Re: Event redefinition/re-enablement

Re: Event redefinition/re-enablement

[Thibault, Daniel]

----------------------------------------------------------------------
Date: Sun, 16 Mar 2014 00:41:28 -0700
From: Ruslan Uvashev <ruslan.uvashev@gmail.com>

> It seems that event once enabled for a channel cannot be reassigned to another channel.
> If events are immutable will Feature #445 (https://bugs.lttng.org/issues/445)
>  account such situation? Or do we need to update man saying that events
> cannot be redefined?
>
> Command output below.
>
> $ sudo lttng create tst1
> Session tst1 created.
> Traces will be written in /home/rusty/lttng-traces/tst1-20140315-173020
> $ sudo lttng enable-event writeback_nothread -k
> Kernel event writeback_nothread created in channel channel0
> $ sudo lttng enable-channel ch1 -k
> Kernel channel ch1 enabled for session tst1
[...]
> $ sudo lttng disable-event writeback_nothread -k -c channel0
> Kernel event writeback_nothread disabled in channel channel0 for session tst1
> $ sudo lttng enable-event writeback_nothread -k -c ch1
> Error: Event writeback_nothread: Enable kernel event failed (channel ch1, session tst1)
> Warning: Some command(s) went wrong

   That is a known feature/limitation of LTTng: kernel events can only be assigned once (within a session).  User-space events can be assigned to multiple channels.

Daniel U. Thibault
Protection des systèmes et contremesures (PSC) | Systems Protection & Countermeasures (SPC)
Cyber sécurité pour les missions essentielles (CME) | Mission Critical Cyber Security (MCCS)
R & D pour la défense Canada - Valcartier (RDDC Valcartier) | Defence R&D Canada - Valcartier (DRDC Valcartier)
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<http://www.valcartier.drdc-rddc.gc.ca/>

Event redefinition/re-enablement

[Ruslan Uvashev]

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Hi,

It seems that event once enabled for a channel cannot be reassigned to
another channel.
If events are immutable will Feature #445 (https://bugs.lttng.org/issues/445)
 account such situation? Or do we need to update man saying that events
cannot be redefined?

Command output below.

Thank you!


Output:

$ sudo lttng create tst1
Session tst1 created.
Traces will be written in /home/rusty/lttng-traces/tst1-20140315-173020
$ sudo lttng enable-event writeback_nothread -k
Kernel event writeback_nothread created in channel channel0
$ sudo lttng enable-channel ch1 -k
Kernel channel ch1 enabled for session tst1
$ sudo lttng list tst1
Tracing session tst1: [inactive]
    Trace path: /home/rusty/lttng-traces/tst1-20140315-173020

=== Domain: Kernel ===

Channels:
-------------
- ch1: [enabled]

    Attributes:
      overwrite mode: 0
      subbufers size: 262144
      number of subbufers: 4
      switch timer interval: 0
      read timer interval: 200000
      output: splice()

    Events:
      None

- channel0: [enabled]

    Attributes:
      overwrite mode: 0
      subbufers size: 262144
      number of subbufers: 4
      switch timer interval: 0
      read timer interval: 200000
      output: splice()

    Events:
      writeback_nothread (loglevel: TRACE_EMERG (0)) (type: tracepoint)
[enabled]

$ sudo lttng disable-event writeback_nothread -k -c channel0
Kernel event writeback_nothread disabled in channel channel0 for session
tst1
$ sudo lttng enable-event writeback_nothread -k -c ch1
Error: Event writeback_nothread: Enable kernel event failed (channel ch1,
session tst1)
Warning: Some command(s) went wrong




-------------------------------------
Best regards,
Ruslan Uvashev

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