Re: [Qemu-devel] [PATCH 0/4] Tracetool cleanup

[Lluís Vilanova]

Stefan Hajnoczi writes:

> On Mon, Feb 17, 2014 at 08:36:19PM +0100, Lluís Vilanova wrote:
>> Minimizes the amount of backend code, making it simpler to add new/different
>> backends.
>> 
>> Also performs other cleanups all around.
>> 
>> Signed-off-by: Lluís Vilanova <address@hidden>
>> ---
>> 
>> Lluís Vilanova (4):
>> trace: [tracetool] Add method 'Event.api' to build event names
>> trace: [tracetool,trivial] Style changes
>> trace: [tracetool] Identify formats directly used by QEMU
>> trace: [tracetool] Minimize the amount of per-backend code

> I think we stretched the concepts of backends and formats too far.
> There are formats that only work with one backend (like 'stap').  And
> there are backends that behave differently from all other backends.

> As a result we're trying to abstract and make common a bunch of stuff
> that isn't really common.  This problem existed before this patch
> series, but I feel we're going further down a direction that
> increasingly seems to be wrong.

> It's simpler if we turn the design inside-out.  Instead of making
> backends export all sorts of interfaces and flags, tracetool should just
> parse trace-events and hand the list over to the backend.

> Let the backend do whatever it wants.  The format option simply becomes
> an option telling the backend which type of output to generate
> (events.h, events.c, .stp, etc).

> Common behavior should live in plain old Python modules/functions.

> TL;DR moving to a library design would simplify and clean up more than
> trying to improve the current framework design

> What do you think?

This series moves into that direction; some of the formats are simply not
handled by backends. For example, the "stap", "events_c" and "events_h" formats
have no backend-specific contents.

Also, having common code for the "format", and then relying on backends for a
small piece of the contents simplifies later patches like the multi-backend
tracing.

The thing here is that maybe we should change format to "file", since it
actually refers to a specific output file.


Thanks,
  Lluis

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