[lttng-dev] Tagging traces with arbitrary data (as in custommetadata)

[David Lindström]

  From: Mathieu Desnoyers 
  Sent: Tuesday, November 05, 2013 3:20 PM
  To: DavidLindström 
  Cc: lttng-dev at lists.lttng.org 
  Subject: Re: [lttng-dev] Tagging traces with arbitrary data (as in custommetadata)


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    From: "David Lindström" <david.lindstrom at percepio.se>
    To: lttng-dev at lists.lttng.org
    Sent: Tuesday, November 5, 2013 9:15:14 AM
    Subject: [lttng-dev] Tagging traces with arbitrary data (as in custom        metadata)


    Hi, I was wondering if there’s a way to tag a trace with some additional information. A general example would be to include a description of the current experiment. One way to do this currently would be to create a custom lttng-message application with some UST tracepoint and then just log that to a separate channel, but that would be pretty ugly. It would be much cleaner to insert extra fields into the metadata stream. Is something like that possible in current versions of LTTng and/or would it be possible to add it for a future version?

  The CTF metadata has an environment (env {}) section that contains this kind of information. LTTng already uses it to store the tracer version and some info about the system. We could eventually add a feature like this, a "tag", that would be added to the CTF environment information. I would guess that users would provide this tag on the lttng command line for their session, and it would be passed to the tracers by sessiond.


  Thoughts ?


I have no idea how this would be implemented, I’m only looking at potential uses. A simple tag field in the env{} section should cover my initial use cases. I have to wonder though, how much more complicated it would be to allow multiple named tags? For example, tags.description = ”Some description” instead of tag = “Some description”?

Also, how would one specify this? As an option to the lttng create command or as a separate command (lttng set-tag ...)?

Mvh
David Lindström

  Thanks,


  Mathieu


    Mvh
    David Lindström

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  -- 

  Mathieu Desnoyers
  EfficiOS Inc.
  http://www.efficios.com
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