[lttng-dev] babeltrace2: reading metadata + events from a single CTF file

[Dave Bort]

Thank you for your prompt and helpful response, Philippe!

I'll find a way to stick to the de facto standard of multiple files as
input to babeltrace. On the device side, I can bundle things up in a simple
container format like cpio, which I can easily extract on any host system
without special tools.

--dbort

On Tue, Sep 8, 2020 at 7:54 AM Philippe Proulx <eeppeliteloop at gmail.com>
wrote:

> On Mon, Sep 7, 2020 at 8:35 AM Dave Bort via lttng-dev
> <lttng-dev at lists.lttng.org> wrote:
> >
> > Hello! I'm adding CTF-compatible tracing to a custom/experimental OS and
> have a question:
> >
> > Can babeltrace2 read from a single CTF output file that contains both
> the metadata stream and the binary trace streams?
>
> No.
>
> >
> > My little trace system would like to bundle everything related to a
> trace into a single file, making it easier to pass around (since there's
> not much filesystem/network support yet). The CTF spec provides a way to
> embed the metadata stream in the same bitstream as the data streams, but
> https://babeltrace.org/docs/v2.0/man7/babeltrace2-source.ctf.fs.7/ says
> that the `metadata` file needs to be separate. I see that LTTng manages
> trace output as a collection of files, with a separate `metadata` file.
> >
> > I'd rather avoid writing a custom tool to find and extract the metadata
> stream from the full stream before passing the data on to babeltrace2 or
> TraceCompass, but so far it looks like I may need to.
>
> You will need to.
>
> >
> > Would it be appropriate to add support for this to
> babeltrace2-source.ctf.fs? Or would this warrant a new source.ctf plugin?
> If I'm going to write some new code to handle this situation, I may as well
> try to add it to the project.
>
> This would need to be specified at the CTF level.
>
> Storing a CTF trace on the file system as a single file has been
> requested a few times, so we _might_ come up with a specified way to do
> it as an addendum to CTF 2 (which is on the roadmap, but not
> finalized/released yet).
>
> As of CTF 1.8, the de facto standard way to store a trace on the file
> system is to write its metadata stream to the `metadata` file and each
> individual data stream to its own file of which the name doesn't begin
> with `.`. This is also explained in the "Input" section of
> `babeltrace2-source.ctf.fs(7)` [1].
>
> >
> > Thank you! I'm really looking forward to benefiting from the
> CTF/babeltrace/LTTng/TraceCompass work you've all done over the years. :)
>
> I can assure you that the EfficiOS team is very glad to hear that.
>
> Phil
>
> [1]:
> https://babeltrace.org/docs/v2.0/man7/babeltrace2-source.ctf.fs.7/#doc-input
>
> >
> > --Dave Bort
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>
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