[lttng-dev] Remote streaming of traces recorded during system bootup

[Jonathan Rajotte-Julien]

Hi Ramith,

On Sat, Jun 02, 2018 at 04:03:38PM +0000, Ramith Shetty wrote:
> Hi,
> 
> We are intending to capture the traces from the bootup time on an embedded linux system.

Interesting!

> 
> The traces are generated at the bootup time, and there is no network connectivity at this point of time.
> 
> Later when the network connectivity is up , we are in need of a mechanism to stream this traces to a remote session. [The traces streamed is expected to even have the traces which are captured during the bootup]

Not sure what you mean by "remote session"?

Do you plan on using the lttng "live mode" or only network streaming of traces
to lttng-relayd?

If streaming only, A session in network-backed snapshot mode could achieve something close to what you
need. This would require that the buffers for the session be big enough to
keep events until network is live. As soon as the network go live you take a
snapshot. The snapshot will be streamed over the network to a lttng-relayd.

Once the network is setup, you can setup a new session in network streaming
mode. When performing analysis on the trace you will need to correlate the
snapshot from the first session to the trace data from the second session.
Babeltrace should handle this relatively easily.

You could also skip the creation of the second session and do time based
snapshots of the first session once the network is up. When reading from
Babeltrace you will need to point it to a collection of snapshots.

Using a session in snapshot mode works since no network communication is needed
with the relayd until a snapshot is actually taken.

For the streaming mode and live mode, there is no "delayed" mode for network
communication. LTTng expects to be able to send data over the network directly.
Communications also occurs at channel initialization when in streaming or live
mode preventing their use when network is not up.

Hope this will give you some ideas.

Others might want to chip in.

Cheers

> 
> The bootup traces are captured using a local mode session
> 
> Regards,
> Ramith
> 
> 

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-- 
Jonathan Rajotte-Julien
EfficiOS