Re: [PATCH v3] ftrace: add a tracepoint for __raise_softirq_irqoff()

Mathieu Desnoyers
2009-05-11T14:27:56Z

* Steven Rostedt (rostedt@goodmis.org) wrote:
>
> On Mon, 11 May 2009, Mathieu Desnoyers wrote:
> >
> > Yes, we should try to fix TRACE_EVENT, but we should fix it _before_ we
> > start using it widely. Circular header dependencies is a real problem
> > with TRACE_EVENT right now.
> >
> > Until we fix this, I will be tempted to stay with a known-good solution,
> > which is DECLARE/DEFINE_TRACE.
>
> The majority of tracepoints happen is C files. Those few cases where they
> are used in headers is where the issues arise.
>
> But...
>
> I did not want to uglify all trace event headers with:
>
> #ifdef CREATE_FOO_TRACE_POINTS
> #undef CREATE_FOO_TRACE_POINTS
> #include <trace/define_trace.h>
> #endif
>
> We would only need to do that for those trace points that need to be
> included in header files. Then the declaration C file would need to define
> both CREATE_FOO_TRACE_POINTS and CREATE_TRACE_POINTS
>
> #define CREATE_FOO_TRACE_POINTS
> #define CRATE_TRACE_POINTS
> #include <trace/events/foo.h>
>
>
> But this is pretty trivial to solve, and I do not consider it a show
> stopper or a major header dependency problem.
>
> -- Steve
>

Hrm, is there any way to solve it elegantly ?

What we really need is to see the cases where TRACE_EVENT() is used as a
declaration vs the case where it expands
TP_STRUCT__entry/TP_fast_assign/TP_printk as having different
dependencies. The problem comes when we bring the include dependencies
of the TP_fast_assign part into the tracepoint header and it becomes
a dependency of the TRACE_EVENT() declaration-only part.

Can we do the following ?

All tracepoint headers could surround the include dependencies by :

#ifdef BUILD_EVENTS
#include <veryannoyingheaderdependency.h>
#endif

And then we follow this by the TRACE_EVENT() declarations.

BUILD_EVENTS would only be defined in kernel/trace/events.c.

I think it should work, but it looks a bit too simple, so I may have
missed something... ?

Mathieu

--
Mathieu Desnoyers
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