[lttng-dev] adding new channel

[Philippe Proulx]

On Fri, Feb 20, 2015 at 2:20 PM, Alexandre Montplaisir
<alexmonthy at voxpopuli.im> wrote:
>
> On 02/20/2015 02:05 PM, Philippe Proulx wrote:
>>
>> On Fri, Feb 20, 2015 at 2:00 PM, Anand Neeli <anand.neeli at gmail.com>
>> wrote:
>>>
>>> Hi All,
>>> Is adding a new channel to an existing(running) session supported?
>>
>> No.
>>>
>>> i get following error when doing this.
>>> Error: Channel myc5: Tracing already started
>>>
>>> Is there any way to add channels on the fly?
>>
>> No. LTTng's documentation [1] states:
>>
>>      Note: Because of a current limitation, all channels must be
>>      created prior to beginning tracing in a given tracing session,
>>      i.e. before the first time you do lttng start.
>
>
> The wording "Because of a current limitation" seems to imply that it could
> and will eventually be rectified. It this actually the case, or is the doc
> just giving the user false hope? ;)

The feature is planned to be completed before 2038; no false hope here.

On a more serious note, it is definitely possible, although not so trivial to
implement. But since it is achievable, given enough time that is, it is
actually... a current limitation.

Phil

>
>
> Alex
>
>
>>
>>      Since a channel is automatically created by enable-event
>>      only for the specified domain, you cannot, for example, enable
>>      a kernel domain event, start tracing and then enable a user
>>      space domain event because no user space channel exists
>>      yet and it's too late to create one.
>>
>>      For this reason, make sure to configure your channels
>>      properly before starting the tracers for the first time!
>>
>> Phil
>>
>> [1] http://lttng.org/docs/#doc-enabling-disabling-channels
>>
>>> I'm using 2.4.1 version
>>>
>>> Thanks,
>>> Anand Neeli
>>>
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>>>
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>
>