seems to me an invocation like:

  ./x86_64-softmmu/qemu-system-x86_64 -qtest
  unix:/tmp/qtest-9458.sock,nowait -qtest-log /dev/null -qmp
  unix:/tmp/qtest-9458.qmp,nowait -machine accel=qtest -display none -M
  pc -device pc-testdev

Shouldn't be generating anything unless an explicit file is set.

AFAICT 41fc57e44ed64cd4ab5393d83624afd897dabd4f is triggering the
default file behaviour.

I'm still digging into this.

--
Alex Bennée