[lttng-dev] Questions about CTF format

[Matthew Khouzam]

On 12-07-05 10:49 AM, Diego Dompe wrote:
> Hi Mathieu,
>
> Thanks for the help. Here is my list of details:
>
> - Clocks: the spec doesn't explain properly that timestamps are an
> offset from the base time of the clock they refer to. Since I was
> using 64bit timestamps I somehow assumed that I was using absolute
> timestamps from the epoch (although the spec doesn't says it either).
This is acceptable AFAIK, just to be clear, you can use arbitrary time
origins, that means epoch is a valid origin too. You can also use a
scaling factor, just be careful applying it since a double has 53 bits
and thus you may lose precision.
>
> - I saw that the lttng-generated traces for metadata are always a
> multiple of 4k in size (at least the ones I generate for either kernel
> or user space). I can't find where in the spec it mentions
> requirements regarding metadata packet padding. I was generating
> metadata packets that ended up right after my TSDL and eclipse wasn't
> happy about it (although I didn't try babeltrace).
Could you send the trace please, I can look into it.

> Also I found that the lttng-generated traces have a "empty" metadata
> packet after the metadata containing the TSDL, I didn't find either
> any documentation regarding this.
>
> Regards,
>
> Diego
>
> On Thu, Jul 5, 2012 at 8:20 AM, Mathieu Desnoyers
> <mathieu.desnoyers at efficios.com
> <mailto:mathieu.desnoyers at efficios.com>> wrote:
>
>     * Diego Dompe (ddompe at gmail.com <mailto:ddompe at gmail.com>) wrote:
>     > Hi,
>     >
>     > I'm developing a custom tracer for an embedded product that will
>     generate
>     > CTF format. I was able to generate generic traces that can be
>     interpreted
>     > properly with babeltrace (but not with eclipse, I already file a
>     bug for
>     > that), but I found the CTF specification lacking in some aspects
>     (I had to
>     > peek into lttng-generated CTF traces to figure out some
>     details). I was
>     > wondering what is the proper mailing list to clear my questions
>     and provide
>     > feedback on the CTF specification for improvement in the areas
>     where the
>     > documentation is not detailed yet. I don't see any CTF-specific
>     mailing
>     > list, it's OK to discuss it here? Or maybe directly with a
>     developer(s)?
>
>     Hi Diego,
>
>     Yes, this mailing list would be the proper place, along maybe with
>     adding the MCA tiwg mailing list in CC, which I'm doing here.
>
>     Thanks,
>
>     Mathieu
>
>     --
>     Mathieu Desnoyers
>     Operating System Efficiency R&D Consultant
>     EfficiOS Inc.
>     http://www.efficios.com
>
>

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