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

["Alex Bennée" <alex.bennee@linaro.org>]

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.


>
> Stefan

-- 
Alex Bennée