Re: [Qemu-devel] [PATCH] trace: teach lttng backend to use format strings

[Mohamad Gebai <mohamad.gebai@polymtl.ca>]

I can confirm that it works for me, I can see the disk image file name 
in the payload of brdv_open_common events.

Mohamad

On 03/26/2014 04:27 AM, Stefan Hajnoczi wrote:
> On Tue, Mar 25, 2014 at 02:49:42PM +0000, Alex Bennée wrote:
>> Stefan Hajnoczi <stefanha@redhat.com> writes:
>>
>>> On Mon, Mar 24, 2014 at 05:04:54PM +0000, alex.bennee@linaro.org wrote:
>>>> From: Alex Bennée <alex.bennee@linaro.org>
>>>>
>>>> This makes the UST backend pay attention to the format string arguments
>>>> that are defined when defining payload data. With this you can now
>>>> ensure integers are reported in hex mode if you want.
>>>>
>>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>> ---
>>>>   scripts/tracetool/__init__.py    | 13 +++++++++++--
>>>>   scripts/tracetool/backend/ust.py | 16 ++++++++++++----
>>>>   2 files changed, 23 insertions(+), 6 deletions(-)
>>> How are strings handled, can LTTng copy them from the QEMU process'
>>> memory space?
>> lttng provides ctf_string for passing strings to the payload. But I
>> wouldn't expect to use them for the result of format string calculations
>> as that would defeat the point of the low impact tracing.
>>
>> There are a number of trace-events that pass strings for various things.
>> I've not actually experimented with the output of any of them though.
> Sounds like it should work but can you test it?  Try enabling the
> bdrv_open_common() trace event when booting a guest.  You should see the
> filename of the disk image file.
>
> Stefan