Re: [PATCH][GIT PULL] tracing: add handler to trace_stat

From: Frederic Weisbecker
Date: Wed Mar 25 2009 - 19:05:31 EST


On Wed, Mar 25, 2009 at 06:49:33PM -0400, Steven Rostedt wrote:
>
> On Wed, 25 Mar 2009, Frederic Weisbecker wrote:
> > >
> > > diff --git a/kernel/trace/trace_stat.h b/kernel/trace/trace_stat.h
> > > index 202274c..f3546a2 100644
> > > --- a/kernel/trace/trace_stat.h
> > > +++ b/kernel/trace/trace_stat.h
> > > @@ -12,7 +12,7 @@ struct tracer_stat {
> > > /* The name of your stat file */
> > > const char *name;
> > > /* Iteration over statistic entries */
> > > - void *(*stat_start)(void);
> > > + void *(*stat_start)(struct tracer_stat *trace);
> >
> >
> >
> > In that case, shoudn't we pass another thing than the struct tracer_stat?
> > Because nothing really private can be stored in it. Moreover, most of the
> > time the handler is dedicated to this tracer_stat so it is able to have
> > an access to it.
> >
> > May be we could add a void *private inside struct trace_stat and then pass
> > it to stat_start() ?
> >
>
>
> Very few tracers need a private field so adding one would be a waste for
> them. I just used the old container_of trick.
>
>
> struct ftrace_profile_stat {
> atomic_t disabled;
> struct hlist_head *hash;
> struct ftrace_profile_page *pages;
> struct ftrace_profile_page *start;
> struct tracer_stat stat;
> };
>
> static void *function_stat_start(struct tracer_stat *trace)
> {
> struct ftrace_profile_stat *stat =
> container_of(trace, struct ftrace_profile_stat, stat);
>
> [...]
>
> And there you have it. I have everything I need unique to the tracer and
> no need of a private pointer.
>
> -- Steve
>


And type safe :-)
Indeed, that's much better.

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