[Spice-devel] RFC: Lightweight tracing mechanism

[Christophe de Dinechin]

> On 9 Jun 2017, at 17:16, Jonathon Jongsma <jjongsma at redhat.com> wrote:
> 
> On Fri, 2017-06-09 at 10:59 +0200, Christophe de Dinechin wrote:
>>>> What I see on the thread:
>>>> - log categorization. This was similar to Djasa bug but I think
>>>> he just
>>>>   proposed to use domains in the glib log sense;
>> 
>> Punchcard analogy: “Printer sheet categorization. This was similar to
>> the report that Djisktra had taken McCarthy's listing by mistake"
>> 
>> I thought it was a good idea to derive glib log domains automatically
>> from spice-traces.def. So it’s there in the branch now. That being
>> said, as noted above, glib does linear searches on domain names, so
>> this does not scale well. In the long term, we may want to have a
>> separate field in a structured log.
> 
> 
> Responding only to this point for the moment: I don't think using
> multiple glib logging domains is necessarily desirable. We already use
> several logging domains, but the vast majority of logging statements
> within each project use a single domain. In spice-server, that primary
> log domain is "Spice", and in spice-gtk that domain is "GSpice". spice-
> server also has some additional domains like "SpiceWorker" and
> "SpiceDispatcher". spice-gtk also has GSpiceController (which isn't
> really used much these days). 
> 
> The problem is that both spice-server and spice-gtk have a way to
> enable debugging with an environment variable. But the code for
> enabling the debugging only actually enables the primary domain.

The ‘traces’ branch enables all trace-related domains if you enable debug.

> So anything that is logged under a different domain does not get enabled.
> (In fact, spice-gtk has 2 ways to enable logging with an environment
> variable but one of the methods is the same one used for spice-server,
> but it doesn't work since it actually enables logging for the "Spice"
> domain which spice-gtk doesn't use.) I'm hoping to send some patches to
> clean up this mess soon. 

Ah, so I was not the only one thinking this was a mess :-)



> 
> But the upshot is that if we use multiple log domains we'll need to
> make sure that if we enable debug, we enable all domains that we're
> interested in. This will require a small maintenance burden (although
> Christophe's approach probably handles it automatically). Or we could
> use a single log domain and segment the different "categories" of log
> messages somehow within that domain.

I would switch to categories, but after we switch to structured logging. Which, once the “mess” is cleaned up, is relatively easy (one function called with consistent input).


> 
> Jonathon
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