Unified tracing buffer

[Martin Bligh]

> I agree to integrate tracing buffer mechanism, but I don't think
> your proposal is the simplest one.
>
> To simplify, I think the layered buffering mechanism is desirable.
> - The lowest layer just provides named circular buffers(both per-cpu and
>  uni-buffer in system) and read/write scheme.
> - Next layer provides user/kernel interface including controls.
> - Top layer defines packet(and event) formatting utilities.
> - Additionally, it would better provide some library routines(timestamp,
>  event-id synchronize, and so on).
>
> Since this unified buffer is used from different kind of tracers/loggers,
> I don't think all of them(and future tracers) want to be tied down by
> "event-id"+"parameter" format.
> So, Sorry, I disagree about that the tracing buffer defines its *data format*,
> it's just overkill for me.

I think you're right that we can layer this, and we didn't make a particularly
good job of splitting those things out. I'll try to pull together
another revision
to reflect this and other suggested changes.

One thing that I think is still important is to have a unified timestamp
mechanism on everything, so we can co-ordinate different things back
together in userspace from different trace tools, so I intend to keep
that at a lower level, but I think you're right that the event id, etc can
move up into separate layers.